1 /*
2 * Copyright (c) 2001, 2013, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/symbolTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "gc_implementation/concurrentMarkSweep/cmsAdaptiveSizePolicy.hpp"
31 #include "gc_implementation/concurrentMarkSweep/cmsCollectorPolicy.hpp"
32 #include "gc_implementation/concurrentMarkSweep/cmsGCAdaptivePolicyCounters.hpp"
33 #include "gc_implementation/concurrentMarkSweep/cmsOopClosures.inline.hpp"
34 #include "gc_implementation/concurrentMarkSweep/compactibleFreeListSpace.hpp"
35 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.inline.hpp"
36 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepThread.hpp"
37 #include "gc_implementation/concurrentMarkSweep/vmCMSOperations.hpp"
38 #include "gc_implementation/parNew/parNewGeneration.hpp"
39 #include "gc_implementation/shared/collectorCounters.hpp"
40 #include "gc_implementation/shared/isGCActiveMark.hpp"
41 #include "gc_interface/collectedHeap.inline.hpp"
42 #include "memory/cardTableRS.hpp"
43 #include "memory/collectorPolicy.hpp"
44 #include "memory/gcLocker.inline.hpp"
45 #include "memory/genCollectedHeap.hpp"
46 #include "memory/genMarkSweep.hpp"
47 #include "memory/genOopClosures.inline.hpp"
48 #include "memory/iterator.hpp"
49 #include "memory/referencePolicy.hpp"
50 #include "memory/resourceArea.hpp"
51 #include "oops/oop.inline.hpp"
52 #include "prims/jvmtiExport.hpp"
53 #include "runtime/globals_extension.hpp"
54 #include "runtime/handles.inline.hpp"
55 #include "runtime/java.hpp"
56 #include "runtime/vmThread.hpp"
57 #include "services/memoryService.hpp"
58 #include "services/runtimeService.hpp"
59
60 // statics
61 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL;
62 bool CMSCollector::_full_gc_requested = false;
63
64 //////////////////////////////////////////////////////////////////
65 // In support of CMS/VM thread synchronization
66 //////////////////////////////////////////////////////////////////
67 // We split use of the CGC_lock into 2 "levels".
68 // The low-level locking is of the usual CGC_lock monitor. We introduce
69 // a higher level "token" (hereafter "CMS token") built on top of the
70 // low level monitor (hereafter "CGC lock").
71 // The token-passing protocol gives priority to the VM thread. The
72 // CMS-lock doesn't provide any fairness guarantees, but clients
73 // should ensure that it is only held for very short, bounded
74 // durations.
75 //
76 // When either of the CMS thread or the VM thread is involved in
77 // collection operations during which it does not want the other
78 // thread to interfere, it obtains the CMS token.
79 //
80 // If either thread tries to get the token while the other has
81 // it, that thread waits. However, if the VM thread and CMS thread
82 // both want the token, then the VM thread gets priority while the
83 // CMS thread waits. This ensures, for instance, that the "concurrent"
84 // phases of the CMS thread's work do not block out the VM thread
85 // for long periods of time as the CMS thread continues to hog
86 // the token. (See bug 4616232).
87 //
88 // The baton-passing functions are, however, controlled by the
89 // flags _foregroundGCShouldWait and _foregroundGCIsActive,
90 // and here the low-level CMS lock, not the high level token,
91 // ensures mutual exclusion.
92 //
93 // Two important conditions that we have to satisfy:
94 // 1. if a thread does a low-level wait on the CMS lock, then it
95 // relinquishes the CMS token if it were holding that token
96 // when it acquired the low-level CMS lock.
97 // 2. any low-level notifications on the low-level lock
98 // should only be sent when a thread has relinquished the token.
99 //
100 // In the absence of either property, we'd have potential deadlock.
101 //
102 // We protect each of the CMS (concurrent and sequential) phases
103 // with the CMS _token_, not the CMS _lock_.
104 //
105 // The only code protected by CMS lock is the token acquisition code
106 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the
107 // baton-passing code.
108 //
109 // Unfortunately, i couldn't come up with a good abstraction to factor and
110 // hide the naked CGC_lock manipulation in the baton-passing code
111 // further below. That's something we should try to do. Also, the proof
112 // of correctness of this 2-level locking scheme is far from obvious,
113 // and potentially quite slippery. We have an uneasy supsicion, for instance,
114 // that there may be a theoretical possibility of delay/starvation in the
115 // low-level lock/wait/notify scheme used for the baton-passing because of
116 // potential intereference with the priority scheme embodied in the
117 // CMS-token-passing protocol. See related comments at a CGC_lock->wait()
118 // invocation further below and marked with "XXX 20011219YSR".
119 // Indeed, as we note elsewhere, this may become yet more slippery
120 // in the presence of multiple CMS and/or multiple VM threads. XXX
121
122 class CMSTokenSync: public StackObj {
123 private:
124 bool _is_cms_thread;
125 public:
126 CMSTokenSync(bool is_cms_thread):
127 _is_cms_thread(is_cms_thread) {
128 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(),
129 "Incorrect argument to constructor");
130 ConcurrentMarkSweepThread::synchronize(_is_cms_thread);
131 }
132
133 ~CMSTokenSync() {
134 assert(_is_cms_thread ?
135 ConcurrentMarkSweepThread::cms_thread_has_cms_token() :
136 ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
137 "Incorrect state");
138 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread);
139 }
140 };
141
142 // Convenience class that does a CMSTokenSync, and then acquires
143 // upto three locks.
144 class CMSTokenSyncWithLocks: public CMSTokenSync {
145 private:
146 // Note: locks are acquired in textual declaration order
147 // and released in the opposite order
148 MutexLockerEx _locker1, _locker2, _locker3;
149 public:
150 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1,
151 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL):
152 CMSTokenSync(is_cms_thread),
153 _locker1(mutex1, Mutex::_no_safepoint_check_flag),
154 _locker2(mutex2, Mutex::_no_safepoint_check_flag),
155 _locker3(mutex3, Mutex::_no_safepoint_check_flag)
156 { }
157 };
158
159
160 // Wrapper class to temporarily disable icms during a foreground cms collection.
161 class ICMSDisabler: public StackObj {
162 public:
163 // The ctor disables icms and wakes up the thread so it notices the change;
164 // the dtor re-enables icms. Note that the CMSCollector methods will check
165 // CMSIncrementalMode.
166 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); }
167 ~ICMSDisabler() { CMSCollector::enable_icms(); }
168 };
169
170 //////////////////////////////////////////////////////////////////
171 // Concurrent Mark-Sweep Generation /////////////////////////////
172 //////////////////////////////////////////////////////////////////
173
174 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;)
175
176 // This struct contains per-thread things necessary to support parallel
177 // young-gen collection.
178 class CMSParGCThreadState: public CHeapObj<mtGC> {
179 public:
180 CFLS_LAB lab;
181 PromotionInfo promo;
182
183 // Constructor.
184 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) {
185 promo.setSpace(cfls);
186 }
187 };
188
189 class CMSPhaseTracing: public StackObj {
190 public:
191 CMSPhaseTracing(bool print, const char* phase);
192 ~CMSPhaseTracing();
193 };
194
195 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration(
196 ReservedSpace rs, size_t initial_byte_size, int level,
197 CardTableRS* ct, bool use_adaptive_freelists,
198 FreeBlockDictionary<FreeChunk>::DictionaryChoice dictionaryChoice) :
199 CardGeneration(rs, initial_byte_size, level, ct),
200 _dilatation_factor(((double)MinChunkSize)/((double)(CollectedHeap::min_fill_size()))),
201 _debug_collection_type(Concurrent_collection_type)
202 {
203 HeapWord* bottom = (HeapWord*) _virtual_space.low();
204 HeapWord* end = (HeapWord*) _virtual_space.high();
205
206 _direct_allocated_words = 0;
207 NOT_PRODUCT(
208 _numObjectsPromoted = 0;
209 _numWordsPromoted = 0;
210 _numObjectsAllocated = 0;
211 _numWordsAllocated = 0;
212 )
213
214 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end),
215 use_adaptive_freelists,
216 dictionaryChoice);
217 NOT_PRODUCT(debug_cms_space = _cmsSpace;)
218 if (_cmsSpace == NULL) {
219 vm_exit_during_initialization(
220 "CompactibleFreeListSpace allocation failure");
221 }
222 _cmsSpace->_gen = this;
223
224 _gc_stats = new CMSGCStats();
225
226 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass
227 // offsets match. The ability to tell free chunks from objects
228 // depends on this property.
229 debug_only(
230 FreeChunk* junk = NULL;
231 assert(UseCompressedKlassPointers ||
232 junk->prev_addr() == (void*)(oop(junk)->klass_addr()),
233 "Offset of FreeChunk::_prev within FreeChunk must match"
234 " that of OopDesc::_klass within OopDesc");
235 )
236 if (CollectedHeap::use_parallel_gc_threads()) {
237 typedef CMSParGCThreadState* CMSParGCThreadStatePtr;
238 _par_gc_thread_states =
239 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads, mtGC);
240 if (_par_gc_thread_states == NULL) {
241 vm_exit_during_initialization("Could not allocate par gc structs");
242 }
243 for (uint i = 0; i < ParallelGCThreads; i++) {
244 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace());
245 if (_par_gc_thread_states[i] == NULL) {
246 vm_exit_during_initialization("Could not allocate par gc structs");
247 }
248 }
249 } else {
250 _par_gc_thread_states = NULL;
251 }
252 _incremental_collection_failed = false;
253 // The "dilatation_factor" is the expansion that can occur on
254 // account of the fact that the minimum object size in the CMS
255 // generation may be larger than that in, say, a contiguous young
256 // generation.
257 // Ideally, in the calculation below, we'd compute the dilatation
258 // factor as: MinChunkSize/(promoting_gen's min object size)
259 // Since we do not have such a general query interface for the
260 // promoting generation, we'll instead just use the mimimum
261 // object size (which today is a header's worth of space);
262 // note that all arithmetic is in units of HeapWords.
263 assert(MinChunkSize >= CollectedHeap::min_fill_size(), "just checking");
264 assert(_dilatation_factor >= 1.0, "from previous assert");
265 }
266
267
268 // The field "_initiating_occupancy" represents the occupancy percentage
269 // at which we trigger a new collection cycle. Unless explicitly specified
270 // via CMSInitiatingOccupancyFraction (argument "io" below), it
271 // is calculated by:
272 //
273 // Let "f" be MinHeapFreeRatio in
274 //
275 // _intiating_occupancy = 100-f +
276 // f * (CMSTriggerRatio/100)
277 // where CMSTriggerRatio is the argument "tr" below.
278 //
279 // That is, if we assume the heap is at its desired maximum occupancy at the
280 // end of a collection, we let CMSTriggerRatio of the (purported) free
281 // space be allocated before initiating a new collection cycle.
282 //
283 void ConcurrentMarkSweepGeneration::init_initiating_occupancy(intx io, uintx tr) {
284 assert(io <= 100 && tr <= 100, "Check the arguments");
285 if (io >= 0) {
286 _initiating_occupancy = (double)io / 100.0;
287 } else {
288 _initiating_occupancy = ((100 - MinHeapFreeRatio) +
289 (double)(tr * MinHeapFreeRatio) / 100.0)
290 / 100.0;
291 }
292 }
293
294 void ConcurrentMarkSweepGeneration::ref_processor_init() {
295 assert(collector() != NULL, "no collector");
296 collector()->ref_processor_init();
297 }
298
299 void CMSCollector::ref_processor_init() {
300 if (_ref_processor == NULL) {
301 // Allocate and initialize a reference processor
302 _ref_processor =
303 new ReferenceProcessor(_span, // span
304 (ParallelGCThreads > 1) && ParallelRefProcEnabled, // mt processing
305 (int) ParallelGCThreads, // mt processing degree
306 _cmsGen->refs_discovery_is_mt(), // mt discovery
307 (int) MAX2(ConcGCThreads, ParallelGCThreads), // mt discovery degree
308 _cmsGen->refs_discovery_is_atomic(), // discovery is not atomic
309 &_is_alive_closure, // closure for liveness info
310 false); // next field updates do not need write barrier
311 // Initialize the _ref_processor field of CMSGen
312 _cmsGen->set_ref_processor(_ref_processor);
313
314 }
315 }
316
317 CMSAdaptiveSizePolicy* CMSCollector::size_policy() {
318 GenCollectedHeap* gch = GenCollectedHeap::heap();
319 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
320 "Wrong type of heap");
321 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
322 gch->gen_policy()->size_policy();
323 assert(sp->is_gc_cms_adaptive_size_policy(),
324 "Wrong type of size policy");
325 return sp;
326 }
327
328 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() {
329 CMSGCAdaptivePolicyCounters* results =
330 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters();
331 assert(
332 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
333 "Wrong gc policy counter kind");
334 return results;
335 }
336
337
338 void ConcurrentMarkSweepGeneration::initialize_performance_counters() {
339
340 const char* gen_name = "old";
341
342 // Generation Counters - generation 1, 1 subspace
343 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space);
344
345 _space_counters = new GSpaceCounters(gen_name, 0,
346 _virtual_space.reserved_size(),
347 this, _gen_counters);
348 }
349
350 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha):
351 _cms_gen(cms_gen)
352 {
353 assert(alpha <= 100, "bad value");
354 _saved_alpha = alpha;
355
356 // Initialize the alphas to the bootstrap value of 100.
357 _gc0_alpha = _cms_alpha = 100;
358
359 _cms_begin_time.update();
360 _cms_end_time.update();
361
362 _gc0_duration = 0.0;
363 _gc0_period = 0.0;
364 _gc0_promoted = 0;
365
366 _cms_duration = 0.0;
367 _cms_period = 0.0;
368 _cms_allocated = 0;
369
370 _cms_used_at_gc0_begin = 0;
371 _cms_used_at_gc0_end = 0;
372 _allow_duty_cycle_reduction = false;
373 _valid_bits = 0;
374 _icms_duty_cycle = CMSIncrementalDutyCycle;
375 }
376
377 double CMSStats::cms_free_adjustment_factor(size_t free) const {
378 // TBD: CR 6909490
379 return 1.0;
380 }
381
382 void CMSStats::adjust_cms_free_adjustment_factor(bool fail, size_t free) {
383 }
384
385 // If promotion failure handling is on use
386 // the padded average size of the promotion for each
387 // young generation collection.
388 double CMSStats::time_until_cms_gen_full() const {
389 size_t cms_free = _cms_gen->cmsSpace()->free();
390 GenCollectedHeap* gch = GenCollectedHeap::heap();
391 size_t expected_promotion = MIN2(gch->get_gen(0)->capacity(),
392 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average());
393 if (cms_free > expected_promotion) {
394 // Start a cms collection if there isn't enough space to promote
395 // for the next minor collection. Use the padded average as
396 // a safety factor.
397 cms_free -= expected_promotion;
398
399 // Adjust by the safety factor.
400 double cms_free_dbl = (double)cms_free;
401 double cms_adjustment = (100.0 - CMSIncrementalSafetyFactor)/100.0;
402 // Apply a further correction factor which tries to adjust
403 // for recent occurance of concurrent mode failures.
404 cms_adjustment = cms_adjustment * cms_free_adjustment_factor(cms_free);
405 cms_free_dbl = cms_free_dbl * cms_adjustment;
406
407 if (PrintGCDetails && Verbose) {
408 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free "
409 SIZE_FORMAT " expected_promotion " SIZE_FORMAT,
410 cms_free, expected_promotion);
411 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f",
412 cms_free_dbl, cms_consumption_rate() + 1.0);
413 }
414 // Add 1 in case the consumption rate goes to zero.
415 return cms_free_dbl / (cms_consumption_rate() + 1.0);
416 }
417 return 0.0;
418 }
419
420 // Compare the duration of the cms collection to the
421 // time remaining before the cms generation is empty.
422 // Note that the time from the start of the cms collection
423 // to the start of the cms sweep (less than the total
424 // duration of the cms collection) can be used. This
425 // has been tried and some applications experienced
426 // promotion failures early in execution. This was
427 // possibly because the averages were not accurate
428 // enough at the beginning.
429 double CMSStats::time_until_cms_start() const {
430 // We add "gc0_period" to the "work" calculation
431 // below because this query is done (mostly) at the
432 // end of a scavenge, so we need to conservatively
433 // account for that much possible delay
434 // in the query so as to avoid concurrent mode failures
435 // due to starting the collection just a wee bit too
436 // late.
437 double work = cms_duration() + gc0_period();
438 double deadline = time_until_cms_gen_full();
439 // If a concurrent mode failure occurred recently, we want to be
440 // more conservative and halve our expected time_until_cms_gen_full()
441 if (work > deadline) {
442 if (Verbose && PrintGCDetails) {
443 gclog_or_tty->print(
444 " CMSCollector: collect because of anticipated promotion "
445 "before full %3.7f + %3.7f > %3.7f ", cms_duration(),
446 gc0_period(), time_until_cms_gen_full());
447 }
448 return 0.0;
449 }
450 return work - deadline;
451 }
452
453 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the
454 // amount of change to prevent wild oscillation.
455 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle,
456 unsigned int new_duty_cycle) {
457 assert(old_duty_cycle <= 100, "bad input value");
458 assert(new_duty_cycle <= 100, "bad input value");
459
460 // Note: use subtraction with caution since it may underflow (values are
461 // unsigned). Addition is safe since we're in the range 0-100.
462 unsigned int damped_duty_cycle = new_duty_cycle;
463 if (new_duty_cycle < old_duty_cycle) {
464 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U);
465 if (new_duty_cycle + largest_delta < old_duty_cycle) {
466 damped_duty_cycle = old_duty_cycle - largest_delta;
467 }
468 } else if (new_duty_cycle > old_duty_cycle) {
469 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U);
470 if (new_duty_cycle > old_duty_cycle + largest_delta) {
471 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U);
472 }
473 }
474 assert(damped_duty_cycle <= 100, "invalid duty cycle computed");
475
476 if (CMSTraceIncrementalPacing) {
477 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ",
478 old_duty_cycle, new_duty_cycle, damped_duty_cycle);
479 }
480 return damped_duty_cycle;
481 }
482
483 unsigned int CMSStats::icms_update_duty_cycle_impl() {
484 assert(CMSIncrementalPacing && valid(),
485 "should be handled in icms_update_duty_cycle()");
486
487 double cms_time_so_far = cms_timer().seconds();
488 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M;
489 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far);
490
491 // Avoid division by 0.
492 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01);
493 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full;
494
495 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U);
496 if (new_duty_cycle > _icms_duty_cycle) {
497 // Avoid very small duty cycles (1 or 2); 0 is allowed.
498 if (new_duty_cycle > 2) {
499 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle,
500 new_duty_cycle);
501 }
502 } else if (_allow_duty_cycle_reduction) {
503 // The duty cycle is reduced only once per cms cycle (see record_cms_end()).
504 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle);
505 // Respect the minimum duty cycle.
506 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin;
507 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle);
508 }
509
510 if (PrintGCDetails || CMSTraceIncrementalPacing) {
511 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle);
512 }
513
514 _allow_duty_cycle_reduction = false;
515 return _icms_duty_cycle;
516 }
517
518 #ifndef PRODUCT
519 void CMSStats::print_on(outputStream *st) const {
520 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha);
521 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT,
522 gc0_duration(), gc0_period(), gc0_promoted());
523 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT,
524 cms_duration(), cms_duration_per_mb(),
525 cms_period(), cms_allocated());
526 st->print(",cms_since_beg=%g,cms_since_end=%g",
527 cms_time_since_begin(), cms_time_since_end());
528 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT,
529 _cms_used_at_gc0_begin, _cms_used_at_gc0_end);
530 if (CMSIncrementalMode) {
531 st->print(",dc=%d", icms_duty_cycle());
532 }
533
534 if (valid()) {
535 st->print(",promo_rate=%g,cms_alloc_rate=%g",
536 promotion_rate(), cms_allocation_rate());
537 st->print(",cms_consumption_rate=%g,time_until_full=%g",
538 cms_consumption_rate(), time_until_cms_gen_full());
539 }
540 st->print(" ");
541 }
542 #endif // #ifndef PRODUCT
543
544 CMSCollector::CollectorState CMSCollector::_collectorState =
545 CMSCollector::Idling;
546 bool CMSCollector::_foregroundGCIsActive = false;
547 bool CMSCollector::_foregroundGCShouldWait = false;
548
549 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen,
550 CardTableRS* ct,
551 ConcurrentMarkSweepPolicy* cp):
552 _cmsGen(cmsGen),
553 _ct(ct),
554 _ref_processor(NULL), // will be set later
555 _conc_workers(NULL), // may be set later
556 _abort_preclean(false),
557 _start_sampling(false),
558 _between_prologue_and_epilogue(false),
559 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"),
560 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize),
561 -1 /* lock-free */, "No_lock" /* dummy */),
562 _modUnionClosure(&_modUnionTable),
563 _modUnionClosurePar(&_modUnionTable),
564 // Adjust my span to cover old (cms) gen
565 _span(cmsGen->reserved()),
566 // Construct the is_alive_closure with _span & markBitMap
567 _is_alive_closure(_span, &_markBitMap),
568 _restart_addr(NULL),
569 _overflow_list(NULL),
570 _stats(cmsGen),
571 _eden_chunk_array(NULL), // may be set in ctor body
572 _eden_chunk_capacity(0), // -- ditto --
573 _eden_chunk_index(0), // -- ditto --
574 _survivor_plab_array(NULL), // -- ditto --
575 _survivor_chunk_array(NULL), // -- ditto --
576 _survivor_chunk_capacity(0), // -- ditto --
577 _survivor_chunk_index(0), // -- ditto --
578 _ser_pmc_preclean_ovflw(0),
579 _ser_kac_preclean_ovflw(0),
580 _ser_pmc_remark_ovflw(0),
581 _par_pmc_remark_ovflw(0),
582 _ser_kac_ovflw(0),
583 _par_kac_ovflw(0),
584 #ifndef PRODUCT
585 _num_par_pushes(0),
586 #endif
587 _collection_count_start(0),
588 _verifying(false),
589 _icms_start_limit(NULL),
590 _icms_stop_limit(NULL),
591 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"),
592 _completed_initialization(false),
593 _collector_policy(cp),
594 _should_unload_classes(false),
595 _concurrent_cycles_since_last_unload(0),
596 _roots_scanning_options(0),
597 _inter_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding),
598 _intra_sweep_estimate(CMS_SweepWeight, CMS_SweepPadding)
599 {
600 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) {
601 ExplicitGCInvokesConcurrent = true;
602 }
603 // Now expand the span and allocate the collection support structures
604 // (MUT, marking bit map etc.) to cover both generations subject to
605 // collection.
606
607 // For use by dirty card to oop closures.
608 _cmsGen->cmsSpace()->set_collector(this);
609
610 // Allocate MUT and marking bit map
611 {
612 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag);
613 if (!_markBitMap.allocate(_span)) {
614 warning("Failed to allocate CMS Bit Map");
615 return;
616 }
617 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?");
618 }
619 {
620 _modUnionTable.allocate(_span);
621 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?");
622 }
623
624 if (!_markStack.allocate(MarkStackSize)) {
625 warning("Failed to allocate CMS Marking Stack");
626 return;
627 }
628
629 // Support for multi-threaded concurrent phases
630 if (CMSConcurrentMTEnabled) {
631 if (FLAG_IS_DEFAULT(ConcGCThreads)) {
632 // just for now
633 FLAG_SET_DEFAULT(ConcGCThreads, (ParallelGCThreads + 3)/4);
634 }
635 if (ConcGCThreads > 1) {
636 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads",
637 ConcGCThreads, true);
638 if (_conc_workers == NULL) {
639 warning("GC/CMS: _conc_workers allocation failure: "
640 "forcing -CMSConcurrentMTEnabled");
641 CMSConcurrentMTEnabled = false;
642 } else {
643 _conc_workers->initialize_workers();
644 }
645 } else {
646 CMSConcurrentMTEnabled = false;
647 }
648 }
649 if (!CMSConcurrentMTEnabled) {
650 ConcGCThreads = 0;
651 } else {
652 // Turn off CMSCleanOnEnter optimization temporarily for
653 // the MT case where it's not fixed yet; see 6178663.
654 CMSCleanOnEnter = false;
655 }
656 assert((_conc_workers != NULL) == (ConcGCThreads > 1),
657 "Inconsistency");
658
659 // Parallel task queues; these are shared for the
660 // concurrent and stop-world phases of CMS, but
661 // are not shared with parallel scavenge (ParNew).
662 {
663 uint i;
664 uint num_queues = (uint) MAX2(ParallelGCThreads, ConcGCThreads);
665
666 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled
667 || ParallelRefProcEnabled)
668 && num_queues > 0) {
669 _task_queues = new OopTaskQueueSet(num_queues);
670 if (_task_queues == NULL) {
671 warning("task_queues allocation failure.");
672 return;
673 }
674 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues, mtGC);
675 if (_hash_seed == NULL) {
676 warning("_hash_seed array allocation failure");
677 return;
678 }
679
680 typedef Padded<OopTaskQueue> PaddedOopTaskQueue;
681 for (i = 0; i < num_queues; i++) {
682 PaddedOopTaskQueue *q = new PaddedOopTaskQueue();
683 if (q == NULL) {
684 warning("work_queue allocation failure.");
685 return;
686 }
687 _task_queues->register_queue(i, q);
688 }
689 for (i = 0; i < num_queues; i++) {
690 _task_queues->queue(i)->initialize();
691 _hash_seed[i] = 17; // copied from ParNew
692 }
693 }
694 }
695
696 _cmsGen ->init_initiating_occupancy(CMSInitiatingOccupancyFraction, CMSTriggerRatio);
697
698 // Clip CMSBootstrapOccupancy between 0 and 100.
699 _bootstrap_occupancy = ((double)MIN2((uintx)100, MAX2((uintx)0, CMSBootstrapOccupancy)))
700 /(double)100;
701
702 _full_gcs_since_conc_gc = 0;
703
704 // Now tell CMS generations the identity of their collector
705 ConcurrentMarkSweepGeneration::set_collector(this);
706
707 // Create & start a CMS thread for this CMS collector
708 _cmsThread = ConcurrentMarkSweepThread::start(this);
709 assert(cmsThread() != NULL, "CMS Thread should have been created");
710 assert(cmsThread()->collector() == this,
711 "CMS Thread should refer to this gen");
712 assert(CGC_lock != NULL, "Where's the CGC_lock?");
713
714 // Support for parallelizing young gen rescan
715 GenCollectedHeap* gch = GenCollectedHeap::heap();
716 _young_gen = gch->prev_gen(_cmsGen);
717 if (gch->supports_inline_contig_alloc()) {
718 _top_addr = gch->top_addr();
719 _end_addr = gch->end_addr();
720 assert(_young_gen != NULL, "no _young_gen");
721 _eden_chunk_index = 0;
722 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain;
723 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity, mtGC);
724 if (_eden_chunk_array == NULL) {
725 _eden_chunk_capacity = 0;
726 warning("GC/CMS: _eden_chunk_array allocation failure");
727 }
728 }
729 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error");
730
731 // Support for parallelizing survivor space rescan
732 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) {
733 const size_t max_plab_samples =
734 ((DefNewGeneration*)_young_gen)->max_survivor_size()/MinTLABSize;
735
736 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads, mtGC);
737 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples, mtGC);
738 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads, mtGC);
739 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL
740 || _cursor == NULL) {
741 warning("Failed to allocate survivor plab/chunk array");
742 if (_survivor_plab_array != NULL) {
743 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
744 _survivor_plab_array = NULL;
745 }
746 if (_survivor_chunk_array != NULL) {
747 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
748 _survivor_chunk_array = NULL;
749 }
750 if (_cursor != NULL) {
751 FREE_C_HEAP_ARRAY(size_t, _cursor, mtGC);
752 _cursor = NULL;
753 }
754 } else {
755 _survivor_chunk_capacity = 2*max_plab_samples;
756 for (uint i = 0; i < ParallelGCThreads; i++) {
757 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples, mtGC);
758 if (vec == NULL) {
759 warning("Failed to allocate survivor plab array");
760 for (int j = i; j > 0; j--) {
761 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array(), mtGC);
762 }
763 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array, mtGC);
764 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array, mtGC);
765 _survivor_plab_array = NULL;
766 _survivor_chunk_array = NULL;
767 _survivor_chunk_capacity = 0;
768 break;
769 } else {
770 ChunkArray* cur =
771 ::new (&_survivor_plab_array[i]) ChunkArray(vec,
772 max_plab_samples);
773 assert(cur->end() == 0, "Should be 0");
774 assert(cur->array() == vec, "Should be vec");
775 assert(cur->capacity() == max_plab_samples, "Error");
776 }
777 }
778 }
779 }
780 assert( ( _survivor_plab_array != NULL
781 && _survivor_chunk_array != NULL)
782 || ( _survivor_chunk_capacity == 0
783 && _survivor_chunk_index == 0),
784 "Error");
785
786 // Choose what strong roots should be scanned depending on verification options
787 if (!CMSClassUnloadingEnabled) {
788 // If class unloading is disabled we want to include all classes into the root set.
789 add_root_scanning_option(SharedHeap::SO_AllClasses);
790 } else {
791 add_root_scanning_option(SharedHeap::SO_SystemClasses);
792 }
793
794 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;)
795 _gc_counters = new CollectorCounters("CMS", 1);
796 _completed_initialization = true;
797 _inter_sweep_timer.start(); // start of time
798 }
799
800 const char* ConcurrentMarkSweepGeneration::name() const {
801 return "concurrent mark-sweep generation";
802 }
803 void ConcurrentMarkSweepGeneration::update_counters() {
804 if (UsePerfData) {
805 _space_counters->update_all();
806 _gen_counters->update_all();
807 }
808 }
809
810 // this is an optimized version of update_counters(). it takes the
811 // used value as a parameter rather than computing it.
812 //
813 void ConcurrentMarkSweepGeneration::update_counters(size_t used) {
814 if (UsePerfData) {
815 _space_counters->update_used(used);
816 _space_counters->update_capacity();
817 _gen_counters->update_all();
818 }
819 }
820
821 void ConcurrentMarkSweepGeneration::print() const {
822 Generation::print();
823 cmsSpace()->print();
824 }
825
826 #ifndef PRODUCT
827 void ConcurrentMarkSweepGeneration::print_statistics() {
828 cmsSpace()->printFLCensus(0);
829 }
830 #endif
831
832 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) {
833 GenCollectedHeap* gch = GenCollectedHeap::heap();
834 if (PrintGCDetails) {
835 if (Verbose) {
836 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]",
837 level(), short_name(), s, used(), capacity());
838 } else {
839 gclog_or_tty->print("[%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]",
840 level(), short_name(), s, used() / K, capacity() / K);
841 }
842 }
843 if (Verbose) {
844 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")",
845 gch->used(), gch->capacity());
846 } else {
847 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)",
848 gch->used() / K, gch->capacity() / K);
849 }
850 }
851
852 size_t
853 ConcurrentMarkSweepGeneration::contiguous_available() const {
854 // dld proposes an improvement in precision here. If the committed
855 // part of the space ends in a free block we should add that to
856 // uncommitted size in the calculation below. Will make this
857 // change later, staying with the approximation below for the
858 // time being. -- ysr.
859 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc());
860 }
861
862 size_t
863 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const {
864 return _cmsSpace->max_alloc_in_words() * HeapWordSize;
865 }
866
867 size_t ConcurrentMarkSweepGeneration::max_available() const {
868 return free() + _virtual_space.uncommitted_size();
869 }
870
871 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe(size_t max_promotion_in_bytes) const {
872 size_t available = max_available();
873 size_t av_promo = (size_t)gc_stats()->avg_promoted()->padded_average();
874 bool res = (available >= av_promo) || (available >= max_promotion_in_bytes);
875 if (Verbose && PrintGCDetails) {
876 gclog_or_tty->print_cr(
877 "CMS: promo attempt is%s safe: available("SIZE_FORMAT") %s av_promo("SIZE_FORMAT"),"
878 "max_promo("SIZE_FORMAT")",
879 res? "":" not", available, res? ">=":"<",
880 av_promo, max_promotion_in_bytes);
881 }
882 return res;
883 }
884
885 // At a promotion failure dump information on block layout in heap
886 // (cms old generation).
887 void ConcurrentMarkSweepGeneration::promotion_failure_occurred() {
888 if (CMSDumpAtPromotionFailure) {
889 cmsSpace()->dump_at_safepoint_with_locks(collector(), gclog_or_tty);
890 }
891 }
892
893 CompactibleSpace*
894 ConcurrentMarkSweepGeneration::first_compaction_space() const {
895 return _cmsSpace;
896 }
897
898 void ConcurrentMarkSweepGeneration::reset_after_compaction() {
899 // Clear the promotion information. These pointers can be adjusted
900 // along with all the other pointers into the heap but
901 // compaction is expected to be a rare event with
902 // a heap using cms so don't do it without seeing the need.
903 if (CollectedHeap::use_parallel_gc_threads()) {
904 for (uint i = 0; i < ParallelGCThreads; i++) {
905 _par_gc_thread_states[i]->promo.reset();
906 }
907 }
908 }
909
910 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) {
911 blk->do_space(_cmsSpace);
912 }
913
914 void ConcurrentMarkSweepGeneration::compute_new_size() {
915 assert_locked_or_safepoint(Heap_lock);
916
917 // If incremental collection failed, we just want to expand
918 // to the limit.
919 if (incremental_collection_failed()) {
920 clear_incremental_collection_failed();
921 grow_to_reserved();
922 return;
923 }
924
925 size_t expand_bytes = 0;
926 double free_percentage = ((double) free()) / capacity();
927 double desired_free_percentage = (double) MinHeapFreeRatio / 100;
928 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100;
929
930 // compute expansion delta needed for reaching desired free percentage
931 if (free_percentage < desired_free_percentage) {
932 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
933 assert(desired_capacity >= capacity(), "invalid expansion size");
934 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes);
935 }
936 if (expand_bytes > 0) {
937 if (PrintGCDetails && Verbose) {
938 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage));
939 gclog_or_tty->print_cr("\nFrom compute_new_size: ");
940 gclog_or_tty->print_cr(" Free fraction %f", free_percentage);
941 gclog_or_tty->print_cr(" Desired free fraction %f",
942 desired_free_percentage);
943 gclog_or_tty->print_cr(" Maximum free fraction %f",
944 maximum_free_percentage);
945 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000);
946 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT,
947 desired_capacity/1000);
948 int prev_level = level() - 1;
949 if (prev_level >= 0) {
950 size_t prev_size = 0;
951 GenCollectedHeap* gch = GenCollectedHeap::heap();
952 Generation* prev_gen = gch->_gens[prev_level];
953 prev_size = prev_gen->capacity();
954 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT,
955 prev_size/1000);
956 }
957 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT,
958 unsafe_max_alloc_nogc()/1000);
959 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT,
960 contiguous_available()/1000);
961 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)",
962 expand_bytes);
963 }
964 // safe if expansion fails
965 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio);
966 if (PrintGCDetails && Verbose) {
967 gclog_or_tty->print_cr(" Expanded free fraction %f",
968 ((double) free()) / capacity());
969 }
970 }
971 }
972
973 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const {
974 return cmsSpace()->freelistLock();
975 }
976
977 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size,
978 bool tlab) {
979 CMSSynchronousYieldRequest yr;
980 MutexLockerEx x(freelistLock(),
981 Mutex::_no_safepoint_check_flag);
982 return have_lock_and_allocate(size, tlab);
983 }
984
985 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size,
986 bool tlab /* ignored */) {
987 assert_lock_strong(freelistLock());
988 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size);
989 HeapWord* res = cmsSpace()->allocate(adjustedSize);
990 // Allocate the object live (grey) if the background collector has
991 // started marking. This is necessary because the marker may
992 // have passed this address and consequently this object will
993 // not otherwise be greyed and would be incorrectly swept up.
994 // Note that if this object contains references, the writing
995 // of those references will dirty the card containing this object
996 // allowing the object to be blackened (and its references scanned)
997 // either during a preclean phase or at the final checkpoint.
998 if (res != NULL) {
999 // We may block here with an uninitialized object with
1000 // its mark-bit or P-bits not yet set. Such objects need
1001 // to be safely navigable by block_start().
1002 assert(oop(res)->klass_or_null() == NULL, "Object should be uninitialized here.");
1003 assert(!((FreeChunk*)res)->is_free(), "Error, block will look free but show wrong size");
1004 collector()->direct_allocated(res, adjustedSize);
1005 _direct_allocated_words += adjustedSize;
1006 // allocation counters
1007 NOT_PRODUCT(
1008 _numObjectsAllocated++;
1009 _numWordsAllocated += (int)adjustedSize;
1010 )
1011 }
1012 return res;
1013 }
1014
1015 // In the case of direct allocation by mutators in a generation that
1016 // is being concurrently collected, the object must be allocated
1017 // live (grey) if the background collector has started marking.
1018 // This is necessary because the marker may
1019 // have passed this address and consequently this object will
1020 // not otherwise be greyed and would be incorrectly swept up.
1021 // Note that if this object contains references, the writing
1022 // of those references will dirty the card containing this object
1023 // allowing the object to be blackened (and its references scanned)
1024 // either during a preclean phase or at the final checkpoint.
1025 void CMSCollector::direct_allocated(HeapWord* start, size_t size) {
1026 assert(_markBitMap.covers(start, size), "Out of bounds");
1027 if (_collectorState >= Marking) {
1028 MutexLockerEx y(_markBitMap.lock(),
1029 Mutex::_no_safepoint_check_flag);
1030 // [see comments preceding SweepClosure::do_blk() below for details]
1031 //
1032 // Can the P-bits be deleted now? JJJ
1033 //
1034 // 1. need to mark the object as live so it isn't collected
1035 // 2. need to mark the 2nd bit to indicate the object may be uninitialized
1036 // 3. need to mark the end of the object so marking, precleaning or sweeping
1037 // can skip over uninitialized or unparsable objects. An allocated
1038 // object is considered uninitialized for our purposes as long as
1039 // its klass word is NULL. All old gen objects are parsable
1040 // as soon as they are initialized.)
1041 _markBitMap.mark(start); // object is live
1042 _markBitMap.mark(start + 1); // object is potentially uninitialized?
1043 _markBitMap.mark(start + size - 1);
1044 // mark end of object
1045 }
1046 // check that oop looks uninitialized
1047 assert(oop(start)->klass_or_null() == NULL, "_klass should be NULL");
1048 }
1049
1050 void CMSCollector::promoted(bool par, HeapWord* start,
1051 bool is_obj_array, size_t obj_size) {
1052 assert(_markBitMap.covers(start), "Out of bounds");
1053 // See comment in direct_allocated() about when objects should
1054 // be allocated live.
1055 if (_collectorState >= Marking) {
1056 // we already hold the marking bit map lock, taken in
1057 // the prologue
1058 if (par) {
1059 _markBitMap.par_mark(start);
1060 } else {
1061 _markBitMap.mark(start);
1062 }
1063 // We don't need to mark the object as uninitialized (as
1064 // in direct_allocated above) because this is being done with the
1065 // world stopped and the object will be initialized by the
1066 // time the marking, precleaning or sweeping get to look at it.
1067 // But see the code for copying objects into the CMS generation,
1068 // where we need to ensure that concurrent readers of the
1069 // block offset table are able to safely navigate a block that
1070 // is in flux from being free to being allocated (and in
1071 // transition while being copied into) and subsequently
1072 // becoming a bona-fide object when the copy/promotion is complete.
1073 assert(SafepointSynchronize::is_at_safepoint(),
1074 "expect promotion only at safepoints");
1075
1076 if (_collectorState < Sweeping) {
1077 // Mark the appropriate cards in the modUnionTable, so that
1078 // this object gets scanned before the sweep. If this is
1079 // not done, CMS generation references in the object might
1080 // not get marked.
1081 // For the case of arrays, which are otherwise precisely
1082 // marked, we need to dirty the entire array, not just its head.
1083 if (is_obj_array) {
1084 // The [par_]mark_range() method expects mr.end() below to
1085 // be aligned to the granularity of a bit's representation
1086 // in the heap. In the case of the MUT below, that's a
1087 // card size.
1088 MemRegion mr(start,
1089 (HeapWord*)round_to((intptr_t)(start + obj_size),
1090 CardTableModRefBS::card_size /* bytes */));
1091 if (par) {
1092 _modUnionTable.par_mark_range(mr);
1093 } else {
1094 _modUnionTable.mark_range(mr);
1095 }
1096 } else { // not an obj array; we can just mark the head
1097 if (par) {
1098 _modUnionTable.par_mark(start);
1099 } else {
1100 _modUnionTable.mark(start);
1101 }
1102 }
1103 }
1104 }
1105 }
1106
1107 static inline size_t percent_of_space(Space* space, HeapWord* addr)
1108 {
1109 size_t delta = pointer_delta(addr, space->bottom());
1110 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize));
1111 }
1112
1113 void CMSCollector::icms_update_allocation_limits()
1114 {
1115 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0);
1116 EdenSpace* eden = gen0->as_DefNewGeneration()->eden();
1117
1118 const unsigned int duty_cycle = stats().icms_update_duty_cycle();
1119 if (CMSTraceIncrementalPacing) {
1120 stats().print();
1121 }
1122
1123 assert(duty_cycle <= 100, "invalid duty cycle");
1124 if (duty_cycle != 0) {
1125 // The duty_cycle is a percentage between 0 and 100; convert to words and
1126 // then compute the offset from the endpoints of the space.
1127 size_t free_words = eden->free() / HeapWordSize;
1128 double free_words_dbl = (double)free_words;
1129 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0);
1130 size_t offset_words = (free_words - duty_cycle_words) / 2;
1131
1132 _icms_start_limit = eden->top() + offset_words;
1133 _icms_stop_limit = eden->end() - offset_words;
1134
1135 // The limits may be adjusted (shifted to the right) by
1136 // CMSIncrementalOffset, to allow the application more mutator time after a
1137 // young gen gc (when all mutators were stopped) and before CMS starts and
1138 // takes away one or more cpus.
1139 if (CMSIncrementalOffset != 0) {
1140 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0;
1141 size_t adjustment = (size_t)adjustment_dbl;
1142 HeapWord* tmp_stop = _icms_stop_limit + adjustment;
1143 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) {
1144 _icms_start_limit += adjustment;
1145 _icms_stop_limit = tmp_stop;
1146 }
1147 }
1148 }
1149 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) {
1150 _icms_start_limit = _icms_stop_limit = eden->end();
1151 }
1152
1153 // Install the new start limit.
1154 eden->set_soft_end(_icms_start_limit);
1155
1156 if (CMSTraceIncrementalMode) {
1157 gclog_or_tty->print(" icms alloc limits: "
1158 PTR_FORMAT "," PTR_FORMAT
1159 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ",
1160 _icms_start_limit, _icms_stop_limit,
1161 percent_of_space(eden, _icms_start_limit),
1162 percent_of_space(eden, _icms_stop_limit));
1163 if (Verbose) {
1164 gclog_or_tty->print("eden: ");
1165 eden->print_on(gclog_or_tty);
1166 }
1167 }
1168 }
1169
1170 // Any changes here should try to maintain the invariant
1171 // that if this method is called with _icms_start_limit
1172 // and _icms_stop_limit both NULL, then it should return NULL
1173 // and not notify the icms thread.
1174 HeapWord*
1175 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top,
1176 size_t word_size)
1177 {
1178 // A start_limit equal to end() means the duty cycle is 0, so treat that as a
1179 // nop.
1180 if (CMSIncrementalMode && _icms_start_limit != space->end()) {
1181 if (top <= _icms_start_limit) {
1182 if (CMSTraceIncrementalMode) {
1183 space->print_on(gclog_or_tty);
1184 gclog_or_tty->stamp();
1185 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT
1186 ", new limit=" PTR_FORMAT
1187 " (" SIZE_FORMAT "%%)",
1188 top, _icms_stop_limit,
1189 percent_of_space(space, _icms_stop_limit));
1190 }
1191 ConcurrentMarkSweepThread::start_icms();
1192 assert(top < _icms_stop_limit, "Tautology");
1193 if (word_size < pointer_delta(_icms_stop_limit, top)) {
1194 return _icms_stop_limit;
1195 }
1196
1197 // The allocation will cross both the _start and _stop limits, so do the
1198 // stop notification also and return end().
1199 if (CMSTraceIncrementalMode) {
1200 space->print_on(gclog_or_tty);
1201 gclog_or_tty->stamp();
1202 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT
1203 ", new limit=" PTR_FORMAT
1204 " (" SIZE_FORMAT "%%)",
1205 top, space->end(),
1206 percent_of_space(space, space->end()));
1207 }
1208 ConcurrentMarkSweepThread::stop_icms();
1209 return space->end();
1210 }
1211
1212 if (top <= _icms_stop_limit) {
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 top, space->end(),
1220 percent_of_space(space, space->end()));
1221 }
1222 ConcurrentMarkSweepThread::stop_icms();
1223 return space->end();
1224 }
1225
1226 if (CMSTraceIncrementalMode) {
1227 space->print_on(gclog_or_tty);
1228 gclog_or_tty->stamp();
1229 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT
1230 ", new limit=" PTR_FORMAT,
1231 top, NULL);
1232 }
1233 }
1234
1235 return NULL;
1236 }
1237
1238 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size) {
1239 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in");
1240 // allocate, copy and if necessary update promoinfo --
1241 // delegate to underlying space.
