1 /*
2 * Copyright (c) 2001, 2014, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.hpp"
27 #include "gc_implementation/parNew/parNewGeneration.hpp"
28 #include "gc_implementation/parNew/parOopClosures.inline.hpp"
29 #include "gc_implementation/shared/adaptiveSizePolicy.hpp"
30 #include "gc_implementation/shared/ageTable.hpp"
31 #include "gc_implementation/shared/copyFailedInfo.hpp"
32 #include "gc_implementation/shared/gcHeapSummary.hpp"
33 #include "gc_implementation/shared/gcTimer.hpp"
34 #include "gc_implementation/shared/gcTrace.hpp"
35 #include "gc_implementation/shared/gcTraceTime.hpp"
36 #include "gc_implementation/shared/parGCAllocBuffer.inline.hpp"
37 #include "gc_implementation/shared/spaceDecorator.hpp"
38 #include "memory/defNewGeneration.inline.hpp"
39 #include "memory/genCollectedHeap.hpp"
40 #include "memory/genOopClosures.inline.hpp"
41 #include "memory/generation.hpp"
42 #include "memory/referencePolicy.hpp"
43 #include "memory/resourceArea.hpp"
44 #include "memory/sharedHeap.hpp"
45 #include "memory/space.hpp"
46 #include "oops/objArrayOop.hpp"
47 #include "oops/oop.inline.hpp"
48 #include "oops/oop.pcgc.inline.hpp"
49 #include "runtime/atomic.inline.hpp"
50 #include "runtime/handles.hpp"
51 #include "runtime/handles.inline.hpp"
52 #include "runtime/java.hpp"
53 #include "runtime/thread.inline.hpp"
54 #include "utilities/copy.hpp"
55 #include "utilities/globalDefinitions.hpp"
56 #include "utilities/workgroup.hpp"
57
58 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
59
60 ParScanThreadState::ParScanThreadState(Space* to_space_,
61 ParNewGeneration* gen_,
62 Generation* old_gen_,
63 int thread_num_,
64 ObjToScanQueueSet* work_queue_set_,
65 Stack<oop, mtGC>* overflow_stacks_,
66 size_t desired_plab_sz_,
67 ParallelTaskTerminator& term_) :
68 _to_space(to_space_), _old_gen(old_gen_), _young_gen(gen_), _thread_num(thread_num_),
69 _work_queue(work_queue_set_->queue(thread_num_)), _to_space_full(false),
70 _overflow_stack(overflow_stacks_ ? overflow_stacks_ + thread_num_ : NULL),
71 _ageTable(false), // false ==> not the global age table, no perf data.
72 _to_space_alloc_buffer(desired_plab_sz_),
73 _is_alive_closure(gen_),
74 _keep_alive_closure(&_scan_weak_ref_closure),
75 _strong_roots_time(0.0), _term_time(0.0)
76 {
77 _to_space_closure = ParScanWithoutBarrierClosure(gen_, this);
78 _old_gen_closure = ParScanWithBarrierClosure(gen_, this);
79 _to_space_root_closure = ParRootScanWithoutBarrierClosure(gen_, this);
80 _old_gen_root_closure = ParRootScanWithBarrierTwoGensClosure(gen_, this);
81 _older_gen_closure = ParRootScanWithBarrierTwoGensClosure(gen_, this);
82 _scan_weak_ref_closure = ParScanWeakRefClosure(gen_, this);
83
84 _evacuate_followers = ParEvacuateFollowersClosure(this,
85 &_to_space_closure,
86 &_old_gen_closure,
87 &_to_space_root_closure,
88 gen_,
89 &_old_gen_root_closure,
90 work_queue_set_,
91 &term_);
92
93
94 #if TASKQUEUE_STATS
95 _term_attempts = 0;
96 _overflow_refills = 0;
97 _overflow_refill_objs = 0;
98 #endif // TASKQUEUE_STATS
99
100 _survivor_chunk_array =
101 (ChunkArray*) old_gen()->get_data_recorder(thread_num());
102 _hash_seed = 17; // Might want to take time-based random value.
103 _start = os::elapsedTime();
104 _old_gen_closure.set_generation(old_gen_);
105 _old_gen_root_closure.set_generation(old_gen_);
106 }
107
108 void ParScanThreadState::record_survivor_plab(HeapWord* plab_start,
109 size_t plab_word_size) {
110 ChunkArray* sca = survivor_chunk_array();
111 if (sca != NULL) {
112 // A non-null SCA implies that we want the PLAB data recorded.
113 sca->record_sample(plab_start, plab_word_size);
114 }
115 }
116
117 bool ParScanThreadState::should_be_partially_scanned(oop new_obj, oop old_obj) const {
118 return new_obj->is_objArray() &&
119 arrayOop(new_obj)->length() > ParGCArrayScanChunk &&
120 new_obj != old_obj;
121 }
122
123 void ParScanThreadState::scan_partial_array_and_push_remainder(oop old) {
124 assert(old->is_objArray(), "must be obj array");
125 assert(old->is_forwarded(), "must be forwarded");
126 assert(Universe::heap()->is_in_reserved(old), "must be in heap.");
127 assert(!old_gen()->is_in(old), "must be in young generation.");
128
129 objArrayOop obj = objArrayOop(old->forwardee());
130 // Process ParGCArrayScanChunk elements now
131 // and push the remainder back onto queue
132 int start = arrayOop(old)->length();
133 int end = obj->length();
134 int remainder = end - start;
135 assert(start <= end, "just checking");
136 if (remainder > 2 * ParGCArrayScanChunk) {
137 // Test above combines last partial chunk with a full chunk
138 end = start + ParGCArrayScanChunk;
139 arrayOop(old)->set_length(end);
140 // Push remainder.
141 bool ok = work_queue()->push(old);
142 assert(ok, "just popped, push must be okay");
143 } else {
144 // Restore length so that it can be used if there
145 // is a promotion failure and forwarding pointers
146 // must be removed.
147 arrayOop(old)->set_length(end);
148 }
149
150 // process our set of indices (include header in first chunk)
151 // should make sure end is even (aligned to HeapWord in case of compressed oops)
152 if ((HeapWord *)obj < young_old_boundary()) {
153 // object is in to_space
154 obj->oop_iterate_range(&_to_space_closure, start, end);
155 } else {
156 // object is in old generation
157 obj->oop_iterate_range(&_old_gen_closure, start, end);
158 }
159 }
160
161
162 void ParScanThreadState::trim_queues(int max_size) {
163 ObjToScanQueue* queue = work_queue();
164 do {
165 while (queue->size() > (juint)max_size) {
166 oop obj_to_scan;
167 if (queue->pop_local(obj_to_scan)) {
168 if ((HeapWord *)obj_to_scan < young_old_boundary()) {
169 if (obj_to_scan->is_objArray() &&
170 obj_to_scan->is_forwarded() &&
171 obj_to_scan->forwardee() != obj_to_scan) {
172 scan_partial_array_and_push_remainder(obj_to_scan);
173 } else {
174 // object is in to_space
175 obj_to_scan->oop_iterate(&_to_space_closure);
176 }
177 } else {
178 // object is in old generation
179 obj_to_scan->oop_iterate(&_old_gen_closure);
180 }
181 }
182 }
183 // For the case of compressed oops, we have a private, non-shared
184 // overflow stack, so we eagerly drain it so as to more evenly
185 // distribute load early. Note: this may be good to do in
186 // general rather than delay for the final stealing phase.
187 // If applicable, we'll transfer a set of objects over to our
188 // work queue, allowing them to be stolen and draining our
189 // private overflow stack.
190 } while (ParGCTrimOverflow && young_gen()->take_from_overflow_list(this));
191 }
192
193 bool ParScanThreadState::take_from_overflow_stack() {
194 assert(ParGCUseLocalOverflow, "Else should not call");
195 assert(young_gen()->overflow_list() == NULL, "Error");
196 ObjToScanQueue* queue = work_queue();
197 Stack<oop, mtGC>* const of_stack = overflow_stack();
198 const size_t num_overflow_elems = of_stack->size();
199 const size_t space_available = queue->max_elems() - queue->size();
200 const size_t num_take_elems = MIN3(space_available / 4,
201 ParGCDesiredObjsFromOverflowList,
202 num_overflow_elems);
203 // Transfer the most recent num_take_elems from the overflow
204 // stack to our work queue.
205 for (size_t i = 0; i != num_take_elems; i++) {
206 oop cur = of_stack->pop();
207 oop obj_to_push = cur->forwardee();
208 assert(Universe::heap()->is_in_reserved(cur), "Should be in heap");
209 assert(!old_gen()->is_in_reserved(cur), "Should be in young gen");
210 assert(Universe::heap()->is_in_reserved(obj_to_push), "Should be in heap");
211 if (should_be_partially_scanned(obj_to_push, cur)) {
212 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
213 obj_to_push = cur;
214 }
215 bool ok = queue->push(obj_to_push);
216 assert(ok, "Should have succeeded");
217 }
218 assert(young_gen()->overflow_list() == NULL, "Error");
219 return num_take_elems > 0; // was something transferred?
220 }
221
222 void ParScanThreadState::push_on_overflow_stack(oop p) {
223 assert(ParGCUseLocalOverflow, "Else should not call");
224 overflow_stack()->push(p);
225 assert(young_gen()->overflow_list() == NULL, "Error");
226 }
227
228 HeapWord* ParScanThreadState::alloc_in_to_space_slow(size_t word_sz) {
229
230 // Otherwise, if the object is small enough, try to reallocate the
231 // buffer.
232 HeapWord* obj = NULL;
233 if (!_to_space_full) {
234 ParGCAllocBuffer* const plab = to_space_alloc_buffer();
235 Space* const sp = to_space();
236 if (word_sz * 100 <
237 ParallelGCBufferWastePct * plab->word_sz()) {
238 // Is small enough; abandon this buffer and start a new one.
239 plab->retire(false, false);
240 size_t buf_size = plab->word_sz();
241 HeapWord* buf_space = sp->par_allocate(buf_size);
242 if (buf_space == NULL) {
243 const size_t min_bytes =
244 ParGCAllocBuffer::min_size() << LogHeapWordSize;
245 size_t free_bytes = sp->free();
246 while(buf_space == NULL && free_bytes >= min_bytes) {
247 buf_size = free_bytes >> LogHeapWordSize;
248 assert(buf_size == (size_t)align_object_size(buf_size),
249 "Invariant");
250 buf_space = sp->par_allocate(buf_size);
251 free_bytes = sp->free();
252 }
253 }
254 if (buf_space != NULL) {
255 plab->set_word_size(buf_size);
256 plab->set_buf(buf_space);
257 record_survivor_plab(buf_space, buf_size);
258 obj = plab->allocate_aligned(word_sz, SurvivorAlignmentInBytes);
259 // Note that we cannot compare buf_size < word_sz below
260 // because of AlignmentReserve (see ParGCAllocBuffer::allocate()).
261 assert(obj != NULL || plab->words_remaining() < word_sz,
262 "Else should have been able to allocate");
263 // It's conceivable that we may be able to use the
264 // buffer we just grabbed for subsequent small requests
265 // even if not for this one.
266 } else {
267 // We're used up.
268 _to_space_full = true;
269 }
270
271 } else {
272 // Too large; allocate the object individually.
273 obj = sp->par_allocate(word_sz);
274 }
275 }
276 return obj;
277 }
278
279
280 void ParScanThreadState::undo_alloc_in_to_space(HeapWord* obj,
281 size_t word_sz) {
282 // Is the alloc in the current alloc buffer?
283 if (to_space_alloc_buffer()->contains(obj)) {
284 assert(to_space_alloc_buffer()->contains(obj + word_sz - 1),
285 "Should contain whole object.");
286 to_space_alloc_buffer()->undo_allocation(obj, word_sz);
287 } else {
288 CollectedHeap::fill_with_object(obj, word_sz);
289 }
290 }
291
292 void ParScanThreadState::print_promotion_failure_size() {
293 if (_promotion_failed_info.has_failed() && PrintPromotionFailure) {
294 gclog_or_tty->print(" (%d: promotion failure size = " SIZE_FORMAT ") ",
295 _thread_num, _promotion_failed_info.first_size());
296 }
297 }
298
299 class ParScanThreadStateSet: private ResourceArray {
300 public:
301 // Initializes states for the specified number of threads;
302 ParScanThreadStateSet(int num_threads,
303 Space& to_space,
304 ParNewGeneration& gen,
305 Generation& old_gen,
306 ObjToScanQueueSet& queue_set,
307 Stack<oop, mtGC>* overflow_stacks_,
308 size_t desired_plab_sz,
309 ParallelTaskTerminator& term);
310
311 ~ParScanThreadStateSet() { TASKQUEUE_STATS_ONLY(reset_stats()); }
312
313 inline ParScanThreadState& thread_state(int i);
314
315 void trace_promotion_failed(YoungGCTracer& gc_tracer);
316 void reset(int active_workers, bool promotion_failed);
317 void flush();
318
319 #if TASKQUEUE_STATS
320 static void
321 print_termination_stats_hdr(outputStream* const st = gclog_or_tty);
322 void print_termination_stats(outputStream* const st = gclog_or_tty);
323 static void
324 print_taskqueue_stats_hdr(outputStream* const st = gclog_or_tty);
325 void print_taskqueue_stats(outputStream* const st = gclog_or_tty);
326 void reset_stats();
327 #endif // TASKQUEUE_STATS
328
329 private:
330 ParallelTaskTerminator& _term;
331 ParNewGeneration& _gen;
332 Generation& _next_gen;
333 public:
334 bool is_valid(int id) const { return id < length(); }
335 ParallelTaskTerminator* terminator() { return &_term; }
336 };
337
338
339 ParScanThreadStateSet::ParScanThreadStateSet(
340 int num_threads, Space& to_space, ParNewGeneration& gen,
341 Generation& old_gen, ObjToScanQueueSet& queue_set,
342 Stack<oop, mtGC>* overflow_stacks,
343 size_t desired_plab_sz, ParallelTaskTerminator& term)
344 : ResourceArray(sizeof(ParScanThreadState), num_threads),
345 _gen(gen), _next_gen(old_gen), _term(term)
346 {
347 assert(num_threads > 0, "sanity check!");
348 assert(ParGCUseLocalOverflow == (overflow_stacks != NULL),
349 "overflow_stack allocation mismatch");
350 // Initialize states.