1242 assert_lock_strong(freelistLock());
1243
1244 #ifndef PRODUCT
1245 if (Universe::heap()->promotion_should_fail()) {
1246 return NULL;
1247 }
1248 #endif // #ifndef PRODUCT
1249
1250 oop res = _cmsSpace->promote(obj, obj_size);
1251 if (res == NULL) {
1252 // expand and retry
1253 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords
1254 expand(s*HeapWordSize, MinHeapDeltaBytes,
1255 CMSExpansionCause::_satisfy_promotion);
1256 // Since there's currently no next generation, we don't try to promote
1257 // into a more senior generation.
1258 assert(next_gen() == NULL, "assumption, based upon which no attempt "
1259 "is made to pass on a possibly failing "
1260 "promotion to next generation");
1261 res = _cmsSpace->promote(obj, obj_size);
1262 }
1263 if (res != NULL) {
1264 // See comment in allocate() about when objects should
1265 // be allocated live.
1266 assert(obj->is_oop(), "Will dereference klass pointer below");
1267 collector()->promoted(false, // Not parallel
1268 (HeapWord*)res, obj->is_objArray(), obj_size);
1269 // promotion counters
1270 NOT_PRODUCT(
1271 _numObjectsPromoted++;
1272 _numWordsPromoted +=
1273 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size()));
1274 )
1275 }
1276 return res;
1277 }
1278
1279
1280 HeapWord*
1281 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space,
1282 HeapWord* top,
1283 size_t word_sz)
1284 {
1285 return collector()->allocation_limit_reached(space, top, word_sz);
1286 }
1287
1288 // IMPORTANT: Notes on object size recognition in CMS.
1289 // ---------------------------------------------------
1290 // A block of storage in the CMS generation is always in
1291 // one of three states. A free block (FREE), an allocated
1292 // object (OBJECT) whose size() method reports the correct size,
1293 // and an intermediate state (TRANSIENT) in which its size cannot
1294 // be accurately determined.
1295 // STATE IDENTIFICATION: (32 bit and 64 bit w/o COOPS)
1296 // -----------------------------------------------------
1297 // FREE: klass_word & 1 == 1; mark_word holds block size
1298 //
1299 // OBJECT: klass_word installed; klass_word != 0 && klass_word & 1 == 0;
1300 // obj->size() computes correct size
1301 //
1302 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1303 //
1304 // STATE IDENTIFICATION: (64 bit+COOPS)
1305 // ------------------------------------
1306 // FREE: mark_word & CMS_FREE_BIT == 1; mark_word & ~CMS_FREE_BIT gives block_size
1307 //
1308 // OBJECT: klass_word installed; klass_word != 0;
1309 // obj->size() computes correct size
1310 //
1311 // TRANSIENT: klass_word == 0; size is indeterminate until we become an OBJECT
1312 //
1313 //
1314 // STATE TRANSITION DIAGRAM
1315 //
1316 // mut / parnew mut / parnew
1317 // FREE --------------------> TRANSIENT ---------------------> OBJECT --|
1318 // ^ |
1319 // |------------------------ DEAD <------------------------------------|
1320 // sweep mut
1321 //
1322 // While a block is in TRANSIENT state its size cannot be determined
1323 // so readers will either need to come back later or stall until
1324 // the size can be determined. Note that for the case of direct
1325 // allocation, P-bits, when available, may be used to determine the
1326 // size of an object that may not yet have been initialized.
1327
1328 // Things to support parallel young-gen collection.
1329 oop
1330 ConcurrentMarkSweepGeneration::par_promote(int thread_num,
1331 oop old, markOop m,
1332 size_t word_sz) {
1333 #ifndef PRODUCT
1334 if (Universe::heap()->promotion_should_fail()) {
1335 return NULL;
1336 }
1337 #endif // #ifndef PRODUCT
1338
1339 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1340 PromotionInfo* promoInfo = &ps->promo;
1341 // if we are tracking promotions, then first ensure space for
1342 // promotion (including spooling space for saving header if necessary).
1343 // then allocate and copy, then track promoted info if needed.
1344 // When tracking (see PromotionInfo::track()), the mark word may
1345 // be displaced and in this case restoration of the mark word
1346 // occurs in the (oop_since_save_marks_)iterate phase.
1347 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) {
1348 // Out of space for allocating spooling buffers;
1349 // try expanding and allocating spooling buffers.
1350 if (!expand_and_ensure_spooling_space(promoInfo)) {
1351 return NULL;
1352 }
1353 }
1354 assert(promoInfo->has_spooling_space(), "Control point invariant");
1355 const size_t alloc_sz = CompactibleFreeListSpace::adjustObjectSize(word_sz);
1356 HeapWord* obj_ptr = ps->lab.alloc(alloc_sz);
1357 if (obj_ptr == NULL) {
1358 obj_ptr = expand_and_par_lab_allocate(ps, alloc_sz);
1359 if (obj_ptr == NULL) {
1360 return NULL;
1361 }
1362 }
1363 oop obj = oop(obj_ptr);
1364 OrderAccess::storestore();
1365 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1366 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1367 // IMPORTANT: See note on object initialization for CMS above.
1368 // Otherwise, copy the object. Here we must be careful to insert the
1369 // klass pointer last, since this marks the block as an allocated object.
1370 // Except with compressed oops it's the mark word.
1371 HeapWord* old_ptr = (HeapWord*)old;
1372 // Restore the mark word copied above.
1373 obj->set_mark(m);
1374 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1375 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1376 OrderAccess::storestore();
1377
1378 if (UseCompressedKlassPointers) {
1379 // Copy gap missed by (aligned) header size calculation below
1380 obj->set_klass_gap(old->klass_gap());
1381 }
1382 if (word_sz > (size_t)oopDesc::header_size()) {
1383 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(),
1384 obj_ptr + oopDesc::header_size(),
1385 word_sz - oopDesc::header_size());
1386 }
1387
1388 // Now we can track the promoted object, if necessary. We take care
1389 // to delay the transition from uninitialized to full object
1390 // (i.e., insertion of klass pointer) until after, so that it
1391 // atomically becomes a promoted object.
1392 if (promoInfo->tracking()) {
1393 promoInfo->track((PromotedObject*)obj, old->klass());
1394 }
1395 assert(obj->klass_or_null() == NULL, "Object should be uninitialized here.");
1396 assert(!((FreeChunk*)obj_ptr)->is_free(), "Error, block will look free but show wrong size");
1397 assert(old->is_oop(), "Will use and dereference old klass ptr below");
1398
1399 // Finally, install the klass pointer (this should be volatile).
1400 OrderAccess::storestore();
1401 obj->set_klass(old->klass());
1402 // We should now be able to calculate the right size for this object
1403 assert(obj->is_oop() && obj->size() == (int)word_sz, "Error, incorrect size computed for promoted object");
1404
1405 collector()->promoted(true, // parallel
1406 obj_ptr, old->is_objArray(), word_sz);
1407
1408 NOT_PRODUCT(
1409 Atomic::inc_ptr(&_numObjectsPromoted);
1410 Atomic::add_ptr(alloc_sz, &_numWordsPromoted);
1411 )
1412
1413 return obj;
1414 }
1415
1416 void
1417 ConcurrentMarkSweepGeneration::
1418 par_promote_alloc_undo(int thread_num,
1419 HeapWord* obj, size_t word_sz) {
1420 // CMS does not support promotion undo.
1421 ShouldNotReachHere();
1422 }
1423
1424 void
1425 ConcurrentMarkSweepGeneration::
1426 par_promote_alloc_done(int thread_num) {
1427 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1428 ps->lab.retire(thread_num);
1429 }
1430
1431 void
1432 ConcurrentMarkSweepGeneration::
1433 par_oop_since_save_marks_iterate_done(int thread_num) {
1434 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num];
1435 ParScanWithoutBarrierClosure* dummy_cl = NULL;
1436 ps->promo.promoted_oops_iterate_nv(dummy_cl);
1437 }
1438
1439 bool ConcurrentMarkSweepGeneration::should_collect(bool full,
1440 size_t size,
1441 bool tlab)
1442 {
1443 // We allow a STW collection only if a full
1444 // collection was requested.
1445 return full || should_allocate(size, tlab); // FIX ME !!!
1446 // This and promotion failure handling are connected at the
1447 // hip and should be fixed by untying them.
1448 }
1449
1450 bool CMSCollector::shouldConcurrentCollect() {
1451 if (_full_gc_requested) {
1452 if (Verbose && PrintGCDetails) {
1453 gclog_or_tty->print_cr("CMSCollector: collect because of explicit "
1454 " gc request (or gc_locker)");
1455 }
1456 return true;
1457 }
1458
1459 // For debugging purposes, change the type of collection.
1460 // If the rotation is not on the concurrent collection
1461 // type, don't start a concurrent collection.
1462 NOT_PRODUCT(
1463 if (RotateCMSCollectionTypes &&
1464 (_cmsGen->debug_collection_type() !=
1465 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) {
1466 assert(_cmsGen->debug_collection_type() !=
1467 ConcurrentMarkSweepGeneration::Unknown_collection_type,
1468 "Bad cms collection type");
1469 return false;
1470 }
1471 )
1472
1473 FreelistLocker x(this);
1474 // ------------------------------------------------------------------
1475 // Print out lots of information which affects the initiation of
1476 // a collection.
1477 if (PrintCMSInitiationStatistics && stats().valid()) {
1478 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: ");
1479 gclog_or_tty->stamp();
1480 gclog_or_tty->print_cr("");
1481 stats().print_on(gclog_or_tty);
1482 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f",
1483 stats().time_until_cms_gen_full());
1484 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free());
1485 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT,
1486 _cmsGen->contiguous_available());
1487 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate());
1488 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate());
1489 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy());
1490 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", _cmsGen->initiating_occupancy());
1491 gclog_or_tty->print_cr("metadata initialized %d",
1492 MetaspaceGC::should_concurrent_collect());
1493 }
1494 // ------------------------------------------------------------------
1495
1496 // If the estimated time to complete a cms collection (cms_duration())
1497 // is less than the estimated time remaining until the cms generation
1498 // is full, start a collection.
1499 if (!UseCMSInitiatingOccupancyOnly) {
1500 if (stats().valid()) {
1501 if (stats().time_until_cms_start() == 0.0) {
1502 return true;
1503 }
1504 } else {
1505 // We want to conservatively collect somewhat early in order
1506 // to try and "bootstrap" our CMS/promotion statistics;
1507 // this branch will not fire after the first successful CMS
1508 // collection because the stats should then be valid.
1509 if (_cmsGen->occupancy() >= _bootstrap_occupancy) {
1510 if (Verbose && PrintGCDetails) {
1511 gclog_or_tty->print_cr(
1512 " CMSCollector: collect for bootstrapping statistics:"
1513 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(),
1514 _bootstrap_occupancy);
1515 }
1516 return true;
1517 }
1518 }
1519 }
1520
1521 // Otherwise, we start a collection cycle if
1522 // old gen want a collection cycle started. Each may use
1523 // an appropriate criterion for making this decision.
1524 // XXX We need to make sure that the gen expansion
1525 // criterion dovetails well with this. XXX NEED TO FIX THIS
1526 if (_cmsGen->should_concurrent_collect()) {
1527 if (Verbose && PrintGCDetails) {
1528 gclog_or_tty->print_cr("CMS old gen initiated");
1529 }
1530 return true;
1531 }
1532
1533 // We start a collection if we believe an incremental collection may fail;
1534 // this is not likely to be productive in practice because it's probably too
1535 // late anyway.
1536 GenCollectedHeap* gch = GenCollectedHeap::heap();
1537 assert(gch->collector_policy()->is_two_generation_policy(),
1538 "You may want to check the correctness of the following");
1539 if (gch->incremental_collection_will_fail(true /* consult_young */)) {
1540 if (Verbose && PrintGCDetails) {
1541 gclog_or_tty->print("CMSCollector: collect because incremental collection will fail ");
1542 }
1543 return true;
1544 }
1545
1546 if (MetaspaceGC::should_concurrent_collect()) {
1547 if (Verbose && PrintGCDetails) {
1548 gclog_or_tty->print("CMSCollector: collect for metadata allocation ");
1549 }
1550 return true;
1551 }
1552
1553 return false;
1554 }
1555
1556 // Clear _expansion_cause fields of constituent generations
1557 void CMSCollector::clear_expansion_cause() {
1558 _cmsGen->clear_expansion_cause();
1559 }
1560
1561 // We should be conservative in starting a collection cycle. To
1562 // start too eagerly runs the risk of collecting too often in the
1563 // extreme. To collect too rarely falls back on full collections,
1564 // which works, even if not optimum in terms of concurrent work.
1565 // As a work around for too eagerly collecting, use the flag
1566 // UseCMSInitiatingOccupancyOnly. This also has the advantage of
1567 // giving the user an easily understandable way of controlling the
1568 // collections.
1569 // We want to start a new collection cycle if any of the following
1570 // conditions hold:
1571 // . our current occupancy exceeds the configured initiating occupancy
1572 // for this generation, or
1573 // . we recently needed to expand this space and have not, since that
1574 // expansion, done a collection of this generation, or
1575 // . the underlying space believes that it may be a good idea to initiate
1576 // a concurrent collection (this may be based on criteria such as the
1577 // following: the space uses linear allocation and linear allocation is
1578 // going to fail, or there is believed to be excessive fragmentation in
1579 // the generation, etc... or ...
1580 // [.(currently done by CMSCollector::shouldConcurrentCollect() only for
1581 // the case of the old generation; see CR 6543076):
1582 // we may be approaching a point at which allocation requests may fail because
1583 // we will be out of sufficient free space given allocation rate estimates.]
1584 bool ConcurrentMarkSweepGeneration::should_concurrent_collect() const {
1585
1586 assert_lock_strong(freelistLock());
1587 if (occupancy() > initiating_occupancy()) {
1588 if (PrintGCDetails && Verbose) {
1589 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ",
1590 short_name(), occupancy(), initiating_occupancy());
1591 }
1592 return true;
1593 }
1594 if (UseCMSInitiatingOccupancyOnly) {
1595 return false;
1596 }
1597 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) {
1598 if (PrintGCDetails && Verbose) {
1599 gclog_or_tty->print(" %s: collect because expanded for allocation ",
1600 short_name());
1601 }
1602 return true;
1603 }
1604 if (_cmsSpace->should_concurrent_collect()) {
1605 if (PrintGCDetails && Verbose) {
1606 gclog_or_tty->print(" %s: collect because cmsSpace says so ",
1607 short_name());
1608 }
1609 return true;
1610 }
1611 return false;
1612 }
1613
1614 void ConcurrentMarkSweepGeneration::collect(bool full,
1615 bool clear_all_soft_refs,
1616 size_t size,
1617 bool tlab)
1618 {
1619 collector()->collect(full, clear_all_soft_refs, size, tlab);
1620 }
1621
1622 void CMSCollector::collect(bool full,
1623 bool clear_all_soft_refs,
1624 size_t size,
1625 bool tlab)
1626 {
1627 if (!UseCMSCollectionPassing && _collectorState > Idling) {
1628 // For debugging purposes skip the collection if the state
1629 // is not currently idle
1630 if (TraceCMSState) {
1631 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d",
1632 Thread::current(), full, _collectorState);
1633 }
1634 return;
1635 }
1636
1637 // The following "if" branch is present for defensive reasons.
1638 // In the current uses of this interface, it can be replaced with:
1639 // assert(!GC_locker.is_active(), "Can't be called otherwise");
1640 // But I am not placing that assert here to allow future
1641 // generality in invoking this interface.
1642 if (GC_locker::is_active()) {
1643 // A consistency test for GC_locker
1644 assert(GC_locker::needs_gc(), "Should have been set already");
1645 // Skip this foreground collection, instead
1646 // expanding the heap if necessary.
1647 // Need the free list locks for the call to free() in compute_new_size()
1648 compute_new_size();
1649 return;
1650 }
1651 acquire_control_and_collect(full, clear_all_soft_refs);
1652 _full_gcs_since_conc_gc++;
1653
1654 }
1655
1656 void CMSCollector::request_full_gc(unsigned int full_gc_count) {
1657 GenCollectedHeap* gch = GenCollectedHeap::heap();
1658 unsigned int gc_count = gch->total_full_collections();
1659 if (gc_count == full_gc_count) {
1660 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag);
1661 _full_gc_requested = true;
1662 CGC_lock->notify(); // nudge CMS thread
1663 } else {
1664 assert(gc_count > full_gc_count, "Error: causal loop");
1665 }
1666 }
1667
1668
1669 // The foreground and background collectors need to coordinate in order
1670 // to make sure that they do not mutually interfere with CMS collections.
1671 // When a background collection is active,
1672 // the foreground collector may need to take over (preempt) and
1673 // synchronously complete an ongoing collection. Depending on the
1674 // frequency of the background collections and the heap usage
1675 // of the application, this preemption can be seldom or frequent.
1676 // There are only certain
1677 // points in the background collection that the "collection-baton"
1678 // can be passed to the foreground collector.
1679 //
1680 // The foreground collector will wait for the baton before
1681 // starting any part of the collection. The foreground collector
1682 // will only wait at one location.
1683 //
1684 // The background collector will yield the baton before starting a new
1685 // phase of the collection (e.g., before initial marking, marking from roots,
1686 // precleaning, final re-mark, sweep etc.) This is normally done at the head
1687 // of the loop which switches the phases. The background collector does some
1688 // of the phases (initial mark, final re-mark) with the world stopped.
1689 // Because of locking involved in stopping the world,
1690 // the foreground collector should not block waiting for the background
1691 // collector when it is doing a stop-the-world phase. The background
1692 // collector will yield the baton at an additional point just before
1693 // it enters a stop-the-world phase. Once the world is stopped, the
1694 // background collector checks the phase of the collection. If the
1695 // phase has not changed, it proceeds with the collection. If the
1696 // phase has changed, it skips that phase of the collection. See
1697 // the comments on the use of the Heap_lock in collect_in_background().
1698 //
1699 // Variable used in baton passing.
1700 // _foregroundGCIsActive - Set to true by the foreground collector when
1701 // it wants the baton. The foreground clears it when it has finished
1702 // the collection.
1703 // _foregroundGCShouldWait - Set to true by the background collector
1704 // when it is running. The foreground collector waits while
1705 // _foregroundGCShouldWait is true.
1706 // CGC_lock - monitor used to protect access to the above variables
1707 // and to notify the foreground and background collectors.
1708 // _collectorState - current state of the CMS collection.
1709 //
1710 // The foreground collector
1711 // acquires the CGC_lock
1712 // sets _foregroundGCIsActive
1713 // waits on the CGC_lock for _foregroundGCShouldWait to be false
1714 // various locks acquired in preparation for the collection
1715 // are released so as not to block the background collector
1716 // that is in the midst of a collection
1717 // proceeds with the collection
1718 // clears _foregroundGCIsActive
1719 // returns
1720 //
1721 // The background collector in a loop iterating on the phases of the
1722 // collection
1723 // acquires the CGC_lock
1724 // sets _foregroundGCShouldWait
1725 // if _foregroundGCIsActive is set
1726 // clears _foregroundGCShouldWait, notifies _CGC_lock
1727 // waits on _CGC_lock for _foregroundGCIsActive to become false
1728 // and exits the loop.
1729 // otherwise
1730 // proceed with that phase of the collection
1731 // if the phase is a stop-the-world phase,
1732 // yield the baton once more just before enqueueing
1733 // the stop-world CMS operation (executed by the VM thread).
1734 // returns after all phases of the collection are done
1735 //
1736
1737 void CMSCollector::acquire_control_and_collect(bool full,
1738 bool clear_all_soft_refs) {
1739 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint");
1740 assert(!Thread::current()->is_ConcurrentGC_thread(),
1741 "shouldn't try to acquire control from self!");
1742
1743 // Start the protocol for acquiring control of the
1744 // collection from the background collector (aka CMS thread).
1745 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1746 "VM thread should have CMS token");
1747 // Remember the possibly interrupted state of an ongoing
1748 // concurrent collection
1749 CollectorState first_state = _collectorState;
1750
1751 // Signal to a possibly ongoing concurrent collection that
1752 // we want to do a foreground collection.
1753 _foregroundGCIsActive = true;
1754
1755 // Disable incremental mode during a foreground collection.
1756 ICMSDisabler icms_disabler;
1757
1758 // release locks and wait for a notify from the background collector
1759 // releasing the locks in only necessary for phases which
1760 // do yields to improve the granularity of the collection.
1761 assert_lock_strong(bitMapLock());
1762 // We need to lock the Free list lock for the space that we are
1763 // currently collecting.
1764 assert(haveFreelistLocks(), "Must be holding free list locks");
1765 bitMapLock()->unlock();
1766 releaseFreelistLocks();
1767 {
1768 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
1769 if (_foregroundGCShouldWait) {
1770 // We are going to be waiting for action for the CMS thread;
1771 // it had better not be gone (for instance at shutdown)!
1772 assert(ConcurrentMarkSweepThread::cmst() != NULL,
1773 "CMS thread must be running");
1774 // Wait here until the background collector gives us the go-ahead
1775 ConcurrentMarkSweepThread::clear_CMS_flag(
1776 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token
1777 // Get a possibly blocked CMS thread going:
1778 // Note that we set _foregroundGCIsActive true above,
1779 // without protection of the CGC_lock.
1780 CGC_lock->notify();
1781 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(),
1782 "Possible deadlock");
1783 while (_foregroundGCShouldWait) {
1784 // wait for notification
1785 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
1786 // Possibility of delay/starvation here, since CMS token does
1787 // not know to give priority to VM thread? Actually, i think
1788 // there wouldn't be any delay/starvation, but the proof of
1789 // that "fact" (?) appears non-trivial. XXX 20011219YSR
1790 }
1791 ConcurrentMarkSweepThread::set_CMS_flag(
1792 ConcurrentMarkSweepThread::CMS_vm_has_token);
1793 }
1794 }
1795 // The CMS_token is already held. Get back the other locks.
1796 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
1797 "VM thread should have CMS token");
1798 getFreelistLocks();
1799 bitMapLock()->lock_without_safepoint_check();
1800 if (TraceCMSState) {
1801 gclog_or_tty->print_cr("CMS foreground collector has asked for control "
1802 INTPTR_FORMAT " with first state %d", Thread::current(), first_state);
1803 gclog_or_tty->print_cr(" gets control with state %d", _collectorState);
1804 }
1805
1806 // Check if we need to do a compaction, or if not, whether
1807 // we need to start the mark-sweep from scratch.
1808 bool should_compact = false;
1809 bool should_start_over = false;
1810 decide_foreground_collection_type(clear_all_soft_refs,
1811 &should_compact, &should_start_over);
1812
1813 NOT_PRODUCT(
1814 if (RotateCMSCollectionTypes) {
1815 if (_cmsGen->debug_collection_type() ==
1816 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) {
1817 should_compact = true;
1818 } else if (_cmsGen->debug_collection_type() ==
1819 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) {
1820 should_compact = false;
1821 }
1822 }
1823 )
1824
1825 if (PrintGCDetails && first_state > Idling) {
1826 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause();
1827 if (GCCause::is_user_requested_gc(cause) ||
1828 GCCause::is_serviceability_requested_gc(cause)) {
1829 gclog_or_tty->print(" (concurrent mode interrupted)");
1830 } else {
1831 gclog_or_tty->print(" (concurrent mode failure)");
1832 }
1833 }
1834
1835 if (should_compact) {
1836 // If the collection is being acquired from the background
1837 // collector, there may be references on the discovered
1838 // references lists that have NULL referents (being those
1839 // that were concurrently cleared by a mutator) or
1840 // that are no longer active (having been enqueued concurrently
1841 // by the mutator).
1842 // Scrub the list of those references because Mark-Sweep-Compact
1843 // code assumes referents are not NULL and that all discovered
1844 // Reference objects are active.
1845 ref_processor()->clean_up_discovered_references();
1846
1847 do_compaction_work(clear_all_soft_refs);
1848
1849 // Has the GC time limit been exceeded?
1850 DefNewGeneration* young_gen = _young_gen->as_DefNewGeneration();
1851 size_t max_eden_size = young_gen->max_capacity() -
1852 young_gen->to()->capacity() -
1853 young_gen->from()->capacity();
1854 GenCollectedHeap* gch = GenCollectedHeap::heap();
1855 GCCause::Cause gc_cause = gch->gc_cause();
1856 size_policy()->check_gc_overhead_limit(_young_gen->used(),
1857 young_gen->eden()->used(),
1858 _cmsGen->max_capacity(),
1859 max_eden_size,
1860 full,
1861 gc_cause,
1862 gch->collector_policy());
1863 } else {
1864 do_mark_sweep_work(clear_all_soft_refs, first_state,
1865 should_start_over);
1866 }
1867 // Reset the expansion cause, now that we just completed
1868 // a collection cycle.
1869 clear_expansion_cause();
1870 _foregroundGCIsActive = false;
1871 return;
1872 }
1873
1874 // Resize the tenured generation
1875 // after obtaining the free list locks for the
1876 // two generations.
1877 void CMSCollector::compute_new_size() {
1878 assert_locked_or_safepoint(Heap_lock);
1879 FreelistLocker z(this);
1880 MetaspaceGC::compute_new_size();
1881 _cmsGen->compute_new_size();
1882 }
1883
1884 // A work method used by foreground collection to determine
1885 // what type of collection (compacting or not, continuing or fresh)
1886 // it should do.
1887 // NOTE: the intent is to make UseCMSCompactAtFullCollection
1888 // and CMSCompactWhenClearAllSoftRefs the default in the future
1889 // and do away with the flags after a suitable period.
1890 void CMSCollector::decide_foreground_collection_type(
1891 bool clear_all_soft_refs, bool* should_compact,
1892 bool* should_start_over) {
1893 // Normally, we'll compact only if the UseCMSCompactAtFullCollection
1894 // flag is set, and we have either requested a System.gc() or
1895 // the number of full gc's since the last concurrent cycle
1896 // has exceeded the threshold set by CMSFullGCsBeforeCompaction,
1897 // or if an incremental collection has failed
1898 GenCollectedHeap* gch = GenCollectedHeap::heap();
1899 assert(gch->collector_policy()->is_two_generation_policy(),
1900 "You may want to check the correctness of the following");
1901 // Inform cms gen if this was due to partial collection failing.
1902 // The CMS gen may use this fact to determine its expansion policy.
1903 if (gch->incremental_collection_will_fail(false /* don't consult_young */)) {
1904 assert(!_cmsGen->incremental_collection_failed(),
1905 "Should have been noticed, reacted to and cleared");
1906 _cmsGen->set_incremental_collection_failed();
1907 }
1908 *should_compact =
1909 UseCMSCompactAtFullCollection &&
1910 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) ||
1911 GCCause::is_user_requested_gc(gch->gc_cause()) ||
1912 gch->incremental_collection_will_fail(true /* consult_young */));
1913 *should_start_over = false;
1914 if (clear_all_soft_refs && !*should_compact) {
1915 // We are about to do a last ditch collection attempt
1916 // so it would normally make sense to do a compaction
1917 // to reclaim as much space as possible.
1918 if (CMSCompactWhenClearAllSoftRefs) {
1919 // Default: The rationale is that in this case either
1920 // we are past the final marking phase, in which case
1921 // we'd have to start over, or so little has been done
1922 // that there's little point in saving that work. Compaction
1923 // appears to be the sensible choice in either case.
1924 *should_compact = true;
1925 } else {
1926 // We have been asked to clear all soft refs, but not to
1927 // compact. Make sure that we aren't past the final checkpoint
1928 // phase, for that is where we process soft refs. If we are already
1929 // past that phase, we'll need to redo the refs discovery phase and
1930 // if necessary clear soft refs that weren't previously
1931 // cleared. We do so by remembering the phase in which
1932 // we came in, and if we are past the refs processing
1933 // phase, we'll choose to just redo the mark-sweep
1934 // collection from scratch.
1935 if (_collectorState > FinalMarking) {
1936 // We are past the refs processing phase;
1937 // start over and do a fresh synchronous CMS cycle
1938 _collectorState = Resetting; // skip to reset to start new cycle
1939 reset(false /* == !asynch */);
1940 *should_start_over = true;
1941 } // else we can continue a possibly ongoing current cycle
1942 }
1943 }
1944 }
1945
1946 // A work method used by the foreground collector to do
1947 // a mark-sweep-compact.
1948 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) {
1949 GenCollectedHeap* gch = GenCollectedHeap::heap();
1950 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty);
1951 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) {
1952 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d "
1953 "collections passed to foreground collector", _full_gcs_since_conc_gc);
1954 }
1955
1956 // Sample collection interval time and reset for collection pause.
1957 if (UseAdaptiveSizePolicy) {
1958 size_policy()->msc_collection_begin();
1959 }
1960
1961 // Temporarily widen the span of the weak reference processing to
1962 // the entire heap.
1963 MemRegion new_span(GenCollectedHeap::heap()->reserved_region());
1964 ReferenceProcessorSpanMutator rp_mut_span(ref_processor(), new_span);
1965 // Temporarily, clear the "is_alive_non_header" field of the
1966 // reference processor.
1967 ReferenceProcessorIsAliveMutator rp_mut_closure(ref_processor(), NULL);
1968 // Temporarily make reference _processing_ single threaded (non-MT).
1969 ReferenceProcessorMTProcMutator rp_mut_mt_processing(ref_processor(), false);
1970 // Temporarily make refs discovery atomic
1971 ReferenceProcessorAtomicMutator rp_mut_atomic(ref_processor(), true);
1972 // Temporarily make reference _discovery_ single threaded (non-MT)
1973 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
1974
1975 ref_processor()->set_enqueuing_is_done(false);
1976 ref_processor()->enable_discovery(false /*verify_disabled*/, false /*check_no_refs*/);
1977 ref_processor()->setup_policy(clear_all_soft_refs);
1978 // If an asynchronous collection finishes, the _modUnionTable is
1979 // all clear. If we are assuming the collection from an asynchronous
1980 // collection, clear the _modUnionTable.
1981 assert(_collectorState != Idling || _modUnionTable.isAllClear(),
1982 "_modUnionTable should be clear if the baton was not passed");
1983 _modUnionTable.clear_all();
1984 assert(_collectorState != Idling || _ct->klass_rem_set()->mod_union_is_clear(),
1985 "mod union for klasses should be clear if the baton was passed");
1986 _ct->klass_rem_set()->clear_mod_union();
1987
1988 // We must adjust the allocation statistics being maintained
1989 // in the free list space. We do so by reading and clearing
1990 // the sweep timer and updating the block flux rate estimates below.
1991 assert(!_intra_sweep_timer.is_active(), "_intra_sweep_timer should be inactive");
1992 if (_inter_sweep_timer.is_active()) {
1993 _inter_sweep_timer.stop();
1994 // Note that we do not use this sample to update the _inter_sweep_estimate.
1995 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
1996 _inter_sweep_estimate.padded_average(),
1997 _intra_sweep_estimate.padded_average());
1998 }
1999
2000 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(),
2001 ref_processor(), clear_all_soft_refs);
2002 #ifdef ASSERT
2003 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
2004 size_t free_size = cms_space->free();
2005 assert(free_size ==
2006 pointer_delta(cms_space->end(), cms_space->compaction_top())
2007 * HeapWordSize,
2008 "All the free space should be compacted into one chunk at top");
2009 assert(cms_space->dictionary()->total_chunk_size(
2010 debug_only(cms_space->freelistLock())) == 0 ||
2011 cms_space->totalSizeInIndexedFreeLists() == 0,
2012 "All the free space should be in a single chunk");
2013 size_t num = cms_space->totalCount();
2014 assert((free_size == 0 && num == 0) ||
2015 (free_size > 0 && (num == 1 || num == 2)),
2016 "There should be at most 2 free chunks after compaction");
2017 #endif // ASSERT
2018 _collectorState = Resetting;
2019 assert(_restart_addr == NULL,
2020 "Should have been NULL'd before baton was passed");
2021 reset(false /* == !asynch */);
2022 _cmsGen->reset_after_compaction();
2023 _concurrent_cycles_since_last_unload = 0;
2024
2025 // Clear any data recorded in the PLAB chunk arrays.
2026 if (_survivor_plab_array != NULL) {
2027 reset_survivor_plab_arrays();
2028 }
2029
2030 // Adjust the per-size allocation stats for the next epoch.
2031 _cmsGen->cmsSpace()->endSweepFLCensus(sweep_count() /* fake */);
2032 // Restart the "inter sweep timer" for the next epoch.
2033 _inter_sweep_timer.reset();
2034 _inter_sweep_timer.start();
2035
2036 // Sample collection pause time and reset for collection interval.
2037 if (UseAdaptiveSizePolicy) {
2038 size_policy()->msc_collection_end(gch->gc_cause());
2039 }
2040
2041 // For a mark-sweep-compact, compute_new_size() will be called
2042 // in the heap's do_collection() method.
2043 }
2044
2045 // A work method used by the foreground collector to do
2046 // a mark-sweep, after taking over from a possibly on-going
2047 // concurrent mark-sweep collection.
2048 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs,
2049 CollectorState first_state, bool should_start_over) {
2050 if (PrintGC && Verbose) {
2051 gclog_or_tty->print_cr("Pass concurrent collection to foreground "
2052 "collector with count %d",
2053 _full_gcs_since_conc_gc);
2054 }
2055 switch (_collectorState) {
2056 case Idling:
2057 if (first_state == Idling || should_start_over) {
2058 // The background GC was not active, or should
2059 // restarted from scratch; start the cycle.
2060 _collectorState = InitialMarking;
2061 }
2062 // If first_state was not Idling, then a background GC
2063 // was in progress and has now finished. No need to do it
2064 // again. Leave the state as Idling.
2065 break;
2066 case Precleaning:
2067 // In the foreground case don't do the precleaning since
2068 // it is not done concurrently and there is extra work
2069 // required.
2070 _collectorState = FinalMarking;
2071 }
2072 if (PrintGCDetails &&
2073 (_collectorState > Idling ||
2074 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) {
2075 gclog_or_tty->print(" (concurrent mode failure)");
2076 }
2077 collect_in_foreground(clear_all_soft_refs);
2078
2079 // For a mark-sweep, compute_new_size() will be called
2080 // in the heap's do_collection() method.
2081 }
2082
2083
2084 void CMSCollector::getFreelistLocks() const {
2085 // Get locks for all free lists in all generations that this
2086 // collector is responsible for
2087 _cmsGen->freelistLock()->lock_without_safepoint_check();
2088 }
2089
2090 void CMSCollector::releaseFreelistLocks() const {
2091 // Release locks for all free lists in all generations that this
2092 // collector is responsible for
2093 _cmsGen->freelistLock()->unlock();
2094 }
2095
2096 bool CMSCollector::haveFreelistLocks() const {
2097 // Check locks for all free lists in all generations that this
2098 // collector is responsible for
2099 assert_lock_strong(_cmsGen->freelistLock());
2100 PRODUCT_ONLY(ShouldNotReachHere());
2101 return true;
2102 }
2103
2104 // A utility class that is used by the CMS collector to
2105 // temporarily "release" the foreground collector from its
2106 // usual obligation to wait for the background collector to
2107 // complete an ongoing phase before proceeding.
2108 class ReleaseForegroundGC: public StackObj {
2109 private:
2110 CMSCollector* _c;
2111 public:
2112 ReleaseForegroundGC(CMSCollector* c) : _c(c) {
2113 assert(_c->_foregroundGCShouldWait, "Else should not need to call");
2114 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2115 // allow a potentially blocked foreground collector to proceed
2116 _c->_foregroundGCShouldWait = false;
2117 if (_c->_foregroundGCIsActive) {
2118 CGC_lock->notify();
2119 }
2120 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2121 "Possible deadlock");
2122 }
2123
2124 ~ReleaseForegroundGC() {
2125 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?");
2126 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2127 _c->_foregroundGCShouldWait = true;
2128 }
2129 };
2130
2131 // There are separate collect_in_background and collect_in_foreground because of
2132 // the different locking requirements of the background collector and the
2133 // foreground collector. There was originally an attempt to share
2134 // one "collect" method between the background collector and the foreground
2135 // collector but the if-then-else required made it cleaner to have
2136 // separate methods.
2137 void CMSCollector::collect_in_background(bool clear_all_soft_refs) {
2138 assert(Thread::current()->is_ConcurrentGC_thread(),
2139 "A CMS asynchronous collection is only allowed on a CMS thread.");
2140
2141 GenCollectedHeap* gch = GenCollectedHeap::heap();
2142 {
2143 bool safepoint_check = Mutex::_no_safepoint_check_flag;
2144 MutexLockerEx hl(Heap_lock, safepoint_check);
2145 FreelistLocker fll(this);
2146 MutexLockerEx x(CGC_lock, safepoint_check);
2147 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) {
2148 // The foreground collector is active or we're
2149 // not using asynchronous collections. Skip this
2150 // background collection.
2151 assert(!_foregroundGCShouldWait, "Should be clear");
2152 return;
2153 } else {
2154 assert(_collectorState == Idling, "Should be idling before start.");
2155 _collectorState = InitialMarking;
2156 // Reset the expansion cause, now that we are about to begin
2157 // a new cycle.
2158 clear_expansion_cause();
2159
2160 // Clear the MetaspaceGC flag since a concurrent collection
2161 // is starting but also clear it after the collection.
2162 MetaspaceGC::set_should_concurrent_collect(false);
2163 }
2164 // Decide if we want to enable class unloading as part of the
2165 // ensuing concurrent GC cycle.
2166 update_should_unload_classes();
2167 _full_gc_requested = false; // acks all outstanding full gc requests
2168 // Signal that we are about to start a collection
2169 gch->increment_total_full_collections(); // ... starting a collection cycle
2170 _collection_count_start = gch->total_full_collections();
2171 }
2172
2173 // Used for PrintGCDetails
2174 size_t prev_used = 0;
2175 size_t metaspace_pre_unloading = 0;
2176 if (PrintGCDetails) {
2177 prev_used = _cmsGen->used();
2178 metaspace_pre_unloading = MetaspaceAux::used_in_bytes();
2179 }
2180
2181 // The change of the collection state is normally done at this level;
2182 // the exceptions are phases that are executed while the world is
2183 // stopped. For those phases the change of state is done while the
2184 // world is stopped. For baton passing purposes this allows the
2185 // background collector to finish the phase and change state atomically.
2186 // The foreground collector cannot wait on a phase that is done
2187 // while the world is stopped because the foreground collector already
2188 // has the world stopped and would deadlock.
2189 while (_collectorState != Idling) {
2190 if (TraceCMSState) {
2191 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2192 Thread::current(), _collectorState);
2193 }
2194 // The foreground collector
2195 // holds the Heap_lock throughout its collection.
2196 // holds the CMS token (but not the lock)
2197 // except while it is waiting for the background collector to yield.
2198 //
2199 // The foreground collector should be blocked (not for long)
2200 // if the background collector is about to start a phase
2201 // executed with world stopped. If the background
2202 // collector has already started such a phase, the
2203 // foreground collector is blocked waiting for the
2204 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking)
2205 // are executed in the VM thread.
2206 //
2207 // The locking order is
2208 // PendingListLock (PLL) -- if applicable (FinalMarking)
2209 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue())
2210 // CMS token (claimed in
2211 // stop_world_and_do() -->
2212 // safepoint_synchronize() -->
2213 // CMSThread::synchronize())
2214
2215 {
2216 // Check if the FG collector wants us to yield.
2217 CMSTokenSync x(true); // is cms thread
2218 if (waitForForegroundGC()) {
2219 // We yielded to a foreground GC, nothing more to be
2220 // done this round.
2221 assert(_foregroundGCShouldWait == false, "We set it to false in "
2222 "waitForForegroundGC()");
2223 if (TraceCMSState) {
2224 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2225 " exiting collection CMS state %d",
2226 Thread::current(), _collectorState);
2227 }
2228 return;
2229 } else {
2230 // The background collector can run but check to see if the
2231 // foreground collector has done a collection while the
2232 // background collector was waiting to get the CGC_lock
2233 // above. If yes, break so that _foregroundGCShouldWait
2234 // is cleared before returning.
2235 if (_collectorState == Idling) {
2236 break;
2237 }
2238 }
2239 }
2240
2241 assert(_foregroundGCShouldWait, "Foreground collector, if active, "
2242 "should be waiting");
2243
2244 switch (_collectorState) {
2245 case InitialMarking:
2246 {
2247 ReleaseForegroundGC x(this);
2248 stats().record_cms_begin();
2249
2250 VM_CMS_Initial_Mark initial_mark_op(this);
2251 VMThread::execute(&initial_mark_op);
2252 }
2253 // The collector state may be any legal state at this point
2254 // since the background collector may have yielded to the
2255 // foreground collector.
2256 break;
2257 case Marking:
2258 // initial marking in checkpointRootsInitialWork has been completed
2259 if (markFromRoots(true)) { // we were successful
2260 assert(_collectorState == Precleaning, "Collector state should "
2261 "have changed");
2262 } else {
2263 assert(_foregroundGCIsActive, "Internal state inconsistency");
2264 }
2265 break;
2266 case Precleaning:
2267 if (UseAdaptiveSizePolicy) {
2268 size_policy()->concurrent_precleaning_begin();
2269 }
2270 // marking from roots in markFromRoots has been completed
2271 preclean();
2272 if (UseAdaptiveSizePolicy) {
2273 size_policy()->concurrent_precleaning_end();
2274 }
2275 assert(_collectorState == AbortablePreclean ||
2276 _collectorState == FinalMarking,
2277 "Collector state should have changed");
2278 break;
2279 case AbortablePreclean:
2280 if (UseAdaptiveSizePolicy) {
2281 size_policy()->concurrent_phases_resume();
2282 }
2283 abortable_preclean();
2284 if (UseAdaptiveSizePolicy) {
2285 size_policy()->concurrent_precleaning_end();
2286 }
2287 assert(_collectorState == FinalMarking, "Collector state should "
2288 "have changed");
2289 break;
2290 case FinalMarking:
2291 {
2292 ReleaseForegroundGC x(this);
2293
2294 VM_CMS_Final_Remark final_remark_op(this);
2295 VMThread::execute(&final_remark_op);
2296 }
2297 assert(_foregroundGCShouldWait, "block post-condition");
2298 break;
2299 case Sweeping:
2300 if (UseAdaptiveSizePolicy) {
2301 size_policy()->concurrent_sweeping_begin();
2302 }
2303 // final marking in checkpointRootsFinal has been completed
2304 sweep(true);
2305 assert(_collectorState == Resizing, "Collector state change "
2306 "to Resizing must be done under the free_list_lock");
2307 _full_gcs_since_conc_gc = 0;
2308
2309 // Stop the timers for adaptive size policy for the concurrent phases
2310 if (UseAdaptiveSizePolicy) {
2311 size_policy()->concurrent_sweeping_end();
2312 size_policy()->concurrent_phases_end(gch->gc_cause(),
2313 gch->prev_gen(_cmsGen)->capacity(),
2314 _cmsGen->free());
2315 }
2316
2317 case Resizing: {
2318 // Sweeping has been completed...
2319 // At this point the background collection has completed.
2320 // Don't move the call to compute_new_size() down
2321 // into code that might be executed if the background
2322 // collection was preempted.
2323 {
2324 ReleaseForegroundGC x(this); // unblock FG collection
2325 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag);
2326 CMSTokenSync z(true); // not strictly needed.
2327 if (_collectorState == Resizing) {
2328 compute_new_size();
2329 if (PrintGCDetails) {
2330 CMSPhaseTracing pt(true, "[CMS-resizing: ");
2331 gclog_or_tty->print("[%s:", cmsGen()->short_name());
2332 cmsGen()->print_heap_change(prev_used);
2333 gclog_or_tty->print("]");
2334 MetaspaceAux::print_metaspace_change(metaspace_pre_unloading);
2335 gclog_or_tty->print_cr(" ]");
2336 }
2337
2338 _collectorState = Resetting;
2339 } else {
2340 assert(_collectorState == Idling, "The state should only change"
2341 " because the foreground collector has finished the collection");
2342 }
2343 }
2344 break;
2345 }
2346 case Resetting:
2347 // CMS heap resizing has been completed
2348 reset(true);
2349 assert(_collectorState == Idling, "Collector state should "
2350 "have changed");
2351
2352 MetaspaceGC::set_should_concurrent_collect(false);
2353
2354 stats().record_cms_end();
2355 // Don't move the concurrent_phases_end() and compute_new_size()
2356 // calls to here because a preempted background collection
2357 // has it's state set to "Resetting".
2358 break;
2359 case Idling:
2360 default:
2361 ShouldNotReachHere();
2362 break;
2363 }
2364 if (TraceCMSState) {
2365 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2366 Thread::current(), _collectorState);
2367 }
2368 assert(_foregroundGCShouldWait, "block post-condition");
2369 }
2370
2371 // Should this be in gc_epilogue?
2372 collector_policy()->counters()->update_counters();
2373
2374 {
2375 // Clear _foregroundGCShouldWait and, in the event that the
2376 // foreground collector is waiting, notify it, before
2377 // returning.
2378 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2379 _foregroundGCShouldWait = false;
2380 if (_foregroundGCIsActive) {
2381 CGC_lock->notify();
2382 }
2383 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2384 "Possible deadlock");
2385 }
2386 if (TraceCMSState) {
2387 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2388 " exiting collection CMS state %d",
2389 Thread::current(), _collectorState);
2390 }
2391 }
2392
2393 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) {
2394 assert(_foregroundGCIsActive && !_foregroundGCShouldWait,
2395 "Foreground collector should be waiting, not executing");
2396 assert(Thread::current()->is_VM_thread(), "A foreground collection"
2397 "may only be done by the VM Thread with the world stopped");
2398 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(),
2399 "VM thread should have CMS token");
2400
2401 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose,
2402 true, gclog_or_tty);)
2403 if (UseAdaptiveSizePolicy) {
2404 size_policy()->ms_collection_begin();
2405 }
2406 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact);
2407
2408 HandleMark hm; // Discard invalid handles created during verification
2409
2410 if (VerifyBeforeGC &&
2411 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2412 Universe::verify();
2413 }
2414
2415 // Snapshot the soft reference policy to be used in this collection cycle.
2416 ref_processor()->setup_policy(clear_all_soft_refs);
2417
2418 bool init_mark_was_synchronous = false; // until proven otherwise
2419 while (_collectorState != Idling) {
2420 if (TraceCMSState) {
2421 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d",
2422 Thread::current(), _collectorState);
2423 }
2424 switch (_collectorState) {
2425 case InitialMarking:
2426 init_mark_was_synchronous = true; // fact to be exploited in re-mark
2427 checkpointRootsInitial(false);
2428 assert(_collectorState == Marking, "Collector state should have changed"
2429 " within checkpointRootsInitial()");
2430 break;
2431 case Marking:
2432 // initial marking in checkpointRootsInitialWork has been completed
2433 if (VerifyDuringGC &&
2434 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2435 gclog_or_tty->print("Verify before initial mark: ");
2436 Universe::verify();
2437 }
2438 {
2439 bool res = markFromRoots(false);
2440 assert(res && _collectorState == FinalMarking, "Collector state should "
2441 "have changed");
2442 break;
2443 }
2444 case FinalMarking:
2445 if (VerifyDuringGC &&
2446 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2447 gclog_or_tty->print("Verify before re-mark: ");
2448 Universe::verify();
2449 }
2450 checkpointRootsFinal(false, clear_all_soft_refs,
2451 init_mark_was_synchronous);
2452 assert(_collectorState == Sweeping, "Collector state should not "
2453 "have changed within checkpointRootsFinal()");
2454 break;
2455 case Sweeping:
2456 // final marking in checkpointRootsFinal has been completed
2457 if (VerifyDuringGC &&
2458 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2459 gclog_or_tty->print("Verify before sweep: ");
2460 Universe::verify();
2461 }
2462 sweep(false);
2463 assert(_collectorState == Resizing, "Incorrect state");
2464 break;
2465 case Resizing: {
2466 // Sweeping has been completed; the actual resize in this case
2467 // is done separately; nothing to be done in this state.
2468 _collectorState = Resetting;
2469 break;
2470 }
2471 case Resetting:
2472 // The heap has been resized.
2473 if (VerifyDuringGC &&
2474 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2475 gclog_or_tty->print("Verify before reset: ");
2476 Universe::verify();
2477 }
2478 reset(false);
2479 assert(_collectorState == Idling, "Collector state should "
2480 "have changed");
2481 break;
2482 case Precleaning:
2483 case AbortablePreclean:
2484 // Elide the preclean phase
2485 _collectorState = FinalMarking;
2486 break;
2487 default:
2488 ShouldNotReachHere();
2489 }
2490 if (TraceCMSState) {
2491 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d",
2492 Thread::current(), _collectorState);
2493 }
2494 }
2495
2496 if (UseAdaptiveSizePolicy) {
2497 GenCollectedHeap* gch = GenCollectedHeap::heap();
2498 size_policy()->ms_collection_end(gch->gc_cause());
2499 }
2500
2501 if (VerifyAfterGC &&
2502 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
2503 Universe::verify();
2504 }
2505 if (TraceCMSState) {
2506 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT
2507 " exiting collection CMS state %d",
2508 Thread::current(), _collectorState);
2509 }
2510 }
2511
2512 bool CMSCollector::waitForForegroundGC() {
2513 bool res = false;
2514 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
2515 "CMS thread should have CMS token");
2516 // Block the foreground collector until the
2517 // background collectors decides whether to
2518 // yield.
2519 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
2520 _foregroundGCShouldWait = true;
2521 if (_foregroundGCIsActive) {
2522 // The background collector yields to the
2523 // foreground collector and returns a value
2524 // indicating that it has yielded. The foreground
2525 // collector can proceed.
2526 res = true;
2527 _foregroundGCShouldWait = false;
2528 ConcurrentMarkSweepThread::clear_CMS_flag(
2529 ConcurrentMarkSweepThread::CMS_cms_has_token);
2530 ConcurrentMarkSweepThread::set_CMS_flag(
2531 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2532 // Get a possibly blocked foreground thread going
2533 CGC_lock->notify();
2534 if (TraceCMSState) {
2535 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d",
2536 Thread::current(), _collectorState);
2537 }
2538 while (_foregroundGCIsActive) {
2539 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
2540 }
2541 ConcurrentMarkSweepThread::set_CMS_flag(
2542 ConcurrentMarkSweepThread::CMS_cms_has_token);
2543 ConcurrentMarkSweepThread::clear_CMS_flag(
2544 ConcurrentMarkSweepThread::CMS_cms_wants_token);
2545 }
2546 if (TraceCMSState) {
2547 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d",
2548 Thread::current(), _collectorState);
2549 }
2550 return res;
2551 }
2552
2553 // Because of the need to lock the free lists and other structures in
2554 // the collector, common to all the generations that the collector is
2555 // collecting, we need the gc_prologues of individual CMS generations
2556 // delegate to their collector. It may have been simpler had the
2557 // current infrastructure allowed one to call a prologue on a
2558 // collector. In the absence of that we have the generation's
2559 // prologue delegate to the collector, which delegates back
2560 // some "local" work to a worker method in the individual generations
2561 // that it's responsible for collecting, while itself doing any
2562 // work common to all generations it's responsible for. A similar
2563 // comment applies to the gc_epilogue()'s.
2564 // The role of the varaible _between_prologue_and_epilogue is to
2565 // enforce the invocation protocol.
2566 void CMSCollector::gc_prologue(bool full) {
2567 // Call gc_prologue_work() for the CMSGen
2568 // we are responsible for.
2569
2570 // The following locking discipline assumes that we are only called
2571 // when the world is stopped.
2572 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption");
2573
2574 // The CMSCollector prologue must call the gc_prologues for the
2575 // "generations" that it's responsible
2576 // for.
2577
2578 assert( Thread::current()->is_VM_thread()
2579 || ( CMSScavengeBeforeRemark
2580 && Thread::current()->is_ConcurrentGC_thread()),
2581 "Incorrect thread type for prologue execution");
2582
2583 if (_between_prologue_and_epilogue) {
2584 // We have already been invoked; this is a gc_prologue delegation
2585 // from yet another CMS generation that we are responsible for, just
2586 // ignore it since all relevant work has already been done.
2587 return;
2588 }
2589
2590 // set a bit saying prologue has been called; cleared in epilogue
2591 _between_prologue_and_epilogue = true;
2592 // Claim locks for common data structures, then call gc_prologue_work()
2593 // for each CMSGen.
2594
2595 getFreelistLocks(); // gets free list locks on constituent spaces
2596 bitMapLock()->lock_without_safepoint_check();
2597
2598 // Should call gc_prologue_work() for all cms gens we are responsible for
2599 bool duringMarking = _collectorState >= Marking
2600 && _collectorState < Sweeping;
2601
2602 // The young collections clear the modified oops state, which tells if
2603 // there are any modified oops in the class. The remark phase also needs
2604 // that information. Tell the young collection to save the union of all
2605 // modified klasses.
2606 if (duringMarking) {
2607 _ct->klass_rem_set()->set_accumulate_modified_oops(true);
2608 }
2609
2610 bool registerClosure = duringMarking;
2611
2612 ModUnionClosure* muc = CollectedHeap::use_parallel_gc_threads() ?
2613 &_modUnionClosurePar
2614 : &_modUnionClosure;
2615 _cmsGen->gc_prologue_work(full, registerClosure, muc);
2616
2617 if (!full) {
2618 stats().record_gc0_begin();
2619 }
2620 }
2621
2622 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) {
2623 // Delegate to CMScollector which knows how to coordinate between
2624 // this and any other CMS generations that it is responsible for
2625 // collecting.
2626 collector()->gc_prologue(full);
2627 }
2628
2629 // This is a "private" interface for use by this generation's CMSCollector.
2630 // Not to be called directly by any other entity (for instance,
2631 // GenCollectedHeap, which calls the "public" gc_prologue method above).
2632 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full,
2633 bool registerClosure, ModUnionClosure* modUnionClosure) {
2634 assert(!incremental_collection_failed(), "Shouldn't be set yet");
2635 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL,
2636 "Should be NULL");
2637 if (registerClosure) {
2638 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure);
2639 }
2640 cmsSpace()->gc_prologue();
2641 // Clear stat counters
2642 NOT_PRODUCT(
2643 assert(_numObjectsPromoted == 0, "check");
2644 assert(_numWordsPromoted == 0, "check");
2645 if (Verbose && PrintGC) {
2646 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, "
2647 SIZE_FORMAT" bytes concurrently",
2648 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord));
2649 }
2650 _numObjectsAllocated = 0;
2651 _numWordsAllocated = 0;
2652 )
2653 }
2654
2655 void CMSCollector::gc_epilogue(bool full) {
2656 // The following locking discipline assumes that we are only called
2657 // when the world is stopped.
2658 assert(SafepointSynchronize::is_at_safepoint(),
2659 "world is stopped assumption");
2660
2661 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks
2662 // if linear allocation blocks need to be appropriately marked to allow the
2663 // the blocks to be parsable. We also check here whether we need to nudge the
2664 // CMS collector thread to start a new cycle (if it's not already active).
2665 assert( Thread::current()->is_VM_thread()
2666 || ( CMSScavengeBeforeRemark
2667 && Thread::current()->is_ConcurrentGC_thread()),
2668 "Incorrect thread type for epilogue execution");
2669
2670 if (!_between_prologue_and_epilogue) {
2671 // We have already been invoked; this is a gc_epilogue delegation
2672 // from yet another CMS generation that we are responsible for, just
2673 // ignore it since all relevant work has already been done.
2674 return;
2675 }
2676 assert(haveFreelistLocks(), "must have freelist locks");
2677 assert_lock_strong(bitMapLock());
2678
2679 _ct->klass_rem_set()->set_accumulate_modified_oops(false);
2680
2681 _cmsGen->gc_epilogue_work(full);
2682
2683 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) {
2684 // in case sampling was not already enabled, enable it
2685 _start_sampling = true;
2686 }
2687 // reset _eden_chunk_array so sampling starts afresh
2688 _eden_chunk_index = 0;
2689
2690 size_t cms_used = _cmsGen->cmsSpace()->used();
2691
2692 // update performance counters - this uses a special version of
2693 // update_counters() that allows the utilization to be passed as a
2694 // parameter, avoiding multiple calls to used().
2695 //
2696 _cmsGen->update_counters(cms_used);
2697
2698 if (CMSIncrementalMode) {
2699 icms_update_allocation_limits();
2700 }
2701
2702 bitMapLock()->unlock();
2703 releaseFreelistLocks();
2704
2705 if (!CleanChunkPoolAsync) {
2706 Chunk::clean_chunk_pool();
2707 }
2708
2709 _between_prologue_and_epilogue = false; // ready for next cycle
2710 }
2711
2712 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) {
2713 collector()->gc_epilogue(full);
2714
2715 // Also reset promotion tracking in par gc thread states.
2716 if (CollectedHeap::use_parallel_gc_threads()) {
2717 for (uint i = 0; i < ParallelGCThreads; i++) {
2718 _par_gc_thread_states[i]->promo.stopTrackingPromotions(i);
2719 }
2720 }
2721 }
2722
2723 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) {
2724 assert(!incremental_collection_failed(), "Should have been cleared");
2725 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL);
2726 cmsSpace()->gc_epilogue();
2727 // Print stat counters
2728 NOT_PRODUCT(
2729 assert(_numObjectsAllocated == 0, "check");
2730 assert(_numWordsAllocated == 0, "check");
2731 if (Verbose && PrintGC) {
2732 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, "
2733 SIZE_FORMAT" bytes",
2734 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord));
2735 }
2736 _numObjectsPromoted = 0;
2737 _numWordsPromoted = 0;
2738 )
2739
2740 if (PrintGC && Verbose) {
2741 // Call down the chain in contiguous_available needs the freelistLock
2742 // so print this out before releasing the freeListLock.
2743 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ",
2744 contiguous_available());
2745 }
2746 }
2747
2748 #ifndef PRODUCT
2749 bool CMSCollector::have_cms_token() {
2750 Thread* thr = Thread::current();
2751 if (thr->is_VM_thread()) {
2752 return ConcurrentMarkSweepThread::vm_thread_has_cms_token();
2753 } else if (thr->is_ConcurrentGC_thread()) {
2754 return ConcurrentMarkSweepThread::cms_thread_has_cms_token();
2755 } else if (thr->is_GC_task_thread()) {
2756 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() &&
2757 ParGCRareEvent_lock->owned_by_self();
2758 }
2759 return false;
2760 }
2761 #endif
2762
2763 // Check reachability of the given heap address in CMS generation,
2764 // treating all other generations as roots.
2765 bool CMSCollector::is_cms_reachable(HeapWord* addr) {
2766 // We could "guarantee" below, rather than assert, but i'll
2767 // leave these as "asserts" so that an adventurous debugger
2768 // could try this in the product build provided some subset of
2769 // the conditions were met, provided they were intersted in the
2770 // results and knew that the computation below wouldn't interfere
2771 // with other concurrent computations mutating the structures
2772 // being read or written.
2773 assert(SafepointSynchronize::is_at_safepoint(),
2774 "Else mutations in object graph will make answer suspect");
2775 assert(have_cms_token(), "Should hold cms token");
2776 assert(haveFreelistLocks(), "must hold free list locks");
2777 assert_lock_strong(bitMapLock());
2778
2779 // Clear the marking bit map array before starting, but, just
2780 // for kicks, first report if the given address is already marked
2781 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr,
2782 _markBitMap.isMarked(addr) ? "" : " not");
2783
2784 if (verify_after_remark()) {
2785 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2786 bool result = verification_mark_bm()->isMarked(addr);
2787 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr,
2788 result ? "IS" : "is NOT");
2789 return result;
2790 } else {
2791 gclog_or_tty->print_cr("Could not compute result");
2792 return false;
2793 }
2794 }
2795
2796 ////////////////////////////////////////////////////////
2797 // CMS Verification Support
2798 ////////////////////////////////////////////////////////
2799 // Following the remark phase, the following invariant
2800 // should hold -- each object in the CMS heap which is
2801 // marked in markBitMap() should be marked in the verification_mark_bm().
2802
2803 class VerifyMarkedClosure: public BitMapClosure {
2804 CMSBitMap* _marks;
2805 bool _failed;
2806
2807 public:
2808 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {}
2809
2810 bool do_bit(size_t offset) {
2811 HeapWord* addr = _marks->offsetToHeapWord(offset);
2812 if (!_marks->isMarked(addr)) {
2813 oop(addr)->print_on(gclog_or_tty);
2814 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr);
2815 _failed = true;
2816 }
2817 return true;
2818 }
2819
2820 bool failed() { return _failed; }
2821 };
2822
2823 bool CMSCollector::verify_after_remark() {
2824 gclog_or_tty->print(" [Verifying CMS Marking... ");
2825 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag);
2826 static bool init = false;
2827
2828 assert(SafepointSynchronize::is_at_safepoint(),
2829 "Else mutations in object graph will make answer suspect");
2830 assert(have_cms_token(),
2831 "Else there may be mutual interference in use of "
2832 " verification data structures");
2833 assert(_collectorState > Marking && _collectorState <= Sweeping,
2834 "Else marking info checked here may be obsolete");
2835 assert(haveFreelistLocks(), "must hold free list locks");
2836 assert_lock_strong(bitMapLock());
2837
2838
2839 // Allocate marking bit map if not already allocated
2840 if (!init) { // first time
2841 if (!verification_mark_bm()->allocate(_span)) {
2842 return false;
2843 }
2844 init = true;
2845 }
2846
2847 assert(verification_mark_stack()->isEmpty(), "Should be empty");
2848
2849 // Turn off refs discovery -- so we will be tracing through refs.
2850 // This is as intended, because by this time
2851 // GC must already have cleared any refs that need to be cleared,
2852 // and traced those that need to be marked; moreover,
2853 // the marking done here is not going to intefere in any
2854 // way with the marking information used by GC.
2855 NoRefDiscovery no_discovery(ref_processor());
2856
2857 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
2858
2859 // Clear any marks from a previous round
2860 verification_mark_bm()->clear_all();
2861 assert(verification_mark_stack()->isEmpty(), "markStack should be empty");
2862 verify_work_stacks_empty();
2863
2864 GenCollectedHeap* gch = GenCollectedHeap::heap();
2865 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
2866 // Update the saved marks which may affect the root scans.
2867 gch->save_marks();
2868
2869 if (CMSRemarkVerifyVariant == 1) {
2870 // In this first variant of verification, we complete
2871 // all marking, then check if the new marks-verctor is
2872 // a subset of the CMS marks-vector.
2873 verify_after_remark_work_1();
2874 } else if (CMSRemarkVerifyVariant == 2) {
2875 // In this second variant of verification, we flag an error
2876 // (i.e. an object reachable in the new marks-vector not reachable
2877 // in the CMS marks-vector) immediately, also indicating the
2878 // identify of an object (A) that references the unmarked object (B) --
2879 // presumably, a mutation to A failed to be picked up by preclean/remark?
2880 verify_after_remark_work_2();
2881 } else {
2882 warning("Unrecognized value %d for CMSRemarkVerifyVariant",
2883 CMSRemarkVerifyVariant);
2884 }
2885 gclog_or_tty->print(" done] ");
2886 return true;
2887 }
2888
2889 void CMSCollector::verify_after_remark_work_1() {
2890 ResourceMark rm;
2891 HandleMark hm;
2892 GenCollectedHeap* gch = GenCollectedHeap::heap();
2893
2894 // Get a clear set of claim bits for the strong roots processing to work with.
2895 ClassLoaderDataGraph::clear_claimed_marks();
2896
2897 // Mark from roots one level into CMS
2898 MarkRefsIntoClosure notOlder(_span, verification_mark_bm());
2899 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2900
2901 gch->gen_process_strong_roots(_cmsGen->level(),
2902 true, // younger gens are roots
2903 true, // activate StrongRootsScope
2904 false, // not scavenging
2905 SharedHeap::ScanningOption(roots_scanning_options()),
2906 ¬Older,
2907 true, // walk code active on stacks
2908 NULL,
2909 NULL); // SSS: Provide correct closure
2910
2911 // Now mark from the roots
2912 MarkFromRootsClosure markFromRootsClosure(this, _span,
2913 verification_mark_bm(), verification_mark_stack(),
2914 false /* don't yield */, true /* verifying */);
2915 assert(_restart_addr == NULL, "Expected pre-condition");
2916 verification_mark_bm()->iterate(&markFromRootsClosure);
2917 while (_restart_addr != NULL) {
2918 // Deal with stack overflow: by restarting at the indicated
2919 // address.
2920 HeapWord* ra = _restart_addr;
2921 markFromRootsClosure.reset(ra);
2922 _restart_addr = NULL;
2923 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2924 }
2925 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2926 verify_work_stacks_empty();
2927
2928 // Marking completed -- now verify that each bit marked in
2929 // verification_mark_bm() is also marked in markBitMap(); flag all
2930 // errors by printing corresponding objects.
2931 VerifyMarkedClosure vcl(markBitMap());
2932 verification_mark_bm()->iterate(&vcl);
2933 if (vcl.failed()) {
2934 gclog_or_tty->print("Verification failed");
2935 Universe::heap()->print_on(gclog_or_tty);
2936 fatal("CMS: failed marking verification after remark");
2937 }
2938 }
2939
2940 class VerifyKlassOopsKlassClosure : public KlassClosure {
2941 class VerifyKlassOopsClosure : public OopClosure {
2942 CMSBitMap* _bitmap;
2943 public:
2944 VerifyKlassOopsClosure(CMSBitMap* bitmap) : _bitmap(bitmap) { }
2945 void do_oop(oop* p) { guarantee(*p == NULL || _bitmap->isMarked((HeapWord*) *p), "Should be marked"); }
2946 void do_oop(narrowOop* p) { ShouldNotReachHere(); }
2947 } _oop_closure;
2948 public:
2949 VerifyKlassOopsKlassClosure(CMSBitMap* bitmap) : _oop_closure(bitmap) {}
2950 void do_klass(Klass* k) {
2951 k->oops_do(&_oop_closure);
2952 }
2953 };
2954
2955 void CMSCollector::verify_after_remark_work_2() {
2956 ResourceMark rm;
2957 HandleMark hm;
2958 GenCollectedHeap* gch = GenCollectedHeap::heap();
2959
2960 // Get a clear set of claim bits for the strong roots processing to work with.
2961 ClassLoaderDataGraph::clear_claimed_marks();
2962
2963 // Mark from roots one level into CMS
2964 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(),
2965 markBitMap());
2966 CMKlassClosure klass_closure(¬Older);
2967
2968 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
2969 gch->gen_process_strong_roots(_cmsGen->level(),
2970 true, // younger gens are roots
2971 true, // activate StrongRootsScope
2972 false, // not scavenging
2973 SharedHeap::ScanningOption(roots_scanning_options()),
2974 ¬Older,
2975 true, // walk code active on stacks
2976 NULL,
2977 &klass_closure);
2978
2979 // Now mark from the roots
2980 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span,
2981 verification_mark_bm(), markBitMap(), verification_mark_stack());
2982 assert(_restart_addr == NULL, "Expected pre-condition");
2983 verification_mark_bm()->iterate(&markFromRootsClosure);
2984 while (_restart_addr != NULL) {
2985 // Deal with stack overflow: by restarting at the indicated
2986 // address.
2987 HeapWord* ra = _restart_addr;
2988 markFromRootsClosure.reset(ra);
2989 _restart_addr = NULL;
2990 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end());
2991 }
2992 assert(verification_mark_stack()->isEmpty(), "Should have been drained");
2993 verify_work_stacks_empty();
2994
2995 VerifyKlassOopsKlassClosure verify_klass_oops(verification_mark_bm());
2996 ClassLoaderDataGraph::classes_do(&verify_klass_oops);
2997
2998 // Marking completed -- now verify that each bit marked in
2999 // verification_mark_bm() is also marked in markBitMap(); flag all
3000 // errors by printing corresponding objects.
3001 VerifyMarkedClosure vcl(markBitMap());
3002 verification_mark_bm()->iterate(&vcl);
3003 assert(!vcl.failed(), "Else verification above should not have succeeded");
3004 }
3005
3006 void ConcurrentMarkSweepGeneration::save_marks() {
3007 // delegate to CMS space
3008 cmsSpace()->save_marks();
3009 for (uint i = 0; i < ParallelGCThreads; i++) {
3010 _par_gc_thread_states[i]->promo.startTrackingPromotions();
3011 }
3012 }
3013
3014 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() {
3015 return cmsSpace()->no_allocs_since_save_marks();
3016 }
3017
3018 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \
3019 \
3020 void ConcurrentMarkSweepGeneration:: \
3021 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \
3022 cl->set_generation(this); \
3023 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \
3024 cl->reset_generation(); \
3025 save_marks(); \
3026 }
3027
3028 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN)
3029
3030 void
3031 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk)
3032 {
3033 // Not currently implemented; need to do the following. -- ysr.
3034 // dld -- I think that is used for some sort of allocation profiler. So it
3035 // really means the objects allocated by the mutator since the last
3036 // GC. We could potentially implement this cheaply by recording only
3037 // the direct allocations in a side data structure.
3038 //
3039 // I think we probably ought not to be required to support these
3040 // iterations at any arbitrary point; I think there ought to be some
3041 // call to enable/disable allocation profiling in a generation/space,
3042 // and the iterator ought to return the objects allocated in the
3043 // gen/space since the enable call, or the last iterator call (which
3044 // will probably be at a GC.) That way, for gens like CM&S that would
3045 // require some extra data structure to support this, we only pay the
3046 // cost when it's in use...
3047 cmsSpace()->object_iterate_since_last_GC(blk);
3048 }
3049
3050 void
3051 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) {
3052 cl->set_generation(this);
3053 younger_refs_in_space_iterate(_cmsSpace, cl);
3054 cl->reset_generation();
3055 }
3056
3057 void
3058 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, ExtendedOopClosure* cl) {
3059 if (freelistLock()->owned_by_self()) {
3060 Generation::oop_iterate(mr, cl);
3061 } else {
3062 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3063 Generation::oop_iterate(mr, cl);
3064 }
3065 }
3066
3067 void
3068 ConcurrentMarkSweepGeneration::oop_iterate(ExtendedOopClosure* cl) {
3069 if (freelistLock()->owned_by_self()) {
3070 Generation::oop_iterate(cl);
3071 } else {
3072 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3073 Generation::oop_iterate(cl);
3074 }
3075 }
3076
3077 void
3078 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) {
3079 if (freelistLock()->owned_by_self()) {
3080 Generation::object_iterate(cl);
3081 } else {
3082 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3083 Generation::object_iterate(cl);
3084 }
3085 }
3086
3087 void
3088 ConcurrentMarkSweepGeneration::safe_object_iterate(ObjectClosure* cl) {
3089 if (freelistLock()->owned_by_self()) {
3090 Generation::safe_object_iterate(cl);
3091 } else {
3092 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3093 Generation::safe_object_iterate(cl);
3094 }
3095 }
3096
3097 void
3098 ConcurrentMarkSweepGeneration::post_compact() {
3099 }
3100
3101 void
3102 ConcurrentMarkSweepGeneration::prepare_for_verify() {
3103 // Fix the linear allocation blocks to look like free blocks.
3104
3105 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3106 // are not called when the heap is verified during universe initialization and
3107 // at vm shutdown.
3108 if (freelistLock()->owned_by_self()) {
3109 cmsSpace()->prepare_for_verify();
3110 } else {
3111 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3112 cmsSpace()->prepare_for_verify();
3113 }
3114 }
3115
3116 void
3117 ConcurrentMarkSweepGeneration::verify() {
3118 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those
3119 // are not called when the heap is verified during universe initialization and
3120 // at vm shutdown.
3121 if (freelistLock()->owned_by_self()) {
3122 cmsSpace()->verify();
3123 } else {
3124 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag);
3125 cmsSpace()->verify();
3126 }
3127 }
3128
3129 void CMSCollector::verify() {
3130 _cmsGen->verify();
3131 }
3132
3133 #ifndef PRODUCT
3134 bool CMSCollector::overflow_list_is_empty() const {
3135 assert(_num_par_pushes >= 0, "Inconsistency");
3136 if (_overflow_list == NULL) {
3137 assert(_num_par_pushes == 0, "Inconsistency");
3138 }
3139 return _overflow_list == NULL;
3140 }
3141
3142 // The methods verify_work_stacks_empty() and verify_overflow_empty()
3143 // merely consolidate assertion checks that appear to occur together frequently.
3144 void CMSCollector::verify_work_stacks_empty() const {
3145 assert(_markStack.isEmpty(), "Marking stack should be empty");
3146 assert(overflow_list_is_empty(), "Overflow list should be empty");
3147 }
3148
3149 void CMSCollector::verify_overflow_empty() const {
3150 assert(overflow_list_is_empty(), "Overflow list should be empty");
3151 assert(no_preserved_marks(), "No preserved marks");
3152 }
3153 #endif // PRODUCT
3154
3155 // Decide if we want to enable class unloading as part of the
3156 // ensuing concurrent GC cycle. We will collect and
3157 // unload classes if it's the case that:
3158 // (1) an explicit gc request has been made and the flag
3159 // ExplicitGCInvokesConcurrentAndUnloadsClasses is set, OR
3160 // (2) (a) class unloading is enabled at the command line, and
3161 // (b) old gen is getting really full
3162 // NOTE: Provided there is no change in the state of the heap between
3163 // calls to this method, it should have idempotent results. Moreover,
3164 // its results should be monotonically increasing (i.e. going from 0 to 1,
3165 // but not 1 to 0) between successive calls between which the heap was
3166 // not collected. For the implementation below, it must thus rely on
3167 // the property that concurrent_cycles_since_last_unload()
3168 // will not decrease unless a collection cycle happened and that
3169 // _cmsGen->is_too_full() are
3170 // themselves also monotonic in that sense. See check_monotonicity()
3171 // below.
3172 void CMSCollector::update_should_unload_classes() {
3173 _should_unload_classes = false;
3174 // Condition 1 above
3175 if (_full_gc_requested && ExplicitGCInvokesConcurrentAndUnloadsClasses) {
3176 _should_unload_classes = true;
3177 } else if (CMSClassUnloadingEnabled) { // Condition 2.a above
3178 // Disjuncts 2.b.(i,ii,iii) above
3179 _should_unload_classes = (concurrent_cycles_since_last_unload() >=
3180 CMSClassUnloadingMaxInterval)
3181 || _cmsGen->is_too_full();
3182 }
3183 }
3184
3185 bool ConcurrentMarkSweepGeneration::is_too_full() const {
3186 bool res = should_concurrent_collect();
3187 res = res && (occupancy() > (double)CMSIsTooFullPercentage/100.0);
3188 return res;
3189 }
3190
3191 void CMSCollector::setup_cms_unloading_and_verification_state() {
3192 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC
3193 || VerifyBeforeExit;
3194 const int rso = SharedHeap::SO_Strings | SharedHeap::SO_CodeCache;
3195
3196 if (should_unload_classes()) { // Should unload classes this cycle
3197 remove_root_scanning_option(rso); // Shrink the root set appropriately
3198 set_verifying(should_verify); // Set verification state for this cycle
3199 return; // Nothing else needs to be done at this time
3200 }
3201
3202 // Not unloading classes this cycle
3203 assert(!should_unload_classes(), "Inconsitency!");
3204 if ((!verifying() || unloaded_classes_last_cycle()) && should_verify) {
3205 // Include symbols, strings and code cache elements to prevent their resurrection.
3206 add_root_scanning_option(rso);
3207 set_verifying(true);
3208 } else if (verifying() && !should_verify) {
3209 // We were verifying, but some verification flags got disabled.
3210 set_verifying(false);
3211 // Exclude symbols, strings and code cache elements from root scanning to
3212 // reduce IM and RM pauses.
3213 remove_root_scanning_option(rso);
3214 }
3215 }
3216
3217
3218 #ifndef PRODUCT
3219 HeapWord* CMSCollector::block_start(const void* p) const {
3220 const HeapWord* addr = (HeapWord*)p;
3221 if (_span.contains(p)) {
3222 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) {
3223 return _cmsGen->cmsSpace()->block_start(p);
3224 }
3225 }
3226 return NULL;
3227 }
3228 #endif
3229
3230 HeapWord*
3231 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size,
3232 bool tlab,
3233 bool parallel) {
3234 CMSSynchronousYieldRequest yr;
3235 assert(!tlab, "Can't deal with TLAB allocation");
3236 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag);
3237 expand(word_size*HeapWordSize, MinHeapDeltaBytes,
3238 CMSExpansionCause::_satisfy_allocation);
3239 if (GCExpandToAllocateDelayMillis > 0) {
3240 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3241 }
3242 return have_lock_and_allocate(word_size, tlab);
3243 }
3244
3245 // YSR: All of this generation expansion/shrinking stuff is an exact copy of
3246 // OneContigSpaceCardGeneration, which makes me wonder if we should move this
3247 // to CardGeneration and share it...
3248 bool ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes) {
3249 return CardGeneration::expand(bytes, expand_bytes);
3250 }
3251
3252 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes,
3253 CMSExpansionCause::Cause cause)
3254 {
3255
3256 bool success = expand(bytes, expand_bytes);
3257
3258 // remember why we expanded; this information is used
3259 // by shouldConcurrentCollect() when making decisions on whether to start
3260 // a new CMS cycle.
3261 if (success) {
3262 set_expansion_cause(cause);
3263 if (PrintGCDetails && Verbose) {
3264 gclog_or_tty->print_cr("Expanded CMS gen for %s",
3265 CMSExpansionCause::to_string(cause));
3266 }
3267 }
3268 }
3269
3270 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) {
3271 HeapWord* res = NULL;
3272 MutexLocker x(ParGCRareEvent_lock);
3273 while (true) {
3274 // Expansion by some other thread might make alloc OK now:
3275 res = ps->lab.alloc(word_sz);
3276 if (res != NULL) return res;
3277 // If there's not enough expansion space available, give up.
3278 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) {
3279 return NULL;
3280 }
3281 // Otherwise, we try expansion.
3282 expand(word_sz*HeapWordSize, MinHeapDeltaBytes,
3283 CMSExpansionCause::_allocate_par_lab);
3284 // Now go around the loop and try alloc again;
3285 // A competing par_promote might beat us to the expansion space,
3286 // so we may go around the loop again if promotion fails agaion.
3287 if (GCExpandToAllocateDelayMillis > 0) {
3288 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3289 }
3290 }
3291 }
3292
3293
3294 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space(
3295 PromotionInfo* promo) {
3296 MutexLocker x(ParGCRareEvent_lock);
3297 size_t refill_size_bytes = promo->refillSize() * HeapWordSize;
3298 while (true) {
3299 // Expansion by some other thread might make alloc OK now:
3300 if (promo->ensure_spooling_space()) {
3301 assert(promo->has_spooling_space(),
3302 "Post-condition of successful ensure_spooling_space()");
3303 return true;
3304 }
3305 // If there's not enough expansion space available, give up.
3306 if (_virtual_space.uncommitted_size() < refill_size_bytes) {
3307 return false;
3308 }
3309 // Otherwise, we try expansion.
3310 expand(refill_size_bytes, MinHeapDeltaBytes,
3311 CMSExpansionCause::_allocate_par_spooling_space);
3312 // Now go around the loop and try alloc again;
3313 // A competing allocation might beat us to the expansion space,
3314 // so we may go around the loop again if allocation fails again.
3315 if (GCExpandToAllocateDelayMillis > 0) {
3316 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false);
3317 }
3318 }
3319 }
3320
3321
3322
3323 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) {
3324 assert_locked_or_safepoint(Heap_lock);
3325 size_t size = ReservedSpace::page_align_size_down(bytes);
3326 if (size > 0) {
3327 shrink_by(size);
3328 }
3329 }
3330
3331 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) {
3332 assert_locked_or_safepoint(Heap_lock);
3333 bool result = _virtual_space.expand_by(bytes);
3334 if (result) {
3335 HeapWord* old_end = _cmsSpace->end();
3336 size_t new_word_size =
3337 heap_word_size(_virtual_space.committed_size());
3338 MemRegion mr(_cmsSpace->bottom(), new_word_size);
3339 _bts->resize(new_word_size); // resize the block offset shared array
3340 Universe::heap()->barrier_set()->resize_covered_region(mr);
3341 // Hmmmm... why doesn't CFLS::set_end verify locking?
3342 // This is quite ugly; FIX ME XXX
3343 _cmsSpace->assert_locked(freelistLock());
3344 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
3345
3346 // update the space and generation capacity counters
3347 if (UsePerfData) {
3348 _space_counters->update_capacity();
3349 _gen_counters->update_all();
3350 }
3351
3352 if (Verbose && PrintGC) {
3353 size_t new_mem_size = _virtual_space.committed_size();
3354 size_t old_mem_size = new_mem_size - bytes;
3355 gclog_or_tty->print_cr("Expanding %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
3356 name(), old_mem_size/K, bytes/K, new_mem_size/K);
3357 }
3358 }
3359 return result;
3360 }
3361
3362 bool ConcurrentMarkSweepGeneration::grow_to_reserved() {
3363 assert_locked_or_safepoint(Heap_lock);
3364 bool success = true;
3365 const size_t remaining_bytes = _virtual_space.uncommitted_size();
3366 if (remaining_bytes > 0) {
3367 success = grow_by(remaining_bytes);
3368 DEBUG_ONLY(if (!success) warning("grow to reserved failed");)
3369 }
3370 return success;
3371 }
3372
3373 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) {
3374 assert_locked_or_safepoint(Heap_lock);
3375 assert_lock_strong(freelistLock());
3376 // XXX Fix when compaction is implemented.
3377 warning("Shrinking of CMS not yet implemented");
3378 return;
3379 }
3380
3381 CMSPhaseTracing::CMSPhaseTracing(bool print, const char* phase) {
3382 if (print) {
3383 gclog_or_tty->date_stamp(PrintGCDateStamps);
3384 gclog_or_tty->stamp(PrintGCTimeStamps);
3385 gclog_or_tty->print("%s", phase);
3386 }
3387 }
3388
3389 CMSPhaseTracing::~CMSPhaseTracing() {}
3390
3391 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent
3392 // phases.
3393 class CMSPhaseAccounting: public CMSPhaseTracing {
3394 public:
3395 CMSPhaseAccounting(CMSCollector *collector,
3396 const char *phase,
3397 bool print_cr = true);
3398 ~CMSPhaseAccounting();
3399
3400 private:
3401 CMSCollector *_collector;
3402 const char *_phase;
3403 elapsedTimer _wallclock;
3404 bool _print_cr;
3405
3406 public:
3407 // Not MT-safe; so do not pass around these StackObj's
3408 // where they may be accessed by other threads.
3409 jlong wallclock_millis() {
3410 assert(_wallclock.is_active(), "Wall clock should not stop");
3411 _wallclock.stop(); // to record time
3412 jlong ret = _wallclock.milliseconds();
3413 _wallclock.start(); // restart
3414 return ret;
3415 }
3416 };
3417
3418 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector,
3419 const char *phase,
3420 bool print_cr) :
3421 CMSPhaseTracing(PrintGCDetails, ""),
3422 _collector(collector), _phase(phase), _print_cr(print_cr) {
3423
3424 if (PrintCMSStatistics != 0) {
3425 _collector->resetYields();
3426 }
3427 if (PrintGCDetails && PrintGCTimeStamps) {
3428 gclog_or_tty->print_cr("[%s-concurrent-%s-start]",
3429 _collector->cmsGen()->short_name(), _phase);
3430 }
3431 _collector->resetTimer();
3432 _wallclock.start();
3433 _collector->startTimer();
3434 }
3435
3436 CMSPhaseAccounting::~CMSPhaseAccounting() {
3437 assert(_wallclock.is_active(), "Wall clock should not have stopped");
3438 _collector->stopTimer();
3439 _wallclock.stop();
3440 if (PrintGCDetails) {
3441 gclog_or_tty->date_stamp(PrintGCDateStamps);
3442 gclog_or_tty->stamp(PrintGCTimeStamps);
3443 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]",
3444 _collector->cmsGen()->short_name(),
3445 _phase, _collector->timerValue(), _wallclock.seconds());
3446 if (_print_cr) {
3447 gclog_or_tty->print_cr("");
3448 }
3449 if (PrintCMSStatistics != 0) {
3450 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase,
3451 _collector->yields());
3452 }
3453 }
3454 }
3455
3456 // CMS work
3457
3458 // Checkpoint the roots into this generation from outside
3459 // this generation. [Note this initial checkpoint need only
3460 // be approximate -- we'll do a catch up phase subsequently.]
3461 void CMSCollector::checkpointRootsInitial(bool asynch) {
3462 assert(_collectorState == InitialMarking, "Wrong collector state");
3463 check_correct_thread_executing();
3464 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
3465
3466 ReferenceProcessor* rp = ref_processor();
3467 SpecializationStats::clear();
3468 assert(_restart_addr == NULL, "Control point invariant");
3469 if (asynch) {
3470 // acquire locks for subsequent manipulations
3471 MutexLockerEx x(bitMapLock(),
3472 Mutex::_no_safepoint_check_flag);
3473 checkpointRootsInitialWork(asynch);
3474 // enable ("weak") refs discovery
3475 rp->enable_discovery(true /*verify_disabled*/, true /*check_no_refs*/);
3476 _collectorState = Marking;
3477 } else {
3478 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection
3479 // which recognizes if we are a CMS generation, and doesn't try to turn on
3480 // discovery; verify that they aren't meddling.
3481 assert(!rp->discovery_is_atomic(),
3482 "incorrect setting of discovery predicate");
3483 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control "
3484 "ref discovery for this generation kind");
3485 // already have locks
3486 checkpointRootsInitialWork(asynch);
3487 // now enable ("weak") refs discovery
3488 rp->enable_discovery(true /*verify_disabled*/, false /*verify_no_refs*/);
3489 _collectorState = Marking;
3490 }
3491 SpecializationStats::print();
3492 }
3493
3494 void CMSCollector::checkpointRootsInitialWork(bool asynch) {
3495 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped");
3496 assert(_collectorState == InitialMarking, "just checking");
3497
3498 // If there has not been a GC[n-1] since last GC[n] cycle completed,
3499 // precede our marking with a collection of all
3500 // younger generations to keep floating garbage to a minimum.
3501 // XXX: we won't do this for now -- it's an optimization to be done later.
3502
3503 // already have locks
3504 assert_lock_strong(bitMapLock());
3505 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle");
3506
3507 // Setup the verification and class unloading state for this
3508 // CMS collection cycle.
3509 setup_cms_unloading_and_verification_state();
3510
3511 NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork",
3512 PrintGCDetails && Verbose, true, gclog_or_tty);)
3513 if (UseAdaptiveSizePolicy) {
3514 size_policy()->checkpoint_roots_initial_begin();
3515 }
3516
3517 // Reset all the PLAB chunk arrays if necessary.
3518 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) {
3519 reset_survivor_plab_arrays();
3520 }
3521
3522 ResourceMark rm;
3523 HandleMark hm;
3524
3525 FalseClosure falseClosure;
3526 // In the case of a synchronous collection, we will elide the
3527 // remark step, so it's important to catch all the nmethod oops
3528 // in this step.
3529 // The final 'true' flag to gen_process_strong_roots will ensure this.
3530 // If 'async' is true, we can relax the nmethod tracing.
3531 MarkRefsIntoClosure notOlder(_span, &_markBitMap);
3532 GenCollectedHeap* gch = GenCollectedHeap::heap();
3533
3534 verify_work_stacks_empty();
3535 verify_overflow_empty();
3536
3537 gch->ensure_parsability(false); // fill TLABs, but no need to retire them
3538 // Update the saved marks which may affect the root scans.
3539 gch->save_marks();
3540
3541 // weak reference processing has not started yet.
3542 ref_processor()->set_enqueuing_is_done(false);
3543
3544 // Need to remember all newly created CLDs,
3545 // so that we can guarantee that the remark finds them.
3546 ClassLoaderDataGraph::remember_new_clds(true);
3547
3548 // Whenever a CLD is found, it will be claimed before proceeding to mark
3549 // the klasses. The claimed marks need to be cleared before marking starts.
3550 ClassLoaderDataGraph::clear_claimed_marks();
3551
3552 CMKlassClosure klass_closure(¬Older);
3553 {
3554 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
3555 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
3556 gch->gen_process_strong_roots(_cmsGen->level(),
3557 true, // younger gens are roots
3558 true, // activate StrongRootsScope
3559 false, // not scavenging
3560 SharedHeap::ScanningOption(roots_scanning_options()),
3561 ¬Older,
3562 true, // walk all of code cache if (so & SO_CodeCache)
3563 NULL,
3564 &klass_closure);
3565 }
3566
3567 // Clear mod-union table; it will be dirtied in the prologue of
3568 // CMS generation per each younger generation collection.
3569
3570 assert(_modUnionTable.isAllClear(),
3571 "Was cleared in most recent final checkpoint phase"
3572 " or no bits are set in the gc_prologue before the start of the next "
3573 "subsequent marking phase.");
3574
3575 assert(_ct->klass_rem_set()->mod_union_is_clear(), "Must be");
3576
3577 // Save the end of the used_region of the constituent generations
3578 // to be used to limit the extent of sweep in each generation.
3579 save_sweep_limits();
3580 if (UseAdaptiveSizePolicy) {
3581 size_policy()->checkpoint_roots_initial_end(gch->gc_cause());
3582 }
3583 verify_overflow_empty();
3584 }
3585
3586 bool CMSCollector::markFromRoots(bool asynch) {
3587 // we might be tempted to assert that:
3588 // assert(asynch == !SafepointSynchronize::is_at_safepoint(),
3589 // "inconsistent argument?");
3590 // However that wouldn't be right, because it's possible that
3591 // a safepoint is indeed in progress as a younger generation
3592 // stop-the-world GC happens even as we mark in this generation.
3593 assert(_collectorState == Marking, "inconsistent state?");
3594 check_correct_thread_executing();
3595 verify_overflow_empty();
3596
3597 bool res;
3598 if (asynch) {
3599
3600 // Start the timers for adaptive size policy for the concurrent phases
3601 // Do it here so that the foreground MS can use the concurrent
3602 // timer since a foreground MS might has the sweep done concurrently
3603 // or STW.
3604 if (UseAdaptiveSizePolicy) {
3605 size_policy()->concurrent_marking_begin();
3606 }
3607
3608 // Weak ref discovery note: We may be discovering weak
3609 // refs in this generation concurrent (but interleaved) with
3610 // weak ref discovery by a younger generation collector.