351 for (int i = 0; i < num_threads; ++i) {
352 new ((ParScanThreadState*)_data + i)
353 ParScanThreadState(&to_space, &gen, &old_gen, i, &queue_set,
354 overflow_stacks, desired_plab_sz, term);
355 }
356 }
357
358 inline ParScanThreadState& ParScanThreadStateSet::thread_state(int i)
359 {
360 assert(i >= 0 && i < length(), "sanity check!");
361 return ((ParScanThreadState*)_data)[i];
362 }
363
364 void ParScanThreadStateSet::trace_promotion_failed(YoungGCTracer& gc_tracer) {
365 for (int i = 0; i < length(); ++i) {
366 if (thread_state(i).promotion_failed()) {
367 gc_tracer.report_promotion_failed(thread_state(i).promotion_failed_info());
368 thread_state(i).promotion_failed_info().reset();
369 }
370 }
371 }
372
373 void ParScanThreadStateSet::reset(int active_threads, bool promotion_failed)
374 {
375 _term.reset_for_reuse(active_threads);
376 if (promotion_failed) {
377 for (int i = 0; i < length(); ++i) {
378 thread_state(i).print_promotion_failure_size();
379 }
380 }
381 }
382
383 #if TASKQUEUE_STATS
384 void
385 ParScanThreadState::reset_stats()
386 {
387 taskqueue_stats().reset();
388 _term_attempts = 0;
389 _overflow_refills = 0;
390 _overflow_refill_objs = 0;
391 }
392
393 void ParScanThreadStateSet::reset_stats()
394 {
395 for (int i = 0; i < length(); ++i) {
396 thread_state(i).reset_stats();
397 }
398 }
399
400 void
401 ParScanThreadStateSet::print_termination_stats_hdr(outputStream* const st)
402 {
403 st->print_raw_cr("GC Termination Stats");
404 st->print_raw_cr(" elapsed --strong roots-- "
405 "-------termination-------");
406 st->print_raw_cr("thr ms ms % "
407 " ms % attempts");
408 st->print_raw_cr("--- --------- --------- ------ "
409 "--------- ------ --------");
410 }
411
412 void ParScanThreadStateSet::print_termination_stats(outputStream* const st)
413 {
414 print_termination_stats_hdr(st);
415
416 for (int i = 0; i < length(); ++i) {
417 const ParScanThreadState & pss = thread_state(i);
418 const double elapsed_ms = pss.elapsed_time() * 1000.0;
419 const double s_roots_ms = pss.strong_roots_time() * 1000.0;
420 const double term_ms = pss.term_time() * 1000.0;
421 st->print_cr("%3d %9.2f %9.2f %6.2f "
422 "%9.2f %6.2f " SIZE_FORMAT_W(8),
423 i, elapsed_ms, s_roots_ms, s_roots_ms * 100 / elapsed_ms,
424 term_ms, term_ms * 100 / elapsed_ms, pss.term_attempts());
425 }
426 }
427
428 // Print stats related to work queue activity.
429 void ParScanThreadStateSet::print_taskqueue_stats_hdr(outputStream* const st)
430 {
431 st->print_raw_cr("GC Task Stats");
432 st->print_raw("thr "); TaskQueueStats::print_header(1, st); st->cr();
433 st->print_raw("--- "); TaskQueueStats::print_header(2, st); st->cr();
434 }
435
436 void ParScanThreadStateSet::print_taskqueue_stats(outputStream* const st)
437 {
438 print_taskqueue_stats_hdr(st);
439
440 TaskQueueStats totals;
441 for (int i = 0; i < length(); ++i) {
442 const ParScanThreadState & pss = thread_state(i);
443 const TaskQueueStats & stats = pss.taskqueue_stats();
444 st->print("%3d ", i); stats.print(st); st->cr();
445 totals += stats;
446
447 if (pss.overflow_refills() > 0) {
448 st->print_cr(" " SIZE_FORMAT_W(10) " overflow refills "
449 SIZE_FORMAT_W(10) " overflow objects",
450 pss.overflow_refills(), pss.overflow_refill_objs());
451 }
452 }
453 st->print("tot "); totals.print(st); st->cr();
454
455 DEBUG_ONLY(totals.verify());
456 }
457 #endif // TASKQUEUE_STATS
458
459 void ParScanThreadStateSet::flush()
460 {
461 // Work in this loop should be kept as lightweight as
462 // possible since this might otherwise become a bottleneck
463 // to scaling. Should we add heavy-weight work into this
464 // loop, consider parallelizing the loop into the worker threads.
465 for (int i = 0; i < length(); ++i) {
466 ParScanThreadState& par_scan_state = thread_state(i);
467
468 // Flush stats related to To-space PLAB activity and
469 // retire the last buffer.
470 par_scan_state.to_space_alloc_buffer()->
471 flush_stats_and_retire(_gen.plab_stats(),
472 true /* end_of_gc */,
473 false /* retain */);
474
475 // Every thread has its own age table. We need to merge
476 // them all into one.
477 ageTable *local_table = par_scan_state.age_table();
478 _gen.age_table()->merge(local_table);
479
480 // Inform old gen that we're done.
481 _next_gen.par_promote_alloc_done(i);
482 _next_gen.par_oop_since_save_marks_iterate_done(i);
483 }
484
485 if (UseConcMarkSweepGC) {
486 // We need to call this even when ResizeOldPLAB is disabled
487 // so as to avoid breaking some asserts. While we may be able
488 // to avoid this by reorganizing the code a bit, I am loathe
489 // to do that unless we find cases where ergo leads to bad
490 // performance.
491 CFLS_LAB::compute_desired_plab_size();
492 }
493 }
494
495 ParScanClosure::ParScanClosure(ParNewGeneration* g,
496 ParScanThreadState* par_scan_state) :
497 OopsInKlassOrGenClosure(g), _par_scan_state(par_scan_state), _g(g)
498 {
499 assert(_g->level() == 0, "Optimized for youngest generation");
500 _boundary = _g->reserved().end();
501 }
502
503 void ParScanWithBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, false); }
504 void ParScanWithBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, false); }
505
506 void ParScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, false); }
507 void ParScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, false); }
508
509 void ParRootScanWithBarrierTwoGensClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, true, true); }
510 void ParRootScanWithBarrierTwoGensClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, true, true); }
511
512 void ParRootScanWithoutBarrierClosure::do_oop(oop* p) { ParScanClosure::do_oop_work(p, false, true); }
513 void ParRootScanWithoutBarrierClosure::do_oop(narrowOop* p) { ParScanClosure::do_oop_work(p, false, true); }
514
515 ParScanWeakRefClosure::ParScanWeakRefClosure(ParNewGeneration* g,
516 ParScanThreadState* par_scan_state)
517 : ScanWeakRefClosure(g), _par_scan_state(par_scan_state)
518 {}
519
520 void ParScanWeakRefClosure::do_oop(oop* p) { ParScanWeakRefClosure::do_oop_work(p); }
521 void ParScanWeakRefClosure::do_oop(narrowOop* p) { ParScanWeakRefClosure::do_oop_work(p); }
522
523 ParEvacuateFollowersClosure::ParEvacuateFollowersClosure(
524 ParScanThreadState* par_scan_state_,
525 ParScanWithoutBarrierClosure* to_space_closure_,
526 ParScanWithBarrierClosure* old_gen_closure_,
527 ParRootScanWithoutBarrierClosure* to_space_root_closure_,
528 ParNewGeneration* par_gen_,
529 ParRootScanWithBarrierTwoGensClosure* old_gen_root_closure_,
530 ObjToScanQueueSet* task_queues_,
531 ParallelTaskTerminator* terminator_) :
532
533 _par_scan_state(par_scan_state_),
534 _to_space_closure(to_space_closure_),
535 _old_gen_closure(old_gen_closure_),
536 _to_space_root_closure(to_space_root_closure_),
537 _old_gen_root_closure(old_gen_root_closure_),
538 _par_gen(par_gen_),
539 _task_queues(task_queues_),
540 _terminator(terminator_)
541 {}
542
543 void ParEvacuateFollowersClosure::do_void() {
544 ObjToScanQueue* work_q = par_scan_state()->work_queue();
545
546 while (true) {
547
548 // Scan to-space and old-gen objs until we run out of both.
549 oop obj_to_scan;
550 par_scan_state()->trim_queues(0);
551
552 // We have no local work, attempt to steal from other threads.
553
554 // attempt to steal work from promoted.
555 if (task_queues()->steal(par_scan_state()->thread_num(),
556 par_scan_state()->hash_seed(),
557 obj_to_scan)) {
558 bool res = work_q->push(obj_to_scan);
559 assert(res, "Empty queue should have room for a push.");
560
561 // if successful, goto Start.
562 continue;
563
564 // try global overflow list.
565 } else if (par_gen()->take_from_overflow_list(par_scan_state())) {
566 continue;
567 }
568
569 // Otherwise, offer termination.
570 par_scan_state()->start_term_time();
571 if (terminator()->offer_termination()) break;
572 par_scan_state()->end_term_time();
573 }
574 assert(par_gen()->_overflow_list == NULL && par_gen()->_num_par_pushes == 0,
575 "Broken overflow list?");
576 // Finish the last termination pause.
577 par_scan_state()->end_term_time();
578 }
579
580 ParNewGenTask::ParNewGenTask(ParNewGeneration* gen, Generation* next_gen,
581 HeapWord* young_old_boundary, ParScanThreadStateSet* state_set) :
582 AbstractGangTask("ParNewGeneration collection"),
583 _gen(gen), _next_gen(next_gen),
584 _young_old_boundary(young_old_boundary),
585 _state_set(state_set)
586 {}
587
588 // Reset the terminator for the given number of
589 // active threads.
590 void ParNewGenTask::set_for_termination(int active_workers) {
591 _state_set->reset(active_workers, _gen->promotion_failed());
592 // Should the heap be passed in? There's only 1 for now so
593 // grab it instead.
594 GenCollectedHeap* gch = GenCollectedHeap::heap();
595 gch->set_n_termination(active_workers);
596 }
597
598 void ParNewGenTask::work(uint worker_id) {
599 GenCollectedHeap* gch = GenCollectedHeap::heap();
600 // Since this is being done in a separate thread, need new resource
601 // and handle marks.
602 ResourceMark rm;
603 HandleMark hm;
604 // We would need multiple old-gen queues otherwise.
605 assert(gch->n_gens() == 2, "Par young collection currently only works with one older gen.");
606
607 Generation* old_gen = gch->next_gen(_gen);
608
609 ParScanThreadState& par_scan_state = _state_set->thread_state(worker_id);
610 assert(_state_set->is_valid(worker_id), "Should not have been called");
611
612 par_scan_state.set_young_old_boundary(_young_old_boundary);
613
614 KlassScanClosure klass_scan_closure(&par_scan_state.to_space_root_closure(),
615 gch->rem_set()->klass_rem_set());
616 CLDToKlassAndOopClosure cld_scan_closure(&klass_scan_closure,
617 &par_scan_state.to_space_root_closure(),
618 false);
619
620 par_scan_state.start_strong_roots();
621 gch->gen_process_roots(_gen->level(),
622 true, // Process younger gens, if any,
623 // as strong roots.
624 false, // no scope; this is parallel code
625 SharedHeap::SO_ScavengeCodeCache,
626 GenCollectedHeap::StrongAndWeakRoots,
627 &par_scan_state.to_space_root_closure(),
628 &par_scan_state.older_gen_closure(),
629 &cld_scan_closure);
630
631 par_scan_state.end_strong_roots();
632
633 // "evacuate followers".
634 par_scan_state.evacuate_followers_closure().do_void();
635 }
636
637 ParNewGeneration::
638 ParNewGeneration(ReservedSpace rs, size_t initial_byte_size, int level)
639 : DefNewGeneration(rs, initial_byte_size, level, "PCopy"),
640 _overflow_list(NULL),
641 _plab_stats(YoungPLABSize, PLABWeight)
642 {
643 _is_alive_closure = DefNewGeneration::IsAliveClosure(this);
644 NOT_PRODUCT(_overflow_counter = ParGCWorkQueueOverflowInterval;)
645 NOT_PRODUCT(_num_par_pushes = 0;)
646 _task_queues = new ObjToScanQueueSet(ParallelGCThreads);
647 guarantee(_task_queues != NULL, "task_queues allocation failure.");
648
649 for (uint i1 = 0; i1 < ParallelGCThreads; i1++) {
650 ObjToScanQueue *q = new ObjToScanQueue();
651 guarantee(q != NULL, "work_queue Allocation failure.");
652 _task_queues->register_queue(i1, q);
653 }
654
655 for (uint i2 = 0; i2 < ParallelGCThreads; i2++)
656 _task_queues->queue(i2)->initialize();
657
658 _overflow_stacks = NULL;
659 if (ParGCUseLocalOverflow) {
660
661 // typedef to workaround NEW_C_HEAP_ARRAY macro, which can not deal
662 // with ','
663 typedef Stack<oop, mtGC> GCOopStack;
664
665 _overflow_stacks = NEW_C_HEAP_ARRAY(GCOopStack, ParallelGCThreads, mtGC);
666 for (size_t i = 0; i < ParallelGCThreads; ++i) {
667 new (_overflow_stacks + i) Stack<oop, mtGC>();
668 }
669 }
670
671 if (UsePerfData) {
672 EXCEPTION_MARK;
673 ResourceMark rm;
674
675 const char* cname =
676 PerfDataManager::counter_name(_gen_counters->name_space(), "threads");
677 PerfDataManager::create_constant(SUN_GC, cname, PerfData::U_None,
678 ParallelGCThreads, CHECK);
679 }
680 }
681
682 // ParNewGeneration::
683 ParKeepAliveClosure::ParKeepAliveClosure(ParScanWeakRefClosure* cl) :
684 DefNewGeneration::KeepAliveClosure(cl), _par_cl(cl) {}
685
686 template <class T>
687 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop_work(T* p) {
688 #ifdef ASSERT
689 {
690 assert(!oopDesc::is_null(*p), "expected non-null ref");
691 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
692 // We never expect to see a null reference being processed
693 // as a weak reference.
694 assert(obj->is_oop(), "expected an oop while scanning weak refs");
695 }
696 #endif // ASSERT
697
698 _par_cl->do_oop_nv(p);
699
700 if (Universe::heap()->is_in_reserved(p)) {
701 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
702 _rs->write_ref_field_gc_par(p, obj);
703 }
704 }
705
706 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(oop* p) { ParKeepAliveClosure::do_oop_work(p); }
707 void /*ParNewGeneration::*/ParKeepAliveClosure::do_oop(narrowOop* p) { ParKeepAliveClosure::do_oop_work(p); }
708
709 // ParNewGeneration::
710 KeepAliveClosure::KeepAliveClosure(ScanWeakRefClosure* cl) :
711 DefNewGeneration::KeepAliveClosure(cl) {}
712
713 template <class T>
714 void /*ParNewGeneration::*/KeepAliveClosure::do_oop_work(T* p) {
715 #ifdef ASSERT
716 {
717 assert(!oopDesc::is_null(*p), "expected non-null ref");
718 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
719 // We never expect to see a null reference being processed
720 // as a weak reference.