3611
3612 CMSTokenSyncWithLocks ts(true, bitMapLock());
3613 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
3614 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails);
3615 res = markFromRootsWork(asynch);
3616 if (res) {
3617 _collectorState = Precleaning;
3618 } else { // We failed and a foreground collection wants to take over
3619 assert(_foregroundGCIsActive, "internal state inconsistency");
3620 assert(_restart_addr == NULL, "foreground will restart from scratch");
3621 if (PrintGCDetails) {
3622 gclog_or_tty->print_cr("bailing out to foreground collection");
3623 }
3624 }
3625 if (UseAdaptiveSizePolicy) {
3626 size_policy()->concurrent_marking_end();
3627 }
3628 } else {
3629 assert(SafepointSynchronize::is_at_safepoint(),
3630 "inconsistent with asynch == false");
3631 if (UseAdaptiveSizePolicy) {
3632 size_policy()->ms_collection_marking_begin();
3633 }
3634 // already have locks
3635 res = markFromRootsWork(asynch);
3636 _collectorState = FinalMarking;
3637 if (UseAdaptiveSizePolicy) {
3638 GenCollectedHeap* gch = GenCollectedHeap::heap();
3639 size_policy()->ms_collection_marking_end(gch->gc_cause());
3640 }
3641 }
3642 verify_overflow_empty();
3643 return res;
3644 }
3645
3646 bool CMSCollector::markFromRootsWork(bool asynch) {
3647 // iterate over marked bits in bit map, doing a full scan and mark
3648 // from these roots using the following algorithm:
3649 // . if oop is to the right of the current scan pointer,
3650 // mark corresponding bit (we'll process it later)
3651 // . else (oop is to left of current scan pointer)
3652 // push oop on marking stack
3653 // . drain the marking stack
3654
3655 // Note that when we do a marking step we need to hold the
3656 // bit map lock -- recall that direct allocation (by mutators)
3657 // and promotion (by younger generation collectors) is also
3658 // marking the bit map. [the so-called allocate live policy.]
3659 // Because the implementation of bit map marking is not
3660 // robust wrt simultaneous marking of bits in the same word,
3661 // we need to make sure that there is no such interference
3662 // between concurrent such updates.
3663
3664 // already have locks
3665 assert_lock_strong(bitMapLock());
3666
3667 verify_work_stacks_empty();
3668 verify_overflow_empty();
3669 bool result = false;
3670 if (CMSConcurrentMTEnabled && ConcGCThreads > 0) {
3671 result = do_marking_mt(asynch);
3672 } else {
3673 result = do_marking_st(asynch);
3674 }
3675 return result;
3676 }
3677
3678 // Forward decl
3679 class CMSConcMarkingTask;
3680
3681 class CMSConcMarkingTerminator: public ParallelTaskTerminator {
3682 CMSCollector* _collector;
3683 CMSConcMarkingTask* _task;
3684 public:
3685 virtual void yield();
3686
3687 // "n_threads" is the number of threads to be terminated.
3688 // "queue_set" is a set of work queues of other threads.
3689 // "collector" is the CMS collector associated with this task terminator.
3690 // "yield" indicates whether we need the gang as a whole to yield.
3691 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, CMSCollector* collector) :
3692 ParallelTaskTerminator(n_threads, queue_set),
3693 _collector(collector) { }
3694
3695 void set_task(CMSConcMarkingTask* task) {
3696 _task = task;
3697 }
3698 };
3699
3700 class CMSConcMarkingTerminatorTerminator: public TerminatorTerminator {
3701 CMSConcMarkingTask* _task;
3702 public:
3703 bool should_exit_termination();
3704 void set_task(CMSConcMarkingTask* task) {
3705 _task = task;
3706 }
3707 };
3708
3709 // MT Concurrent Marking Task
3710 class CMSConcMarkingTask: public YieldingFlexibleGangTask {
3711 CMSCollector* _collector;
3712 int _n_workers; // requested/desired # workers
3713 bool _asynch;
3714 bool _result;
3715 CompactibleFreeListSpace* _cms_space;
3716 char _pad_front[64]; // padding to ...
3717 HeapWord* _global_finger; // ... avoid sharing cache line
3718 char _pad_back[64];
3719 HeapWord* _restart_addr;
3720
3721 // Exposed here for yielding support
3722 Mutex* const _bit_map_lock;
3723
3724 // The per thread work queues, available here for stealing
3725 OopTaskQueueSet* _task_queues;
3726
3727 // Termination (and yielding) support
3728 CMSConcMarkingTerminator _term;
3729 CMSConcMarkingTerminatorTerminator _term_term;
3730
3731 public:
3732 CMSConcMarkingTask(CMSCollector* collector,
3733 CompactibleFreeListSpace* cms_space,
3734 bool asynch,
3735 YieldingFlexibleWorkGang* workers,
3736 OopTaskQueueSet* task_queues):
3737 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"),
3738 _collector(collector),
3739 _cms_space(cms_space),
3740 _asynch(asynch), _n_workers(0), _result(true),
3741 _task_queues(task_queues),
3742 _term(_n_workers, task_queues, _collector),
3743 _bit_map_lock(collector->bitMapLock())
3744 {
3745 _requested_size = _n_workers;
3746 _term.set_task(this);
3747 _term_term.set_task(this);
3748 _restart_addr = _global_finger = _cms_space->bottom();
3749 }
3750
3751
3752 OopTaskQueueSet* task_queues() { return _task_queues; }
3753
3754 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
3755
3756 HeapWord** global_finger_addr() { return &_global_finger; }
3757
3758 CMSConcMarkingTerminator* terminator() { return &_term; }
3759
3760 virtual void set_for_termination(int active_workers) {
3761 terminator()->reset_for_reuse(active_workers);
3762 }
3763
3764 void work(uint worker_id);
3765 bool should_yield() {
3766 return ConcurrentMarkSweepThread::should_yield()
3767 && !_collector->foregroundGCIsActive()
3768 && _asynch;
3769 }
3770
3771 virtual void coordinator_yield(); // stuff done by coordinator
3772 bool result() { return _result; }
3773
3774 void reset(HeapWord* ra) {
3775 assert(_global_finger >= _cms_space->end(), "Postcondition of ::work(i)");
3776 _restart_addr = _global_finger = ra;
3777 _term.reset_for_reuse();
3778 }
3779
3780 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3781 OopTaskQueue* work_q);
3782
3783 private:
3784 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp);
3785 void do_work_steal(int i);
3786 void bump_global_finger(HeapWord* f);
3787 };
3788
3789 bool CMSConcMarkingTerminatorTerminator::should_exit_termination() {
3790 assert(_task != NULL, "Error");
3791 return _task->yielding();
3792 // Note that we do not need the disjunct || _task->should_yield() above
3793 // because we want terminating threads to yield only if the task
3794 // is already in the midst of yielding, which happens only after at least one
3795 // thread has yielded.
3796 }
3797
3798 void CMSConcMarkingTerminator::yield() {
3799 if (_task->should_yield()) {
3800 _task->yield();
3801 } else {
3802 ParallelTaskTerminator::yield();
3803 }
3804 }
3805
3806 ////////////////////////////////////////////////////////////////
3807 // Concurrent Marking Algorithm Sketch
3808 ////////////////////////////////////////////////////////////////
3809 // Until all tasks exhausted (both spaces):
3810 // -- claim next available chunk
3811 // -- bump global finger via CAS
3812 // -- find first object that starts in this chunk
3813 // and start scanning bitmap from that position
3814 // -- scan marked objects for oops
3815 // -- CAS-mark target, and if successful:
3816 // . if target oop is above global finger (volatile read)
3817 // nothing to do
3818 // . if target oop is in chunk and above local finger
3819 // then nothing to do
3820 // . else push on work-queue
3821 // -- Deal with possible overflow issues:
3822 // . local work-queue overflow causes stuff to be pushed on
3823 // global (common) overflow queue
3824 // . always first empty local work queue
3825 // . then get a batch of oops from global work queue if any
3826 // . then do work stealing
3827 // -- When all tasks claimed (both spaces)
3828 // and local work queue empty,
3829 // then in a loop do:
3830 // . check global overflow stack; steal a batch of oops and trace
3831 // . try to steal from other threads oif GOS is empty
3832 // . if neither is available, offer termination
3833 // -- Terminate and return result
3834 //
3835 void CMSConcMarkingTask::work(uint worker_id) {
3836 elapsedTimer _timer;
3837 ResourceMark rm;
3838 HandleMark hm;
3839
3840 DEBUG_ONLY(_collector->verify_overflow_empty();)
3841
3842 // Before we begin work, our work queue should be empty
3843 assert(work_queue(worker_id)->size() == 0, "Expected to be empty");
3844 // Scan the bitmap covering _cms_space, tracing through grey objects.
3845 _timer.start();
3846 do_scan_and_mark(worker_id, _cms_space);
3847 _timer.stop();
3848 if (PrintCMSStatistics != 0) {
3849 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec",
3850 worker_id, _timer.seconds());
3851 // XXX: need xxx/xxx type of notation, two timers
3852 }
3853
3854 // ... do work stealing
3855 _timer.reset();
3856 _timer.start();
3857 do_work_steal(worker_id);
3858 _timer.stop();
3859 if (PrintCMSStatistics != 0) {
3860 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec",
3861 worker_id, _timer.seconds());
3862 // XXX: need xxx/xxx type of notation, two timers
3863 }
3864 assert(_collector->_markStack.isEmpty(), "Should have been emptied");
3865 assert(work_queue(worker_id)->size() == 0, "Should have been emptied");
3866 // Note that under the current task protocol, the
3867 // following assertion is true even of the spaces
3868 // expanded since the completion of the concurrent
3869 // marking. XXX This will likely change under a strict
3870 // ABORT semantics.
3871 // After perm removal the comparison was changed to
3872 // greater than or equal to from strictly greater than.
3873 // Before perm removal the highest address sweep would
3874 // have been at the end of perm gen but now is at the
3875 // end of the tenured gen.
3876 assert(_global_finger >= _cms_space->end(),
3877 "All tasks have been completed");
3878 DEBUG_ONLY(_collector->verify_overflow_empty();)
3879 }
3880
3881 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) {
3882 HeapWord* read = _global_finger;
3883 HeapWord* cur = read;
3884 while (f > read) {
3885 cur = read;
3886 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur);
3887 if (cur == read) {
3888 // our cas succeeded
3889 assert(_global_finger >= f, "protocol consistency");
3890 break;
3891 }
3892 }
3893 }
3894
3895 // This is really inefficient, and should be redone by
3896 // using (not yet available) block-read and -write interfaces to the
3897 // stack and the work_queue. XXX FIX ME !!!
3898 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk,
3899 OopTaskQueue* work_q) {
3900 // Fast lock-free check
3901 if (ovflw_stk->length() == 0) {
3902 return false;
3903 }
3904 assert(work_q->size() == 0, "Shouldn't steal");
3905 MutexLockerEx ml(ovflw_stk->par_lock(),
3906 Mutex::_no_safepoint_check_flag);
3907 // Grab up to 1/4 the size of the work queue
3908 size_t num = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
3909 (size_t)ParGCDesiredObjsFromOverflowList);
3910 num = MIN2(num, ovflw_stk->length());
3911 for (int i = (int) num; i > 0; i--) {
3912 oop cur = ovflw_stk->pop();
3913 assert(cur != NULL, "Counted wrong?");
3914 work_q->push(cur);
3915 }
3916 return num > 0;
3917 }
3918
3919 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) {
3920 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
3921 int n_tasks = pst->n_tasks();
3922 // We allow that there may be no tasks to do here because
3923 // we are restarting after a stack overflow.
3924 assert(pst->valid() || n_tasks == 0, "Uninitialized use?");
3925 uint nth_task = 0;
3926
3927 HeapWord* aligned_start = sp->bottom();
3928 if (sp->used_region().contains(_restart_addr)) {
3929 // Align down to a card boundary for the start of 0th task
3930 // for this space.
3931 aligned_start =
3932 (HeapWord*)align_size_down((uintptr_t)_restart_addr,
3933 CardTableModRefBS::card_size);
3934 }
3935
3936 size_t chunk_size = sp->marking_task_size();
3937 while (!pst->is_task_claimed(/* reference */ nth_task)) {
3938 // Having claimed the nth task in this space,
3939 // compute the chunk that it corresponds to:
3940 MemRegion span = MemRegion(aligned_start + nth_task*chunk_size,
3941 aligned_start + (nth_task+1)*chunk_size);
3942 // Try and bump the global finger via a CAS;
3943 // note that we need to do the global finger bump
3944 // _before_ taking the intersection below, because
3945 // the task corresponding to that region will be
3946 // deemed done even if the used_region() expands
3947 // because of allocation -- as it almost certainly will
3948 // during start-up while the threads yield in the
3949 // closure below.
3950 HeapWord* finger = span.end();
3951 bump_global_finger(finger); // atomically
3952 // There are null tasks here corresponding to chunks
3953 // beyond the "top" address of the space.
3954 span = span.intersection(sp->used_region());
3955 if (!span.is_empty()) { // Non-null task
3956 HeapWord* prev_obj;
3957 assert(!span.contains(_restart_addr) || nth_task == 0,
3958 "Inconsistency");
3959 if (nth_task == 0) {
3960 // For the 0th task, we'll not need to compute a block_start.
3961 if (span.contains(_restart_addr)) {
3962 // In the case of a restart because of stack overflow,
3963 // we might additionally skip a chunk prefix.
3964 prev_obj = _restart_addr;
3965 } else {
3966 prev_obj = span.start();
3967 }
3968 } else {
3969 // We want to skip the first object because
3970 // the protocol is to scan any object in its entirety
3971 // that _starts_ in this span; a fortiori, any
3972 // object starting in an earlier span is scanned
3973 // as part of an earlier claimed task.
3974 // Below we use the "careful" version of block_start
3975 // so we do not try to navigate uninitialized objects.
3976 prev_obj = sp->block_start_careful(span.start());
3977 // Below we use a variant of block_size that uses the
3978 // Printezis bits to avoid waiting for allocated
3979 // objects to become initialized/parsable.
3980 while (prev_obj < span.start()) {
3981 size_t sz = sp->block_size_no_stall(prev_obj, _collector);
3982 if (sz > 0) {
3983 prev_obj += sz;
3984 } else {
3985 // In this case we may end up doing a bit of redundant
3986 // scanning, but that appears unavoidable, short of
3987 // locking the free list locks; see bug 6324141.
3988 break;
3989 }
3990 }
3991 }
3992 if (prev_obj < span.end()) {
3993 MemRegion my_span = MemRegion(prev_obj, span.end());
3994 // Do the marking work within a non-empty span --
3995 // the last argument to the constructor indicates whether the
3996 // iteration should be incremental with periodic yields.
3997 Par_MarkFromRootsClosure cl(this, _collector, my_span,
3998 &_collector->_markBitMap,
3999 work_queue(i),
4000 &_collector->_markStack,
4001 _asynch);
4002 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end());
4003 } // else nothing to do for this task
4004 } // else nothing to do for this task
4005 }
4006 // We'd be tempted to assert here that since there are no
4007 // more tasks left to claim in this space, the global_finger
4008 // must exceed space->top() and a fortiori space->end(). However,
4009 // that would not quite be correct because the bumping of
4010 // global_finger occurs strictly after the claiming of a task,
4011 // so by the time we reach here the global finger may not yet
4012 // have been bumped up by the thread that claimed the last
4013 // task.
4014 pst->all_tasks_completed();
4015 }
4016
4017 class Par_ConcMarkingClosure: public CMSOopClosure {
4018 private:
4019 CMSCollector* _collector;
4020 CMSConcMarkingTask* _task;
4021 MemRegion _span;
4022 CMSBitMap* _bit_map;
4023 CMSMarkStack* _overflow_stack;
4024 OopTaskQueue* _work_queue;
4025 protected:
4026 DO_OOP_WORK_DEFN
4027 public:
4028 Par_ConcMarkingClosure(CMSCollector* collector, CMSConcMarkingTask* task, OopTaskQueue* work_queue,
4029 CMSBitMap* bit_map, CMSMarkStack* overflow_stack):
4030 CMSOopClosure(collector->ref_processor()),
4031 _collector(collector),
4032 _task(task),
4033 _span(collector->_span),
4034 _work_queue(work_queue),
4035 _bit_map(bit_map),
4036 _overflow_stack(overflow_stack)
4037 { }
4038 virtual void do_oop(oop* p);
4039 virtual void do_oop(narrowOop* p);
4040
4041 void trim_queue(size_t max);
4042 void handle_stack_overflow(HeapWord* lost);
4043 void do_yield_check() {
4044 if (_task->should_yield()) {
4045 _task->yield();
4046 }
4047 }
4048 };
4049
4050 // Grey object scanning during work stealing phase --
4051 // the salient assumption here is that any references
4052 // that are in these stolen objects being scanned must
4053 // already have been initialized (else they would not have
4054 // been published), so we do not need to check for
4055 // uninitialized objects before pushing here.
4056 void Par_ConcMarkingClosure::do_oop(oop obj) {
4057 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
4058 HeapWord* addr = (HeapWord*)obj;
4059 // Check if oop points into the CMS generation
4060 // and is not marked
4061 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
4062 // a white object ...
4063 // If we manage to "claim" the object, by being the
4064 // first thread to mark it, then we push it on our
4065 // marking stack
4066 if (_bit_map->par_mark(addr)) { // ... now grey
4067 // push on work queue (grey set)
4068 bool simulate_overflow = false;
4069 NOT_PRODUCT(
4070 if (CMSMarkStackOverflowALot &&
4071 _collector->simulate_overflow()) {
4072 // simulate a stack overflow
4073 simulate_overflow = true;
4074 }
4075 )
4076 if (simulate_overflow ||
4077 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
4078 // stack overflow
4079 if (PrintCMSStatistics != 0) {
4080 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
4081 SIZE_FORMAT, _overflow_stack->capacity());
4082 }
4083 // We cannot assert that the overflow stack is full because
4084 // it may have been emptied since.
4085 assert(simulate_overflow ||
4086 _work_queue->size() == _work_queue->max_elems(),
4087 "Else push should have succeeded");
4088 handle_stack_overflow(addr);
4089 }
4090 } // Else, some other thread got there first
4091 do_yield_check();
4092 }
4093 }
4094
4095 void Par_ConcMarkingClosure::do_oop(oop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4096 void Par_ConcMarkingClosure::do_oop(narrowOop* p) { Par_ConcMarkingClosure::do_oop_work(p); }
4097
4098 void Par_ConcMarkingClosure::trim_queue(size_t max) {
4099 while (_work_queue->size() > max) {
4100 oop new_oop;
4101 if (_work_queue->pop_local(new_oop)) {
4102 assert(new_oop->is_oop(), "Should be an oop");
4103 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object");
4104 assert(_span.contains((HeapWord*)new_oop), "Not in span");
4105 new_oop->oop_iterate(this); // do_oop() above
4106 do_yield_check();
4107 }
4108 }
4109 }
4110
4111 // Upon stack overflow, we discard (part of) the stack,
4112 // remembering the least address amongst those discarded
4113 // in CMSCollector's _restart_address.
4114 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) {
4115 // We need to do this under a mutex to prevent other
4116 // workers from interfering with the work done below.
4117 MutexLockerEx ml(_overflow_stack->par_lock(),
4118 Mutex::_no_safepoint_check_flag);
4119 // Remember the least grey address discarded
4120 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
4121 _collector->lower_restart_addr(ra);
4122 _overflow_stack->reset(); // discard stack contents
4123 _overflow_stack->expand(); // expand the stack if possible
4124 }
4125
4126
4127 void CMSConcMarkingTask::do_work_steal(int i) {
4128 OopTaskQueue* work_q = work_queue(i);
4129 oop obj_to_scan;
4130 CMSBitMap* bm = &(_collector->_markBitMap);
4131 CMSMarkStack* ovflw = &(_collector->_markStack);
4132 int* seed = _collector->hash_seed(i);
4133 Par_ConcMarkingClosure cl(_collector, this, work_q, bm, ovflw);
4134 while (true) {
4135 cl.trim_queue(0);
4136 assert(work_q->size() == 0, "Should have been emptied above");
4137 if (get_work_from_overflow_stack(ovflw, work_q)) {
4138 // Can't assert below because the work obtained from the
4139 // overflow stack may already have been stolen from us.
4140 // assert(work_q->size() > 0, "Work from overflow stack");
4141 continue;
4142 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
4143 assert(obj_to_scan->is_oop(), "Should be an oop");
4144 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object");
4145 obj_to_scan->oop_iterate(&cl);
4146 } else if (terminator()->offer_termination(&_term_term)) {
4147 assert(work_q->size() == 0, "Impossible!");
4148 break;
4149 } else if (yielding() || should_yield()) {
4150 yield();
4151 }
4152 }
4153 }
4154
4155 // This is run by the CMS (coordinator) thread.
4156 void CMSConcMarkingTask::coordinator_yield() {
4157 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4158 "CMS thread should hold CMS token");
4159 // First give up the locks, then yield, then re-lock
4160 // We should probably use a constructor/destructor idiom to
4161 // do this unlock/lock or modify the MutexUnlocker class to
4162 // serve our purpose. XXX
4163 assert_lock_strong(_bit_map_lock);
4164 _bit_map_lock->unlock();
4165 ConcurrentMarkSweepThread::desynchronize(true);
4166 ConcurrentMarkSweepThread::acknowledge_yield_request();
4167 _collector->stopTimer();
4168 if (PrintCMSStatistics != 0) {
4169 _collector->incrementYields();
4170 }
4171 _collector->icms_wait();
4172
4173 // It is possible for whichever thread initiated the yield request
4174 // not to get a chance to wake up and take the bitmap lock between
4175 // this thread releasing it and reacquiring it. So, while the
4176 // should_yield() flag is on, let's sleep for a bit to give the
4177 // other thread a chance to wake up. The limit imposed on the number
4178 // of iterations is defensive, to avoid any unforseen circumstances
4179 // putting us into an infinite loop. Since it's always been this
4180 // (coordinator_yield()) method that was observed to cause the
4181 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount)
4182 // which is by default non-zero. For the other seven methods that
4183 // also perform the yield operation, as are using a different
4184 // parameter (CMSYieldSleepCount) which is by default zero. This way we
4185 // can enable the sleeping for those methods too, if necessary.
4186 // See 6442774.
4187 //
4188 // We really need to reconsider the synchronization between the GC
4189 // thread and the yield-requesting threads in the future and we
4190 // should really use wait/notify, which is the recommended
4191 // way of doing this type of interaction. Additionally, we should
4192 // consolidate the eight methods that do the yield operation and they
4193 // are almost identical into one for better maintenability and
4194 // readability. See 6445193.
4195 //
4196 // Tony 2006.06.29
4197 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount &&
4198 ConcurrentMarkSweepThread::should_yield() &&
4199 !CMSCollector::foregroundGCIsActive(); ++i) {
4200 os::sleep(Thread::current(), 1, false);
4201 ConcurrentMarkSweepThread::acknowledge_yield_request();
4202 }
4203
4204 ConcurrentMarkSweepThread::synchronize(true);
4205 _bit_map_lock->lock_without_safepoint_check();
4206 _collector->startTimer();
4207 }
4208
4209 bool CMSCollector::do_marking_mt(bool asynch) {
4210 assert(ConcGCThreads > 0 && conc_workers() != NULL, "precondition");
4211 int num_workers = AdaptiveSizePolicy::calc_active_conc_workers(
4212 conc_workers()->total_workers(),
4213 conc_workers()->active_workers(),
4214 Threads::number_of_non_daemon_threads());
4215 conc_workers()->set_active_workers(num_workers);
4216
4217 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
4218
4219 CMSConcMarkingTask tsk(this,
4220 cms_space,
4221 asynch,
4222 conc_workers(),
4223 task_queues());
4224
4225 // Since the actual number of workers we get may be different
4226 // from the number we requested above, do we need to do anything different
4227 // below? In particular, may be we need to subclass the SequantialSubTasksDone
4228 // class?? XXX
4229 cms_space ->initialize_sequential_subtasks_for_marking(num_workers);
4230
4231 // Refs discovery is already non-atomic.
4232 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic");
4233 assert(ref_processor()->discovery_is_mt(), "Discovery should be MT");
4234 conc_workers()->start_task(&tsk);
4235 while (tsk.yielded()) {
4236 tsk.coordinator_yield();
4237 conc_workers()->continue_task(&tsk);
4238 }
4239 // If the task was aborted, _restart_addr will be non-NULL
4240 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency");
4241 while (_restart_addr != NULL) {
4242 // XXX For now we do not make use of ABORTED state and have not
4243 // yet implemented the right abort semantics (even in the original
4244 // single-threaded CMS case). That needs some more investigation
4245 // and is deferred for now; see CR# TBF. 07252005YSR. XXX
4246 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency");
4247 // If _restart_addr is non-NULL, a marking stack overflow
4248 // occurred; we need to do a fresh marking iteration from the
4249 // indicated restart address.
4250 if (_foregroundGCIsActive && asynch) {
4251 // We may be running into repeated stack overflows, having
4252 // reached the limit of the stack size, while making very
4253 // slow forward progress. It may be best to bail out and
4254 // let the foreground collector do its job.
4255 // Clear _restart_addr, so that foreground GC
4256 // works from scratch. This avoids the headache of
4257 // a "rescan" which would otherwise be needed because
4258 // of the dirty mod union table & card table.
4259 _restart_addr = NULL;
4260 return false;
4261 }
4262 // Adjust the task to restart from _restart_addr
4263 tsk.reset(_restart_addr);
4264 cms_space ->initialize_sequential_subtasks_for_marking(num_workers,
4265 _restart_addr);
4266 _restart_addr = NULL;
4267 // Get the workers going again
4268 conc_workers()->start_task(&tsk);
4269 while (tsk.yielded()) {
4270 tsk.coordinator_yield();
4271 conc_workers()->continue_task(&tsk);
4272 }
4273 }
4274 assert(tsk.completed(), "Inconsistency");
4275 assert(tsk.result() == true, "Inconsistency");
4276 return true;
4277 }
4278
4279 bool CMSCollector::do_marking_st(bool asynch) {
4280 ResourceMark rm;
4281 HandleMark hm;
4282
4283 // Temporarily make refs discovery single threaded (non-MT)
4284 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(ref_processor(), false);
4285 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap,
4286 &_markStack, CMSYield && asynch);
4287 // the last argument to iterate indicates whether the iteration
4288 // should be incremental with periodic yields.
4289 _markBitMap.iterate(&markFromRootsClosure);
4290 // If _restart_addr is non-NULL, a marking stack overflow
4291 // occurred; we need to do a fresh iteration from the
4292 // indicated restart address.
4293 while (_restart_addr != NULL) {
4294 if (_foregroundGCIsActive && asynch) {
4295 // We may be running into repeated stack overflows, having
4296 // reached the limit of the stack size, while making very
4297 // slow forward progress. It may be best to bail out and
4298 // let the foreground collector do its job.
4299 // Clear _restart_addr, so that foreground GC
4300 // works from scratch. This avoids the headache of
4301 // a "rescan" which would otherwise be needed because
4302 // of the dirty mod union table & card table.
4303 _restart_addr = NULL;
4304 return false; // indicating failure to complete marking
4305 }
4306 // Deal with stack overflow:
4307 // we restart marking from _restart_addr
4308 HeapWord* ra = _restart_addr;
4309 markFromRootsClosure.reset(ra);
4310 _restart_addr = NULL;
4311 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end());
4312 }
4313 return true;
4314 }
4315
4316 void CMSCollector::preclean() {
4317 check_correct_thread_executing();
4318 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread");
4319 verify_work_stacks_empty();
4320 verify_overflow_empty();
4321 _abort_preclean = false;
4322 if (CMSPrecleaningEnabled) {
4323 _eden_chunk_index = 0;
4324 size_t used = get_eden_used();
4325 size_t capacity = get_eden_capacity();
4326 // Don't start sampling unless we will get sufficiently
4327 // many samples.
4328 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100)
4329 * CMSScheduleRemarkEdenPenetration)) {
4330 _start_sampling = true;
4331 } else {
4332 _start_sampling = false;
4333 }
4334 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4335 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails);
4336 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1);
4337 }
4338 CMSTokenSync x(true); // is cms thread
4339 if (CMSPrecleaningEnabled) {
4340 sample_eden();
4341 _collectorState = AbortablePreclean;
4342 } else {
4343 _collectorState = FinalMarking;
4344 }
4345 verify_work_stacks_empty();
4346 verify_overflow_empty();
4347 }
4348
4349 // Try and schedule the remark such that young gen
4350 // occupancy is CMSScheduleRemarkEdenPenetration %.
4351 void CMSCollector::abortable_preclean() {
4352 check_correct_thread_executing();
4353 assert(CMSPrecleaningEnabled, "Inconsistent control state");
4354 assert(_collectorState == AbortablePreclean, "Inconsistent control state");
4355
4356 // If Eden's current occupancy is below this threshold,
4357 // immediately schedule the remark; else preclean
4358 // past the next scavenge in an effort to
4359 // schedule the pause as described avove. By choosing
4360 // CMSScheduleRemarkEdenSizeThreshold >= max eden size
4361 // we will never do an actual abortable preclean cycle.
4362 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) {
4363 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
4364 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails);
4365 // We need more smarts in the abortable preclean
4366 // loop below to deal with cases where allocation
4367 // in young gen is very very slow, and our precleaning
4368 // is running a losing race against a horde of
4369 // mutators intent on flooding us with CMS updates
4370 // (dirty cards).
4371 // One, admittedly dumb, strategy is to give up
4372 // after a certain number of abortable precleaning loops
4373 // or after a certain maximum time. We want to make
4374 // this smarter in the next iteration.
4375 // XXX FIX ME!!! YSR
4376 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0;
4377 while (!(should_abort_preclean() ||
4378 ConcurrentMarkSweepThread::should_terminate())) {
4379 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2);
4380 cumworkdone += workdone;
4381 loops++;
4382 // Voluntarily terminate abortable preclean phase if we have
4383 // been at it for too long.
4384 if ((CMSMaxAbortablePrecleanLoops != 0) &&
4385 loops >= CMSMaxAbortablePrecleanLoops) {
4386 if (PrintGCDetails) {
4387 gclog_or_tty->print(" CMS: abort preclean due to loops ");
4388 }
4389 break;
4390 }
4391 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) {
4392 if (PrintGCDetails) {
4393 gclog_or_tty->print(" CMS: abort preclean due to time ");
4394 }
4395 break;
4396 }
4397 // If we are doing little work each iteration, we should
4398 // take a short break.
4399 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) {
4400 // Sleep for some time, waiting for work to accumulate
4401 stopTimer();
4402 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis);
4403 startTimer();
4404 waited++;
4405 }
4406 }
4407 if (PrintCMSStatistics > 0) {
4408 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ",
4409 loops, waited, cumworkdone);
4410 }
4411 }
4412 CMSTokenSync x(true); // is cms thread
4413 if (_collectorState != Idling) {
4414 assert(_collectorState == AbortablePreclean,
4415 "Spontaneous state transition?");
4416 _collectorState = FinalMarking;
4417 } // Else, a foreground collection completed this CMS cycle.
4418 return;
4419 }
4420
4421 // Respond to an Eden sampling opportunity
4422 void CMSCollector::sample_eden() {
4423 // Make sure a young gc cannot sneak in between our
4424 // reading and recording of a sample.
4425 assert(Thread::current()->is_ConcurrentGC_thread(),
4426 "Only the cms thread may collect Eden samples");
4427 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
4428 "Should collect samples while holding CMS token");
4429 if (!_start_sampling) {
4430 return;
4431 }
4432 if (_eden_chunk_array) {
4433 if (_eden_chunk_index < _eden_chunk_capacity) {
4434 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample
4435 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr,
4436 "Unexpected state of Eden");
4437 // We'd like to check that what we just sampled is an oop-start address;
4438 // however, we cannot do that here since the object may not yet have been
4439 // initialized. So we'll instead do the check when we _use_ this sample
4440 // later.
4441 if (_eden_chunk_index == 0 ||
4442 (pointer_delta(_eden_chunk_array[_eden_chunk_index],
4443 _eden_chunk_array[_eden_chunk_index-1])
4444 >= CMSSamplingGrain)) {
4445 _eden_chunk_index++; // commit sample
4446 }
4447 }
4448 }
4449 if ((_collectorState == AbortablePreclean) && !_abort_preclean) {
4450 size_t used = get_eden_used();
4451 size_t capacity = get_eden_capacity();
4452 assert(used <= capacity, "Unexpected state of Eden");
4453 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) {
4454 _abort_preclean = true;
4455 }
4456 }
4457 }
4458
4459
4460 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) {
4461 assert(_collectorState == Precleaning ||
4462 _collectorState == AbortablePreclean, "incorrect state");
4463 ResourceMark rm;
4464 HandleMark hm;
4465
4466 // Precleaning is currently not MT but the reference processor
4467 // may be set for MT. Disable it temporarily here.
4468 ReferenceProcessor* rp = ref_processor();
4469 ReferenceProcessorMTDiscoveryMutator rp_mut_discovery(rp, false);
4470
4471 // Do one pass of scrubbing the discovered reference lists
4472 // to remove any reference objects with strongly-reachable
4473 // referents.
4474 if (clean_refs) {
4475 CMSPrecleanRefsYieldClosure yield_cl(this);
4476 assert(rp->span().equals(_span), "Spans should be equal");
4477 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap,
4478 &_markStack, true /* preclean */);
4479 CMSDrainMarkingStackClosure complete_trace(this,
4480 _span, &_markBitMap, &_markStack,
4481 &keep_alive, true /* preclean */);
4482
4483 // We don't want this step to interfere with a young
4484 // collection because we don't want to take CPU
4485 // or memory bandwidth away from the young GC threads
4486 // (which may be as many as there are CPUs).
4487 // Note that we don't need to protect ourselves from
4488 // interference with mutators because they can't
4489 // manipulate the discovered reference lists nor affect
4490 // the computed reachability of the referents, the
4491 // only properties manipulated by the precleaning
4492 // of these reference lists.
4493 stopTimer();
4494 CMSTokenSyncWithLocks x(true /* is cms thread */,
4495 bitMapLock());
4496 startTimer();
4497 sample_eden();
4498
4499 // The following will yield to allow foreground
4500 // collection to proceed promptly. XXX YSR:
4501 // The code in this method may need further
4502 // tweaking for better performance and some restructuring
4503 // for cleaner interfaces.
4504 rp->preclean_discovered_references(
4505 rp->is_alive_non_header(), &keep_alive, &complete_trace, &yield_cl);
4506 }
4507
4508 if (clean_survivor) { // preclean the active survivor space(s)
4509 assert(_young_gen->kind() == Generation::DefNew ||
4510 _young_gen->kind() == Generation::ParNew ||
4511 _young_gen->kind() == Generation::ASParNew,
4512 "incorrect type for cast");
4513 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
4514 PushAndMarkClosure pam_cl(this, _span, ref_processor(),
4515 &_markBitMap, &_modUnionTable,
4516 &_markStack, true /* precleaning phase */);
4517 stopTimer();
4518 CMSTokenSyncWithLocks ts(true /* is cms thread */,
4519 bitMapLock());
4520 startTimer();
4521 unsigned int before_count =
4522 GenCollectedHeap::heap()->total_collections();
4523 SurvivorSpacePrecleanClosure
4524 sss_cl(this, _span, &_markBitMap, &_markStack,
4525 &pam_cl, before_count, CMSYield);
4526 dng->from()->object_iterate_careful(&sss_cl);
4527 dng->to()->object_iterate_careful(&sss_cl);
4528 }
4529 MarkRefsIntoAndScanClosure
4530 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable,
4531 &_markStack, this, CMSYield,
4532 true /* precleaning phase */);
4533 // CAUTION: The following closure has persistent state that may need to
4534 // be reset upon a decrease in the sequence of addresses it
4535 // processes.
4536 ScanMarkedObjectsAgainCarefullyClosure
4537 smoac_cl(this, _span,
4538 &_markBitMap, &_markStack, &mrias_cl, CMSYield);
4539
4540 // Preclean dirty cards in ModUnionTable and CardTable using
4541 // appropriate convergence criterion;
4542 // repeat CMSPrecleanIter times unless we find that
4543 // we are losing.
4544 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large");
4545 assert(CMSPrecleanNumerator < CMSPrecleanDenominator,
4546 "Bad convergence multiplier");
4547 assert(CMSPrecleanThreshold >= 100,
4548 "Unreasonably low CMSPrecleanThreshold");
4549
4550 size_t numIter, cumNumCards, lastNumCards, curNumCards;
4551 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0;
4552 numIter < CMSPrecleanIter;
4553 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) {
4554 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl);
4555 if (Verbose && PrintGCDetails) {
4556 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards);
4557 }
4558 // Either there are very few dirty cards, so re-mark
4559 // pause will be small anyway, or our pre-cleaning isn't
4560 // that much faster than the rate at which cards are being
4561 // dirtied, so we might as well stop and re-mark since
4562 // precleaning won't improve our re-mark time by much.
4563 if (curNumCards <= CMSPrecleanThreshold ||
4564 (numIter > 0 &&
4565 (curNumCards * CMSPrecleanDenominator >
4566 lastNumCards * CMSPrecleanNumerator))) {
4567 numIter++;
4568 cumNumCards += curNumCards;
4569 break;
4570 }
4571 }
4572
4573 preclean_klasses(&mrias_cl, _cmsGen->freelistLock());
4574
4575 curNumCards = preclean_card_table(_cmsGen, &smoac_cl);
4576 cumNumCards += curNumCards;
4577 if (PrintGCDetails && PrintCMSStatistics != 0) {
4578 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)",
4579 curNumCards, cumNumCards, numIter);
4580 }
4581 return cumNumCards; // as a measure of useful work done
4582 }
4583
4584 // PRECLEANING NOTES:
4585 // Precleaning involves:
4586 // . reading the bits of the modUnionTable and clearing the set bits.
4587 // . For the cards corresponding to the set bits, we scan the
4588 // objects on those cards. This means we need the free_list_lock
4589 // so that we can safely iterate over the CMS space when scanning
4590 // for oops.
4591 // . When we scan the objects, we'll be both reading and setting
4592 // marks in the marking bit map, so we'll need the marking bit map.
4593 // . For protecting _collector_state transitions, we take the CGC_lock.
4594 // Note that any races in the reading of of card table entries by the
4595 // CMS thread on the one hand and the clearing of those entries by the
4596 // VM thread or the setting of those entries by the mutator threads on the
4597 // other are quite benign. However, for efficiency it makes sense to keep
4598 // the VM thread from racing with the CMS thread while the latter is
4599 // dirty card info to the modUnionTable. We therefore also use the
4600 // CGC_lock to protect the reading of the card table and the mod union
4601 // table by the CM thread.
4602 // . We run concurrently with mutator updates, so scanning
4603 // needs to be done carefully -- we should not try to scan
4604 // potentially uninitialized objects.
4605 //
4606 // Locking strategy: While holding the CGC_lock, we scan over and
4607 // reset a maximal dirty range of the mod union / card tables, then lock
4608 // the free_list_lock and bitmap lock to do a full marking, then
4609 // release these locks; and repeat the cycle. This allows for a
4610 // certain amount of fairness in the sharing of these locks between
4611 // the CMS collector on the one hand, and the VM thread and the
4612 // mutators on the other.
4613
4614 // NOTE: preclean_mod_union_table() and preclean_card_table()
4615 // further below are largely identical; if you need to modify
4616 // one of these methods, please check the other method too.
4617
4618 size_t CMSCollector::preclean_mod_union_table(
4619 ConcurrentMarkSweepGeneration* gen,
4620 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4621 verify_work_stacks_empty();
4622 verify_overflow_empty();
4623
4624 // strategy: starting with the first card, accumulate contiguous
4625 // ranges of dirty cards; clear these cards, then scan the region
4626 // covered by these cards.
4627
4628 // Since all of the MUT is committed ahead, we can just use
4629 // that, in case the generations expand while we are precleaning.
4630 // It might also be fine to just use the committed part of the
4631 // generation, but we might potentially miss cards when the
4632 // generation is rapidly expanding while we are in the midst
4633 // of precleaning.
4634 HeapWord* startAddr = gen->reserved().start();
4635 HeapWord* endAddr = gen->reserved().end();
4636
4637 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4638
4639 size_t numDirtyCards, cumNumDirtyCards;
4640 HeapWord *nextAddr, *lastAddr;
4641 for (cumNumDirtyCards = numDirtyCards = 0,
4642 nextAddr = lastAddr = startAddr;
4643 nextAddr < endAddr;
4644 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4645
4646 ResourceMark rm;
4647 HandleMark hm;
4648
4649 MemRegion dirtyRegion;
4650 {
4651 stopTimer();
4652 // Potential yield point
4653 CMSTokenSync ts(true);
4654 startTimer();
4655 sample_eden();
4656 // Get dirty region starting at nextOffset (inclusive),
4657 // simultaneously clearing it.
4658 dirtyRegion =
4659 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr);
4660 assert(dirtyRegion.start() >= nextAddr,
4661 "returned region inconsistent?");
4662 }
4663 // Remember where the next search should begin.
4664 // The returned region (if non-empty) is a right open interval,
4665 // so lastOffset is obtained from the right end of that
4666 // interval.
4667 lastAddr = dirtyRegion.end();
4668 // Should do something more transparent and less hacky XXX
4669 numDirtyCards =
4670 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size());
4671
4672 // We'll scan the cards in the dirty region (with periodic
4673 // yields for foreground GC as needed).
4674 if (!dirtyRegion.is_empty()) {
4675 assert(numDirtyCards > 0, "consistency check");
4676 HeapWord* stop_point = NULL;
4677 stopTimer();
4678 // Potential yield point
4679 CMSTokenSyncWithLocks ts(true, gen->freelistLock(),
4680 bitMapLock());
4681 startTimer();
4682 {
4683 verify_work_stacks_empty();
4684 verify_overflow_empty();
4685 sample_eden();
4686 stop_point =
4687 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4688 }
4689 if (stop_point != NULL) {
4690 // The careful iteration stopped early either because it found an
4691 // uninitialized object, or because we were in the midst of an
4692 // "abortable preclean", which should now be aborted. Redirty
4693 // the bits corresponding to the partially-scanned or unscanned
4694 // cards. We'll either restart at the next block boundary or
4695 // abort the preclean.
4696 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4697 "Should only be AbortablePreclean.");
4698 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end()));
4699 if (should_abort_preclean()) {
4700 break; // out of preclean loop
4701 } else {
4702 // Compute the next address at which preclean should pick up;
4703 // might need bitMapLock in order to read P-bits.
4704 lastAddr = next_card_start_after_block(stop_point);
4705 }
4706 }
4707 } else {
4708 assert(lastAddr == endAddr, "consistency check");
4709 assert(numDirtyCards == 0, "consistency check");
4710 break;
4711 }
4712 }
4713 verify_work_stacks_empty();
4714 verify_overflow_empty();
4715 return cumNumDirtyCards;
4716 }
4717
4718 // NOTE: preclean_mod_union_table() above and preclean_card_table()
4719 // below are largely identical; if you need to modify
4720 // one of these methods, please check the other method too.
4721
4722 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen,
4723 ScanMarkedObjectsAgainCarefullyClosure* cl) {
4724 // strategy: it's similar to precleamModUnionTable above, in that
4725 // we accumulate contiguous ranges of dirty cards, mark these cards
4726 // precleaned, then scan the region covered by these cards.
4727 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high());
4728 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low());
4729
4730 cl->setFreelistLock(gen->freelistLock()); // needed for yielding
4731
4732 size_t numDirtyCards, cumNumDirtyCards;
4733 HeapWord *lastAddr, *nextAddr;
4734
4735 for (cumNumDirtyCards = numDirtyCards = 0,
4736 nextAddr = lastAddr = startAddr;
4737 nextAddr < endAddr;
4738 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) {
4739
4740 ResourceMark rm;
4741 HandleMark hm;
4742
4743 MemRegion dirtyRegion;
4744 {
4745 // See comments in "Precleaning notes" above on why we
4746 // do this locking. XXX Could the locking overheads be
4747 // too high when dirty cards are sparse? [I don't think so.]
4748 stopTimer();
4749 CMSTokenSync x(true); // is cms thread
4750 startTimer();
4751 sample_eden();
4752 // Get and clear dirty region from card table
4753 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_reset(
4754 MemRegion(nextAddr, endAddr),
4755 true,
4756 CardTableModRefBS::precleaned_card_val());
4757
4758 assert(dirtyRegion.start() >= nextAddr,
4759 "returned region inconsistent?");
4760 }
4761 lastAddr = dirtyRegion.end();
4762 numDirtyCards =
4763 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words;
4764
4765 if (!dirtyRegion.is_empty()) {
4766 stopTimer();
4767 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock());
4768 startTimer();
4769 sample_eden();
4770 verify_work_stacks_empty();
4771 verify_overflow_empty();
4772 HeapWord* stop_point =
4773 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl);
4774 if (stop_point != NULL) {
4775 assert((_collectorState == AbortablePreclean && should_abort_preclean()),
4776 "Should only be AbortablePreclean.");
4777 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end()));
4778 if (should_abort_preclean()) {
4779 break; // out of preclean loop
4780 } else {
4781 // Compute the next address at which preclean should pick up.
4782 lastAddr = next_card_start_after_block(stop_point);
4783 }
4784 }
4785 } else {
4786 break;
4787 }
4788 }
4789 verify_work_stacks_empty();
4790 verify_overflow_empty();
4791 return cumNumDirtyCards;
4792 }
4793
4794 class PrecleanKlassClosure : public KlassClosure {
4795 CMKlassClosure _cm_klass_closure;
4796 public:
4797 PrecleanKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
4798 void do_klass(Klass* k) {
4799 if (k->has_accumulated_modified_oops()) {
4800 k->clear_accumulated_modified_oops();
4801
4802 _cm_klass_closure.do_klass(k);
4803 }
4804 }
4805 };
4806
4807 // The freelist lock is needed to prevent asserts, is it really needed?
4808 void CMSCollector::preclean_klasses(MarkRefsIntoAndScanClosure* cl, Mutex* freelistLock) {
4809
4810 cl->set_freelistLock(freelistLock);
4811
4812 CMSTokenSyncWithLocks ts(true, freelistLock, bitMapLock());
4813
4814 // SSS: Add equivalent to ScanMarkedObjectsAgainCarefullyClosure::do_yield_check and should_abort_preclean?
4815 // SSS: We should probably check if precleaning should be aborted, at suitable intervals?
4816 PrecleanKlassClosure preclean_klass_closure(cl);
4817 ClassLoaderDataGraph::classes_do(&preclean_klass_closure);
4818
4819 verify_work_stacks_empty();
4820 verify_overflow_empty();
4821 }
4822
4823 void CMSCollector::checkpointRootsFinal(bool asynch,
4824 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4825 assert(_collectorState == FinalMarking, "incorrect state transition?");
4826 check_correct_thread_executing();
4827 // world is stopped at this checkpoint
4828 assert(SafepointSynchronize::is_at_safepoint(),
4829 "world should be stopped");
4830 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
4831
4832 verify_work_stacks_empty();
4833 verify_overflow_empty();
4834
4835 SpecializationStats::clear();
4836 if (PrintGCDetails) {
4837 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]",
4838 _young_gen->used() / K,
4839 _young_gen->capacity() / K);
4840 }
4841 if (asynch) {
4842 if (CMSScavengeBeforeRemark) {
4843 GenCollectedHeap* gch = GenCollectedHeap::heap();
4844 // Temporarily set flag to false, GCH->do_collection will
4845 // expect it to be false and set to true
4846 FlagSetting fl(gch->_is_gc_active, false);
4847 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark",
4848 PrintGCDetails && Verbose, true, gclog_or_tty);)
4849 int level = _cmsGen->level() - 1;
4850 if (level >= 0) {
4851 gch->do_collection(true, // full (i.e. force, see below)
4852 false, // !clear_all_soft_refs
4853 0, // size
4854 false, // is_tlab
4855 level // max_level
4856 );
4857 }
4858 }
4859 FreelistLocker x(this);
4860 MutexLockerEx y(bitMapLock(),
4861 Mutex::_no_safepoint_check_flag);
4862 assert(!init_mark_was_synchronous, "but that's impossible!");
4863 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false);
4864 } else {
4865 // already have all the locks
4866 checkpointRootsFinalWork(asynch, clear_all_soft_refs,
4867 init_mark_was_synchronous);
4868 }
4869 verify_work_stacks_empty();
4870 verify_overflow_empty();
4871 SpecializationStats::print();
4872 }
4873
4874 void CMSCollector::checkpointRootsFinalWork(bool asynch,
4875 bool clear_all_soft_refs, bool init_mark_was_synchronous) {
4876
4877 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);)
4878
4879 assert(haveFreelistLocks(), "must have free list locks");
4880 assert_lock_strong(bitMapLock());
4881
4882 if (UseAdaptiveSizePolicy) {
4883 size_policy()->checkpoint_roots_final_begin();
4884 }
4885
4886 ResourceMark rm;
4887 HandleMark hm;
4888
4889 GenCollectedHeap* gch = GenCollectedHeap::heap();
4890
4891 if (should_unload_classes()) {
4892 CodeCache::gc_prologue();
4893 }
4894 assert(haveFreelistLocks(), "must have free list locks");
4895 assert_lock_strong(bitMapLock());
4896
4897 if (!init_mark_was_synchronous) {
4898 // We might assume that we need not fill TLAB's when
4899 // CMSScavengeBeforeRemark is set, because we may have just done
4900 // a scavenge which would have filled all TLAB's -- and besides
4901 // Eden would be empty. This however may not always be the case --
4902 // for instance although we asked for a scavenge, it may not have
4903 // happened because of a JNI critical section. We probably need
4904 // a policy for deciding whether we can in that case wait until
4905 // the critical section releases and then do the remark following
4906 // the scavenge, and skip it here. In the absence of that policy,
4907 // or of an indication of whether the scavenge did indeed occur,
4908 // we cannot rely on TLAB's having been filled and must do
4909 // so here just in case a scavenge did not happen.
4910 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them
4911 // Update the saved marks which may affect the root scans.
4912 gch->save_marks();
4913
4914 {
4915 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;)
4916
4917 // Note on the role of the mod union table:
4918 // Since the marker in "markFromRoots" marks concurrently with
4919 // mutators, it is possible for some reachable objects not to have been
4920 // scanned. For instance, an only reference to an object A was
4921 // placed in object B after the marker scanned B. Unless B is rescanned,
4922 // A would be collected. Such updates to references in marked objects
4923 // are detected via the mod union table which is the set of all cards
4924 // dirtied since the first checkpoint in this GC cycle and prior to
4925 // the most recent young generation GC, minus those cleaned up by the
4926 // concurrent precleaning.
4927 if (CMSParallelRemarkEnabled && CollectedHeap::use_parallel_gc_threads()) {
4928 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty);
4929 do_remark_parallel();
4930 } else {
4931 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false,
4932 gclog_or_tty);
4933 do_remark_non_parallel();
4934 }
4935 }
4936 } else {
4937 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode");
4938 // The initial mark was stop-world, so there's no rescanning to
4939 // do; go straight on to the next step below.
4940 }
4941 verify_work_stacks_empty();
4942 verify_overflow_empty();
4943
4944 {
4945 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);)
4946 refProcessingWork(asynch, clear_all_soft_refs);
4947 }
4948 verify_work_stacks_empty();
4949 verify_overflow_empty();
4950
4951 if (should_unload_classes()) {
4952 CodeCache::gc_epilogue();
4953 }
4954 JvmtiExport::gc_epilogue();
4955
4956 // If we encountered any (marking stack / work queue) overflow
4957 // events during the current CMS cycle, take appropriate
4958 // remedial measures, where possible, so as to try and avoid
4959 // recurrence of that condition.
4960 assert(_markStack.isEmpty(), "No grey objects");
4961 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw +
4962 _ser_kac_ovflw + _ser_kac_preclean_ovflw;
4963 if (ser_ovflw > 0) {
4964 if (PrintCMSStatistics != 0) {
4965 gclog_or_tty->print_cr("Marking stack overflow (benign) "
4966 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT
4967 ", kac_preclean="SIZE_FORMAT")",
4968 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw,
4969 _ser_kac_ovflw, _ser_kac_preclean_ovflw);
4970 }
4971 _markStack.expand();
4972 _ser_pmc_remark_ovflw = 0;
4973 _ser_pmc_preclean_ovflw = 0;
4974 _ser_kac_preclean_ovflw = 0;
4975 _ser_kac_ovflw = 0;
4976 }
4977 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) {
4978 if (PrintCMSStatistics != 0) {
4979 gclog_or_tty->print_cr("Work queue overflow (benign) "
4980 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")",
4981 _par_pmc_remark_ovflw, _par_kac_ovflw);
4982 }
4983 _par_pmc_remark_ovflw = 0;
4984 _par_kac_ovflw = 0;
4985 }
4986 if (PrintCMSStatistics != 0) {
4987 if (_markStack._hit_limit > 0) {
4988 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")",
4989 _markStack._hit_limit);
4990 }
4991 if (_markStack._failed_double > 0) {
4992 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT"),"
4993 " current capacity "SIZE_FORMAT,
4994 _markStack._failed_double,
4995 _markStack.capacity());
4996 }
4997 }
4998 _markStack._hit_limit = 0;
4999 _markStack._failed_double = 0;
5000
5001 if ((VerifyAfterGC || VerifyDuringGC) &&
5002 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5003 verify_after_remark();
5004 }
5005
5006 // Change under the freelistLocks.
5007 _collectorState = Sweeping;
5008 // Call isAllClear() under bitMapLock
5009 assert(_modUnionTable.isAllClear(),
5010 "Should be clear by end of the final marking");
5011 assert(_ct->klass_rem_set()->mod_union_is_clear(),
5012 "Should be clear by end of the final marking");
5013 if (UseAdaptiveSizePolicy) {
5014 size_policy()->checkpoint_roots_final_end(gch->gc_cause());
5015 }
5016 }
5017
5018 // Parallel remark task
5019 class CMSParRemarkTask: public AbstractGangTask {
5020 CMSCollector* _collector;
5021 int _n_workers;
5022 CompactibleFreeListSpace* _cms_space;
5023
5024 // The per-thread work queues, available here for stealing.
5025 OopTaskQueueSet* _task_queues;
5026 ParallelTaskTerminator _term;
5027
5028 public:
5029 // A value of 0 passed to n_workers will cause the number of
5030 // workers to be taken from the active workers in the work gang.
5031 CMSParRemarkTask(CMSCollector* collector,
5032 CompactibleFreeListSpace* cms_space,
5033 int n_workers, FlexibleWorkGang* workers,
5034 OopTaskQueueSet* task_queues):
5035 AbstractGangTask("Rescan roots and grey objects in parallel"),
5036 _collector(collector),
5037 _cms_space(cms_space),
5038 _n_workers(n_workers),
5039 _task_queues(task_queues),
5040 _term(n_workers, task_queues) { }
5041
5042 OopTaskQueueSet* task_queues() { return _task_queues; }
5043
5044 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5045
5046 ParallelTaskTerminator* terminator() { return &_term; }
5047 int n_workers() { return _n_workers; }
5048
5049 void work(uint worker_id);
5050
5051 private:
5052 // Work method in support of parallel rescan ... of young gen spaces
5053 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl,
5054 ContiguousSpace* space,
5055 HeapWord** chunk_array, size_t chunk_top);
5056
5057 // ... of dirty cards in old space
5058 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i,
5059 Par_MarkRefsIntoAndScanClosure* cl);
5060
5061 // ... work stealing for the above
5062 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed);
5063 };
5064
5065 class RemarkKlassClosure : public KlassClosure {
5066 CMKlassClosure _cm_klass_closure;
5067 public:
5068 RemarkKlassClosure(OopClosure* oop_closure) : _cm_klass_closure(oop_closure) {}
5069 void do_klass(Klass* k) {
5070 // Check if we have modified any oops in the Klass during the concurrent marking.
5071 if (k->has_accumulated_modified_oops()) {
5072 k->clear_accumulated_modified_oops();
5073
5074 // We could have transfered the current modified marks to the accumulated marks,
5075 // like we do with the Card Table to Mod Union Table. But it's not really necessary.
5076 } else if (k->has_modified_oops()) {
5077 // Don't clear anything, this info is needed by the next young collection.
5078 } else {
5079 // No modified oops in the Klass.
5080 return;
5081 }
5082
5083 // The klass has modified fields, need to scan the klass.
5084 _cm_klass_closure.do_klass(k);
5085 }
5086 };
5087
5088 // work_queue(i) is passed to the closure
5089 // Par_MarkRefsIntoAndScanClosure. The "i" parameter
5090 // also is passed to do_dirty_card_rescan_tasks() and to
5091 // do_work_steal() to select the i-th task_queue.
5092
5093 void CMSParRemarkTask::work(uint worker_id) {
5094 elapsedTimer _timer;
5095 ResourceMark rm;
5096 HandleMark hm;
5097
5098 // ---------- rescan from roots --------------
5099 _timer.start();
5100 GenCollectedHeap* gch = GenCollectedHeap::heap();
5101 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector,
5102 _collector->_span, _collector->ref_processor(),
5103 &(_collector->_markBitMap),
5104 work_queue(worker_id));
5105
5106 // Rescan young gen roots first since these are likely
5107 // coarsely partitioned and may, on that account, constitute
5108 // the critical path; thus, it's best to start off that
5109 // work first.
5110 // ---------- young gen roots --------------
5111 {
5112 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration();
5113 EdenSpace* eden_space = dng->eden();
5114 ContiguousSpace* from_space = dng->from();
5115 ContiguousSpace* to_space = dng->to();
5116
5117 HeapWord** eca = _collector->_eden_chunk_array;
5118 size_t ect = _collector->_eden_chunk_index;
5119 HeapWord** sca = _collector->_survivor_chunk_array;
5120 size_t sct = _collector->_survivor_chunk_index;
5121
5122 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds");
5123 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds");
5124
5125 do_young_space_rescan(worker_id, &par_mrias_cl, to_space, NULL, 0);
5126 do_young_space_rescan(worker_id, &par_mrias_cl, from_space, sca, sct);
5127 do_young_space_rescan(worker_id, &par_mrias_cl, eden_space, eca, ect);
5128
5129 _timer.stop();
5130 if (PrintCMSStatistics != 0) {
5131 gclog_or_tty->print_cr(
5132 "Finished young gen rescan work in %dth thread: %3.3f sec",
5133 worker_id, _timer.seconds());
5134 }
5135 }
5136
5137 // ---------- remaining roots --------------
5138 _timer.reset();
5139 _timer.start();
5140 gch->gen_process_strong_roots(_collector->_cmsGen->level(),
5141 false, // yg was scanned above
5142 false, // this is parallel code
5143 false, // not scavenging
5144 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()),
5145 &par_mrias_cl,
5146 true, // walk all of code cache if (so & SO_CodeCache)
5147 NULL,
5148 NULL); // The dirty klasses will be handled below
5149 assert(_collector->should_unload_classes()
5150 || (_collector->CMSCollector::roots_scanning_options() & SharedHeap::SO_CodeCache),
5151 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5152 _timer.stop();
5153 if (PrintCMSStatistics != 0) {
5154 gclog_or_tty->print_cr(
5155 "Finished remaining root rescan work in %dth thread: %3.3f sec",
5156 worker_id, _timer.seconds());
5157 }
5158
5159 // ---------- unhandled CLD scanning ----------
5160 if (worker_id == 0) { // Single threaded at the moment.
5161 _timer.reset();
5162 _timer.start();
5163
5164 // Scan all new class loader data objects and new dependencies that were
5165 // introduced during concurrent marking.
5166 ResourceMark rm;
5167 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5168 for (int i = 0; i < array->length(); i++) {
5169 par_mrias_cl.do_class_loader_data(array->at(i));
5170 }
5171
5172 // We don't need to keep track of new CLDs anymore.
5173 ClassLoaderDataGraph::remember_new_clds(false);
5174
5175 _timer.stop();
5176 if (PrintCMSStatistics != 0) {
5177 gclog_or_tty->print_cr(
5178 "Finished unhandled CLD scanning work in %dth thread: %3.3f sec",
5179 worker_id, _timer.seconds());
5180 }
5181 }
5182
5183 // ---------- dirty klass scanning ----------
5184 if (worker_id == 0) { // Single threaded at the moment.
5185 _timer.reset();
5186 _timer.start();
5187
5188 // Scan all classes that was dirtied during the concurrent marking phase.
5189 RemarkKlassClosure remark_klass_closure(&par_mrias_cl);
5190 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5191
5192 _timer.stop();
5193 if (PrintCMSStatistics != 0) {
5194 gclog_or_tty->print_cr(
5195 "Finished dirty klass scanning work in %dth thread: %3.3f sec",
5196 worker_id, _timer.seconds());
5197 }
5198 }
5199
5200 // We might have added oops to ClassLoaderData::_handles during the
5201 // concurrent marking phase. These oops point to newly allocated objects
5202 // that are guaranteed to be kept alive. Either by the direct allocation
5203 // code, or when the young collector processes the strong roots. Hence,
5204 // we don't have to revisit the _handles block during the remark phase.
5205
5206 // ---------- rescan dirty cards ------------
5207 _timer.reset();
5208 _timer.start();
5209
5210 // Do the rescan tasks for each of the two spaces
5211 // (cms_space) in turn.
5212 // "worker_id" is passed to select the task_queue for "worker_id"
5213 do_dirty_card_rescan_tasks(_cms_space, worker_id, &par_mrias_cl);
5214 _timer.stop();
5215 if (PrintCMSStatistics != 0) {
5216 gclog_or_tty->print_cr(
5217 "Finished dirty card rescan work in %dth thread: %3.3f sec",
5218 worker_id, _timer.seconds());
5219 }
5220
5221 // ---------- steal work from other threads ...
5222 // ---------- ... and drain overflow list.
5223 _timer.reset();
5224 _timer.start();
5225 do_work_steal(worker_id, &par_mrias_cl, _collector->hash_seed(worker_id));
5226 _timer.stop();
5227 if (PrintCMSStatistics != 0) {
5228 gclog_or_tty->print_cr(
5229 "Finished work stealing in %dth thread: %3.3f sec",
5230 worker_id, _timer.seconds());
5231 }
5232 }
5233
5234 // Note that parameter "i" is not used.
5235 void
5236 CMSParRemarkTask::do_young_space_rescan(int i,
5237 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space,
5238 HeapWord** chunk_array, size_t chunk_top) {
5239 // Until all tasks completed:
5240 // . claim an unclaimed task
5241 // . compute region boundaries corresponding to task claimed
5242 // using chunk_array
5243 // . par_oop_iterate(cl) over that region
5244
5245 ResourceMark rm;
5246 HandleMark hm;
5247
5248 SequentialSubTasksDone* pst = space->par_seq_tasks();
5249 assert(pst->valid(), "Uninitialized use?");
5250
5251 uint nth_task = 0;
5252 uint n_tasks = pst->n_tasks();
5253
5254 HeapWord *start, *end;
5255 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5256 // We claimed task # nth_task; compute its boundaries.
5257 if (chunk_top == 0) { // no samples were taken
5258 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task");
5259 start = space->bottom();
5260 end = space->top();
5261 } else if (nth_task == 0) {
5262 start = space->bottom();
5263 end = chunk_array[nth_task];
5264 } else if (nth_task < (uint)chunk_top) {
5265 assert(nth_task >= 1, "Control point invariant");
5266 start = chunk_array[nth_task - 1];
5267 end = chunk_array[nth_task];
5268 } else {
5269 assert(nth_task == (uint)chunk_top, "Control point invariant");
5270 start = chunk_array[chunk_top - 1];
5271 end = space->top();
5272 }
5273 MemRegion mr(start, end);
5274 // Verify that mr is in space
5275 assert(mr.is_empty() || space->used_region().contains(mr),
5276 "Should be in space");
5277 // Verify that "start" is an object boundary
5278 assert(mr.is_empty() || oop(mr.start())->is_oop(),
5279 "Should be an oop");
5280 space->par_oop_iterate(mr, cl);
5281 }
5282 pst->all_tasks_completed();
5283 }
5284
5285 void
5286 CMSParRemarkTask::do_dirty_card_rescan_tasks(
5287 CompactibleFreeListSpace* sp, int i,
5288 Par_MarkRefsIntoAndScanClosure* cl) {
5289 // Until all tasks completed:
5290 // . claim an unclaimed task
5291 // . compute region boundaries corresponding to task claimed
5292 // . transfer dirty bits ct->mut for that region
5293 // . apply rescanclosure to dirty mut bits for that region
5294
5295 ResourceMark rm;
5296 HandleMark hm;
5297
5298 OopTaskQueue* work_q = work_queue(i);
5299 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable));
5300 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION!
5301 // CAUTION: This closure has state that persists across calls to
5302 // the work method dirty_range_iterate_clear() in that it has
5303 // imbedded in it a (subtype of) UpwardsObjectClosure. The
5304 // use of that state in the imbedded UpwardsObjectClosure instance
5305 // assumes that the cards are always iterated (even if in parallel
5306 // by several threads) in monotonically increasing order per each
5307 // thread. This is true of the implementation below which picks
5308 // card ranges (chunks) in monotonically increasing order globally
5309 // and, a-fortiori, in monotonically increasing order per thread
5310 // (the latter order being a subsequence of the former).
5311 // If the work code below is ever reorganized into a more chaotic
5312 // work-partitioning form than the current "sequential tasks"
5313 // paradigm, the use of that persistent state will have to be
5314 // revisited and modified appropriately. See also related
5315 // bug 4756801 work on which should examine this code to make
5316 // sure that the changes there do not run counter to the
5317 // assumptions made here and necessary for correctness and
5318 // efficiency. Note also that this code might yield inefficient
5319 // behaviour in the case of very large objects that span one or
5320 // more work chunks. Such objects would potentially be scanned
5321 // several times redundantly. Work on 4756801 should try and
5322 // address that performance anomaly if at all possible. XXX
5323 MemRegion full_span = _collector->_span;
5324 CMSBitMap* bm = &(_collector->_markBitMap); // shared
5325 MarkFromDirtyCardsClosure
5326 greyRescanClosure(_collector, full_span, // entire span of interest
5327 sp, bm, work_q, cl);
5328
5329 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks();
5330 assert(pst->valid(), "Uninitialized use?");
5331 uint nth_task = 0;
5332 const int alignment = CardTableModRefBS::card_size * BitsPerWord;
5333 MemRegion span = sp->used_region();
5334 HeapWord* start_addr = span.start();
5335 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(),
5336 alignment);
5337 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units
5338 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) ==
5339 start_addr, "Check alignment");
5340 assert((size_t)round_to((intptr_t)chunk_size, alignment) ==
5341 chunk_size, "Check alignment");
5342
5343 while (!pst->is_task_claimed(/* reference */ nth_task)) {
5344 // Having claimed the nth_task, compute corresponding mem-region,
5345 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary).
5346 // The alignment restriction ensures that we do not need any
5347 // synchronization with other gang-workers while setting or
5348 // clearing bits in thus chunk of the MUT.
5349 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size,
5350 start_addr + (nth_task+1)*chunk_size);
5351 // The last chunk's end might be way beyond end of the
5352 // used region. In that case pull back appropriately.
5353 if (this_span.end() > end_addr) {
5354 this_span.set_end(end_addr);
5355 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)");
5356 }
5357 // Iterate over the dirty cards covering this chunk, marking them
5358 // precleaned, and setting the corresponding bits in the mod union
5359 // table. Since we have been careful to partition at Card and MUT-word
5360 // boundaries no synchronization is needed between parallel threads.
5361 _collector->_ct->ct_bs()->dirty_card_iterate(this_span,
5362 &modUnionClosure);
5363
5364 // Having transferred these marks into the modUnionTable,
5365 // rescan the marked objects on the dirty cards in the modUnionTable.
5366 // Even if this is at a synchronous collection, the initial marking
5367 // may have been done during an asynchronous collection so there
5368 // may be dirty bits in the mod-union table.
5369 _collector->_modUnionTable.dirty_range_iterate_clear(
5370 this_span, &greyRescanClosure);
5371 _collector->_modUnionTable.verifyNoOneBitsInRange(
5372 this_span.start(),
5373 this_span.end());
5374 }
5375 pst->all_tasks_completed(); // declare that i am done
5376 }
5377
5378 // . see if we can share work_queues with ParNew? XXX
5379 void
5380 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl,
5381 int* seed) {
5382 OopTaskQueue* work_q = work_queue(i);
5383 NOT_PRODUCT(int num_steals = 0;)
5384 oop obj_to_scan;
5385 CMSBitMap* bm = &(_collector->_markBitMap);
5386
5387 while (true) {
5388 // Completely finish any left over work from (an) earlier round(s)
5389 cl->trim_queue(0);
5390 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5391 (size_t)ParGCDesiredObjsFromOverflowList);
5392 // Now check if there's any work in the overflow list
5393 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5394 // only affects the number of attempts made to get work from the
5395 // overflow list and does not affect the number of workers. Just
5396 // pass ParallelGCThreads so this behavior is unchanged.
5397 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5398 work_q,
5399 ParallelGCThreads)) {
5400 // found something in global overflow list;
5401 // not yet ready to go stealing work from others.
5402 // We'd like to assert(work_q->size() != 0, ...)
5403 // because we just took work from the overflow list,
5404 // but of course we can't since all of that could have
5405 // been already stolen from us.
5406 // "He giveth and He taketh away."
5407 continue;
5408 }
5409 // Verify that we have no work before we resort to stealing
5410 assert(work_q->size() == 0, "Have work, shouldn't steal");
5411 // Try to steal from other queues that have work
5412 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5413 NOT_PRODUCT(num_steals++;)
5414 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5415 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5416 // Do scanning work
5417 obj_to_scan->oop_iterate(cl);
5418 // Loop around, finish this work, and try to steal some more
5419 } else if (terminator()->offer_termination()) {
5420 break; // nirvana from the infinite cycle
5421 }
5422 }
5423 NOT_PRODUCT(
5424 if (PrintCMSStatistics != 0) {
5425 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5426 }
5427 )
5428 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(),
5429 "Else our work is not yet done");
5430 }
5431
5432 // Return a thread-local PLAB recording array, as appropriate.
5433 void* CMSCollector::get_data_recorder(int thr_num) {
5434 if (_survivor_plab_array != NULL &&
5435 (CMSPLABRecordAlways ||
5436 (_collectorState > Marking && _collectorState < FinalMarking))) {
5437 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds");
5438 ChunkArray* ca = &_survivor_plab_array[thr_num];
5439 ca->reset(); // clear it so that fresh data is recorded
5440 return (void*) ca;
5441 } else {
5442 return NULL;
5443 }
5444 }
5445
5446 // Reset all the thread-local PLAB recording arrays
5447 void CMSCollector::reset_survivor_plab_arrays() {
5448 for (uint i = 0; i < ParallelGCThreads; i++) {
5449 _survivor_plab_array[i].reset();
5450 }
5451 }
5452
5453 // Merge the per-thread plab arrays into the global survivor chunk
5454 // array which will provide the partitioning of the survivor space
5455 // for CMS rescan.
5456 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv,
5457 int no_of_gc_threads) {
5458 assert(_survivor_plab_array != NULL, "Error");
5459 assert(_survivor_chunk_array != NULL, "Error");
5460 assert(_collectorState == FinalMarking, "Error");
5461 for (int j = 0; j < no_of_gc_threads; j++) {
5462 _cursor[j] = 0;
5463 }
5464 HeapWord* top = surv->top();
5465 size_t i;
5466 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries
5467 HeapWord* min_val = top; // Higher than any PLAB address
5468 uint min_tid = 0; // position of min_val this round
5469 for (int j = 0; j < no_of_gc_threads; j++) {
5470 ChunkArray* cur_sca = &_survivor_plab_array[j];
5471 if (_cursor[j] == cur_sca->end()) {
5472 continue;
5473 }
5474 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant");
5475 HeapWord* cur_val = cur_sca->nth(_cursor[j]);
5476 assert(surv->used_region().contains(cur_val), "Out of bounds value");
5477 if (cur_val < min_val) {
5478 min_tid = j;
5479 min_val = cur_val;
5480 } else {
5481 assert(cur_val < top, "All recorded addresses should be less");
5482 }
5483 }
5484 // At this point min_val and min_tid are respectively
5485 // the least address in _survivor_plab_array[j]->nth(_cursor[j])
5486 // and the thread (j) that witnesses that address.
5487 // We record this address in the _survivor_chunk_array[i]
5488 // and increment _cursor[min_tid] prior to the next round i.
5489 if (min_val == top) {
5490 break;
5491 }
5492 _survivor_chunk_array[i] = min_val;
5493 _cursor[min_tid]++;
5494 }
5495 // We are all done; record the size of the _survivor_chunk_array
5496 _survivor_chunk_index = i; // exclusive: [0, i)
5497 if (PrintCMSStatistics > 0) {
5498 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i);
5499 }
5500 // Verify that we used up all the recorded entries
5501 #ifdef ASSERT
5502 size_t total = 0;
5503 for (int j = 0; j < no_of_gc_threads; j++) {
5504 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant");
5505 total += _cursor[j];
5506 }
5507 assert(total == _survivor_chunk_index, "Ctl Pt Invariant");
5508 // Check that the merged array is in sorted order
5509 if (total > 0) {
5510 for (size_t i = 0; i < total - 1; i++) {
5511 if (PrintCMSStatistics > 0) {
5512 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ",
5513 i, _survivor_chunk_array[i]);
5514 }
5515 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1],
5516 "Not sorted");
5517 }
5518 }
5519 #endif // ASSERT
5520 }
5521
5522 // Set up the space's par_seq_tasks structure for work claiming
5523 // for parallel rescan of young gen.
5524 // See ParRescanTask where this is currently used.
5525 void
5526 CMSCollector::
5527 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) {
5528 assert(n_threads > 0, "Unexpected n_threads argument");
5529 DefNewGeneration* dng = (DefNewGeneration*)_young_gen;
5530
5531 // Eden space
5532 {
5533 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks();
5534 assert(!pst->valid(), "Clobbering existing data?");
5535 // Each valid entry in [0, _eden_chunk_index) represents a task.
5536 size_t n_tasks = _eden_chunk_index + 1;
5537 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error");
5538 // Sets the condition for completion of the subtask (how many threads
5539 // need to finish in order to be done).
5540 pst->set_n_threads(n_threads);
5541 pst->set_n_tasks((int)n_tasks);
5542 }
5543
5544 // Merge the survivor plab arrays into _survivor_chunk_array
5545 if (_survivor_plab_array != NULL) {
5546 merge_survivor_plab_arrays(dng->from(), n_threads);
5547 } else {
5548 assert(_survivor_chunk_index == 0, "Error");
5549 }
5550
5551 // To space
5552 {
5553 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks();
5554 assert(!pst->valid(), "Clobbering existing data?");
5555 // Sets the condition for completion of the subtask (how many threads
5556 // need to finish in order to be done).
5557 pst->set_n_threads(n_threads);
5558 pst->set_n_tasks(1);
5559 assert(pst->valid(), "Error");
5560 }
5561
5562 // From space
5563 {
5564 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks();
5565 assert(!pst->valid(), "Clobbering existing data?");
5566 size_t n_tasks = _survivor_chunk_index + 1;
5567 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error");
5568 // Sets the condition for completion of the subtask (how many threads
5569 // need to finish in order to be done).
5570 pst->set_n_threads(n_threads);
5571 pst->set_n_tasks((int)n_tasks);
5572 assert(pst->valid(), "Error");
5573 }
5574 }
5575
5576 // Parallel version of remark
5577 void CMSCollector::do_remark_parallel() {
5578 GenCollectedHeap* gch = GenCollectedHeap::heap();
5579 FlexibleWorkGang* workers = gch->workers();
5580 assert(workers != NULL, "Need parallel worker threads.");
5581 // Choose to use the number of GC workers most recently set
5582 // into "active_workers". If active_workers is not set, set it
5583 // to ParallelGCThreads.
5584 int n_workers = workers->active_workers();
5585 if (n_workers == 0) {
5586 assert(n_workers > 0, "Should have been set during scavenge");
5587 n_workers = ParallelGCThreads;
5588 workers->set_active_workers(n_workers);
5589 }
5590 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace();
5591
5592 CMSParRemarkTask tsk(this,
5593 cms_space,
5594 n_workers, workers, task_queues());
5595
5596 // Set up for parallel process_strong_roots work.
5597 gch->set_par_threads(n_workers);
5598 // We won't be iterating over the cards in the card table updating
5599 // the younger_gen cards, so we shouldn't call the following else
5600 // the verification code as well as subsequent younger_refs_iterate
5601 // code would get confused. XXX
5602 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel
5603
5604 // The young gen rescan work will not be done as part of
5605 // process_strong_roots (which currently doesn't knw how to
5606 // parallelize such a scan), but rather will be broken up into
5607 // a set of parallel tasks (via the sampling that the [abortable]
5608 // preclean phase did of EdenSpace, plus the [two] tasks of
5609 // scanning the [two] survivor spaces. Further fine-grain
5610 // parallelization of the scanning of the survivor spaces
5611 // themselves, and of precleaning of the younger gen itself
5612 // is deferred to the future.
5613 initialize_sequential_subtasks_for_young_gen_rescan(n_workers);
5614
5615 // The dirty card rescan work is broken up into a "sequence"
5616 // of parallel tasks (per constituent space) that are dynamically
5617 // claimed by the parallel threads.
5618 cms_space->initialize_sequential_subtasks_for_rescan(n_workers);
5619
5620 // It turns out that even when we're using 1 thread, doing the work in a
5621 // separate thread causes wide variance in run times. We can't help this
5622 // in the multi-threaded case, but we special-case n=1 here to get
5623 // repeatable measurements of the 1-thread overhead of the parallel code.
5624 if (n_workers > 1) {
5625 // Make refs discovery MT-safe, if it isn't already: it may not
5626 // necessarily be so, since it's possible that we are doing
5627 // ST marking.
5628 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), true);
5629 GenCollectedHeap::StrongRootsScope srs(gch);
5630 workers->run_task(&tsk);
5631 } else {
5632 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5633 GenCollectedHeap::StrongRootsScope srs(gch);
5634 tsk.work(0);
5635 }
5636
5637 gch->set_par_threads(0); // 0 ==> non-parallel.
5638 // restore, single-threaded for now, any preserved marks
5639 // as a result of work_q overflow
5640 restore_preserved_marks_if_any();
5641 }
5642
5643 // Non-parallel version of remark
5644 void CMSCollector::do_remark_non_parallel() {
5645 ResourceMark rm;
5646 HandleMark hm;
5647 GenCollectedHeap* gch = GenCollectedHeap::heap();
5648 ReferenceProcessorMTDiscoveryMutator mt(ref_processor(), false);
5649
5650 MarkRefsIntoAndScanClosure
5651 mrias_cl(_span, ref_processor(), &_markBitMap, NULL /* not precleaning */,
5652 &_markStack, this,
5653 false /* should_yield */, false /* not precleaning */);
5654 MarkFromDirtyCardsClosure
5655 markFromDirtyCardsClosure(this, _span,
5656 NULL, // space is set further below
5657 &_markBitMap, &_markStack, &mrias_cl);
5658 {
5659 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty);
5660 // Iterate over the dirty cards, setting the corresponding bits in the
5661 // mod union table.
5662 {
5663 ModUnionClosure modUnionClosure(&_modUnionTable);
5664 _ct->ct_bs()->dirty_card_iterate(
5665 _cmsGen->used_region(),
5666 &modUnionClosure);
5667 }
5668 // Having transferred these marks into the modUnionTable, we just need
5669 // to rescan the marked objects on the dirty cards in the modUnionTable.
5670 // The initial marking may have been done during an asynchronous
5671 // collection so there may be dirty bits in the mod-union table.
5672 const int alignment =
5673 CardTableModRefBS::card_size * BitsPerWord;
5674 {
5675 // ... First handle dirty cards in CMS gen
5676 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace());
5677 MemRegion ur = _cmsGen->used_region();
5678 HeapWord* lb = ur.start();
5679 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment);
5680 MemRegion cms_span(lb, ub);
5681 _modUnionTable.dirty_range_iterate_clear(cms_span,
5682 &markFromDirtyCardsClosure);
5683 verify_work_stacks_empty();
5684 if (PrintCMSStatistics != 0) {
5685 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ",
5686 markFromDirtyCardsClosure.num_dirty_cards());
5687 }
5688 }
5689 }
5690 if (VerifyDuringGC &&
5691 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) {
5692 HandleMark hm; // Discard invalid handles created during verification
5693 Universe::verify();
5694 }
5695 {
5696 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty);
5697
5698 verify_work_stacks_empty();
5699
5700 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel.
5701 GenCollectedHeap::StrongRootsScope srs(gch);
5702 gch->gen_process_strong_roots(_cmsGen->level(),
5703 true, // younger gens as roots
5704 false, // use the local StrongRootsScope
5705 false, // not scavenging
5706 SharedHeap::ScanningOption(roots_scanning_options()),
5707 &mrias_cl,
5708 true, // walk code active on stacks
5709 NULL,
5710 NULL); // The dirty klasses will be handled below
5711
5712 assert(should_unload_classes()
5713 || (roots_scanning_options() & SharedHeap::SO_CodeCache),
5714 "if we didn't scan the code cache, we have to be ready to drop nmethods with expired weak oops");
5715 }
5716
5717 {
5718 TraceTime t("visit unhandled CLDs", PrintGCDetails, false, gclog_or_tty);
5719
5720 verify_work_stacks_empty();
5721
5722 // Scan all class loader data objects that might have been introduced
5723 // during concurrent marking.
5724 ResourceMark rm;
5725 GrowableArray<ClassLoaderData*>* array = ClassLoaderDataGraph::new_clds();
5726 for (int i = 0; i < array->length(); i++) {
5727 mrias_cl.do_class_loader_data(array->at(i));
5728 }
5729
5730 // We don't need to keep track of new CLDs anymore.
5731 ClassLoaderDataGraph::remember_new_clds(false);
5732
5733 verify_work_stacks_empty();
5734 }
5735
5736 {
5737 TraceTime t("dirty klass scan", PrintGCDetails, false, gclog_or_tty);
5738
5739 verify_work_stacks_empty();
5740
5741 RemarkKlassClosure remark_klass_closure(&mrias_cl);
5742 ClassLoaderDataGraph::classes_do(&remark_klass_closure);
5743
5744 verify_work_stacks_empty();
5745 }
5746
5747 // We might have added oops to ClassLoaderData::_handles during the
5748 // concurrent marking phase. These oops point to newly allocated objects
5749 // that are guaranteed to be kept alive. Either by the direct allocation
5750 // code, or when the young collector processes the strong roots. Hence,
5751 // we don't have to revisit the _handles block during the remark phase.
5752
5753 verify_work_stacks_empty();
5754 // Restore evacuated mark words, if any, used for overflow list links
5755 if (!CMSOverflowEarlyRestoration) {
5756 restore_preserved_marks_if_any();
5757 }
5758 verify_overflow_empty();
5759 }
5760
5761 ////////////////////////////////////////////////////////
5762 // Parallel Reference Processing Task Proxy Class
5763 ////////////////////////////////////////////////////////
5764 class CMSRefProcTaskProxy: public AbstractGangTaskWOopQueues {
5765 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
5766 CMSCollector* _collector;
5767 CMSBitMap* _mark_bit_map;
5768 const MemRegion _span;
5769 ProcessTask& _task;
5770
5771 public:
5772 CMSRefProcTaskProxy(ProcessTask& task,
5773 CMSCollector* collector,
5774 const MemRegion& span,
5775 CMSBitMap* mark_bit_map,
5776 AbstractWorkGang* workers,
5777 OopTaskQueueSet* task_queues):
5778 // XXX Should superclass AGTWOQ also know about AWG since it knows
5779 // about the task_queues used by the AWG? Then it could initialize
5780 // the terminator() object. See 6984287. The set_for_termination()
5781 // below is a temporary band-aid for the regression in 6984287.
5782 AbstractGangTaskWOopQueues("Process referents by policy in parallel",
5783 task_queues),
5784 _task(task),
5785 _collector(collector), _span(span), _mark_bit_map(mark_bit_map)
5786 {
5787 assert(_collector->_span.equals(_span) && !_span.is_empty(),
5788 "Inconsistency in _span");
5789 set_for_termination(workers->active_workers());
5790 }
5791
5792 OopTaskQueueSet* task_queues() { return queues(); }
5793
5794 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); }
5795
5796 void do_work_steal(int i,
5797 CMSParDrainMarkingStackClosure* drain,
5798 CMSParKeepAliveClosure* keep_alive,
5799 int* seed);
5800
5801 virtual void work(uint worker_id);
5802 };
5803
5804 void CMSRefProcTaskProxy::work(uint worker_id) {
5805 assert(_collector->_span.equals(_span), "Inconsistency in _span");
5806 CMSParKeepAliveClosure par_keep_alive(_collector, _span,
5807 _mark_bit_map,
5808 work_queue(worker_id));
5809 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span,
5810 _mark_bit_map,
5811 work_queue(worker_id));
5812 CMSIsAliveClosure is_alive_closure(_span, _mark_bit_map);
5813 _task.work(worker_id, is_alive_closure, par_keep_alive, par_drain_stack);
5814 if (_task.marks_oops_alive()) {
5815 do_work_steal(worker_id, &par_drain_stack, &par_keep_alive,
5816 _collector->hash_seed(worker_id));
5817 }
5818 assert(work_queue(worker_id)->size() == 0, "work_queue should be empty");
5819 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list");
5820 }
5821
5822 class CMSRefEnqueueTaskProxy: public AbstractGangTask {
5823 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
5824 EnqueueTask& _task;
5825
5826 public:
5827 CMSRefEnqueueTaskProxy(EnqueueTask& task)
5828 : AbstractGangTask("Enqueue reference objects in parallel"),
5829 _task(task)
5830 { }
5831
5832 virtual void work(uint worker_id)
5833 {
5834 _task.work(worker_id);
5835 }
5836 };
5837
5838 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector,
5839 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue):
5840 _span(span),
5841 _bit_map(bit_map),
5842 _work_queue(work_queue),
5843 _mark_and_push(collector, span, bit_map, work_queue),
5844 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
5845 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads)))
5846 { }
5847
5848 // . see if we can share work_queues with ParNew? XXX
5849 void CMSRefProcTaskProxy::do_work_steal(int i,
5850 CMSParDrainMarkingStackClosure* drain,
5851 CMSParKeepAliveClosure* keep_alive,
5852 int* seed) {
5853 OopTaskQueue* work_q = work_queue(i);
5854 NOT_PRODUCT(int num_steals = 0;)
5855 oop obj_to_scan;
5856
5857 while (true) {
5858 // Completely finish any left over work from (an) earlier round(s)
5859 drain->trim_queue(0);
5860 size_t num_from_overflow_list = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
5861 (size_t)ParGCDesiredObjsFromOverflowList);
5862 // Now check if there's any work in the overflow list
5863 // Passing ParallelGCThreads as the third parameter, no_of_gc_threads,
5864 // only affects the number of attempts made to get work from the
5865 // overflow list and does not affect the number of workers. Just
5866 // pass ParallelGCThreads so this behavior is unchanged.
5867 if (_collector->par_take_from_overflow_list(num_from_overflow_list,
5868 work_q,
5869 ParallelGCThreads)) {
5870 // Found something in global overflow list;
5871 // not yet ready to go stealing work from others.
5872 // We'd like to assert(work_q->size() != 0, ...)
5873 // because we just took work from the overflow list,
5874 // but of course we can't, since all of that might have
5875 // been already stolen from us.
5876 continue;
5877 }
5878 // Verify that we have no work before we resort to stealing
5879 assert(work_q->size() == 0, "Have work, shouldn't steal");
5880 // Try to steal from other queues that have work
5881 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) {
5882 NOT_PRODUCT(num_steals++;)
5883 assert(obj_to_scan->is_oop(), "Oops, not an oop!");
5884 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?");
5885 // Do scanning work
5886 obj_to_scan->oop_iterate(keep_alive);
5887 // Loop around, finish this work, and try to steal some more
5888 } else if (terminator()->offer_termination()) {
5889 break; // nirvana from the infinite cycle
5890 }
5891 }
5892 NOT_PRODUCT(
5893 if (PrintCMSStatistics != 0) {
5894 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals);
5895 }
5896 )
5897 }
5898
5899 void CMSRefProcTaskExecutor::execute(ProcessTask& task)
5900 {
5901 GenCollectedHeap* gch = GenCollectedHeap::heap();
5902 FlexibleWorkGang* workers = gch->workers();
5903 assert(workers != NULL, "Need parallel worker threads.");
5904 CMSRefProcTaskProxy rp_task(task, &_collector,
5905 _collector.ref_processor()->span(),
5906 _collector.markBitMap(),
5907 workers, _collector.task_queues());
5908 workers->run_task(&rp_task);
5909 }
5910
5911 void CMSRefProcTaskExecutor::execute(EnqueueTask& task)
5912 {
5913
5914 GenCollectedHeap* gch = GenCollectedHeap::heap();
5915 FlexibleWorkGang* workers = gch->workers();
5916 assert(workers != NULL, "Need parallel worker threads.");
5917 CMSRefEnqueueTaskProxy enq_task(task);
5918 workers->run_task(&enq_task);
5919 }
5920
5921 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) {
5922
5923 ResourceMark rm;
5924 HandleMark hm;
5925
5926 ReferenceProcessor* rp = ref_processor();
5927 assert(rp->span().equals(_span), "Spans should be equal");
5928 assert(!rp->enqueuing_is_done(), "Enqueuing should not be complete");
5929 // Process weak references.
5930 rp->setup_policy(clear_all_soft_refs);
5931 verify_work_stacks_empty();
5932
5933 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap,
5934 &_markStack, false /* !preclean */);
5935 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this,
5936 _span, &_markBitMap, &_markStack,
5937 &cmsKeepAliveClosure, false /* !preclean */);
5938 {
5939 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty);
5940 if (rp->processing_is_mt()) {
5941 // Set the degree of MT here. If the discovery is done MT, there
5942 // may have been a different number of threads doing the discovery
5943 // and a different number of discovered lists may have Ref objects.
5944 // That is OK as long as the Reference lists are balanced (see
5945 // balance_all_queues() and balance_queues()).
5946 GenCollectedHeap* gch = GenCollectedHeap::heap();
5947 int active_workers = ParallelGCThreads;
5948 FlexibleWorkGang* workers = gch->workers();
5949 if (workers != NULL) {
5950 active_workers = workers->active_workers();
5951 // The expectation is that active_workers will have already
5952 // been set to a reasonable value. If it has not been set,
5953 // investigate.