721 assert(obj->is_oop(), "expected an oop while scanning weak refs");
722 }
723 #endif // ASSERT
724
725 _cl->do_oop_nv(p);
726
727 if (Universe::heap()->is_in_reserved(p)) {
728 oop obj = oopDesc::load_decode_heap_oop_not_null(p);
729 _rs->write_ref_field_gc_par(p, obj);
730 }
731 }
732
733 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(oop* p) { KeepAliveClosure::do_oop_work(p); }
734 void /*ParNewGeneration::*/KeepAliveClosure::do_oop(narrowOop* p) { KeepAliveClosure::do_oop_work(p); }
735
736 template <class T> void ScanClosureWithParBarrier::do_oop_work(T* p) {
737 T heap_oop = oopDesc::load_heap_oop(p);
738 if (!oopDesc::is_null(heap_oop)) {
739 oop obj = oopDesc::decode_heap_oop_not_null(heap_oop);
740 if ((HeapWord*)obj < _boundary) {
741 assert(!_g->to()->is_in_reserved(obj), "Scanning field twice?");
742 oop new_obj = obj->is_forwarded()
743 ? obj->forwardee()
744 : _g->DefNewGeneration::copy_to_survivor_space(obj);
745 oopDesc::encode_store_heap_oop_not_null(p, new_obj);
746 }
747 if (_gc_barrier) {
748 // If p points to a younger generation, mark the card.
749 if ((HeapWord*)obj < _gen_boundary) {
750 _rs->write_ref_field_gc_par(p, obj);
751 }
752 }
753 }
754 }
755
756 void ScanClosureWithParBarrier::do_oop(oop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
757 void ScanClosureWithParBarrier::do_oop(narrowOop* p) { ScanClosureWithParBarrier::do_oop_work(p); }
758
759 class ParNewRefProcTaskProxy: public AbstractGangTask {
760 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask;
761 public:
762 ParNewRefProcTaskProxy(ProcessTask& task, ParNewGeneration& gen,
763 Generation& next_gen,
764 HeapWord* young_old_boundary,
765 ParScanThreadStateSet& state_set);
766
767 private:
768 virtual void work(uint worker_id);
769 virtual void set_for_termination(int active_workers) {
770 _state_set.terminator()->reset_for_reuse(active_workers);
771 }
772 private:
773 ParNewGeneration& _gen;
774 ProcessTask& _task;
775 Generation& _next_gen;
776 HeapWord* _young_old_boundary;
777 ParScanThreadStateSet& _state_set;
778 };
779
780 ParNewRefProcTaskProxy::ParNewRefProcTaskProxy(
781 ProcessTask& task, ParNewGeneration& gen,
782 Generation& next_gen,
783 HeapWord* young_old_boundary,
784 ParScanThreadStateSet& state_set)
785 : AbstractGangTask("ParNewGeneration parallel reference processing"),
786 _gen(gen),
787 _task(task),
788 _next_gen(next_gen),
789 _young_old_boundary(young_old_boundary),
790 _state_set(state_set)
791 {
792 }
793
794 void ParNewRefProcTaskProxy::work(uint worker_id)
795 {
796 ResourceMark rm;
797 HandleMark hm;
798 ParScanThreadState& par_scan_state = _state_set.thread_state(worker_id);
799 par_scan_state.set_young_old_boundary(_young_old_boundary);
800 _task.work(worker_id, par_scan_state.is_alive_closure(),
801 par_scan_state.keep_alive_closure(),
802 par_scan_state.evacuate_followers_closure());
803 }
804
805 class ParNewRefEnqueueTaskProxy: public AbstractGangTask {
806 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask;
807 EnqueueTask& _task;
808
809 public:
810 ParNewRefEnqueueTaskProxy(EnqueueTask& task)
811 : AbstractGangTask("ParNewGeneration parallel reference enqueue"),
812 _task(task)
813 { }
814
815 virtual void work(uint worker_id)
816 {
817 _task.work(worker_id);
818 }
819 };
820
821
822 void ParNewRefProcTaskExecutor::execute(ProcessTask& task)
823 {
824 GenCollectedHeap* gch = GenCollectedHeap::heap();
825 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
826 "not a generational heap");
827 FlexibleWorkGang* workers = gch->workers();
828 assert(workers != NULL, "Need parallel worker threads.");
829 _state_set.reset(workers->active_workers(), _generation.promotion_failed());
830 ParNewRefProcTaskProxy rp_task(task, _generation, *_generation.next_gen(),
831 _generation.reserved().end(), _state_set);
832 workers->run_task(&rp_task);
833 _state_set.reset(0 /* bad value in debug if not reset */,
834 _generation.promotion_failed());
835 }
836
837 void ParNewRefProcTaskExecutor::execute(EnqueueTask& task)
838 {
839 GenCollectedHeap* gch = GenCollectedHeap::heap();
840 FlexibleWorkGang* workers = gch->workers();
841 assert(workers != NULL, "Need parallel worker threads.");
842 ParNewRefEnqueueTaskProxy enq_task(task);
843 workers->run_task(&enq_task);
844 }
845
846 void ParNewRefProcTaskExecutor::set_single_threaded_mode()
847 {
848 _state_set.flush();
849 GenCollectedHeap* gch = GenCollectedHeap::heap();
850 gch->set_par_threads(0); // 0 ==> non-parallel.
851 gch->save_marks();
852 }
853
854 ScanClosureWithParBarrier::
855 ScanClosureWithParBarrier(ParNewGeneration* g, bool gc_barrier) :
856 ScanClosure(g, gc_barrier) {}
857
858 EvacuateFollowersClosureGeneral::
859 EvacuateFollowersClosureGeneral(GenCollectedHeap* gch, int level,
860 OopsInGenClosure* cur,
861 OopsInGenClosure* older) :
862 _gch(gch), _level(level),
863 _scan_cur_or_nonheap(cur), _scan_older(older)
864 {}
865
866 void EvacuateFollowersClosureGeneral::do_void() {
867 do {
868 // Beware: this call will lead to closure applications via virtual
869 // calls.
870 _gch->oop_since_save_marks_iterate(_level,
871 _scan_cur_or_nonheap,
872 _scan_older);
873 } while (!_gch->no_allocs_since_save_marks(_level));
874 }
875
876
877 // A Generation that does parallel young-gen collection.
878
879 void ParNewGeneration::handle_promotion_failed(GenCollectedHeap* gch, ParScanThreadStateSet& thread_state_set, ParNewTracer& gc_tracer) {
880 assert(_promo_failure_scan_stack.is_empty(), "post condition");
881 _promo_failure_scan_stack.clear(true); // Clear cached segments.
882
883 remove_forwarding_pointers();
884 if (PrintGCDetails) {
885 gclog_or_tty->print(" (promotion failed)");
886 }
887 // All the spaces are in play for mark-sweep.
888 swap_spaces(); // Make life simpler for CMS || rescan; see 6483690.
889 from()->set_next_compaction_space(to());
890 gch->set_incremental_collection_failed();
891 // Inform the next generation that a promotion failure occurred.
892 _next_gen->promotion_failure_occurred();
893
894 // Trace promotion failure in the parallel GC threads
895 thread_state_set.trace_promotion_failed(gc_tracer);
896 // Single threaded code may have reported promotion failure to the global state
897 if (_promotion_failed_info.has_failed()) {
898 gc_tracer.report_promotion_failed(_promotion_failed_info);
899 }
900 // Reset the PromotionFailureALot counters.