5954 assert(active_workers > 0, "Should have been set during scavenge");
5955 }
5956 rp->set_active_mt_degree(active_workers);
5957 CMSRefProcTaskExecutor task_executor(*this);
5958 rp->process_discovered_references(&_is_alive_closure,
5959 &cmsKeepAliveClosure,
5960 &cmsDrainMarkingStackClosure,
5961 &task_executor);
5962 } else {
5963 rp->process_discovered_references(&_is_alive_closure,
5964 &cmsKeepAliveClosure,
5965 &cmsDrainMarkingStackClosure,
5966 NULL);
5967 }
5968 verify_work_stacks_empty();
5969 }
5970
5971 if (should_unload_classes()) {
5972 {
5973 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty);
5974
5975 // Follow SystemDictionary roots and unload classes
5976 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure);
5977
5978 // Follow CodeCache roots and unload any methods marked for unloading
5979 CodeCache::do_unloading(&_is_alive_closure, purged_class);
5980
5981 cmsDrainMarkingStackClosure.do_void();
5982 verify_work_stacks_empty();
5983
5984 // Update subklass/sibling/implementor links in KlassKlass descendants
5985 Klass::clean_weak_klass_links(&_is_alive_closure);
5986 // Nothing should have been pushed onto the working stacks.
5987 verify_work_stacks_empty();
5988 }
5989
5990 {
5991 TraceTime t("scrub symbol table", PrintGCDetails, false, gclog_or_tty);
5992 // Clean up unreferenced symbols in symbol table.
5993 SymbolTable::unlink();
5994 }
5995 }
5996
5997 // CMS doesn't use the StringTable as hard roots when class unloading is turned off.
5998 // Need to check if we really scanned the StringTable.
5999 if ((roots_scanning_options() & SharedHeap::SO_Strings) == 0) {
6000 TraceTime t("scrub string table", PrintGCDetails, false, gclog_or_tty);
6001 // Now clean up stale oops in StringTable
6002 StringTable::unlink(&_is_alive_closure);
6003 }
6004
6005 verify_work_stacks_empty();
6006 // Restore any preserved marks as a result of mark stack or
6007 // work queue overflow
6008 restore_preserved_marks_if_any(); // done single-threaded for now
6009
6010 rp->set_enqueuing_is_done(true);
6011 if (rp->processing_is_mt()) {
6012 rp->balance_all_queues();
6013 CMSRefProcTaskExecutor task_executor(*this);
6014 rp->enqueue_discovered_references(&task_executor);
6015 } else {
6016 rp->enqueue_discovered_references(NULL);
6017 }
6018 rp->verify_no_references_recorded();
6019 assert(!rp->discovery_enabled(), "should have been disabled");
6020 }
6021
6022 #ifndef PRODUCT
6023 void CMSCollector::check_correct_thread_executing() {
6024 Thread* t = Thread::current();
6025 // Only the VM thread or the CMS thread should be here.
6026 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(),
6027 "Unexpected thread type");
6028 // If this is the vm thread, the foreground process
6029 // should not be waiting. Note that _foregroundGCIsActive is
6030 // true while the foreground collector is waiting.
6031 if (_foregroundGCShouldWait) {
6032 // We cannot be the VM thread
6033 assert(t->is_ConcurrentGC_thread(),
6034 "Should be CMS thread");
6035 } else {
6036 // We can be the CMS thread only if we are in a stop-world
6037 // phase of CMS collection.
6038 if (t->is_ConcurrentGC_thread()) {
6039 assert(_collectorState == InitialMarking ||
6040 _collectorState == FinalMarking,
6041 "Should be a stop-world phase");
6042 // The CMS thread should be holding the CMS_token.
6043 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6044 "Potential interference with concurrently "
6045 "executing VM thread");
6046 }
6047 }
6048 }
6049 #endif
6050
6051 void CMSCollector::sweep(bool asynch) {
6052 assert(_collectorState == Sweeping, "just checking");
6053 check_correct_thread_executing();
6054 verify_work_stacks_empty();
6055 verify_overflow_empty();
6056 increment_sweep_count();
6057 TraceCMSMemoryManagerStats tms(_collectorState,GenCollectedHeap::heap()->gc_cause());
6058
6059 _inter_sweep_timer.stop();
6060 _inter_sweep_estimate.sample(_inter_sweep_timer.seconds());
6061 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free());
6062
6063 assert(!_intra_sweep_timer.is_active(), "Should not be active");
6064 _intra_sweep_timer.reset();
6065 _intra_sweep_timer.start();
6066 if (asynch) {
6067 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6068 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails);
6069 // First sweep the old gen
6070 {
6071 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(),
6072 bitMapLock());
6073 sweepWork(_cmsGen, asynch);
6074 }
6075
6076 // Update Universe::_heap_*_at_gc figures.
6077 // We need all the free list locks to make the abstract state
6078 // transition from Sweeping to Resetting. See detailed note
6079 // further below.
6080 {
6081 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock());
6082 // Update heap occupancy information which is used as
6083 // input to soft ref clearing policy at the next gc.
6084 Universe::update_heap_info_at_gc();
6085 _collectorState = Resizing;
6086 }
6087 } else {
6088 // already have needed locks
6089 sweepWork(_cmsGen, asynch);
6090 // Update heap occupancy information which is used as
6091 // input to soft ref clearing policy at the next gc.
6092 Universe::update_heap_info_at_gc();
6093 _collectorState = Resizing;
6094 }
6095 verify_work_stacks_empty();
6096 verify_overflow_empty();
6097
6098 if (should_unload_classes()) {
6099 ClassLoaderDataGraph::purge();
6100 }
6101
6102 _intra_sweep_timer.stop();
6103 _intra_sweep_estimate.sample(_intra_sweep_timer.seconds());
6104
6105 _inter_sweep_timer.reset();
6106 _inter_sweep_timer.start();
6107
6108 // We need to use a monotonically non-deccreasing time in ms
6109 // or we will see time-warp warnings and os::javaTimeMillis()
6110 // does not guarantee monotonicity.
6111 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
6112 update_time_of_last_gc(now);
6113
6114 // NOTE on abstract state transitions:
6115 // Mutators allocate-live and/or mark the mod-union table dirty
6116 // based on the state of the collection. The former is done in
6117 // the interval [Marking, Sweeping] and the latter in the interval
6118 // [Marking, Sweeping). Thus the transitions into the Marking state
6119 // and out of the Sweeping state must be synchronously visible
6120 // globally to the mutators.
6121 // The transition into the Marking state happens with the world
6122 // stopped so the mutators will globally see it. Sweeping is
6123 // done asynchronously by the background collector so the transition
6124 // from the Sweeping state to the Resizing state must be done
6125 // under the freelistLock (as is the check for whether to
6126 // allocate-live and whether to dirty the mod-union table).
6127 assert(_collectorState == Resizing, "Change of collector state to"
6128 " Resizing must be done under the freelistLocks (plural)");
6129
6130 // Now that sweeping has been completed, we clear
6131 // the incremental_collection_failed flag,
6132 // thus inviting a younger gen collection to promote into
6133 // this generation. If such a promotion may still fail,
6134 // the flag will be set again when a young collection is
6135 // attempted.
6136 GenCollectedHeap* gch = GenCollectedHeap::heap();
6137 gch->clear_incremental_collection_failed(); // Worth retrying as fresh space may have been freed up
6138 gch->update_full_collections_completed(_collection_count_start);
6139 }
6140
6141 // FIX ME!!! Looks like this belongs in CFLSpace, with
6142 // CMSGen merely delegating to it.
6143 void ConcurrentMarkSweepGeneration::setNearLargestChunk() {
6144 double nearLargestPercent = FLSLargestBlockCoalesceProximity;
6145 HeapWord* minAddr = _cmsSpace->bottom();
6146 HeapWord* largestAddr =
6147 (HeapWord*) _cmsSpace->dictionary()->find_largest_dict();
6148 if (largestAddr == NULL) {
6149 // The dictionary appears to be empty. In this case
6150 // try to coalesce at the end of the heap.
6151 largestAddr = _cmsSpace->end();
6152 }
6153 size_t largestOffset = pointer_delta(largestAddr, minAddr);
6154 size_t nearLargestOffset =
6155 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize;
6156 if (PrintFLSStatistics != 0) {
6157 gclog_or_tty->print_cr(
6158 "CMS: Large Block: " PTR_FORMAT ";"
6159 " Proximity: " PTR_FORMAT " -> " PTR_FORMAT,
6160 largestAddr,
6161 _cmsSpace->nearLargestChunk(), minAddr + nearLargestOffset);
6162 }
6163 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset);
6164 }
6165
6166 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) {
6167 return addr >= _cmsSpace->nearLargestChunk();
6168 }
6169
6170 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() {
6171 return _cmsSpace->find_chunk_at_end();
6172 }
6173
6174 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level,
6175 bool full) {
6176 // The next lower level has been collected. Gather any statistics
6177 // that are of interest at this point.
6178 if (!full && (current_level + 1) == level()) {
6179 // Gather statistics on the young generation collection.
6180 collector()->stats().record_gc0_end(used());
6181 }
6182 }
6183
6184 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() {
6185 GenCollectedHeap* gch = GenCollectedHeap::heap();
6186 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
6187 "Wrong type of heap");
6188 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*)
6189 gch->gen_policy()->size_policy();
6190 assert(sp->is_gc_cms_adaptive_size_policy(),
6191 "Wrong type of size policy");
6192 return sp;
6193 }
6194
6195 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() {
6196 if (PrintGCDetails && Verbose) {
6197 gclog_or_tty->print("Rotate from %d ", _debug_collection_type);
6198 }
6199 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1);
6200 _debug_collection_type =
6201 (CollectionTypes) (_debug_collection_type % Unknown_collection_type);
6202 if (PrintGCDetails && Verbose) {
6203 gclog_or_tty->print_cr("to %d ", _debug_collection_type);
6204 }
6205 }
6206
6207 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen,
6208 bool asynch) {
6209 // We iterate over the space(s) underlying this generation,
6210 // checking the mark bit map to see if the bits corresponding
6211 // to specific blocks are marked or not. Blocks that are
6212 // marked are live and are not swept up. All remaining blocks
6213 // are swept up, with coalescing on-the-fly as we sweep up
6214 // contiguous free and/or garbage blocks:
6215 // We need to ensure that the sweeper synchronizes with allocators
6216 // and stop-the-world collectors. In particular, the following
6217 // locks are used:
6218 // . CMS token: if this is held, a stop the world collection cannot occur
6219 // . freelistLock: if this is held no allocation can occur from this
6220 // generation by another thread
6221 // . bitMapLock: if this is held, no other thread can access or update
6222 //
6223
6224 // Note that we need to hold the freelistLock if we use
6225 // block iterate below; else the iterator might go awry if
6226 // a mutator (or promotion) causes block contents to change
6227 // (for instance if the allocator divvies up a block).
6228 // If we hold the free list lock, for all practical purposes
6229 // young generation GC's can't occur (they'll usually need to
6230 // promote), so we might as well prevent all young generation
6231 // GC's while we do a sweeping step. For the same reason, we might
6232 // as well take the bit map lock for the entire duration
6233
6234 // check that we hold the requisite locks
6235 assert(have_cms_token(), "Should hold cms token");
6236 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token())
6237 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()),
6238 "Should possess CMS token to sweep");
6239 assert_lock_strong(gen->freelistLock());
6240 assert_lock_strong(bitMapLock());
6241
6242 assert(!_inter_sweep_timer.is_active(), "Was switched off in an outer context");
6243 assert(_intra_sweep_timer.is_active(), "Was switched on in an outer context");
6244 gen->cmsSpace()->beginSweepFLCensus((float)(_inter_sweep_timer.seconds()),
6245 _inter_sweep_estimate.padded_average(),
6246 _intra_sweep_estimate.padded_average());
6247 gen->setNearLargestChunk();
6248
6249 {
6250 SweepClosure sweepClosure(this, gen, &_markBitMap,
6251 CMSYield && asynch);
6252 gen->cmsSpace()->blk_iterate_careful(&sweepClosure);
6253 // We need to free-up/coalesce garbage/blocks from a
6254 // co-terminal free run. This is done in the SweepClosure
6255 // destructor; so, do not remove this scope, else the
6256 // end-of-sweep-census below will be off by a little bit.
6257 }
6258 gen->cmsSpace()->sweep_completed();
6259 gen->cmsSpace()->endSweepFLCensus(sweep_count());
6260 if (should_unload_classes()) { // unloaded classes this cycle,
6261 _concurrent_cycles_since_last_unload = 0; // ... reset count
6262 } else { // did not unload classes,
6263 _concurrent_cycles_since_last_unload++; // ... increment count
6264 }
6265 }
6266
6267 // Reset CMS data structures (for now just the marking bit map)
6268 // preparatory for the next cycle.
6269 void CMSCollector::reset(bool asynch) {
6270 GenCollectedHeap* gch = GenCollectedHeap::heap();
6271 CMSAdaptiveSizePolicy* sp = size_policy();
6272 AdaptiveSizePolicyOutput(sp, gch->total_collections());
6273 if (asynch) {
6274 CMSTokenSyncWithLocks ts(true, bitMapLock());
6275
6276 // If the state is not "Resetting", the foreground thread
6277 // has done a collection and the resetting.
6278 if (_collectorState != Resetting) {
6279 assert(_collectorState == Idling, "The state should only change"
6280 " because the foreground collector has finished the collection");
6281 return;
6282 }
6283
6284 // Clear the mark bitmap (no grey objects to start with)
6285 // for the next cycle.
6286 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6287 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails);
6288
6289 HeapWord* curAddr = _markBitMap.startWord();
6290 while (curAddr < _markBitMap.endWord()) {
6291 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr);
6292 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining));
6293 _markBitMap.clear_large_range(chunk);
6294 if (ConcurrentMarkSweepThread::should_yield() &&
6295 !foregroundGCIsActive() &&
6296 CMSYield) {
6297 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6298 "CMS thread should hold CMS token");
6299 assert_lock_strong(bitMapLock());
6300 bitMapLock()->unlock();
6301 ConcurrentMarkSweepThread::desynchronize(true);
6302 ConcurrentMarkSweepThread::acknowledge_yield_request();
6303 stopTimer();
6304 if (PrintCMSStatistics != 0) {
6305 incrementYields();
6306 }
6307 icms_wait();
6308
6309 // See the comment in coordinator_yield()
6310 for (unsigned i = 0; i < CMSYieldSleepCount &&
6311 ConcurrentMarkSweepThread::should_yield() &&
6312 !CMSCollector::foregroundGCIsActive(); ++i) {
6313 os::sleep(Thread::current(), 1, false);
6314 ConcurrentMarkSweepThread::acknowledge_yield_request();
6315 }
6316
6317 ConcurrentMarkSweepThread::synchronize(true);
6318 bitMapLock()->lock_without_safepoint_check();
6319 startTimer();
6320 }
6321 curAddr = chunk.end();
6322 }
6323 // A successful mostly concurrent collection has been done.
6324 // Because only the full (i.e., concurrent mode failure) collections
6325 // are being measured for gc overhead limits, clean the "near" flag
6326 // and count.
6327 sp->reset_gc_overhead_limit_count();
6328 _collectorState = Idling;
6329 } else {
6330 // already have the lock
6331 assert(_collectorState == Resetting, "just checking");
6332 assert_lock_strong(bitMapLock());
6333 _markBitMap.clear_all();
6334 _collectorState = Idling;
6335 }
6336
6337 // Stop incremental mode after a cycle completes, so that any future cycles
6338 // are triggered by allocation.
6339 stop_icms();
6340
6341 NOT_PRODUCT(
6342 if (RotateCMSCollectionTypes) {
6343 _cmsGen->rotate_debug_collection_type();
6344 }
6345 )
6346 }
6347
6348 void CMSCollector::do_CMS_operation(CMS_op_type op, GCCause::Cause gc_cause) {
6349 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps);
6350 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty);
6351 TraceTime t(GCCauseString("GC", gc_cause), PrintGC, !PrintGCDetails, gclog_or_tty);
6352 TraceCollectorStats tcs(counters());
6353
6354 switch (op) {
6355 case CMS_op_checkpointRootsInitial: {
6356 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6357 checkpointRootsInitial(true); // asynch
6358 if (PrintGC) {
6359 _cmsGen->printOccupancy("initial-mark");
6360 }
6361 break;
6362 }
6363 case CMS_op_checkpointRootsFinal: {
6364 SvcGCMarker sgcm(SvcGCMarker::OTHER);
6365 checkpointRootsFinal(true, // asynch
6366 false, // !clear_all_soft_refs
6367 false); // !init_mark_was_synchronous
6368 if (PrintGC) {
6369 _cmsGen->printOccupancy("remark");
6370 }
6371 break;
6372 }
6373 default:
6374 fatal("No such CMS_op");
6375 }
6376 }
6377
6378 #ifndef PRODUCT
6379 size_t const CMSCollector::skip_header_HeapWords() {
6380 return FreeChunk::header_size();
6381 }
6382
6383 // Try and collect here conditions that should hold when
6384 // CMS thread is exiting. The idea is that the foreground GC
6385 // thread should not be blocked if it wants to terminate
6386 // the CMS thread and yet continue to run the VM for a while
6387 // after that.
6388 void CMSCollector::verify_ok_to_terminate() const {
6389 assert(Thread::current()->is_ConcurrentGC_thread(),
6390 "should be called by CMS thread");
6391 assert(!_foregroundGCShouldWait, "should be false");
6392 // We could check here that all the various low-level locks
6393 // are not held by the CMS thread, but that is overkill; see
6394 // also CMSThread::verify_ok_to_terminate() where the CGC_lock
6395 // is checked.
6396 }
6397 #endif
6398
6399 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const {
6400 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1),
6401 "missing Printezis mark?");
6402 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6403 size_t size = pointer_delta(nextOneAddr + 1, addr);
6404 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6405 "alignment problem");
6406 assert(size >= 3, "Necessary for Printezis marks to work");
6407 return size;
6408 }
6409
6410 // A variant of the above (block_size_using_printezis_bits()) except
6411 // that we return 0 if the P-bits are not yet set.
6412 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const {
6413 if (_markBitMap.isMarked(addr + 1)) {
6414 assert(_markBitMap.isMarked(addr), "P-bit can be set only for marked objects");
6415 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2);
6416 size_t size = pointer_delta(nextOneAddr + 1, addr);
6417 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6418 "alignment problem");
6419 assert(size >= 3, "Necessary for Printezis marks to work");
6420 return size;
6421 }
6422 return 0;
6423 }
6424
6425 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const {
6426 size_t sz = 0;
6427 oop p = (oop)addr;
6428 if (p->klass_or_null() != NULL) {
6429 sz = CompactibleFreeListSpace::adjustObjectSize(p->size());
6430 } else {
6431 sz = block_size_using_printezis_bits(addr);
6432 }
6433 assert(sz > 0, "size must be nonzero");
6434 HeapWord* next_block = addr + sz;
6435 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block,
6436 CardTableModRefBS::card_size);
6437 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) <
6438 round_down((uintptr_t)next_card, CardTableModRefBS::card_size),
6439 "must be different cards");
6440 return next_card;
6441 }
6442
6443
6444 // CMS Bit Map Wrapper /////////////////////////////////////////
6445
6446 // Construct a CMS bit map infrastructure, but don't create the
6447 // bit vector itself. That is done by a separate call CMSBitMap::allocate()
6448 // further below.
6449 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name):
6450 _bm(),
6451 _shifter(shifter),
6452 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL)
6453 {
6454 _bmStartWord = 0;
6455 _bmWordSize = 0;
6456 }
6457
6458 bool CMSBitMap::allocate(MemRegion mr) {
6459 _bmStartWord = mr.start();
6460 _bmWordSize = mr.word_size();
6461 ReservedSpace brs(ReservedSpace::allocation_align_size_up(
6462 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1));
6463 if (!brs.is_reserved()) {
6464 warning("CMS bit map allocation failure");
6465 return false;
6466 }
6467 // For now we'll just commit all of the bit map up fromt.
6468 // Later on we'll try to be more parsimonious with swap.
6469 if (!_virtual_space.initialize(brs, brs.size())) {
6470 warning("CMS bit map backing store failure");
6471 return false;
6472 }
6473 assert(_virtual_space.committed_size() == brs.size(),
6474 "didn't reserve backing store for all of CMS bit map?");
6475 _bm.set_map((BitMap::bm_word_t*)_virtual_space.low());
6476 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >=
6477 _bmWordSize, "inconsistency in bit map sizing");
6478 _bm.set_size(_bmWordSize >> _shifter);
6479
6480 // bm.clear(); // can we rely on getting zero'd memory? verify below
6481 assert(isAllClear(),
6482 "Expected zero'd memory from ReservedSpace constructor");
6483 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()),
6484 "consistency check");
6485 return true;
6486 }
6487
6488 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) {
6489 HeapWord *next_addr, *end_addr, *last_addr;
6490 assert_locked();
6491 assert(covers(mr), "out-of-range error");
6492 // XXX assert that start and end are appropriately aligned
6493 for (next_addr = mr.start(), end_addr = mr.end();
6494 next_addr < end_addr; next_addr = last_addr) {
6495 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr);
6496 last_addr = dirty_region.end();
6497 if (!dirty_region.is_empty()) {
6498 cl->do_MemRegion(dirty_region);
6499 } else {
6500 assert(last_addr == end_addr, "program logic");
6501 return;
6502 }
6503 }
6504 }
6505
6506 #ifndef PRODUCT
6507 void CMSBitMap::assert_locked() const {
6508 CMSLockVerifier::assert_locked(lock());
6509 }
6510
6511 bool CMSBitMap::covers(MemRegion mr) const {
6512 // assert(_bm.map() == _virtual_space.low(), "map inconsistency");
6513 assert((size_t)_bm.size() == (_bmWordSize >> _shifter),
6514 "size inconsistency");
6515 return (mr.start() >= _bmStartWord) &&
6516 (mr.end() <= endWord());
6517 }
6518
6519 bool CMSBitMap::covers(HeapWord* start, size_t size) const {
6520 return (start >= _bmStartWord && (start + size) <= endWord());
6521 }
6522
6523 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) {
6524 // verify that there are no 1 bits in the interval [left, right)
6525 FalseBitMapClosure falseBitMapClosure;
6526 iterate(&falseBitMapClosure, left, right);
6527 }
6528
6529 void CMSBitMap::region_invariant(MemRegion mr)
6530 {
6531 assert_locked();
6532 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize));
6533 assert(!mr.is_empty(), "unexpected empty region");
6534 assert(covers(mr), "mr should be covered by bit map");
6535 // convert address range into offset range
6536 size_t start_ofs = heapWordToOffset(mr.start());
6537 // Make sure that end() is appropriately aligned
6538 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(),
6539 (1 << (_shifter+LogHeapWordSize))),
6540 "Misaligned mr.end()");
6541 size_t end_ofs = heapWordToOffset(mr.end());
6542 assert(end_ofs > start_ofs, "Should mark at least one bit");
6543 }
6544
6545 #endif
6546
6547 bool CMSMarkStack::allocate(size_t size) {
6548 // allocate a stack of the requisite depth
6549 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6550 size * sizeof(oop)));
6551 if (!rs.is_reserved()) {
6552 warning("CMSMarkStack allocation failure");
6553 return false;
6554 }
6555 if (!_virtual_space.initialize(rs, rs.size())) {
6556 warning("CMSMarkStack backing store failure");
6557 return false;
6558 }
6559 assert(_virtual_space.committed_size() == rs.size(),
6560 "didn't reserve backing store for all of CMS stack?");
6561 _base = (oop*)(_virtual_space.low());
6562 _index = 0;
6563 _capacity = size;
6564 NOT_PRODUCT(_max_depth = 0);
6565 return true;
6566 }
6567
6568 // XXX FIX ME !!! In the MT case we come in here holding a
6569 // leaf lock. For printing we need to take a further lock
6570 // which has lower rank. We need to recallibrate the two
6571 // lock-ranks involved in order to be able to rpint the
6572 // messages below. (Or defer the printing to the caller.
6573 // For now we take the expedient path of just disabling the
6574 // messages for the problematic case.)
6575 void CMSMarkStack::expand() {
6576 assert(_capacity <= MarkStackSizeMax, "stack bigger than permitted");
6577 if (_capacity == MarkStackSizeMax) {
6578 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6579 // We print a warning message only once per CMS cycle.
6580 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit");
6581 }
6582 return;
6583 }
6584 // Double capacity if possible
6585 size_t new_capacity = MIN2(_capacity*2, MarkStackSizeMax);
6586 // Do not give up existing stack until we have managed to
6587 // get the double capacity that we desired.
6588 ReservedSpace rs(ReservedSpace::allocation_align_size_up(
6589 new_capacity * sizeof(oop)));
6590 if (rs.is_reserved()) {
6591 // Release the backing store associated with old stack
6592 _virtual_space.release();
6593 // Reinitialize virtual space for new stack
6594 if (!_virtual_space.initialize(rs, rs.size())) {
6595 fatal("Not enough swap for expanded marking stack");
6596 }
6597 _base = (oop*)(_virtual_space.low());
6598 _index = 0;
6599 _capacity = new_capacity;
6600 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) {
6601 // Failed to double capacity, continue;
6602 // we print a detail message only once per CMS cycle.
6603 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to "
6604 SIZE_FORMAT"K",
6605 _capacity / K, new_capacity / K);
6606 }
6607 }
6608
6609
6610 // Closures
6611 // XXX: there seems to be a lot of code duplication here;
6612 // should refactor and consolidate common code.
6613
6614 // This closure is used to mark refs into the CMS generation in
6615 // the CMS bit map. Called at the first checkpoint. This closure
6616 // assumes that we do not need to re-mark dirty cards; if the CMS
6617 // generation on which this is used is not an oldest
6618 // generation then this will lose younger_gen cards!
6619
6620 MarkRefsIntoClosure::MarkRefsIntoClosure(
6621 MemRegion span, CMSBitMap* bitMap):
6622 _span(span),
6623 _bitMap(bitMap)
6624 {
6625 assert(_ref_processor == NULL, "deliberately left NULL");
6626 assert(_bitMap->covers(_span), "_bitMap/_span mismatch");
6627 }
6628
6629 void MarkRefsIntoClosure::do_oop(oop obj) {
6630 // if p points into _span, then mark corresponding bit in _markBitMap
6631 assert(obj->is_oop(), "expected an oop");
6632 HeapWord* addr = (HeapWord*)obj;
6633 if (_span.contains(addr)) {
6634 // this should be made more efficient
6635 _bitMap->mark(addr);
6636 }
6637 }
6638
6639 void MarkRefsIntoClosure::do_oop(oop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6640 void MarkRefsIntoClosure::do_oop(narrowOop* p) { MarkRefsIntoClosure::do_oop_work(p); }
6641
6642 // A variant of the above, used for CMS marking verification.
6643 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure(
6644 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm):
6645 _span(span),
6646 _verification_bm(verification_bm),
6647 _cms_bm(cms_bm)
6648 {
6649 assert(_ref_processor == NULL, "deliberately left NULL");
6650 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch");
6651 }
6652
6653 void MarkRefsIntoVerifyClosure::do_oop(oop obj) {
6654 // if p points into _span, then mark corresponding bit in _markBitMap
6655 assert(obj->is_oop(), "expected an oop");
6656 HeapWord* addr = (HeapWord*)obj;
6657 if (_span.contains(addr)) {
6658 _verification_bm->mark(addr);
6659 if (!_cms_bm->isMarked(addr)) {
6660 oop(addr)->print();
6661 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)", addr);
6662 fatal("... aborting");
6663 }
6664 }
6665 }
6666
6667 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6668 void MarkRefsIntoVerifyClosure::do_oop(narrowOop* p) { MarkRefsIntoVerifyClosure::do_oop_work(p); }
6669
6670 //////////////////////////////////////////////////
6671 // MarkRefsIntoAndScanClosure
6672 //////////////////////////////////////////////////
6673
6674 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span,
6675 ReferenceProcessor* rp,
6676 CMSBitMap* bit_map,
6677 CMSBitMap* mod_union_table,
6678 CMSMarkStack* mark_stack,
6679 CMSCollector* collector,
6680 bool should_yield,
6681 bool concurrent_precleaning):
6682 _collector(collector),
6683 _span(span),
6684 _bit_map(bit_map),
6685 _mark_stack(mark_stack),
6686 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table,
6687 mark_stack, concurrent_precleaning),
6688 _yield(should_yield),
6689 _concurrent_precleaning(concurrent_precleaning),
6690 _freelistLock(NULL)
6691 {
6692 _ref_processor = rp;
6693 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6694 }
6695
6696 // This closure is used to mark refs into the CMS generation at the
6697 // second (final) checkpoint, and to scan and transitively follow
6698 // the unmarked oops. It is also used during the concurrent precleaning
6699 // phase while scanning objects on dirty cards in the CMS generation.
6700 // The marks are made in the marking bit map and the marking stack is
6701 // used for keeping the (newly) grey objects during the scan.
6702 // The parallel version (Par_...) appears further below.
6703 void MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6704 if (obj != NULL) {
6705 assert(obj->is_oop(), "expected an oop");
6706 HeapWord* addr = (HeapWord*)obj;
6707 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
6708 assert(_collector->overflow_list_is_empty(),
6709 "overflow list should be empty");
6710 if (_span.contains(addr) &&
6711 !_bit_map->isMarked(addr)) {
6712 // mark bit map (object is now grey)
6713 _bit_map->mark(addr);
6714 // push on marking stack (stack should be empty), and drain the
6715 // stack by applying this closure to the oops in the oops popped
6716 // from the stack (i.e. blacken the grey objects)
6717 bool res = _mark_stack->push(obj);
6718 assert(res, "Should have space to push on empty stack");
6719 do {
6720 oop new_oop = _mark_stack->pop();
6721 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6722 assert(_bit_map->isMarked((HeapWord*)new_oop),
6723 "only grey objects on this stack");
6724 // iterate over the oops in this oop, marking and pushing
6725 // the ones in CMS heap (i.e. in _span).
6726 new_oop->oop_iterate(&_pushAndMarkClosure);
6727 // check if it's time to yield
6728 do_yield_check();
6729 } while (!_mark_stack->isEmpty() ||
6730 (!_concurrent_precleaning && take_from_overflow_list()));
6731 // if marking stack is empty, and we are not doing this
6732 // during precleaning, then check the overflow list
6733 }
6734 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
6735 assert(_collector->overflow_list_is_empty(),
6736 "overflow list was drained above");
6737 // We could restore evacuated mark words, if any, used for
6738 // overflow list links here because the overflow list is
6739 // provably empty here. That would reduce the maximum
6740 // size requirements for preserved_{oop,mark}_stack.
6741 // But we'll just postpone it until we are all done
6742 // so we can just stream through.
6743 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) {
6744 _collector->restore_preserved_marks_if_any();
6745 assert(_collector->no_preserved_marks(), "No preserved marks");
6746 }
6747 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(),
6748 "All preserved marks should have been restored above");
6749 }
6750 }
6751
6752 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6753 void MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { MarkRefsIntoAndScanClosure::do_oop_work(p); }
6754
6755 void MarkRefsIntoAndScanClosure::do_yield_work() {
6756 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6757 "CMS thread should hold CMS token");
6758 assert_lock_strong(_freelistLock);
6759 assert_lock_strong(_bit_map->lock());
6760 // relinquish the free_list_lock and bitMaplock()
6761 _bit_map->lock()->unlock();
6762 _freelistLock->unlock();
6763 ConcurrentMarkSweepThread::desynchronize(true);
6764 ConcurrentMarkSweepThread::acknowledge_yield_request();
6765 _collector->stopTimer();
6766 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6767 if (PrintCMSStatistics != 0) {
6768 _collector->incrementYields();
6769 }
6770 _collector->icms_wait();
6771
6772 // See the comment in coordinator_yield()
6773 for (unsigned i = 0;
6774 i < CMSYieldSleepCount &&
6775 ConcurrentMarkSweepThread::should_yield() &&
6776 !CMSCollector::foregroundGCIsActive();
6777 ++i) {
6778 os::sleep(Thread::current(), 1, false);
6779 ConcurrentMarkSweepThread::acknowledge_yield_request();
6780 }
6781
6782 ConcurrentMarkSweepThread::synchronize(true);
6783 _freelistLock->lock_without_safepoint_check();
6784 _bit_map->lock()->lock_without_safepoint_check();
6785 _collector->startTimer();
6786 }
6787
6788 ///////////////////////////////////////////////////////////
6789 // Par_MarkRefsIntoAndScanClosure: a parallel version of
6790 // MarkRefsIntoAndScanClosure
6791 ///////////////////////////////////////////////////////////
6792 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure(
6793 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp,
6794 CMSBitMap* bit_map, OopTaskQueue* work_queue):
6795 _span(span),
6796 _bit_map(bit_map),
6797 _work_queue(work_queue),
6798 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4),
6799 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))),
6800 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue)
6801 {
6802 _ref_processor = rp;
6803 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
6804 }
6805
6806 // This closure is used to mark refs into the CMS generation at the
6807 // second (final) checkpoint, and to scan and transitively follow
6808 // the unmarked oops. The marks are made in the marking bit map and
6809 // the work_queue is used for keeping the (newly) grey objects during
6810 // the scan phase whence they are also available for stealing by parallel
6811 // threads. Since the marking bit map is shared, updates are
6812 // synchronized (via CAS).
6813 void Par_MarkRefsIntoAndScanClosure::do_oop(oop obj) {
6814 if (obj != NULL) {
6815 // Ignore mark word because this could be an already marked oop
6816 // that may be chained at the end of the overflow list.
6817 assert(obj->is_oop(true), "expected an oop");
6818 HeapWord* addr = (HeapWord*)obj;
6819 if (_span.contains(addr) &&
6820 !_bit_map->isMarked(addr)) {
6821 // mark bit map (object will become grey):
6822 // It is possible for several threads to be
6823 // trying to "claim" this object concurrently;
6824 // the unique thread that succeeds in marking the
6825 // object first will do the subsequent push on
6826 // to the work queue (or overflow list).
6827 if (_bit_map->par_mark(addr)) {
6828 // push on work_queue (which may not be empty), and trim the
6829 // queue to an appropriate length by applying this closure to
6830 // the oops in the oops popped from the stack (i.e. blacken the
6831 // grey objects)
6832 bool res = _work_queue->push(obj);
6833 assert(res, "Low water mark should be less than capacity?");
6834 trim_queue(_low_water_mark);
6835 } // Else, another thread claimed the object
6836 }
6837 }
6838 }
6839
6840 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6841 void Par_MarkRefsIntoAndScanClosure::do_oop(narrowOop* p) { Par_MarkRefsIntoAndScanClosure::do_oop_work(p); }
6842
6843 // This closure is used to rescan the marked objects on the dirty cards
6844 // in the mod union table and the card table proper.
6845 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m(
6846 oop p, MemRegion mr) {
6847
6848 size_t size = 0;
6849 HeapWord* addr = (HeapWord*)p;
6850 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6851 assert(_span.contains(addr), "we are scanning the CMS generation");
6852 // check if it's time to yield
6853 if (do_yield_check()) {
6854 // We yielded for some foreground stop-world work,
6855 // and we have been asked to abort this ongoing preclean cycle.
6856 return 0;
6857 }
6858 if (_bitMap->isMarked(addr)) {
6859 // it's marked; is it potentially uninitialized?
6860 if (p->klass_or_null() != NULL) {
6861 // an initialized object; ignore mark word in verification below
6862 // since we are running concurrent with mutators
6863 assert(p->is_oop(true), "should be an oop");
6864 if (p->is_objArray()) {
6865 // objArrays are precisely marked; restrict scanning
6866 // to dirty cards only.
6867 size = CompactibleFreeListSpace::adjustObjectSize(
6868 p->oop_iterate(_scanningClosure, mr));
6869 } else {
6870 // A non-array may have been imprecisely marked; we need
6871 // to scan object in its entirety.
6872 size = CompactibleFreeListSpace::adjustObjectSize(
6873 p->oop_iterate(_scanningClosure));
6874 }
6875 #ifdef DEBUG
6876 size_t direct_size =
6877 CompactibleFreeListSpace::adjustObjectSize(p->size());
6878 assert(size == direct_size, "Inconsistency in size");
6879 assert(size >= 3, "Necessary for Printezis marks to work");
6880 if (!_bitMap->isMarked(addr+1)) {
6881 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size);
6882 } else {
6883 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1);
6884 assert(_bitMap->isMarked(addr+size-1),
6885 "inconsistent Printezis mark");
6886 }
6887 #endif // DEBUG
6888 } else {
6889 // an unitialized object
6890 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?");
6891 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
6892 size = pointer_delta(nextOneAddr + 1, addr);
6893 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
6894 "alignment problem");
6895 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass()
6896 // will dirty the card when the klass pointer is installed in the
6897 // object (signalling the completion of initialization).
6898 }
6899 } else {
6900 // Either a not yet marked object or an uninitialized object
6901 if (p->klass_or_null() == NULL) {
6902 // An uninitialized object, skip to the next card, since
6903 // we may not be able to read its P-bits yet.
6904 assert(size == 0, "Initial value");
6905 } else {
6906 // An object not (yet) reached by marking: we merely need to
6907 // compute its size so as to go look at the next block.
6908 assert(p->is_oop(true), "should be an oop");
6909 size = CompactibleFreeListSpace::adjustObjectSize(p->size());
6910 }
6911 }
6912 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6913 return size;
6914 }
6915
6916 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() {
6917 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6918 "CMS thread should hold CMS token");
6919 assert_lock_strong(_freelistLock);
6920 assert_lock_strong(_bitMap->lock());
6921 // relinquish the free_list_lock and bitMaplock()
6922 _bitMap->lock()->unlock();
6923 _freelistLock->unlock();
6924 ConcurrentMarkSweepThread::desynchronize(true);
6925 ConcurrentMarkSweepThread::acknowledge_yield_request();
6926 _collector->stopTimer();
6927 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
6928 if (PrintCMSStatistics != 0) {
6929 _collector->incrementYields();
6930 }
6931 _collector->icms_wait();
6932
6933 // See the comment in coordinator_yield()
6934 for (unsigned i = 0; i < CMSYieldSleepCount &&
6935 ConcurrentMarkSweepThread::should_yield() &&
6936 !CMSCollector::foregroundGCIsActive(); ++i) {
6937 os::sleep(Thread::current(), 1, false);
6938 ConcurrentMarkSweepThread::acknowledge_yield_request();
6939 }
6940
6941 ConcurrentMarkSweepThread::synchronize(true);
6942 _freelistLock->lock_without_safepoint_check();
6943 _bitMap->lock()->lock_without_safepoint_check();
6944 _collector->startTimer();
6945 }
6946
6947
6948 //////////////////////////////////////////////////////////////////
6949 // SurvivorSpacePrecleanClosure
6950 //////////////////////////////////////////////////////////////////
6951 // This (single-threaded) closure is used to preclean the oops in
6952 // the survivor spaces.
6953 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) {
6954
6955 HeapWord* addr = (HeapWord*)p;
6956 DEBUG_ONLY(_collector->verify_work_stacks_empty();)
6957 assert(!_span.contains(addr), "we are scanning the survivor spaces");
6958 assert(p->klass_or_null() != NULL, "object should be initializd");
6959 // an initialized object; ignore mark word in verification below
6960 // since we are running concurrent with mutators
6961 assert(p->is_oop(true), "should be an oop");
6962 // Note that we do not yield while we iterate over
6963 // the interior oops of p, pushing the relevant ones
6964 // on our marking stack.
6965 size_t size = p->oop_iterate(_scanning_closure);
6966 do_yield_check();
6967 // Observe that below, we do not abandon the preclean
6968 // phase as soon as we should; rather we empty the
6969 // marking stack before returning. This is to satisfy
6970 // some existing assertions. In general, it may be a
6971 // good idea to abort immediately and complete the marking
6972 // from the grey objects at a later time.
6973 while (!_mark_stack->isEmpty()) {
6974 oop new_oop = _mark_stack->pop();
6975 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
6976 assert(_bit_map->isMarked((HeapWord*)new_oop),
6977 "only grey objects on this stack");
6978 // iterate over the oops in this oop, marking and pushing
6979 // the ones in CMS heap (i.e. in _span).
6980 new_oop->oop_iterate(_scanning_closure);
6981 // check if it's time to yield
6982 do_yield_check();
6983 }
6984 unsigned int after_count =
6985 GenCollectedHeap::heap()->total_collections();
6986 bool abort = (_before_count != after_count) ||
6987 _collector->should_abort_preclean();
6988 return abort ? 0 : size;
6989 }
6990
6991 void SurvivorSpacePrecleanClosure::do_yield_work() {
6992 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
6993 "CMS thread should hold CMS token");
6994 assert_lock_strong(_bit_map->lock());
6995 // Relinquish the bit map lock
6996 _bit_map->lock()->unlock();
6997 ConcurrentMarkSweepThread::desynchronize(true);
6998 ConcurrentMarkSweepThread::acknowledge_yield_request();
6999 _collector->stopTimer();
7000 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7001 if (PrintCMSStatistics != 0) {
7002 _collector->incrementYields();
7003 }
7004 _collector->icms_wait();
7005
7006 // See the comment in coordinator_yield()
7007 for (unsigned i = 0; i < CMSYieldSleepCount &&
7008 ConcurrentMarkSweepThread::should_yield() &&
7009 !CMSCollector::foregroundGCIsActive(); ++i) {
7010 os::sleep(Thread::current(), 1, false);
7011 ConcurrentMarkSweepThread::acknowledge_yield_request();
7012 }
7013
7014 ConcurrentMarkSweepThread::synchronize(true);
7015 _bit_map->lock()->lock_without_safepoint_check();
7016 _collector->startTimer();
7017 }
7018
7019 // This closure is used to rescan the marked objects on the dirty cards
7020 // in the mod union table and the card table proper. In the parallel
7021 // case, although the bitMap is shared, we do a single read so the
7022 // isMarked() query is "safe".
7023 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) {
7024 // Ignore mark word because we are running concurrent with mutators
7025 assert(p->is_oop_or_null(true), "expected an oop or null");
7026 HeapWord* addr = (HeapWord*)p;
7027 assert(_span.contains(addr), "we are scanning the CMS generation");
7028 bool is_obj_array = false;
7029 #ifdef DEBUG
7030 if (!_parallel) {
7031 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)");
7032 assert(_collector->overflow_list_is_empty(),
7033 "overflow list should be empty");
7034
7035 }
7036 #endif // DEBUG
7037 if (_bit_map->isMarked(addr)) {
7038 // Obj arrays are precisely marked, non-arrays are not;
7039 // so we scan objArrays precisely and non-arrays in their
7040 // entirety.
7041 if (p->is_objArray()) {
7042 is_obj_array = true;
7043 if (_parallel) {
7044 p->oop_iterate(_par_scan_closure, mr);
7045 } else {
7046 p->oop_iterate(_scan_closure, mr);
7047 }
7048 } else {
7049 if (_parallel) {
7050 p->oop_iterate(_par_scan_closure);
7051 } else {
7052 p->oop_iterate(_scan_closure);
7053 }
7054 }
7055 }
7056 #ifdef DEBUG
7057 if (!_parallel) {
7058 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)");
7059 assert(_collector->overflow_list_is_empty(),
7060 "overflow list should be empty");
7061
7062 }
7063 #endif // DEBUG
7064 return is_obj_array;
7065 }
7066
7067 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector,
7068 MemRegion span,
7069 CMSBitMap* bitMap, CMSMarkStack* markStack,
7070 bool should_yield, bool verifying):
7071 _collector(collector),
7072 _span(span),
7073 _bitMap(bitMap),
7074 _mut(&collector->_modUnionTable),
7075 _markStack(markStack),
7076 _yield(should_yield),
7077 _skipBits(0)
7078 {
7079 assert(_markStack->isEmpty(), "stack should be empty");
7080 _finger = _bitMap->startWord();
7081 _threshold = _finger;
7082 assert(_collector->_restart_addr == NULL, "Sanity check");
7083 assert(_span.contains(_finger), "Out of bounds _finger?");
7084 DEBUG_ONLY(_verifying = verifying;)
7085 }
7086
7087 void MarkFromRootsClosure::reset(HeapWord* addr) {
7088 assert(_markStack->isEmpty(), "would cause duplicates on stack");
7089 assert(_span.contains(addr), "Out of bounds _finger?");
7090 _finger = addr;
7091 _threshold = (HeapWord*)round_to(
7092 (intptr_t)_finger, CardTableModRefBS::card_size);
7093 }
7094
7095 // Should revisit to see if this should be restructured for
7096 // greater efficiency.
7097 bool MarkFromRootsClosure::do_bit(size_t offset) {
7098 if (_skipBits > 0) {
7099 _skipBits--;
7100 return true;
7101 }
7102 // convert offset into a HeapWord*
7103 HeapWord* addr = _bitMap->startWord() + offset;
7104 assert(_bitMap->endWord() && addr < _bitMap->endWord(),
7105 "address out of range");
7106 assert(_bitMap->isMarked(addr), "tautology");
7107 if (_bitMap->isMarked(addr+1)) {
7108 // this is an allocated but not yet initialized object
7109 assert(_skipBits == 0, "tautology");
7110 _skipBits = 2; // skip next two marked bits ("Printezis-marks")
7111 oop p = oop(addr);
7112 if (p->klass_or_null() == NULL) {
7113 DEBUG_ONLY(if (!_verifying) {)
7114 // We re-dirty the cards on which this object lies and increase
7115 // the _threshold so that we'll come back to scan this object
7116 // during the preclean or remark phase. (CMSCleanOnEnter)
7117 if (CMSCleanOnEnter) {
7118 size_t sz = _collector->block_size_using_printezis_bits(addr);
7119 HeapWord* end_card_addr = (HeapWord*)round_to(
7120 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7121 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7122 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7123 // Bump _threshold to end_card_addr; note that
7124 // _threshold cannot possibly exceed end_card_addr, anyhow.
7125 // This prevents future clearing of the card as the scan proceeds
7126 // to the right.
7127 assert(_threshold <= end_card_addr,
7128 "Because we are just scanning into this object");
7129 if (_threshold < end_card_addr) {
7130 _threshold = end_card_addr;
7131 }
7132 if (p->klass_or_null() != NULL) {
7133 // Redirty the range of cards...
7134 _mut->mark_range(redirty_range);
7135 } // ...else the setting of klass will dirty the card anyway.
7136 }
7137 DEBUG_ONLY(})
7138 return true;
7139 }
7140 }
7141 scanOopsInOop(addr);
7142 return true;
7143 }
7144
7145 // We take a break if we've been at this for a while,
7146 // so as to avoid monopolizing the locks involved.
7147 void MarkFromRootsClosure::do_yield_work() {
7148 // First give up the locks, then yield, then re-lock
7149 // We should probably use a constructor/destructor idiom to
7150 // do this unlock/lock or modify the MutexUnlocker class to
7151 // serve our purpose. XXX
7152 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7153 "CMS thread should hold CMS token");
7154 assert_lock_strong(_bitMap->lock());
7155 _bitMap->lock()->unlock();
7156 ConcurrentMarkSweepThread::desynchronize(true);
7157 ConcurrentMarkSweepThread::acknowledge_yield_request();
7158 _collector->stopTimer();
7159 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7160 if (PrintCMSStatistics != 0) {
7161 _collector->incrementYields();
7162 }
7163 _collector->icms_wait();
7164
7165 // See the comment in coordinator_yield()
7166 for (unsigned i = 0; i < CMSYieldSleepCount &&
7167 ConcurrentMarkSweepThread::should_yield() &&
7168 !CMSCollector::foregroundGCIsActive(); ++i) {
7169 os::sleep(Thread::current(), 1, false);
7170 ConcurrentMarkSweepThread::acknowledge_yield_request();
7171 }
7172
7173 ConcurrentMarkSweepThread::synchronize(true);
7174 _bitMap->lock()->lock_without_safepoint_check();
7175 _collector->startTimer();
7176 }
7177
7178 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) {
7179 assert(_bitMap->isMarked(ptr), "expected bit to be set");
7180 assert(_markStack->isEmpty(),
7181 "should drain stack to limit stack usage");
7182 // convert ptr to an oop preparatory to scanning
7183 oop obj = oop(ptr);
7184 // Ignore mark word in verification below, since we
7185 // may be running concurrent with mutators.
7186 assert(obj->is_oop(true), "should be an oop");
7187 assert(_finger <= ptr, "_finger runneth ahead");
7188 // advance the finger to right end of this object
7189 _finger = ptr + obj->size();
7190 assert(_finger > ptr, "we just incremented it above");
7191 // On large heaps, it may take us some time to get through
7192 // the marking phase (especially if running iCMS). During
7193 // this time it's possible that a lot of mutations have
7194 // accumulated in the card table and the mod union table --
7195 // these mutation records are redundant until we have
7196 // actually traced into the corresponding card.
7197 // Here, we check whether advancing the finger would make
7198 // us cross into a new card, and if so clear corresponding
7199 // cards in the MUT (preclean them in the card-table in the
7200 // future).
7201
7202 DEBUG_ONLY(if (!_verifying) {)
7203 // The clean-on-enter optimization is disabled by default,
7204 // until we fix 6178663.
7205 if (CMSCleanOnEnter && (_finger > _threshold)) {
7206 // [_threshold, _finger) represents the interval
7207 // of cards to be cleared in MUT (or precleaned in card table).
7208 // The set of cards to be cleared is all those that overlap
7209 // with the interval [_threshold, _finger); note that
7210 // _threshold is always kept card-aligned but _finger isn't
7211 // always card-aligned.
7212 HeapWord* old_threshold = _threshold;
7213 assert(old_threshold == (HeapWord*)round_to(
7214 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7215 "_threshold should always be card-aligned");
7216 _threshold = (HeapWord*)round_to(
7217 (intptr_t)_finger, CardTableModRefBS::card_size);
7218 MemRegion mr(old_threshold, _threshold);
7219 assert(!mr.is_empty(), "Control point invariant");
7220 assert(_span.contains(mr), "Should clear within span");
7221 _mut->clear_range(mr);
7222 }
7223 DEBUG_ONLY(})
7224 // Note: the finger doesn't advance while we drain
7225 // the stack below.
7226 PushOrMarkClosure pushOrMarkClosure(_collector,
7227 _span, _bitMap, _markStack,
7228 _finger, this);
7229 bool res = _markStack->push(obj);
7230 assert(res, "Empty non-zero size stack should have space for single push");
7231 while (!_markStack->isEmpty()) {
7232 oop new_oop = _markStack->pop();
7233 // Skip verifying header mark word below because we are
7234 // running concurrent with mutators.
7235 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7236 // now scan this oop's oops
7237 new_oop->oop_iterate(&pushOrMarkClosure);
7238 do_yield_check();
7239 }
7240 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition");
7241 }
7242
7243 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task,
7244 CMSCollector* collector, MemRegion span,
7245 CMSBitMap* bit_map,
7246 OopTaskQueue* work_queue,
7247 CMSMarkStack* overflow_stack,
7248 bool should_yield):
7249 _collector(collector),
7250 _whole_span(collector->_span),
7251 _span(span),
7252 _bit_map(bit_map),
7253 _mut(&collector->_modUnionTable),
7254 _work_queue(work_queue),
7255 _overflow_stack(overflow_stack),
7256 _yield(should_yield),
7257 _skip_bits(0),
7258 _task(task)
7259 {
7260 assert(_work_queue->size() == 0, "work_queue should be empty");
7261 _finger = span.start();
7262 _threshold = _finger; // XXX Defer clear-on-enter optimization for now
7263 assert(_span.contains(_finger), "Out of bounds _finger?");
7264 }
7265
7266 // Should revisit to see if this should be restructured for
7267 // greater efficiency.
7268 bool Par_MarkFromRootsClosure::do_bit(size_t offset) {
7269 if (_skip_bits > 0) {
7270 _skip_bits--;
7271 return true;
7272 }
7273 // convert offset into a HeapWord*
7274 HeapWord* addr = _bit_map->startWord() + offset;
7275 assert(_bit_map->endWord() && addr < _bit_map->endWord(),
7276 "address out of range");
7277 assert(_bit_map->isMarked(addr), "tautology");
7278 if (_bit_map->isMarked(addr+1)) {
7279 // this is an allocated object that might not yet be initialized
7280 assert(_skip_bits == 0, "tautology");
7281 _skip_bits = 2; // skip next two marked bits ("Printezis-marks")
7282 oop p = oop(addr);
7283 if (p->klass_or_null() == NULL) {
7284 // in the case of Clean-on-Enter optimization, redirty card
7285 // and avoid clearing card by increasing the threshold.
7286 return true;
7287 }
7288 }
7289 scan_oops_in_oop(addr);
7290 return true;
7291 }
7292
7293 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) {
7294 assert(_bit_map->isMarked(ptr), "expected bit to be set");
7295 // Should we assert that our work queue is empty or
7296 // below some drain limit?
7297 assert(_work_queue->size() == 0,
7298 "should drain stack to limit stack usage");
7299 // convert ptr to an oop preparatory to scanning
7300 oop obj = oop(ptr);
7301 // Ignore mark word in verification below, since we
7302 // may be running concurrent with mutators.
7303 assert(obj->is_oop(true), "should be an oop");
7304 assert(_finger <= ptr, "_finger runneth ahead");
7305 // advance the finger to right end of this object
7306 _finger = ptr + obj->size();
7307 assert(_finger > ptr, "we just incremented it above");
7308 // On large heaps, it may take us some time to get through
7309 // the marking phase (especially if running iCMS). During
7310 // this time it's possible that a lot of mutations have
7311 // accumulated in the card table and the mod union table --
7312 // these mutation records are redundant until we have
7313 // actually traced into the corresponding card.
7314 // Here, we check whether advancing the finger would make
7315 // us cross into a new card, and if so clear corresponding
7316 // cards in the MUT (preclean them in the card-table in the
7317 // future).
7318
7319 // The clean-on-enter optimization is disabled by default,
7320 // until we fix 6178663.
7321 if (CMSCleanOnEnter && (_finger > _threshold)) {
7322 // [_threshold, _finger) represents the interval
7323 // of cards to be cleared in MUT (or precleaned in card table).
7324 // The set of cards to be cleared is all those that overlap
7325 // with the interval [_threshold, _finger); note that
7326 // _threshold is always kept card-aligned but _finger isn't
7327 // always card-aligned.
7328 HeapWord* old_threshold = _threshold;
7329 assert(old_threshold == (HeapWord*)round_to(
7330 (intptr_t)old_threshold, CardTableModRefBS::card_size),
7331 "_threshold should always be card-aligned");
7332 _threshold = (HeapWord*)round_to(
7333 (intptr_t)_finger, CardTableModRefBS::card_size);
7334 MemRegion mr(old_threshold, _threshold);
7335 assert(!mr.is_empty(), "Control point invariant");
7336 assert(_span.contains(mr), "Should clear within span"); // _whole_span ??
7337 _mut->clear_range(mr);
7338 }
7339
7340 // Note: the local finger doesn't advance while we drain
7341 // the stack below, but the global finger sure can and will.
7342 HeapWord** gfa = _task->global_finger_addr();
7343 Par_PushOrMarkClosure pushOrMarkClosure(_collector,
7344 _span, _bit_map,
7345 _work_queue,
7346 _overflow_stack,
7347 _finger,
7348 gfa, this);
7349 bool res = _work_queue->push(obj); // overflow could occur here
7350 assert(res, "Will hold once we use workqueues");
7351 while (true) {
7352 oop new_oop;
7353 if (!_work_queue->pop_local(new_oop)) {
7354 // We emptied our work_queue; check if there's stuff that can
7355 // be gotten from the overflow stack.
7356 if (CMSConcMarkingTask::get_work_from_overflow_stack(
7357 _overflow_stack, _work_queue)) {
7358 do_yield_check();
7359 continue;
7360 } else { // done
7361 break;
7362 }
7363 }
7364 // Skip verifying header mark word below because we are
7365 // running concurrent with mutators.
7366 assert(new_oop->is_oop(true), "Oops! expected to pop an oop");
7367 // now scan this oop's oops
7368 new_oop->oop_iterate(&pushOrMarkClosure);
7369 do_yield_check();
7370 }
7371 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition");
7372 }
7373
7374 // Yield in response to a request from VM Thread or
7375 // from mutators.
7376 void Par_MarkFromRootsClosure::do_yield_work() {
7377 assert(_task != NULL, "sanity");
7378 _task->yield();
7379 }
7380
7381 // A variant of the above used for verifying CMS marking work.
7382 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector,
7383 MemRegion span,
7384 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7385 CMSMarkStack* mark_stack):
7386 _collector(collector),
7387 _span(span),
7388 _verification_bm(verification_bm),
7389 _cms_bm(cms_bm),
7390 _mark_stack(mark_stack),
7391 _pam_verify_closure(collector, span, verification_bm, cms_bm,
7392 mark_stack)
7393 {
7394 assert(_mark_stack->isEmpty(), "stack should be empty");
7395 _finger = _verification_bm->startWord();
7396 assert(_collector->_restart_addr == NULL, "Sanity check");
7397 assert(_span.contains(_finger), "Out of bounds _finger?");
7398 }
7399
7400 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) {
7401 assert(_mark_stack->isEmpty(), "would cause duplicates on stack");
7402 assert(_span.contains(addr), "Out of bounds _finger?");
7403 _finger = addr;
7404 }
7405
7406 // Should revisit to see if this should be restructured for
7407 // greater efficiency.
7408 bool MarkFromRootsVerifyClosure::do_bit(size_t offset) {
7409 // convert offset into a HeapWord*
7410 HeapWord* addr = _verification_bm->startWord() + offset;
7411 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(),
7412 "address out of range");
7413 assert(_verification_bm->isMarked(addr), "tautology");
7414 assert(_cms_bm->isMarked(addr), "tautology");
7415
7416 assert(_mark_stack->isEmpty(),
7417 "should drain stack to limit stack usage");
7418 // convert addr to an oop preparatory to scanning
7419 oop obj = oop(addr);
7420 assert(obj->is_oop(), "should be an oop");
7421 assert(_finger <= addr, "_finger runneth ahead");
7422 // advance the finger to right end of this object
7423 _finger = addr + obj->size();
7424 assert(_finger > addr, "we just incremented it above");
7425 // Note: the finger doesn't advance while we drain
7426 // the stack below.
7427 bool res = _mark_stack->push(obj);
7428 assert(res, "Empty non-zero size stack should have space for single push");
7429 while (!_mark_stack->isEmpty()) {
7430 oop new_oop = _mark_stack->pop();
7431 assert(new_oop->is_oop(), "Oops! expected to pop an oop");
7432 // now scan this oop's oops
7433 new_oop->oop_iterate(&_pam_verify_closure);
7434 }
7435 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition");
7436 return true;
7437 }
7438
7439 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure(
7440 CMSCollector* collector, MemRegion span,
7441 CMSBitMap* verification_bm, CMSBitMap* cms_bm,
7442 CMSMarkStack* mark_stack):
7443 CMSOopClosure(collector->ref_processor()),
7444 _collector(collector),
7445 _span(span),
7446 _verification_bm(verification_bm),
7447 _cms_bm(cms_bm),
7448 _mark_stack(mark_stack)
7449 { }
7450
7451 void PushAndMarkVerifyClosure::do_oop(oop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7452 void PushAndMarkVerifyClosure::do_oop(narrowOop* p) { PushAndMarkVerifyClosure::do_oop_work(p); }
7453
7454 // Upon stack overflow, we discard (part of) the stack,
7455 // remembering the least address amongst those discarded
7456 // in CMSCollector's _restart_address.
7457 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) {
7458 // Remember the least grey address discarded
7459 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost);
7460 _collector->lower_restart_addr(ra);
7461 _mark_stack->reset(); // discard stack contents
7462 _mark_stack->expand(); // expand the stack if possible
7463 }
7464
7465 void PushAndMarkVerifyClosure::do_oop(oop obj) {
7466 assert(obj->is_oop_or_null(), "expected an oop or NULL");
7467 HeapWord* addr = (HeapWord*)obj;
7468 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) {
7469 // Oop lies in _span and isn't yet grey or black
7470 _verification_bm->mark(addr); // now grey
7471 if (!_cms_bm->isMarked(addr)) {
7472 oop(addr)->print();
7473 gclog_or_tty->print_cr(" (" INTPTR_FORMAT " should have been marked)",
7474 addr);
7475 fatal("... aborting");
7476 }
7477
7478 if (!_mark_stack->push(obj)) { // stack overflow
7479 if (PrintCMSStatistics != 0) {
7480 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7481 SIZE_FORMAT, _mark_stack->capacity());
7482 }
7483 assert(_mark_stack->isFull(), "Else push should have succeeded");
7484 handle_stack_overflow(addr);
7485 }
7486 // anything including and to the right of _finger
7487 // will be scanned as we iterate over the remainder of the
7488 // bit map
7489 }
7490 }
7491
7492 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector,
7493 MemRegion span,
7494 CMSBitMap* bitMap, CMSMarkStack* markStack,
7495 HeapWord* finger, MarkFromRootsClosure* parent) :
7496 CMSOopClosure(collector->ref_processor()),
7497 _collector(collector),
7498 _span(span),
7499 _bitMap(bitMap),
7500 _markStack(markStack),
7501 _finger(finger),
7502 _parent(parent)
7503 { }
7504
7505 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector,
7506 MemRegion span,
7507 CMSBitMap* bit_map,
7508 OopTaskQueue* work_queue,
7509 CMSMarkStack* overflow_stack,
7510 HeapWord* finger,
7511 HeapWord** global_finger_addr,
7512 Par_MarkFromRootsClosure* parent) :
7513 CMSOopClosure(collector->ref_processor()),
7514 _collector(collector),
7515 _whole_span(collector->_span),
7516 _span(span),
7517 _bit_map(bit_map),
7518 _work_queue(work_queue),
7519 _overflow_stack(overflow_stack),
7520 _finger(finger),
7521 _global_finger_addr(global_finger_addr),
7522 _parent(parent)
7523 { }
7524
7525 // Assumes thread-safe access by callers, who are
7526 // responsible for mutual exclusion.
7527 void CMSCollector::lower_restart_addr(HeapWord* low) {
7528 assert(_span.contains(low), "Out of bounds addr");
7529 if (_restart_addr == NULL) {
7530 _restart_addr = low;
7531 } else {
7532 _restart_addr = MIN2(_restart_addr, low);
7533 }
7534 }
7535
7536 // Upon stack overflow, we discard (part of) the stack,
7537 // remembering the least address amongst those discarded
7538 // in CMSCollector's _restart_address.
7539 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7540 // Remember the least grey address discarded
7541 HeapWord* ra = (HeapWord*)_markStack->least_value(lost);
7542 _collector->lower_restart_addr(ra);
7543 _markStack->reset(); // discard stack contents
7544 _markStack->expand(); // expand the stack if possible
7545 }
7546
7547 // Upon stack overflow, we discard (part of) the stack,
7548 // remembering the least address amongst those discarded
7549 // in CMSCollector's _restart_address.
7550 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) {
7551 // We need to do this under a mutex to prevent other
7552 // workers from interfering with the work done below.
7553 MutexLockerEx ml(_overflow_stack->par_lock(),
7554 Mutex::_no_safepoint_check_flag);
7555 // Remember the least grey address discarded
7556 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost);
7557 _collector->lower_restart_addr(ra);
7558 _overflow_stack->reset(); // discard stack contents
7559 _overflow_stack->expand(); // expand the stack if possible
7560 }
7561
7562 void CMKlassClosure::do_klass(Klass* k) {
7563 assert(_oop_closure != NULL, "Not initialized?");
7564 k->oops_do(_oop_closure);
7565 }
7566
7567 void PushOrMarkClosure::do_oop(oop obj) {
7568 // Ignore mark word because we are running concurrent with mutators.
7569 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7570 HeapWord* addr = (HeapWord*)obj;
7571 if (_span.contains(addr) && !_bitMap->isMarked(addr)) {
7572 // Oop lies in _span and isn't yet grey or black
7573 _bitMap->mark(addr); // now grey
7574 if (addr < _finger) {
7575 // the bit map iteration has already either passed, or
7576 // sampled, this bit in the bit map; we'll need to
7577 // use the marking stack to scan this oop's oops.
7578 bool simulate_overflow = false;
7579 NOT_PRODUCT(
7580 if (CMSMarkStackOverflowALot &&
7581 _collector->simulate_overflow()) {
7582 // simulate a stack overflow
7583 simulate_overflow = true;
7584 }
7585 )
7586 if (simulate_overflow || !_markStack->push(obj)) { // stack overflow
7587 if (PrintCMSStatistics != 0) {
7588 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7589 SIZE_FORMAT, _markStack->capacity());
7590 }
7591 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded");
7592 handle_stack_overflow(addr);
7593 }
7594 }
7595 // anything including and to the right of _finger
7596 // will be scanned as we iterate over the remainder of the
7597 // bit map
7598 do_yield_check();
7599 }
7600 }
7601
7602 void PushOrMarkClosure::do_oop(oop* p) { PushOrMarkClosure::do_oop_work(p); }
7603 void PushOrMarkClosure::do_oop(narrowOop* p) { PushOrMarkClosure::do_oop_work(p); }
7604
7605 void Par_PushOrMarkClosure::do_oop(oop obj) {
7606 // Ignore mark word because we are running concurrent with mutators.
7607 assert(obj->is_oop_or_null(true), "expected an oop or NULL");
7608 HeapWord* addr = (HeapWord*)obj;
7609 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) {
7610 // Oop lies in _span and isn't yet grey or black
7611 // We read the global_finger (volatile read) strictly after marking oop
7612 bool res = _bit_map->par_mark(addr); // now grey
7613 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr;
7614 // Should we push this marked oop on our stack?
7615 // -- if someone else marked it, nothing to do
7616 // -- if target oop is above global finger nothing to do
7617 // -- if target oop is in chunk and above local finger
7618 // then nothing to do
7619 // -- else push on work queue
7620 if ( !res // someone else marked it, they will deal with it
7621 || (addr >= *gfa) // will be scanned in a later task
7622 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk
7623 return;
7624 }
7625 // the bit map iteration has already either passed, or
7626 // sampled, this bit in the bit map; we'll need to
7627 // use the marking stack to scan this oop's oops.
7628 bool simulate_overflow = false;
7629 NOT_PRODUCT(
7630 if (CMSMarkStackOverflowALot &&
7631 _collector->simulate_overflow()) {
7632 // simulate a stack overflow
7633 simulate_overflow = true;
7634 }
7635 )
7636 if (simulate_overflow ||
7637 !(_work_queue->push(obj) || _overflow_stack->par_push(obj))) {
7638 // stack overflow
7639 if (PrintCMSStatistics != 0) {
7640 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at "
7641 SIZE_FORMAT, _overflow_stack->capacity());
7642 }
7643 // We cannot assert that the overflow stack is full because
7644 // it may have been emptied since.
7645 assert(simulate_overflow ||
7646 _work_queue->size() == _work_queue->max_elems(),
7647 "Else push should have succeeded");
7648 handle_stack_overflow(addr);
7649 }
7650 do_yield_check();
7651 }
7652 }
7653
7654 void Par_PushOrMarkClosure::do_oop(oop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7655 void Par_PushOrMarkClosure::do_oop(narrowOop* p) { Par_PushOrMarkClosure::do_oop_work(p); }
7656
7657 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector,
7658 MemRegion span,
7659 ReferenceProcessor* rp,
7660 CMSBitMap* bit_map,
7661 CMSBitMap* mod_union_table,
7662 CMSMarkStack* mark_stack,
7663 bool concurrent_precleaning):
7664 CMSOopClosure(rp),
7665 _collector(collector),
7666 _span(span),
7667 _bit_map(bit_map),
7668 _mod_union_table(mod_union_table),
7669 _mark_stack(mark_stack),
7670 _concurrent_precleaning(concurrent_precleaning)
7671 {
7672 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7673 }
7674
7675 // Grey object rescan during pre-cleaning and second checkpoint phases --
7676 // the non-parallel version (the parallel version appears further below.)
7677 void PushAndMarkClosure::do_oop(oop obj) {
7678 // Ignore mark word verification. If during concurrent precleaning,
7679 // the object monitor may be locked. If during the checkpoint
7680 // phases, the object may already have been reached by a different
7681 // path and may be at the end of the global overflow list (so
7682 // the mark word may be NULL).
7683 assert(obj->is_oop_or_null(true /* ignore mark word */),
7684 "expected an oop or NULL");
7685 HeapWord* addr = (HeapWord*)obj;
7686 // Check if oop points into the CMS generation
7687 // and is not marked
7688 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7689 // a white object ...
7690 _bit_map->mark(addr); // ... now grey
7691 // push on the marking stack (grey set)
7692 bool simulate_overflow = false;
7693 NOT_PRODUCT(
7694 if (CMSMarkStackOverflowALot &&
7695 _collector->simulate_overflow()) {
7696 // simulate a stack overflow
7697 simulate_overflow = true;
7698 }
7699 )
7700 if (simulate_overflow || !_mark_stack->push(obj)) {
7701 if (_concurrent_precleaning) {
7702 // During precleaning we can just dirty the appropriate card(s)
7703 // in the mod union table, thus ensuring that the object remains
7704 // in the grey set and continue. In the case of object arrays
7705 // we need to dirty all of the cards that the object spans,
7706 // since the rescan of object arrays will be limited to the
7707 // dirty cards.
7708 // Note that no one can be intefering with us in this action
7709 // of dirtying the mod union table, so no locking or atomics
7710 // are required.
7711 if (obj->is_objArray()) {
7712 size_t sz = obj->size();
7713 HeapWord* end_card_addr = (HeapWord*)round_to(
7714 (intptr_t)(addr+sz), CardTableModRefBS::card_size);
7715 MemRegion redirty_range = MemRegion(addr, end_card_addr);
7716 assert(!redirty_range.is_empty(), "Arithmetical tautology");
7717 _mod_union_table->mark_range(redirty_range);
7718 } else {
7719 _mod_union_table->mark(addr);
7720 }
7721 _collector->_ser_pmc_preclean_ovflw++;
7722 } else {
7723 // During the remark phase, we need to remember this oop
7724 // in the overflow list.
7725 _collector->push_on_overflow_list(obj);
7726 _collector->_ser_pmc_remark_ovflw++;
7727 }
7728 }
7729 }
7730 }
7731
7732 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector,
7733 MemRegion span,
7734 ReferenceProcessor* rp,
7735 CMSBitMap* bit_map,
7736 OopTaskQueue* work_queue):
7737 CMSOopClosure(rp),
7738 _collector(collector),
7739 _span(span),
7740 _bit_map(bit_map),
7741 _work_queue(work_queue)
7742 {
7743 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL");
7744 }
7745
7746 void PushAndMarkClosure::do_oop(oop* p) { PushAndMarkClosure::do_oop_work(p); }
7747 void PushAndMarkClosure::do_oop(narrowOop* p) { PushAndMarkClosure::do_oop_work(p); }
7748
7749 // Grey object rescan during second checkpoint phase --
7750 // the parallel version.
7751 void Par_PushAndMarkClosure::do_oop(oop obj) {
7752 // In the assert below, we ignore the mark word because
7753 // this oop may point to an already visited object that is
7754 // on the overflow stack (in which case the mark word has
7755 // been hijacked for chaining into the overflow stack --
7756 // if this is the last object in the overflow stack then
7757 // its mark word will be NULL). Because this object may
7758 // have been subsequently popped off the global overflow
7759 // stack, and the mark word possibly restored to the prototypical
7760 // value, by the time we get to examined this failing assert in
7761 // the debugger, is_oop_or_null(false) may subsequently start
7762 // to hold.
7763 assert(obj->is_oop_or_null(true),
7764 "expected an oop or NULL");
7765 HeapWord* addr = (HeapWord*)obj;
7766 // Check if oop points into the CMS generation
7767 // and is not marked
7768 if (_span.contains(addr) && !_bit_map->isMarked(addr)) {
7769 // a white object ...
7770 // If we manage to "claim" the object, by being the
7771 // first thread to mark it, then we push it on our
7772 // marking stack
7773 if (_bit_map->par_mark(addr)) { // ... now grey
7774 // push on work queue (grey set)
7775 bool simulate_overflow = false;
7776 NOT_PRODUCT(
7777 if (CMSMarkStackOverflowALot &&
7778 _collector->par_simulate_overflow()) {
7779 // simulate a stack overflow
7780 simulate_overflow = true;
7781 }
7782 )
7783 if (simulate_overflow || !_work_queue->push(obj)) {
7784 _collector->par_push_on_overflow_list(obj);
7785 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS
7786 }
7787 } // Else, some other thread got there first
7788 }
7789 }
7790
7791 void Par_PushAndMarkClosure::do_oop(oop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7792 void Par_PushAndMarkClosure::do_oop(narrowOop* p) { Par_PushAndMarkClosure::do_oop_work(p); }
7793
7794 void CMSPrecleanRefsYieldClosure::do_yield_work() {
7795 Mutex* bml = _collector->bitMapLock();
7796 assert_lock_strong(bml);
7797 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
7798 "CMS thread should hold CMS token");
7799
7800 bml->unlock();
7801 ConcurrentMarkSweepThread::desynchronize(true);
7802
7803 ConcurrentMarkSweepThread::acknowledge_yield_request();
7804
7805 _collector->stopTimer();
7806 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
7807 if (PrintCMSStatistics != 0) {
7808 _collector->incrementYields();
7809 }
7810 _collector->icms_wait();
7811
7812 // See the comment in coordinator_yield()
7813 for (unsigned i = 0; i < CMSYieldSleepCount &&
7814 ConcurrentMarkSweepThread::should_yield() &&
7815 !CMSCollector::foregroundGCIsActive(); ++i) {
7816 os::sleep(Thread::current(), 1, false);
7817 ConcurrentMarkSweepThread::acknowledge_yield_request();
7818 }
7819
7820 ConcurrentMarkSweepThread::synchronize(true);
7821 bml->lock();
7822
7823 _collector->startTimer();
7824 }
7825
7826 bool CMSPrecleanRefsYieldClosure::should_return() {
7827 if (ConcurrentMarkSweepThread::should_yield()) {
7828 do_yield_work();
7829 }
7830 return _collector->foregroundGCIsActive();
7831 }
7832
7833 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) {
7834 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0,
7835 "mr should be aligned to start at a card boundary");
7836 // We'd like to assert:
7837 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0,
7838 // "mr should be a range of cards");
7839 // However, that would be too strong in one case -- the last
7840 // partition ends at _unallocated_block which, in general, can be
7841 // an arbitrary boundary, not necessarily card aligned.
7842 if (PrintCMSStatistics != 0) {
7843 _num_dirty_cards +=
7844 mr.word_size()/CardTableModRefBS::card_size_in_words;
7845 }
7846 _space->object_iterate_mem(mr, &_scan_cl);
7847 }
7848
7849 SweepClosure::SweepClosure(CMSCollector* collector,
7850 ConcurrentMarkSweepGeneration* g,
7851 CMSBitMap* bitMap, bool should_yield) :
7852 _collector(collector),
7853 _g(g),
7854 _sp(g->cmsSpace()),
7855 _limit(_sp->sweep_limit()),
7856 _freelistLock(_sp->freelistLock()),
7857 _bitMap(bitMap),
7858 _yield(should_yield),
7859 _inFreeRange(false), // No free range at beginning of sweep
7860 _freeRangeInFreeLists(false), // No free range at beginning of sweep
7861 _lastFreeRangeCoalesced(false),
7862 _freeFinger(g->used_region().start())
7863 {
7864 NOT_PRODUCT(
7865 _numObjectsFreed = 0;
7866 _numWordsFreed = 0;
7867 _numObjectsLive = 0;
7868 _numWordsLive = 0;
7869 _numObjectsAlreadyFree = 0;
7870 _numWordsAlreadyFree = 0;
7871 _last_fc = NULL;
7872
7873 _sp->initializeIndexedFreeListArrayReturnedBytes();
7874 _sp->dictionary()->initialize_dict_returned_bytes();
7875 )
7876 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7877 "sweep _limit out of bounds");
7878 if (CMSTraceSweeper) {
7879 gclog_or_tty->print_cr("\n====================\nStarting new sweep with limit " PTR_FORMAT,
7880 _limit);
7881 }
7882 }
7883
7884 void SweepClosure::print_on(outputStream* st) const {
7885 tty->print_cr("_sp = [" PTR_FORMAT "," PTR_FORMAT ")",
7886 _sp->bottom(), _sp->end());
7887 tty->print_cr("_limit = " PTR_FORMAT, _limit);
7888 tty->print_cr("_freeFinger = " PTR_FORMAT, _freeFinger);
7889 NOT_PRODUCT(tty->print_cr("_last_fc = " PTR_FORMAT, _last_fc);)
7890 tty->print_cr("_inFreeRange = %d, _freeRangeInFreeLists = %d, _lastFreeRangeCoalesced = %d",
7891 _inFreeRange, _freeRangeInFreeLists, _lastFreeRangeCoalesced);
7892 }
7893
7894 #ifndef PRODUCT
7895 // Assertion checking only: no useful work in product mode --
7896 // however, if any of the flags below become product flags,
7897 // you may need to review this code to see if it needs to be
7898 // enabled in product mode.
7899 SweepClosure::~SweepClosure() {
7900 assert_lock_strong(_freelistLock);
7901 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
7902 "sweep _limit out of bounds");
7903 if (inFreeRange()) {
7904 warning("inFreeRange() should have been reset; dumping state of SweepClosure");
7905 print();
7906 ShouldNotReachHere();
7907 }
7908 if (Verbose && PrintGC) {
7909 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " SIZE_FORMAT " bytes",
7910 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord));
7911 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, "
7912 SIZE_FORMAT" bytes "
7913 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes",
7914 _numObjectsLive, _numWordsLive*sizeof(HeapWord),
7915 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord));
7916 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree)
7917 * sizeof(HeapWord);
7918 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes);
7919
7920 if (PrintCMSStatistics && CMSVerifyReturnedBytes) {
7921 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes();
7922 size_t dict_returned_bytes = _sp->dictionary()->sum_dict_returned_bytes();
7923 size_t returned_bytes = indexListReturnedBytes + dict_returned_bytes;
7924 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returned_bytes);
7925 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes",
7926 indexListReturnedBytes);
7927 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes",
7928 dict_returned_bytes);
7929 }
7930 }
7931 if (CMSTraceSweeper) {
7932 gclog_or_tty->print_cr("end of sweep with _limit = " PTR_FORMAT "\n================",
7933 _limit);
7934 }
7935 }
7936 #endif // PRODUCT
7937
7938 void SweepClosure::initialize_free_range(HeapWord* freeFinger,
7939 bool freeRangeInFreeLists) {
7940 if (CMSTraceSweeper) {
7941 gclog_or_tty->print("---- Start free range at 0x%x with free block (%d)\n",
7942 freeFinger, freeRangeInFreeLists);
7943 }
7944 assert(!inFreeRange(), "Trampling existing free range");
7945 set_inFreeRange(true);
7946 set_lastFreeRangeCoalesced(false);
7947
7948 set_freeFinger(freeFinger);
7949 set_freeRangeInFreeLists(freeRangeInFreeLists);
7950 if (CMSTestInFreeList) {
7951 if (freeRangeInFreeLists) {
7952 FreeChunk* fc = (FreeChunk*) freeFinger;
7953 assert(fc->is_free(), "A chunk on the free list should be free.");
7954 assert(fc->size() > 0, "Free range should have a size");
7955 assert(_sp->verify_chunk_in_free_list(fc), "Chunk is not in free lists");
7956 }
7957 }
7958 }
7959
7960 // Note that the sweeper runs concurrently with mutators. Thus,
7961 // it is possible for direct allocation in this generation to happen
7962 // in the middle of the sweep. Note that the sweeper also coalesces
7963 // contiguous free blocks. Thus, unless the sweeper and the allocator
7964 // synchronize appropriately freshly allocated blocks may get swept up.
7965 // This is accomplished by the sweeper locking the free lists while
7966 // it is sweeping. Thus blocks that are determined to be free are
7967 // indeed free. There is however one additional complication:
7968 // blocks that have been allocated since the final checkpoint and
7969 // mark, will not have been marked and so would be treated as
7970 // unreachable and swept up. To prevent this, the allocator marks
7971 // the bit map when allocating during the sweep phase. This leads,
7972 // however, to a further complication -- objects may have been allocated
7973 // but not yet initialized -- in the sense that the header isn't yet
7974 // installed. The sweeper can not then determine the size of the block
7975 // in order to skip over it. To deal with this case, we use a technique
7976 // (due to Printezis) to encode such uninitialized block sizes in the
7977 // bit map. Since the bit map uses a bit per every HeapWord, but the
7978 // CMS generation has a minimum object size of 3 HeapWords, it follows
7979 // that "normal marks" won't be adjacent in the bit map (there will
7980 // always be at least two 0 bits between successive 1 bits). We make use
7981 // of these "unused" bits to represent uninitialized blocks -- the bit
7982 // corresponding to the start of the uninitialized object and the next
7983 // bit are both set. Finally, a 1 bit marks the end of the object that
7984 // started with the two consecutive 1 bits to indicate its potentially
7985 // uninitialized state.
7986
7987 size_t SweepClosure::do_blk_careful(HeapWord* addr) {
7988 FreeChunk* fc = (FreeChunk*)addr;
7989 size_t res;
7990
7991 // Check if we are done sweeping. Below we check "addr >= _limit" rather
7992 // than "addr == _limit" because although _limit was a block boundary when
7993 // we started the sweep, it may no longer be one because heap expansion
7994 // may have caused us to coalesce the block ending at the address _limit
7995 // with a newly expanded chunk (this happens when _limit was set to the
7996 // previous _end of the space), so we may have stepped past _limit:
7997 // see the following Zeno-like trail of CRs 6977970, 7008136, 7042740.
7998 if (addr >= _limit) { // we have swept up to or past the limit: finish up
7999 assert(_limit >= _sp->bottom() && _limit <= _sp->end(),
8000 "sweep _limit out of bounds");
8001 assert(addr < _sp->end(), "addr out of bounds");
8002 // Flush any free range we might be holding as a single
8003 // coalesced chunk to the appropriate free list.
8004 if (inFreeRange()) {
8005 assert(freeFinger() >= _sp->bottom() && freeFinger() < _limit,
8006 err_msg("freeFinger() " PTR_FORMAT" is out-of-bounds", freeFinger()));
8007 flush_cur_free_chunk(freeFinger(),
8008 pointer_delta(addr, freeFinger()));
8009 if (CMSTraceSweeper) {
8010 gclog_or_tty->print("Sweep: last chunk: ");
8011 gclog_or_tty->print("put_free_blk 0x%x ("SIZE_FORMAT") "
8012 "[coalesced:"SIZE_FORMAT"]\n",
8013 freeFinger(), pointer_delta(addr, freeFinger()),
8014 lastFreeRangeCoalesced());
8015 }
8016 }
8017
8018 // help the iterator loop finish
8019 return pointer_delta(_sp->end(), addr);
8020 }
8021
8022 assert(addr < _limit, "sweep invariant");
8023 // check if we should yield
8024 do_yield_check(addr);
8025 if (fc->is_free()) {
8026 // Chunk that is already free
8027 res = fc->size();
8028 do_already_free_chunk(fc);
8029 debug_only(_sp->verifyFreeLists());
8030 // If we flush the chunk at hand in lookahead_and_flush()
8031 // and it's coalesced with a preceding chunk, then the
8032 // process of "mangling" the payload of the coalesced block
8033 // will cause erasure of the size information from the
8034 // (erstwhile) header of all the coalesced blocks but the
8035 // first, so the first disjunct in the assert will not hold
8036 // in that specific case (in which case the second disjunct
8037 // will hold).
8038 assert(res == fc->size() || ((HeapWord*)fc) + res >= _limit,
8039 "Otherwise the size info doesn't change at this step");
8040 NOT_PRODUCT(
8041 _numObjectsAlreadyFree++;
8042 _numWordsAlreadyFree += res;
8043 )
8044 NOT_PRODUCT(_last_fc = fc;)
8045 } else if (!_bitMap->isMarked(addr)) {
8046 // Chunk is fresh garbage
8047 res = do_garbage_chunk(fc);
8048 debug_only(_sp->verifyFreeLists());
8049 NOT_PRODUCT(
8050 _numObjectsFreed++;
8051 _numWordsFreed += res;
8052 )
8053 } else {
8054 // Chunk that is alive.
8055 res = do_live_chunk(fc);
8056 debug_only(_sp->verifyFreeLists());
8057 NOT_PRODUCT(
8058 _numObjectsLive++;
8059 _numWordsLive += res;
8060 )
8061 }
8062 return res;
8063 }
8064
8065 // For the smart allocation, record following
8066 // split deaths - a free chunk is removed from its free list because
8067 // it is being split into two or more chunks.
8068 // split birth - a free chunk is being added to its free list because
8069 // a larger free chunk has been split and resulted in this free chunk.
8070 // coal death - a free chunk is being removed from its free list because
8071 // it is being coalesced into a large free chunk.
8072 // coal birth - a free chunk is being added to its free list because
8073 // it was created when two or more free chunks where coalesced into
8074 // this free chunk.
8075 //
8076 // These statistics are used to determine the desired number of free
8077 // chunks of a given size. The desired number is chosen to be relative
8078 // to the end of a CMS sweep. The desired number at the end of a sweep
8079 // is the
8080 // count-at-end-of-previous-sweep (an amount that was enough)
8081 // - count-at-beginning-of-current-sweep (the excess)
8082 // + split-births (gains in this size during interval)
8083 // - split-deaths (demands on this size during interval)
8084 // where the interval is from the end of one sweep to the end of the
8085 // next.
8086 //
8087 // When sweeping the sweeper maintains an accumulated chunk which is
8088 // the chunk that is made up of chunks that have been coalesced. That
8089 // will be termed the left-hand chunk. A new chunk of garbage that
8090 // is being considered for coalescing will be referred to as the
8091 // right-hand chunk.
8092 //
8093 // When making a decision on whether to coalesce a right-hand chunk with
8094 // the current left-hand chunk, the current count vs. the desired count
8095 // of the left-hand chunk is considered. Also if the right-hand chunk
8096 // is near the large chunk at the end of the heap (see
8097 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the
8098 // left-hand chunk is coalesced.
8099 //
8100 // When making a decision about whether to split a chunk, the desired count
8101 // vs. the current count of the candidate to be split is also considered.
8102 // If the candidate is underpopulated (currently fewer chunks than desired)
8103 // a chunk of an overpopulated (currently more chunks than desired) size may
8104 // be chosen. The "hint" associated with a free list, if non-null, points
8105 // to a free list which may be overpopulated.
8106 //
8107
8108 void SweepClosure::do_already_free_chunk(FreeChunk* fc) {
8109 const size_t size = fc->size();
8110 // Chunks that cannot be coalesced are not in the
8111 // free lists.
8112 if (CMSTestInFreeList && !fc->cantCoalesce()) {
8113 assert(_sp->verify_chunk_in_free_list(fc),
8114 "free chunk should be in free lists");
8115 }
8116 // a chunk that is already free, should not have been
8117 // marked in the bit map
8118 HeapWord* const addr = (HeapWord*) fc;
8119 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked");
8120 // Verify that the bit map has no bits marked between
8121 // addr and purported end of this block.
8122 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8123
8124 // Some chunks cannot be coalesced under any circumstances.
8125 // See the definition of cantCoalesce().
8126 if (!fc->cantCoalesce()) {
8127 // This chunk can potentially be coalesced.
8128 if (_sp->adaptive_freelists()) {
8129 // All the work is done in
8130 do_post_free_or_garbage_chunk(fc, size);
8131 } else { // Not adaptive free lists
8132 // this is a free chunk that can potentially be coalesced by the sweeper;
8133 if (!inFreeRange()) {
8134 // if the next chunk is a free block that can't be coalesced
8135 // it doesn't make sense to remove this chunk from the free lists
8136 FreeChunk* nextChunk = (FreeChunk*)(addr + size);
8137 assert((HeapWord*)nextChunk <= _sp->end(), "Chunk size out of bounds?");
8138 if ((HeapWord*)nextChunk < _sp->end() && // There is another free chunk to the right ...
8139 nextChunk->is_free() && // ... which is free...
8140 nextChunk->cantCoalesce()) { // ... but can't be coalesced
8141 // nothing to do
8142 } else {
8143 // Potentially the start of a new free range:
8144 // Don't eagerly remove it from the free lists.
8145 // No need to remove it if it will just be put
8146 // back again. (Also from a pragmatic point of view
8147 // if it is a free block in a region that is beyond
8148 // any allocated blocks, an assertion will fail)
8149 // Remember the start of a free run.
8150 initialize_free_range(addr, true);
8151 // end - can coalesce with next chunk
8152 }
8153 } else {
8154 // the midst of a free range, we are coalescing
8155 print_free_block_coalesced(fc);
8156 if (CMSTraceSweeper) {
8157 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size);
8158 }
8159 // remove it from the free lists
8160 _sp->removeFreeChunkFromFreeLists(fc);
8161 set_lastFreeRangeCoalesced(true);
8162 // If the chunk is being coalesced and the current free range is
8163 // in the free lists, remove the current free range so that it
8164 // will be returned to the free lists in its entirety - all
8165 // the coalesced pieces included.
8166 if (freeRangeInFreeLists()) {
8167 FreeChunk* ffc = (FreeChunk*) freeFinger();
8168 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8169 "Size of free range is inconsistent with chunk size.");
8170 if (CMSTestInFreeList) {
8171 assert(_sp->verify_chunk_in_free_list(ffc),
8172 "free range is not in free lists");
8173 }
8174 _sp->removeFreeChunkFromFreeLists(ffc);
8175 set_freeRangeInFreeLists(false);
8176 }
8177 }
8178 }
8179 // Note that if the chunk is not coalescable (the else arm
8180 // below), we unconditionally flush, without needing to do
8181 // a "lookahead," as we do below.
8182 if (inFreeRange()) lookahead_and_flush(fc, size);
8183 } else {
8184 // Code path common to both original and adaptive free lists.
8185
8186 // cant coalesce with previous block; this should be treated
8187 // as the end of a free run if any
8188 if (inFreeRange()) {
8189 // we kicked some butt; time to pick up the garbage
8190 assert(freeFinger() < addr, "freeFinger points too high");
8191 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8192 }
8193 // else, nothing to do, just continue
8194 }
8195 }
8196
8197 size_t SweepClosure::do_garbage_chunk(FreeChunk* fc) {
8198 // This is a chunk of garbage. It is not in any free list.
8199 // Add it to a free list or let it possibly be coalesced into
8200 // a larger chunk.
8201 HeapWord* const addr = (HeapWord*) fc;
8202 const size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8203
8204 if (_sp->adaptive_freelists()) {
8205 // Verify that the bit map has no bits marked between
8206 // addr and purported end of just dead object.