901 NOT_PRODUCT(Universe::heap()->reset_promotion_should_fail();)
902 }
903
904 void ParNewGeneration::collect(bool full,
905 bool clear_all_soft_refs,
906 size_t size,
907 bool is_tlab) {
908 assert(full || size > 0, "otherwise we don't want to collect");
909
910 GenCollectedHeap* gch = GenCollectedHeap::heap();
911
912 _gc_timer->register_gc_start();
913
914 assert(gch->kind() == CollectedHeap::GenCollectedHeap,
915 "not a CMS generational heap");
916 AdaptiveSizePolicy* size_policy = gch->gen_policy()->size_policy();
917 FlexibleWorkGang* workers = gch->workers();
918 assert(workers != NULL, "Need workgang for parallel work");
919 int active_workers =
920 AdaptiveSizePolicy::calc_active_workers(workers->total_workers(),
921 workers->active_workers(),
922 Threads::number_of_non_daemon_threads());
923 workers->set_active_workers(active_workers);
924 assert(gch->n_gens() == 2,
925 "Par collection currently only works with single older gen.");
926 _next_gen = gch->next_gen(this);
927
928 // If the next generation is too full to accommodate worst-case promotion
929 // from this generation, pass on collection; let the next generation
930 // do it.
931 if (!collection_attempt_is_safe()) {
932 gch->set_incremental_collection_failed(); // slight lie, in that we did not even attempt one
933 return;
934 }
935 assert(to()->is_empty(), "Else not collection_attempt_is_safe");
936
937 ParNewTracer gc_tracer;
938 gc_tracer.report_gc_start(gch->gc_cause(), _gc_timer->gc_start());
939 gch->trace_heap_before_gc(&gc_tracer);
940
941 init_assuming_no_promotion_failure();
942
943 if (UseAdaptiveSizePolicy) {
944 set_survivor_overflow(false);
945 size_policy->minor_collection_begin();
946 }
947
948 GCTraceTime t1(GCCauseString("GC", gch->gc_cause()), PrintGC && !PrintGCDetails, true, NULL, gc_tracer.gc_id());
949 // Capture heap used before collection (for printing).
950 size_t gch_prev_used = gch->used();
951
952 SpecializationStats::clear();
953
954 age_table()->clear();
955 to()->clear(SpaceDecorator::Mangle);
956
957 gch->save_marks();
958 assert(workers != NULL, "Need parallel worker threads.");
959 int n_workers = active_workers;
960
961 // Set the correct parallelism (number of queues) in the reference processor
962 ref_processor()->set_active_mt_degree(n_workers);
963
964 // Always set the terminator for the active number of workers
965 // because only those workers go through the termination protocol.
966 ParallelTaskTerminator _term(n_workers, task_queues());
967 ParScanThreadStateSet thread_state_set(workers->active_workers(),
968 *to(), *this, *_next_gen, *task_queues(),
969 _overflow_stacks, desired_plab_sz(), _term);
970
971 ParNewGenTask tsk(this, _next_gen, reserved().end(), &thread_state_set);
972 gch->set_par_threads(n_workers);
973 gch->rem_set()->prepare_for_younger_refs_iterate(true);
974 // It turns out that even when we're using 1 thread, doing the work in a
975 // separate thread causes wide variance in run times. We can't help this
976 // in the multi-threaded case, but we special-case n=1 here to get
977 // repeatable measurements of the 1-thread overhead of the parallel code.
978 if (n_workers > 1) {
979 GenCollectedHeap::StrongRootsScope srs(gch);
980 workers->run_task(&tsk);
981 } else {
982 GenCollectedHeap::StrongRootsScope srs(gch);
983 tsk.work(0);
984 }
985 thread_state_set.reset(0 /* Bad value in debug if not reset */,
986 promotion_failed());
987
988 // Trace and reset failed promotion info.
989 if (promotion_failed()) {
990 thread_state_set.trace_promotion_failed(gc_tracer);
991 }
992
993 // Process (weak) reference objects found during scavenge.
994 ReferenceProcessor* rp = ref_processor();
995 IsAliveClosure is_alive(this);
996 ScanWeakRefClosure scan_weak_ref(this);
997 KeepAliveClosure keep_alive(&scan_weak_ref);
998 ScanClosure scan_without_gc_barrier(this, false);
999 ScanClosureWithParBarrier scan_with_gc_barrier(this, true);
1000 set_promo_failure_scan_stack_closure(&scan_without_gc_barrier);
1001 EvacuateFollowersClosureGeneral evacuate_followers(gch, _level,
1002 &scan_without_gc_barrier, &scan_with_gc_barrier);
1003 rp->setup_policy(clear_all_soft_refs);
1004 // Can the mt_degree be set later (at run_task() time would be best)?
1005 rp->set_active_mt_degree(active_workers);
1006 ReferenceProcessorStats stats;
1007 if (rp->processing_is_mt()) {
1008 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
1009 stats = rp->process_discovered_references(&is_alive, &keep_alive,
1010 &evacuate_followers, &task_executor,
1011 _gc_timer, gc_tracer.gc_id());
1012 } else {
1013 thread_state_set.flush();
1014 gch->set_par_threads(0); // 0 ==> non-parallel.
1015 gch->save_marks();
1016 stats = rp->process_discovered_references(&is_alive, &keep_alive,
1017 &evacuate_followers, NULL,
1018 _gc_timer, gc_tracer.gc_id());
1019 }
1020 gc_tracer.report_gc_reference_stats(stats);
1021 if (!promotion_failed()) {
1022 // Swap the survivor spaces.
1023 eden()->clear(SpaceDecorator::Mangle);
1024 from()->clear(SpaceDecorator::Mangle);
1025 if (ZapUnusedHeapArea) {
1026 // This is now done here because of the piece-meal mangling which
1027 // can check for valid mangling at intermediate points in the
1028 // collection(s). When a minor collection fails to collect
1029 // sufficient space resizing of the young generation can occur
1030 // an redistribute the spaces in the young generation. Mangle
1031 // here so that unzapped regions don't get distributed to
1032 // other spaces.
1033 to()->mangle_unused_area();
1034 }
1035 swap_spaces();
1036
1037 // A successful scavenge should restart the GC time limit count which is
1038 // for full GC's.
1039 size_policy->reset_gc_overhead_limit_count();
1040
1041 assert(to()->is_empty(), "to space should be empty now");
1042
1043 adjust_desired_tenuring_threshold();
1044 } else {
1045 handle_promotion_failed(gch, thread_state_set, gc_tracer);
1046 }
1047 // set new iteration safe limit for the survivor spaces
1048 from()->set_concurrent_iteration_safe_limit(from()->top());
1049 to()->set_concurrent_iteration_safe_limit(to()->top());
1050
1051 if (ResizePLAB) {
1052 plab_stats()->adjust_desired_plab_sz(n_workers);
1053 }
1054
1055 if (PrintGC && !PrintGCDetails) {
1056 gch->print_heap_change(gch_prev_used);
1057 }
1058
1059 TASKQUEUE_STATS_ONLY(if (PrintTerminationStats) thread_state_set.print_termination_stats());
1060 TASKQUEUE_STATS_ONLY(if (PrintTaskqueue) thread_state_set.print_taskqueue_stats());
1061
1062 if (UseAdaptiveSizePolicy) {
1063 size_policy->minor_collection_end(gch->gc_cause());
1064 size_policy->avg_survived()->sample(from()->used());
1065 }
1066
1067 // We need to use a monotonically non-decreasing time in ms
1068 // or we will see time-warp warnings and os::javaTimeMillis()
1069 // does not guarantee monotonicity.