8207 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8208
8209 do_post_free_or_garbage_chunk(fc, size);
8210 } else {
8211 if (!inFreeRange()) {
8212 // start of a new free range
8213 assert(size > 0, "A free range should have a size");
8214 initialize_free_range(addr, false);
8215 } else {
8216 // this will be swept up when we hit the end of the
8217 // free range
8218 if (CMSTraceSweeper) {
8219 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size);
8220 }
8221 // If the chunk is being coalesced and the current free range is
8222 // in the free lists, remove the current free range so that it
8223 // will be returned to the free lists in its entirety - all
8224 // the coalesced pieces included.
8225 if (freeRangeInFreeLists()) {
8226 FreeChunk* ffc = (FreeChunk*)freeFinger();
8227 assert(ffc->size() == pointer_delta(addr, freeFinger()),
8228 "Size of free range is inconsistent with chunk size.");
8229 if (CMSTestInFreeList) {
8230 assert(_sp->verify_chunk_in_free_list(ffc),
8231 "free range is not in free lists");
8232 }
8233 _sp->removeFreeChunkFromFreeLists(ffc);
8234 set_freeRangeInFreeLists(false);
8235 }
8236 set_lastFreeRangeCoalesced(true);
8237 }
8238 // this will be swept up when we hit the end of the free range
8239
8240 // Verify that the bit map has no bits marked between
8241 // addr and purported end of just dead object.
8242 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size);
8243 }
8244 assert(_limit >= addr + size,
8245 "A freshly garbage chunk can't possibly straddle over _limit");
8246 if (inFreeRange()) lookahead_and_flush(fc, size);
8247 return size;
8248 }
8249
8250 size_t SweepClosure::do_live_chunk(FreeChunk* fc) {
8251 HeapWord* addr = (HeapWord*) fc;
8252 // The sweeper has just found a live object. Return any accumulated
8253 // left hand chunk to the free lists.
8254 if (inFreeRange()) {
8255 assert(freeFinger() < addr, "freeFinger points too high");
8256 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8257 }
8258
8259 // This object is live: we'd normally expect this to be
8260 // an oop, and like to assert the following:
8261 // assert(oop(addr)->is_oop(), "live block should be an oop");
8262 // However, as we commented above, this may be an object whose
8263 // header hasn't yet been initialized.
8264 size_t size;
8265 assert(_bitMap->isMarked(addr), "Tautology for this control point");
8266 if (_bitMap->isMarked(addr + 1)) {
8267 // Determine the size from the bit map, rather than trying to
8268 // compute it from the object header.
8269 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2);
8270 size = pointer_delta(nextOneAddr + 1, addr);
8271 assert(size == CompactibleFreeListSpace::adjustObjectSize(size),
8272 "alignment problem");
8273
8274 #ifdef DEBUG
8275 if (oop(addr)->klass_or_null() != NULL) {
8276 // Ignore mark word because we are running concurrent with mutators
8277 assert(oop(addr)->is_oop(true), "live block should be an oop");
8278 assert(size ==
8279 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()),
8280 "P-mark and computed size do not agree");
8281 }
8282 #endif
8283
8284 } else {
8285 // This should be an initialized object that's alive.
8286 assert(oop(addr)->klass_or_null() != NULL,
8287 "Should be an initialized object");
8288 // Ignore mark word because we are running concurrent with mutators
8289 assert(oop(addr)->is_oop(true), "live block should be an oop");
8290 // Verify that the bit map has no bits marked between
8291 // addr and purported end of this block.
8292 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size());
8293 assert(size >= 3, "Necessary for Printezis marks to work");
8294 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point");
8295 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);)
8296 }
8297 return size;
8298 }
8299
8300 void SweepClosure::do_post_free_or_garbage_chunk(FreeChunk* fc,
8301 size_t chunkSize) {
8302 // do_post_free_or_garbage_chunk() should only be called in the case
8303 // of the adaptive free list allocator.
8304 const bool fcInFreeLists = fc->is_free();
8305 assert(_sp->adaptive_freelists(), "Should only be used in this case.");
8306 assert((HeapWord*)fc <= _limit, "sweep invariant");
8307 if (CMSTestInFreeList && fcInFreeLists) {
8308 assert(_sp->verify_chunk_in_free_list(fc), "free chunk is not in free lists");
8309 }
8310
8311 if (CMSTraceSweeper) {
8312 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize);
8313 }
8314
8315 HeapWord* const fc_addr = (HeapWord*) fc;
8316
8317 bool coalesce;
8318 const size_t left = pointer_delta(fc_addr, freeFinger());
8319 const size_t right = chunkSize;
8320 switch (FLSCoalescePolicy) {
8321 // numeric value forms a coalition aggressiveness metric
8322 case 0: { // never coalesce
8323 coalesce = false;
8324 break;
8325 }
8326 case 1: { // coalesce if left & right chunks on overpopulated lists
8327 coalesce = _sp->coalOverPopulated(left) &&
8328 _sp->coalOverPopulated(right);
8329 break;
8330 }
8331 case 2: { // coalesce if left chunk on overpopulated list (default)
8332 coalesce = _sp->coalOverPopulated(left);
8333 break;
8334 }
8335 case 3: { // coalesce if left OR right chunk on overpopulated list
8336 coalesce = _sp->coalOverPopulated(left) ||
8337 _sp->coalOverPopulated(right);
8338 break;
8339 }
8340 case 4: { // always coalesce
8341 coalesce = true;
8342 break;
8343 }
8344 default:
8345 ShouldNotReachHere();
8346 }
8347
8348 // Should the current free range be coalesced?
8349 // If the chunk is in a free range and either we decided to coalesce above
8350 // or the chunk is near the large block at the end of the heap
8351 // (isNearLargestChunk() returns true), then coalesce this chunk.
8352 const bool doCoalesce = inFreeRange()
8353 && (coalesce || _g->isNearLargestChunk(fc_addr));
8354 if (doCoalesce) {
8355 // Coalesce the current free range on the left with the new
8356 // chunk on the right. If either is on a free list,
8357 // it must be removed from the list and stashed in the closure.
8358 if (freeRangeInFreeLists()) {
8359 FreeChunk* const ffc = (FreeChunk*)freeFinger();
8360 assert(ffc->size() == pointer_delta(fc_addr, freeFinger()),
8361 "Size of free range is inconsistent with chunk size.");
8362 if (CMSTestInFreeList) {
8363 assert(_sp->verify_chunk_in_free_list(ffc),
8364 "Chunk is not in free lists");
8365 }
8366 _sp->coalDeath(ffc->size());
8367 _sp->removeFreeChunkFromFreeLists(ffc);
8368 set_freeRangeInFreeLists(false);
8369 }
8370 if (fcInFreeLists) {
8371 _sp->coalDeath(chunkSize);
8372 assert(fc->size() == chunkSize,
8373 "The chunk has the wrong size or is not in the free lists");
8374 _sp->removeFreeChunkFromFreeLists(fc);
8375 }
8376 set_lastFreeRangeCoalesced(true);
8377 print_free_block_coalesced(fc);
8378 } else { // not in a free range and/or should not coalesce
8379 // Return the current free range and start a new one.
8380 if (inFreeRange()) {
8381 // In a free range but cannot coalesce with the right hand chunk.
8382 // Put the current free range into the free lists.
8383 flush_cur_free_chunk(freeFinger(),
8384 pointer_delta(fc_addr, freeFinger()));
8385 }
8386 // Set up for new free range. Pass along whether the right hand
8387 // chunk is in the free lists.
8388 initialize_free_range((HeapWord*)fc, fcInFreeLists);
8389 }
8390 }
8391
8392 // Lookahead flush:
8393 // If we are tracking a free range, and this is the last chunk that
8394 // we'll look at because its end crosses past _limit, we'll preemptively
8395 // flush it along with any free range we may be holding on to. Note that
8396 // this can be the case only for an already free or freshly garbage
8397 // chunk. If this block is an object, it can never straddle
8398 // over _limit. The "straddling" occurs when _limit is set at
8399 // the previous end of the space when this cycle started, and
8400 // a subsequent heap expansion caused the previously co-terminal
8401 // free block to be coalesced with the newly expanded portion,
8402 // thus rendering _limit a non-block-boundary making it dangerous
8403 // for the sweeper to step over and examine.
8404 void SweepClosure::lookahead_and_flush(FreeChunk* fc, size_t chunk_size) {
8405 assert(inFreeRange(), "Should only be called if currently in a free range.");
8406 HeapWord* const eob = ((HeapWord*)fc) + chunk_size;
8407 assert(_sp->used_region().contains(eob - 1),
8408 err_msg("eob = " PTR_FORMAT " out of bounds wrt _sp = [" PTR_FORMAT "," PTR_FORMAT ")"
8409 " when examining fc = " PTR_FORMAT "(" SIZE_FORMAT ")",
8410 _limit, _sp->bottom(), _sp->end(), fc, chunk_size));
8411 if (eob >= _limit) {
8412 assert(eob == _limit || fc->is_free(), "Only a free chunk should allow us to cross over the limit");
8413 if (CMSTraceSweeper) {
8414 gclog_or_tty->print_cr("_limit " PTR_FORMAT " reached or crossed by block "
8415 "[" PTR_FORMAT "," PTR_FORMAT ") in space "
8416 "[" PTR_FORMAT "," PTR_FORMAT ")",
8417 _limit, fc, eob, _sp->bottom(), _sp->end());
8418 }
8419 // Return the storage we are tracking back into the free lists.
8420 if (CMSTraceSweeper) {
8421 gclog_or_tty->print_cr("Flushing ... ");
8422 }
8423 assert(freeFinger() < eob, "Error");
8424 flush_cur_free_chunk( freeFinger(), pointer_delta(eob, freeFinger()));
8425 }
8426 }
8427
8428 void SweepClosure::flush_cur_free_chunk(HeapWord* chunk, size_t size) {
8429 assert(inFreeRange(), "Should only be called if currently in a free range.");
8430 assert(size > 0,
8431 "A zero sized chunk cannot be added to the free lists.");
8432 if (!freeRangeInFreeLists()) {
8433 if (CMSTestInFreeList) {
8434 FreeChunk* fc = (FreeChunk*) chunk;
8435 fc->set_size(size);
8436 assert(!_sp->verify_chunk_in_free_list(fc),
8437 "chunk should not be in free lists yet");
8438 }
8439 if (CMSTraceSweeper) {
8440 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists",
8441 chunk, size);
8442 }
8443 // A new free range is going to be starting. The current
8444 // free range has not been added to the free lists yet or
8445 // was removed so add it back.
8446 // If the current free range was coalesced, then the death
8447 // of the free range was recorded. Record a birth now.
8448 if (lastFreeRangeCoalesced()) {
8449 _sp->coalBirth(size);
8450 }
8451 _sp->addChunkAndRepairOffsetTable(chunk, size,
8452 lastFreeRangeCoalesced());
8453 } else if (CMSTraceSweeper) {
8454 gclog_or_tty->print_cr("Already in free list: nothing to flush");
8455 }
8456 set_inFreeRange(false);
8457 set_freeRangeInFreeLists(false);
8458 }
8459
8460 // We take a break if we've been at this for a while,
8461 // so as to avoid monopolizing the locks involved.
8462 void SweepClosure::do_yield_work(HeapWord* addr) {
8463 // Return current free chunk being used for coalescing (if any)
8464 // to the appropriate freelist. After yielding, the next
8465 // free block encountered will start a coalescing range of
8466 // free blocks. If the next free block is adjacent to the
8467 // chunk just flushed, they will need to wait for the next
8468 // sweep to be coalesced.
8469 if (inFreeRange()) {
8470 flush_cur_free_chunk(freeFinger(), pointer_delta(addr, freeFinger()));
8471 }
8472
8473 // First give up the locks, then yield, then re-lock.
8474 // We should probably use a constructor/destructor idiom to
8475 // do this unlock/lock or modify the MutexUnlocker class to
8476 // serve our purpose. XXX
8477 assert_lock_strong(_bitMap->lock());
8478 assert_lock_strong(_freelistLock);
8479 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(),
8480 "CMS thread should hold CMS token");
8481 _bitMap->lock()->unlock();
8482 _freelistLock->unlock();
8483 ConcurrentMarkSweepThread::desynchronize(true);
8484 ConcurrentMarkSweepThread::acknowledge_yield_request();
8485 _collector->stopTimer();
8486 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr());
8487 if (PrintCMSStatistics != 0) {
8488 _collector->incrementYields();
8489 }
8490 _collector->icms_wait();
8491
8492 // See the comment in coordinator_yield()
8493 for (unsigned i = 0; i < CMSYieldSleepCount &&
8494 ConcurrentMarkSweepThread::should_yield() &&
8495 !CMSCollector::foregroundGCIsActive(); ++i) {
8496 os::sleep(Thread::current(), 1, false);
8497 ConcurrentMarkSweepThread::acknowledge_yield_request();
8498 }
8499
8500 ConcurrentMarkSweepThread::synchronize(true);
8501 _freelistLock->lock();
8502 _bitMap->lock()->lock_without_safepoint_check();
8503 _collector->startTimer();
8504 }
8505
8506 #ifndef PRODUCT
8507 // This is actually very useful in a product build if it can
8508 // be called from the debugger. Compile it into the product
8509 // as needed.
8510 bool debug_verify_chunk_in_free_list(FreeChunk* fc) {
8511 return debug_cms_space->verify_chunk_in_free_list(fc);
8512 }
8513 #endif
8514
8515 void SweepClosure::print_free_block_coalesced(FreeChunk* fc) const {
8516 if (CMSTraceSweeper) {
8517 gclog_or_tty->print_cr("Sweep:coal_free_blk " PTR_FORMAT " (" SIZE_FORMAT ")",
8518 fc, fc->size());
8519 }
8520 }
8521
8522 // CMSIsAliveClosure
8523 bool CMSIsAliveClosure::do_object_b(oop obj) {
8524 HeapWord* addr = (HeapWord*)obj;
8525 return addr != NULL &&
8526 (!_span.contains(addr) || _bit_map->isMarked(addr));
8527 }
8528
8529
8530 CMSKeepAliveClosure::CMSKeepAliveClosure( CMSCollector* collector,
8531 MemRegion span,
8532 CMSBitMap* bit_map, CMSMarkStack* mark_stack,
8533 bool cpc):
8534 _collector(collector),
8535 _span(span),
8536 _bit_map(bit_map),
8537 _mark_stack(mark_stack),
8538 _concurrent_precleaning(cpc) {
8539 assert(!_span.is_empty(), "Empty span could spell trouble");
8540 }
8541
8542
8543 // CMSKeepAliveClosure: the serial version
8544 void CMSKeepAliveClosure::do_oop(oop obj) {
8545 HeapWord* addr = (HeapWord*)obj;
8546 if (_span.contains(addr) &&
8547 !_bit_map->isMarked(addr)) {
8548 _bit_map->mark(addr);
8549 bool simulate_overflow = false;
8550 NOT_PRODUCT(
8551 if (CMSMarkStackOverflowALot &&
8552 _collector->simulate_overflow()) {
8553 // simulate a stack overflow
8554 simulate_overflow = true;
8555 }
8556 )
8557 if (simulate_overflow || !_mark_stack->push(obj)) {
8558 if (_concurrent_precleaning) {
8559 // We dirty the overflown object and let the remark
8560 // phase deal with it.
8561 assert(_collector->overflow_list_is_empty(), "Error");
8562 // In the case of object arrays, we need to dirty all of
8563 // the cards that the object spans. No locking or atomics
8564 // are needed since no one else can be mutating the mod union
8565 // table.
8566 if (obj->is_objArray()) {
8567 size_t sz = obj->size();
8568 HeapWord* end_card_addr =
8569 (HeapWord*)round_to((intptr_t)(addr+sz), CardTableModRefBS::card_size);
8570 MemRegion redirty_range = MemRegion(addr, end_card_addr);
8571 assert(!redirty_range.is_empty(), "Arithmetical tautology");
8572 _collector->_modUnionTable.mark_range(redirty_range);
8573 } else {
8574 _collector->_modUnionTable.mark(addr);
8575 }
8576 _collector->_ser_kac_preclean_ovflw++;
8577 } else {
8578 _collector->push_on_overflow_list(obj);
8579 _collector->_ser_kac_ovflw++;
8580 }
8581 }
8582 }
8583 }
8584
8585 void CMSKeepAliveClosure::do_oop(oop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8586 void CMSKeepAliveClosure::do_oop(narrowOop* p) { CMSKeepAliveClosure::do_oop_work(p); }
8587
8588 // CMSParKeepAliveClosure: a parallel version of the above.
8589 // The work queues are private to each closure (thread),
8590 // but (may be) available for stealing by other threads.
8591 void CMSParKeepAliveClosure::do_oop(oop obj) {
8592 HeapWord* addr = (HeapWord*)obj;
8593 if (_span.contains(addr) &&
8594 !_bit_map->isMarked(addr)) {
8595 // In general, during recursive tracing, several threads
8596 // may be concurrently getting here; the first one to
8597 // "tag" it, claims it.
8598 if (_bit_map->par_mark(addr)) {
8599 bool res = _work_queue->push(obj);
8600 assert(res, "Low water mark should be much less than capacity");
8601 // Do a recursive trim in the hope that this will keep
8602 // stack usage lower, but leave some oops for potential stealers
8603 trim_queue(_low_water_mark);
8604 } // Else, another thread got there first
8605 }
8606 }
8607
8608 void CMSParKeepAliveClosure::do_oop(oop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8609 void CMSParKeepAliveClosure::do_oop(narrowOop* p) { CMSParKeepAliveClosure::do_oop_work(p); }
8610
8611 void CMSParKeepAliveClosure::trim_queue(uint max) {
8612 while (_work_queue->size() > max) {
8613 oop new_oop;
8614 if (_work_queue->pop_local(new_oop)) {
8615 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop");
8616 assert(_bit_map->isMarked((HeapWord*)new_oop),
8617 "no white objects on this stack!");
8618 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8619 // iterate over the oops in this oop, marking and pushing
8620 // the ones in CMS heap (i.e. in _span).
8621 new_oop->oop_iterate(&_mark_and_push);
8622 }
8623 }
8624 }
8625
8626 CMSInnerParMarkAndPushClosure::CMSInnerParMarkAndPushClosure(
8627 CMSCollector* collector,
8628 MemRegion span, CMSBitMap* bit_map,
8629 OopTaskQueue* work_queue):
8630 _collector(collector),
8631 _span(span),
8632 _bit_map(bit_map),
8633 _work_queue(work_queue) { }
8634
8635 void CMSInnerParMarkAndPushClosure::do_oop(oop obj) {
8636 HeapWord* addr = (HeapWord*)obj;
8637 if (_span.contains(addr) &&
8638 !_bit_map->isMarked(addr)) {
8639 if (_bit_map->par_mark(addr)) {
8640 bool simulate_overflow = false;
8641 NOT_PRODUCT(
8642 if (CMSMarkStackOverflowALot &&
8643 _collector->par_simulate_overflow()) {
8644 // simulate a stack overflow
8645 simulate_overflow = true;
8646 }
8647 )
8648 if (simulate_overflow || !_work_queue->push(obj)) {
8649 _collector->par_push_on_overflow_list(obj);
8650 _collector->_par_kac_ovflw++;
8651 }
8652 } // Else another thread got there already
8653 }
8654 }
8655
8656 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8657 void CMSInnerParMarkAndPushClosure::do_oop(narrowOop* p) { CMSInnerParMarkAndPushClosure::do_oop_work(p); }
8658
8659 //////////////////////////////////////////////////////////////////
8660 // CMSExpansionCause /////////////////////////////
8661 //////////////////////////////////////////////////////////////////
8662 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) {
8663 switch (cause) {
8664 case _no_expansion:
8665 return "No expansion";
8666 case _satisfy_free_ratio:
8667 return "Free ratio";
8668 case _satisfy_promotion:
8669 return "Satisfy promotion";
8670 case _satisfy_allocation:
8671 return "allocation";
8672 case _allocate_par_lab:
8673 return "Par LAB";
8674 case _allocate_par_spooling_space:
8675 return "Par Spooling Space";
8676 case _adaptive_size_policy:
8677 return "Ergonomics";
8678 default:
8679 return "unknown";
8680 }
8681 }
8682
8683 void CMSDrainMarkingStackClosure::do_void() {
8684 // the max number to take from overflow list at a time
8685 const size_t num = _mark_stack->capacity()/4;
8686 assert(!_concurrent_precleaning || _collector->overflow_list_is_empty(),
8687 "Overflow list should be NULL during concurrent phases");
8688 while (!_mark_stack->isEmpty() ||
8689 // if stack is empty, check the overflow list
8690 _collector->take_from_overflow_list(num, _mark_stack)) {
8691 oop obj = _mark_stack->pop();
8692 HeapWord* addr = (HeapWord*)obj;
8693 assert(_span.contains(addr), "Should be within span");
8694 assert(_bit_map->isMarked(addr), "Should be marked");
8695 assert(obj->is_oop(), "Should be an oop");
8696 obj->oop_iterate(_keep_alive);
8697 }
8698 }
8699
8700 void CMSParDrainMarkingStackClosure::do_void() {
8701 // drain queue
8702 trim_queue(0);
8703 }
8704
8705 // Trim our work_queue so its length is below max at return
8706 void CMSParDrainMarkingStackClosure::trim_queue(uint max) {
8707 while (_work_queue->size() > max) {
8708 oop new_oop;
8709 if (_work_queue->pop_local(new_oop)) {
8710 assert(new_oop->is_oop(), "Expected an oop");
8711 assert(_bit_map->isMarked((HeapWord*)new_oop),
8712 "no white objects on this stack!");
8713 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop");
8714 // iterate over the oops in this oop, marking and pushing
8715 // the ones in CMS heap (i.e. in _span).
8716 new_oop->oop_iterate(&_mark_and_push);
8717 }
8718 }
8719 }
8720
8721 ////////////////////////////////////////////////////////////////////
8722 // Support for Marking Stack Overflow list handling and related code
8723 ////////////////////////////////////////////////////////////////////
8724 // Much of the following code is similar in shape and spirit to the
8725 // code used in ParNewGC. We should try and share that code
8726 // as much as possible in the future.
8727
8728 #ifndef PRODUCT
8729 // Debugging support for CMSStackOverflowALot
8730
8731 // It's OK to call this multi-threaded; the worst thing
8732 // that can happen is that we'll get a bunch of closely
8733 // spaced simulated oveflows, but that's OK, in fact
8734 // probably good as it would exercise the overflow code
8735 // under contention.
8736 bool CMSCollector::simulate_overflow() {
8737 if (_overflow_counter-- <= 0) { // just being defensive
8738 _overflow_counter = CMSMarkStackOverflowInterval;
8739 return true;
8740 } else {
8741 return false;
8742 }
8743 }
8744
8745 bool CMSCollector::par_simulate_overflow() {
8746 return simulate_overflow();
8747 }
8748 #endif
8749
8750 // Single-threaded
8751 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) {
8752 assert(stack->isEmpty(), "Expected precondition");
8753 assert(stack->capacity() > num, "Shouldn't bite more than can chew");
8754 size_t i = num;
8755 oop cur = _overflow_list;
8756 const markOop proto = markOopDesc::prototype();
8757 NOT_PRODUCT(ssize_t n = 0;)
8758 for (oop next; i > 0 && cur != NULL; cur = next, i--) {
8759 next = oop(cur->mark());
8760 cur->set_mark(proto); // until proven otherwise
8761 assert(cur->is_oop(), "Should be an oop");
8762 bool res = stack->push(cur);
8763 assert(res, "Bit off more than can chew?");
8764 NOT_PRODUCT(n++;)
8765 }
8766 _overflow_list = cur;
8767 #ifndef PRODUCT
8768 assert(_num_par_pushes >= n, "Too many pops?");
8769 _num_par_pushes -=n;
8770 #endif
8771 return !stack->isEmpty();
8772 }
8773
8774 #define BUSY (oop(0x1aff1aff))
8775 // (MT-safe) Get a prefix of at most "num" from the list.
8776 // The overflow list is chained through the mark word of
8777 // each object in the list. We fetch the entire list,
8778 // break off a prefix of the right size and return the
8779 // remainder. If other threads try to take objects from
8780 // the overflow list at that time, they will wait for
8781 // some time to see if data becomes available. If (and
8782 // only if) another thread places one or more object(s)
8783 // on the global list before we have returned the suffix
8784 // to the global list, we will walk down our local list
8785 // to find its end and append the global list to
8786 // our suffix before returning it. This suffix walk can
8787 // prove to be expensive (quadratic in the amount of traffic)
8788 // when there are many objects in the overflow list and
8789 // there is much producer-consumer contention on the list.
8790 // *NOTE*: The overflow list manipulation code here and
8791 // in ParNewGeneration:: are very similar in shape,
8792 // except that in the ParNew case we use the old (from/eden)
8793 // copy of the object to thread the list via its klass word.
8794 // Because of the common code, if you make any changes in
8795 // the code below, please check the ParNew version to see if
8796 // similar changes might be needed.
8797 // CR 6797058 has been filed to consolidate the common code.
8798 bool CMSCollector::par_take_from_overflow_list(size_t num,
8799 OopTaskQueue* work_q,
8800 int no_of_gc_threads) {
8801 assert(work_q->size() == 0, "First empty local work queue");
8802 assert(num < work_q->max_elems(), "Can't bite more than we can chew");
8803 if (_overflow_list == NULL) {
8804 return false;
8805 }
8806 // Grab the entire list; we'll put back a suffix
8807 oop prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8808 Thread* tid = Thread::current();
8809 // Before "no_of_gc_threads" was introduced CMSOverflowSpinCount was
8810 // set to ParallelGCThreads.
8811 size_t CMSOverflowSpinCount = (size_t) no_of_gc_threads; // was ParallelGCThreads;
8812 size_t sleep_time_millis = MAX2((size_t)1, num/100);
8813 // If the list is busy, we spin for a short while,
8814 // sleeping between attempts to get the list.
8815 for (size_t spin = 0; prefix == BUSY && spin < CMSOverflowSpinCount; spin++) {
8816 os::sleep(tid, sleep_time_millis, false);
8817 if (_overflow_list == NULL) {
8818 // Nothing left to take
8819 return false;
8820 } else if (_overflow_list != BUSY) {
8821 // Try and grab the prefix
8822 prefix = (oop)Atomic::xchg_ptr(BUSY, &_overflow_list);
8823 }
8824 }
8825 // If the list was found to be empty, or we spun long
8826 // enough, we give up and return empty-handed. If we leave
8827 // the list in the BUSY state below, it must be the case that
8828 // some other thread holds the overflow list and will set it
8829 // to a non-BUSY state in the future.
8830 if (prefix == NULL || prefix == BUSY) {
8831 // Nothing to take or waited long enough
8832 if (prefix == NULL) {
8833 // Write back the NULL in case we overwrote it with BUSY above
8834 // and it is still the same value.
8835 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8836 }
8837 return false;
8838 }
8839 assert(prefix != NULL && prefix != BUSY, "Error");
8840 size_t i = num;
8841 oop cur = prefix;
8842 // Walk down the first "num" objects, unless we reach the end.
8843 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--);
8844 if (cur->mark() == NULL) {
8845 // We have "num" or fewer elements in the list, so there
8846 // is nothing to return to the global list.
8847 // Write back the NULL in lieu of the BUSY we wrote
8848 // above, if it is still the same value.
8849 if (_overflow_list == BUSY) {
8850 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
8851 }
8852 } else {
8853 // Chop off the suffix and rerturn it to the global list.
8854 assert(cur->mark() != BUSY, "Error");
8855 oop suffix_head = cur->mark(); // suffix will be put back on global list
8856 cur->set_mark(NULL); // break off suffix
8857 // It's possible that the list is still in the empty(busy) state
8858 // we left it in a short while ago; in that case we may be
8859 // able to place back the suffix without incurring the cost
8860 // of a walk down the list.
8861 oop observed_overflow_list = _overflow_list;
8862 oop cur_overflow_list = observed_overflow_list;
8863 bool attached = false;
8864 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
8865 observed_overflow_list =
8866 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8867 if (cur_overflow_list == observed_overflow_list) {
8868 attached = true;
8869 break;
8870 } else cur_overflow_list = observed_overflow_list;
8871 }
8872 if (!attached) {
8873 // Too bad, someone else sneaked in (at least) an element; we'll need
8874 // to do a splice. Find tail of suffix so we can prepend suffix to global
8875 // list.
8876 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark()));
8877 oop suffix_tail = cur;
8878 assert(suffix_tail != NULL && suffix_tail->mark() == NULL,
8879 "Tautology");
8880 observed_overflow_list = _overflow_list;
8881 do {
8882 cur_overflow_list = observed_overflow_list;
8883 if (cur_overflow_list != BUSY) {
8884 // Do the splice ...
8885 suffix_tail->set_mark(markOop(cur_overflow_list));
8886 } else { // cur_overflow_list == BUSY
8887 suffix_tail->set_mark(NULL);
8888 }
8889 // ... and try to place spliced list back on overflow_list ...
8890 observed_overflow_list =
8891 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur_overflow_list);
8892 } while (cur_overflow_list != observed_overflow_list);
8893 // ... until we have succeeded in doing so.
8894 }
8895 }
8896
8897 // Push the prefix elements on work_q
8898 assert(prefix != NULL, "control point invariant");
8899 const markOop proto = markOopDesc::prototype();
8900 oop next;
8901 NOT_PRODUCT(ssize_t n = 0;)
8902 for (cur = prefix; cur != NULL; cur = next) {
8903 next = oop(cur->mark());
8904 cur->set_mark(proto); // until proven otherwise
8905 assert(cur->is_oop(), "Should be an oop");
8906 bool res = work_q->push(cur);
8907 assert(res, "Bit off more than we can chew?");
8908 NOT_PRODUCT(n++;)
8909 }
8910 #ifndef PRODUCT
8911 assert(_num_par_pushes >= n, "Too many pops?");
8912 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
8913 #endif
8914 return true;
8915 }
8916
8917 // Single-threaded
8918 void CMSCollector::push_on_overflow_list(oop p) {
8919 NOT_PRODUCT(_num_par_pushes++;)
8920 assert(p->is_oop(), "Not an oop");
8921 preserve_mark_if_necessary(p);
8922 p->set_mark((markOop)_overflow_list);
8923 _overflow_list = p;
8924 }
8925
8926 // Multi-threaded; use CAS to prepend to overflow list
8927 void CMSCollector::par_push_on_overflow_list(oop p) {
8928 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);)
8929 assert(p->is_oop(), "Not an oop");
8930 par_preserve_mark_if_necessary(p);
8931 oop observed_overflow_list = _overflow_list;
8932 oop cur_overflow_list;
8933 do {
8934 cur_overflow_list = observed_overflow_list;
8935 if (cur_overflow_list != BUSY) {
8936 p->set_mark(markOop(cur_overflow_list));
8937 } else {
8938 p->set_mark(NULL);
8939 }
8940 observed_overflow_list =
8941 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list);
8942 } while (cur_overflow_list != observed_overflow_list);
8943 }
8944 #undef BUSY
8945
8946 // Single threaded
8947 // General Note on GrowableArray: pushes may silently fail
8948 // because we are (temporarily) out of C-heap for expanding
8949 // the stack. The problem is quite ubiquitous and affects
8950 // a lot of code in the JVM. The prudent thing for GrowableArray
8951 // to do (for now) is to exit with an error. However, that may
8952 // be too draconian in some cases because the caller may be
8953 // able to recover without much harm. For such cases, we
8954 // should probably introduce a "soft_push" method which returns
8955 // an indication of success or failure with the assumption that
8956 // the caller may be able to recover from a failure; code in
8957 // the VM can then be changed, incrementally, to deal with such
8958 // failures where possible, thus, incrementally hardening the VM
8959 // in such low resource situations.
8960 void CMSCollector::preserve_mark_work(oop p, markOop m) {
8961 _preserved_oop_stack.push(p);
8962 _preserved_mark_stack.push(m);
8963 assert(m == p->mark(), "Mark word changed");
8964 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
8965 "bijection");
8966 }
8967
8968 // Single threaded
8969 void CMSCollector::preserve_mark_if_necessary(oop p) {
8970 markOop m = p->mark();
8971 if (m->must_be_preserved(p)) {
8972 preserve_mark_work(p, m);
8973 }
8974 }
8975
8976 void CMSCollector::par_preserve_mark_if_necessary(oop p) {
8977 markOop m = p->mark();
8978 if (m->must_be_preserved(p)) {
8979 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag);
8980 // Even though we read the mark word without holding
8981 // the lock, we are assured that it will not change
8982 // because we "own" this oop, so no other thread can
8983 // be trying to push it on the overflow list; see
8984 // the assertion in preserve_mark_work() that checks
8985 // that m == p->mark().
8986 preserve_mark_work(p, m);
8987 }
8988 }
8989
8990 // We should be able to do this multi-threaded,
8991 // a chunk of stack being a task (this is
8992 // correct because each oop only ever appears
8993 // once in the overflow list. However, it's
8994 // not very easy to completely overlap this with
8995 // other operations, so will generally not be done
8996 // until all work's been completed. Because we
8997 // expect the preserved oop stack (set) to be small,
8998 // it's probably fine to do this single-threaded.
8999 // We can explore cleverer concurrent/overlapped/parallel
9000 // processing of preserved marks if we feel the
9001 // need for this in the future. Stack overflow should
9002 // be so rare in practice and, when it happens, its
9003 // effect on performance so great that this will
9004 // likely just be in the noise anyway.
9005 void CMSCollector::restore_preserved_marks_if_any() {
9006 assert(SafepointSynchronize::is_at_safepoint(),
9007 "world should be stopped");
9008 assert(Thread::current()->is_ConcurrentGC_thread() ||
9009 Thread::current()->is_VM_thread(),
9010 "should be single-threaded");
9011 assert(_preserved_oop_stack.size() == _preserved_mark_stack.size(),
9012 "bijection");
9013
9014 while (!_preserved_oop_stack.is_empty()) {
9015 oop p = _preserved_oop_stack.pop();
9016 assert(p->is_oop(), "Should be an oop");
9017 assert(_span.contains(p), "oop should be in _span");
9018 assert(p->mark() == markOopDesc::prototype(),
9019 "Set when taken from overflow list");
9020 markOop m = _preserved_mark_stack.pop();
9021 p->set_mark(m);
9022 }
9023 assert(_preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty(),
9024 "stacks were cleared above");
9025 }
9026
9027 #ifndef PRODUCT
9028 bool CMSCollector::no_preserved_marks() const {
9029 return _preserved_mark_stack.is_empty() && _preserved_oop_stack.is_empty();
9030 }
9031 #endif
9032
9033 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const
9034 {
9035 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9036 CMSAdaptiveSizePolicy* size_policy =
9037 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy();
9038 assert(size_policy->is_gc_cms_adaptive_size_policy(),
9039 "Wrong type for size policy");
9040 return size_policy;
9041 }
9042
9043 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size,
9044 size_t desired_promo_size) {
9045 if (cur_promo_size < desired_promo_size) {
9046 size_t expand_bytes = desired_promo_size - cur_promo_size;
9047 if (PrintAdaptiveSizePolicy && Verbose) {
9048 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9049 "Expanding tenured generation by " SIZE_FORMAT " (bytes)",
9050 expand_bytes);
9051 }
9052 expand(expand_bytes,
9053 MinHeapDeltaBytes,
9054 CMSExpansionCause::_adaptive_size_policy);
9055 } else if (desired_promo_size < cur_promo_size) {
9056 size_t shrink_bytes = cur_promo_size - desired_promo_size;
9057 if (PrintAdaptiveSizePolicy && Verbose) {
9058 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize "
9059 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)",
9060 shrink_bytes);
9061 }
9062 shrink(shrink_bytes);
9063 }
9064 }
9065
9066 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() {
9067 GenCollectedHeap* gch = GenCollectedHeap::heap();
9068 CMSGCAdaptivePolicyCounters* counters =
9069 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters();
9070 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind,
9071 "Wrong kind of counters");
9072 return counters;
9073 }
9074
9075
9076 void ASConcurrentMarkSweepGeneration::update_counters() {
9077 if (UsePerfData) {
9078 _space_counters->update_all();
9079 _gen_counters->update_all();
9080 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9081 GenCollectedHeap* gch = GenCollectedHeap::heap();
9082 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9083 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9084 "Wrong gc statistics type");
9085 counters->update_counters(gc_stats_l);
9086 }
9087 }
9088
9089 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) {
9090 if (UsePerfData) {
9091 _space_counters->update_used(used);
9092 _space_counters->update_capacity();
9093 _gen_counters->update_all();
9094
9095 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9096 GenCollectedHeap* gch = GenCollectedHeap::heap();
9097 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats();
9098 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind,
9099 "Wrong gc statistics type");
9100 counters->update_counters(gc_stats_l);
9101 }
9102 }
9103
9104 // The desired expansion delta is computed so that:
9105 // . desired free percentage or greater is used
9106 void ASConcurrentMarkSweepGeneration::compute_new_size() {
9107 assert_locked_or_safepoint(Heap_lock);
9108
9109 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap();
9110
9111 // If incremental collection failed, we just want to expand
9112 // to the limit.
9113 if (incremental_collection_failed()) {
9114 clear_incremental_collection_failed();
9115 grow_to_reserved();
9116 return;
9117 }
9118
9119 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing");
9120
9121 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
9122 "Wrong type of heap");
9123 int prev_level = level() - 1;
9124 assert(prev_level >= 0, "The cms generation is the lowest generation");
9125 Generation* prev_gen = gch->get_gen(prev_level);
9126 assert(prev_gen->kind() == Generation::ASParNew,
9127 "Wrong type of young generation");
9128 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen;
9129 size_t cur_eden = younger_gen->eden()->capacity();
9130 CMSAdaptiveSizePolicy* size_policy = cms_size_policy();
9131 size_t cur_promo = free();
9132 size_policy->compute_tenured_generation_free_space(cur_promo,
9133 max_available(),
9134 cur_eden);
9135 resize(cur_promo, size_policy->promo_size());
9136
9137 // Record the new size of the space in the cms generation
9138 // that is available for promotions. This is temporary.
9139 // It should be the desired promo size.
9140 size_policy->avg_cms_promo()->sample(free());
9141 size_policy->avg_old_live()->sample(used());
9142
9143 if (UsePerfData) {
9144 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters();
9145 counters->update_cms_capacity_counter(capacity());
9146 }
9147 }
9148
9149 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) {
9150 assert_locked_or_safepoint(Heap_lock);
9151 assert_lock_strong(freelistLock());
9152 HeapWord* old_end = _cmsSpace->end();
9153 HeapWord* unallocated_start = _cmsSpace->unallocated_block();
9154 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start");
9155 FreeChunk* chunk_at_end = find_chunk_at_end();
9156 if (chunk_at_end == NULL) {
9157 // No room to shrink
9158 if (PrintGCDetails && Verbose) {
9159 gclog_or_tty->print_cr("No room to shrink: old_end "
9160 PTR_FORMAT " unallocated_start " PTR_FORMAT
9161 " chunk_at_end " PTR_FORMAT,
9162 old_end, unallocated_start, chunk_at_end);
9163 }
9164 return;
9165 } else {
9166
9167 // Find the chunk at the end of the space and determine
9168 // how much it can be shrunk.
9169 size_t shrinkable_size_in_bytes = chunk_at_end->size();
9170 size_t aligned_shrinkable_size_in_bytes =
9171 align_size_down(shrinkable_size_in_bytes, os::vm_page_size());
9172 assert(unallocated_start <= (HeapWord*) chunk_at_end->end(),
9173 "Inconsistent chunk at end of space");
9174 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes);
9175 size_t word_size_before = heap_word_size(_virtual_space.committed_size());
9176
9177 // Shrink the underlying space
9178 _virtual_space.shrink_by(bytes);
9179 if (PrintGCDetails && Verbose) {
9180 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:"
9181 " desired_bytes " SIZE_FORMAT
9182 " shrinkable_size_in_bytes " SIZE_FORMAT
9183 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT
9184 " bytes " SIZE_FORMAT,
9185 desired_bytes, shrinkable_size_in_bytes,
9186 aligned_shrinkable_size_in_bytes, bytes);
9187 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT
9188 " unallocated_start " SIZE_FORMAT,
9189 old_end, unallocated_start);
9190 }
9191
9192 // If the space did shrink (shrinking is not guaranteed),
9193 // shrink the chunk at the end by the appropriate amount.
9194 if (((HeapWord*)_virtual_space.high()) < old_end) {
9195 size_t new_word_size =
9196 heap_word_size(_virtual_space.committed_size());
9197
9198 // Have to remove the chunk from the dictionary because it is changing
9199 // size and might be someplace elsewhere in the dictionary.
9200
9201 // Get the chunk at end, shrink it, and put it
9202 // back.
9203 _cmsSpace->removeChunkFromDictionary(chunk_at_end);
9204 size_t word_size_change = word_size_before - new_word_size;
9205 size_t chunk_at_end_old_size = chunk_at_end->size();
9206 assert(chunk_at_end_old_size >= word_size_change,
9207 "Shrink is too large");
9208 chunk_at_end->set_size(chunk_at_end_old_size -
9209 word_size_change);
9210 _cmsSpace->freed((HeapWord*) chunk_at_end->end(),
9211 word_size_change);
9212
9213 _cmsSpace->returnChunkToDictionary(chunk_at_end);
9214
9215 MemRegion mr(_cmsSpace->bottom(), new_word_size);
9216 _bts->resize(new_word_size); // resize the block offset shared array
9217 Universe::heap()->barrier_set()->resize_covered_region(mr);
9218 _cmsSpace->assert_locked();
9219 _cmsSpace->set_end((HeapWord*)_virtual_space.high());
9220
9221 NOT_PRODUCT(_cmsSpace->dictionary()->verify());
9222
9223 // update the space and generation capacity counters
9224 if (UsePerfData) {
9225 _space_counters->update_capacity();
9226 _gen_counters->update_all();
9227 }
9228
9229 if (Verbose && PrintGCDetails) {
9230 size_t new_mem_size = _virtual_space.committed_size();
9231 size_t old_mem_size = new_mem_size + bytes;
9232 gclog_or_tty->print_cr("Shrinking %s from " SIZE_FORMAT "K by " SIZE_FORMAT "K to " SIZE_FORMAT "K",
9233 name(), old_mem_size/K, bytes/K, new_mem_size/K);
9234 }
9235 }
9236
9237 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(),
9238 "Inconsistency at end of space");
9239 assert(chunk_at_end->end() == (uintptr_t*) _cmsSpace->end(),
9240 "Shrinking is inconsistent");
9241 return;
9242 }
9243 }
9244
9245 // Transfer some number of overflown objects to usual marking
9246 // stack. Return true if some objects were transferred.
9247 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() {
9248 size_t num = MIN2((size_t)(_mark_stack->capacity() - _mark_stack->length())/4,
9249 (size_t)ParGCDesiredObjsFromOverflowList);
9250
9251 bool res = _collector->take_from_overflow_list(num, _mark_stack);
9252 assert(_collector->overflow_list_is_empty() || res,
9253 "If list is not empty, we should have taken something");
9254 assert(!res || !_mark_stack->isEmpty(),
9255 "If we took something, it should now be on our stack");
9256 return res;
9257 }
9258
9259 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) {
9260 size_t res = _sp->block_size_no_stall(addr, _collector);
9261 if (_sp->block_is_obj(addr)) {
9262 if (_live_bit_map->isMarked(addr)) {
9263 // It can't have been dead in a previous cycle
9264 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!");
9265 } else {
9266 _dead_bit_map->mark(addr); // mark the dead object
9267 }
9268 }
9269 // Could be 0, if the block size could not be computed without stalling.
9270 return res;
9271 }
9272
9273 TraceCMSMemoryManagerStats::TraceCMSMemoryManagerStats(CMSCollector::CollectorState phase, GCCause::Cause cause): TraceMemoryManagerStats() {
9274
9275 switch (phase) {
9276 case CMSCollector::InitialMarking:
9277 initialize(true /* fullGC */ ,
9278 cause /* cause of the GC */,
9279 true /* recordGCBeginTime */,
9280 true /* recordPreGCUsage */,
9281 false /* recordPeakUsage */,
9282 false /* recordPostGCusage */,
9283 true /* recordAccumulatedGCTime */,
9284 false /* recordGCEndTime */,
9285 false /* countCollection */ );
9286 break;
9287
9288 case CMSCollector::FinalMarking:
9289 initialize(true /* fullGC */ ,
9290 cause /* cause of the GC */,
9291 false /* recordGCBeginTime */,
9292 false /* recordPreGCUsage */,
9293 false /* recordPeakUsage */,
9294 false /* recordPostGCusage */,
9295 true /* recordAccumulatedGCTime */,
9296 false /* recordGCEndTime */,
9297 false /* countCollection */ );
9298 break;
9299
9300 case CMSCollector::Sweeping:
9301 initialize(true /* fullGC */ ,
9302 cause /* cause of the GC */,
9303 false /* recordGCBeginTime */,
9304 false /* recordPreGCUsage */,
9305 true /* recordPeakUsage */,
9306 true /* recordPostGCusage */,
9307 false /* recordAccumulatedGCTime */,
9308 true /* recordGCEndTime */,
9309 true /* countCollection */ );
9310 break;
9311
9312 default:
9313 ShouldNotReachHere();
9314 }
9315 }
9316