1070 jlong now = os::javaTimeNanos() / NANOSECS_PER_MILLISEC;
1071 update_time_of_last_gc(now);
1072
1073 SpecializationStats::print();
1074
1075 rp->set_enqueuing_is_done(true);
1076 if (rp->processing_is_mt()) {
1077 ParNewRefProcTaskExecutor task_executor(*this, thread_state_set);
1078 rp->enqueue_discovered_references(&task_executor);
1079 } else {
1080 rp->enqueue_discovered_references(NULL);
1081 }
1082 rp->verify_no_references_recorded();
1083
1084 gch->trace_heap_after_gc(&gc_tracer);
1085 gc_tracer.report_tenuring_threshold(tenuring_threshold());
1086
1087 _gc_timer->register_gc_end();
1088
1089 gc_tracer.report_gc_end(_gc_timer->gc_end(), _gc_timer->time_partitions());
1090 }
1091
1092 static int sum;
1093 void ParNewGeneration::waste_some_time() {
1094 for (int i = 0; i < 100; i++) {
1095 sum += i;
1096 }
1097 }
1098
1099 static const oop ClaimedForwardPtr = cast_to_oop<intptr_t>(0x4);
1100
1101 // Because of concurrency, there are times where an object for which
1102 // "is_forwarded()" is true contains an "interim" forwarding pointer
1103 // value. Such a value will soon be overwritten with a real value.
1104 // This method requires "obj" to have a forwarding pointer, and waits, if
1105 // necessary for a real one to be inserted, and returns it.
1106
1107 oop ParNewGeneration::real_forwardee(oop obj) {
1108 oop forward_ptr = obj->forwardee();
1109 if (forward_ptr != ClaimedForwardPtr) {
1110 return forward_ptr;
1111 } else {
1112 return real_forwardee_slow(obj);
1113 }
1114 }
1115
1116 oop ParNewGeneration::real_forwardee_slow(oop obj) {
1117 // Spin-read if it is claimed but not yet written by another thread.
1118 oop forward_ptr = obj->forwardee();
1119 while (forward_ptr == ClaimedForwardPtr) {
1120 waste_some_time();
1121 assert(obj->is_forwarded(), "precondition");
1122 forward_ptr = obj->forwardee();
1123 }
1124 return forward_ptr;
1125 }
1126
1127 #ifdef ASSERT
1128 bool ParNewGeneration::is_legal_forward_ptr(oop p) {
1129 return
1130 (p == ClaimedForwardPtr)
1131 || Universe::heap()->is_in_reserved(p);
1132 }
1133 #endif
1134
1135 void ParNewGeneration::preserve_mark_if_necessary(oop obj, markOop m) {
1136 if (m->must_be_preserved_for_promotion_failure(obj)) {
1137 // We should really have separate per-worker stacks, rather
1138 // than use locking of a common pair of stacks.
1139 MutexLocker ml(ParGCRareEvent_lock);
1140 preserve_mark(obj, m);
1141 }
1142 }
1143
1144 // Multiple GC threads may try to promote an object. If the object
1145 // is successfully promoted, a forwarding pointer will be installed in
1146 // the object in the young generation. This method claims the right
1147 // to install the forwarding pointer before it copies the object,
1148 // thus avoiding the need to undo the copy as in
1149 // copy_to_survivor_space_avoiding_with_undo.
1150
1151 oop ParNewGeneration::copy_to_survivor_space(
1152 ParScanThreadState* par_scan_state, oop old, size_t sz, markOop m) {
1153 // In the sequential version, this assert also says that the object is
1154 // not forwarded. That might not be the case here. It is the case that
1155 // the caller observed it to be not forwarded at some time in the past.
1156 assert(is_in_reserved(old), "shouldn't be scavenging this oop");
1157
1158 // The sequential code read "old->age()" below. That doesn't work here,
1159 // since the age is in the mark word, and that might be overwritten with
1160 // a forwarding pointer by a parallel thread. So we must save the mark
1161 // word in a local and then analyze it.
1162 oopDesc dummyOld;
1163 dummyOld.set_mark(m);
1164 assert(!dummyOld.is_forwarded(),
1165 "should not be called with forwarding pointer mark word.");
1166
1167 oop new_obj = NULL;
1168 oop forward_ptr;
1169
1170 // Try allocating obj in to-space (unless too old)
1171 if (dummyOld.age() < tenuring_threshold()) {
1172 new_obj = (oop)par_scan_state->alloc_in_to_space(sz);
1173 if (new_obj == NULL) {
1174 set_survivor_overflow(true);
1175 }
1176 }
1177
1178 if (new_obj == NULL) {
1179 // Either to-space is full or we decided to promote
1180 // try allocating obj tenured
1181
1182 // Attempt to install a null forwarding pointer (atomically),
1183 // to claim the right to install the real forwarding pointer.
1184 forward_ptr = old->forward_to_atomic(ClaimedForwardPtr);
1185 if (forward_ptr != NULL) {
1186 // someone else beat us to it.
1187 return real_forwardee(old);
1188 }
1189
1190 new_obj = _next_gen->par_promote(par_scan_state->thread_num(),
1191 old, m, sz);
1192
1193 if (new_obj == NULL) {
1194 // promotion failed, forward to self
1195 _promotion_failed = true;
1196 new_obj = old;
1197
1198 preserve_mark_if_necessary(old, m);
1199 par_scan_state->register_promotion_failure(sz);
1200 }
1201
1202 old->forward_to(new_obj);
1203 forward_ptr = NULL;
1204 } else {
1205 // Is in to-space; do copying ourselves.
1206 Copy::aligned_disjoint_words((HeapWord*)old, (HeapWord*)new_obj, sz);
1207 forward_ptr = old->forward_to_atomic(new_obj);
1208 // Restore the mark word copied above.
1209 new_obj->set_mark(m);
1210 // Increment age if obj still in new generation
1211 new_obj->incr_age();
1212 par_scan_state->age_table()->add(new_obj, sz);
1213 }
1214 assert(new_obj != NULL, "just checking");
1215
1216 #ifndef PRODUCT
1217 // This code must come after the CAS test, or it will print incorrect
1218 // information.
1219 if (TraceScavenge) {
1220 gclog_or_tty->print_cr("{%s %s " PTR_FORMAT " -> " PTR_FORMAT " (%d)}",
1221 is_in_reserved(new_obj) ? "copying" : "tenuring",
1222 new_obj->klass()->internal_name(), (void *)old, (void *)new_obj, new_obj->size());
1223 }
1224 #endif
1225
1226 if (forward_ptr == NULL) {
1227 oop obj_to_push = new_obj;
1228 if (par_scan_state->should_be_partially_scanned(obj_to_push, old)) {
1229 // Length field used as index of next element to be scanned.
1230 // Real length can be obtained from real_forwardee()
1231 arrayOop(old)->set_length(0);
1232 obj_to_push = old;
1233 assert(obj_to_push->is_forwarded() && obj_to_push->forwardee() != obj_to_push,
1234 "push forwarded object");
1235 }
1236 // Push it on one of the queues of to-be-scanned objects.
1237 bool simulate_overflow = false;
1238 NOT_PRODUCT(
1239 if (ParGCWorkQueueOverflowALot && should_simulate_overflow()) {
1240 // simulate a stack overflow
1241 simulate_overflow = true;
1242 }
1243 )
1244 if (simulate_overflow || !par_scan_state->work_queue()->push(obj_to_push)) {
1245 // Add stats for overflow pushes.
1246 if (Verbose && PrintGCDetails) {
1247 gclog_or_tty->print("queue overflow!\n");
1248 }
1249 push_on_overflow_list(old, par_scan_state);
1250 TASKQUEUE_STATS_ONLY(par_scan_state->taskqueue_stats().record_overflow(0));
1251 }
1252
1253 return new_obj;
1254 }
1255
1256 // Oops. Someone beat us to it. Undo the allocation. Where did we
1257 // allocate it?
1258 if (is_in_reserved(new_obj)) {
1259 // Must be in to_space.
1260 assert(to()->is_in_reserved(new_obj), "Checking");
1261 if (forward_ptr == ClaimedForwardPtr) {
1262 // Wait to get the real forwarding pointer value.
1263 forward_ptr = real_forwardee(old);
1264 }
1265 par_scan_state->undo_alloc_in_to_space((HeapWord*)new_obj, sz);
1266 }
1267
1268 return forward_ptr;
1269 }
1270
1271 #ifndef PRODUCT
1272 // It's OK to call this multi-threaded; the worst thing
1273 // that can happen is that we'll get a bunch of closely
1274 // spaced simulated overflows, but that's OK, in fact
1275 // probably good as it would exercise the overflow code
1276 // under contention.
1277 bool ParNewGeneration::should_simulate_overflow() {
1278 if (_overflow_counter-- <= 0) { // just being defensive
1279 _overflow_counter = ParGCWorkQueueOverflowInterval;
1280 return true;
1281 } else {
1282 return false;
1283 }
1284 }
1285 #endif
1286
1287 // In case we are using compressed oops, we need to be careful.
1288 // If the object being pushed is an object array, then its length
1289 // field keeps track of the "grey boundary" at which the next
1290 // incremental scan will be done (see ParGCArrayScanChunk).
1291 // When using compressed oops, this length field is kept in the
1292 // lower 32 bits of the erstwhile klass word and cannot be used
1293 // for the overflow chaining pointer (OCP below). As such the OCP
1294 // would itself need to be compressed into the top 32-bits in this
1295 // case. Unfortunately, see below, in the event that we have a
1296 // promotion failure, the node to be pushed on the list can be
1297 // outside of the Java heap, so the heap-based pointer compression
1298 // would not work (we would have potential aliasing between C-heap
1299 // and Java-heap pointers). For this reason, when using compressed
1300 // oops, we simply use a worker-thread-local, non-shared overflow
1301 // list in the form of a growable array, with a slightly different
1302 // overflow stack draining strategy. If/when we start using fat
1303 // stacks here, we can go back to using (fat) pointer chains
1304 // (although some performance comparisons would be useful since
1305 // single global lists have their own performance disadvantages
1306 // as we were made painfully aware not long ago, see 6786503).
1307 #define BUSY (cast_to_oop<intptr_t>(0x1aff1aff))
1308 void ParNewGeneration::push_on_overflow_list(oop from_space_obj, ParScanThreadState* par_scan_state) {
1309 assert(is_in_reserved(from_space_obj), "Should be from this generation");
1310 if (ParGCUseLocalOverflow) {
1311 // In the case of compressed oops, we use a private, not-shared
1312 // overflow stack.
1313 par_scan_state->push_on_overflow_stack(from_space_obj);
1314 } else {
1315 assert(!UseCompressedOops, "Error");
1316 // if the object has been forwarded to itself, then we cannot
1317 // use the klass pointer for the linked list. Instead we have
1318 // to allocate an oopDesc in the C-Heap and use that for the linked list.
1319 // XXX This is horribly inefficient when a promotion failure occurs
1320 // and should be fixed. XXX FIX ME !!!
1321 #ifndef PRODUCT
1322 Atomic::inc_ptr(&_num_par_pushes);
1323 assert(_num_par_pushes > 0, "Tautology");
1324 #endif
1325 if (from_space_obj->forwardee() == from_space_obj) {
1326 oopDesc* listhead = NEW_C_HEAP_ARRAY(oopDesc, 1, mtGC);
1327 listhead->forward_to(from_space_obj);
1328 from_space_obj = listhead;
1329 }
1330 oop observed_overflow_list = _overflow_list;
1331 oop cur_overflow_list;
1332 do {
1333 cur_overflow_list = observed_overflow_list;
1334 if (cur_overflow_list != BUSY) {
1335 from_space_obj->set_klass_to_list_ptr(cur_overflow_list);
1336 } else {
1337 from_space_obj->set_klass_to_list_ptr(NULL);
1338 }
1339 observed_overflow_list =
1340 (oop)Atomic::cmpxchg_ptr(from_space_obj, &_overflow_list, cur_overflow_list);
1341 } while (cur_overflow_list != observed_overflow_list);
1342 }
1343 }
1344
1345 bool ParNewGeneration::take_from_overflow_list(ParScanThreadState* par_scan_state) {
1346 bool res;
1347
1348 if (ParGCUseLocalOverflow) {
1349 res = par_scan_state->take_from_overflow_stack();
1350 } else {
1351 assert(!UseCompressedOops, "Error");
1352 res = take_from_overflow_list_work(par_scan_state);
1353 }
1354 return res;
1355 }
1356
1357
1358 // *NOTE*: The overflow list manipulation code here and
1359 // in CMSCollector:: are very similar in shape,
1360 // except that in the CMS case we thread the objects
1361 // directly into the list via their mark word, and do
1362 // not need to deal with special cases below related
1363 // to chunking of object arrays and promotion failure
1364 // handling.
1365 // CR 6797058 has been filed to attempt consolidation of
1366 // the common code.
1367 // Because of the common code, if you make any changes in
1368 // the code below, please check the CMS version to see if
1369 // similar changes might be needed.
1370 // See CMSCollector::par_take_from_overflow_list() for
1371 // more extensive documentation comments.
1372 bool ParNewGeneration::take_from_overflow_list_work(ParScanThreadState* par_scan_state) {
1373 ObjToScanQueue* work_q = par_scan_state->work_queue();
1374 // How many to take?
1375 size_t objsFromOverflow = MIN2((size_t)(work_q->max_elems() - work_q->size())/4,
1376 (size_t)ParGCDesiredObjsFromOverflowList);
1377
1378 assert(!UseCompressedOops, "Error");
1379 assert(par_scan_state->overflow_stack() == NULL, "Error");
1380 if (_overflow_list == NULL) return false;
1381
1382 // Otherwise, there was something there; try claiming the list.
1383 oop prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1384 // Trim off a prefix of at most objsFromOverflow items
1385 Thread* tid = Thread::current();
1386 size_t spin_count = (size_t)ParallelGCThreads;
1387 size_t sleep_time_millis = MAX2((size_t)1, objsFromOverflow/100);
1388 for (size_t spin = 0; prefix == BUSY && spin < spin_count; spin++) {
1389 // someone grabbed it before we did ...
1390 // ... we spin for a short while...
1391 os::sleep(tid, sleep_time_millis, false);
1392 if (_overflow_list == NULL) {
1393 // nothing left to take
1394 return false;
1395 } else if (_overflow_list != BUSY) {
1396 // try and grab the prefix
1397 prefix = cast_to_oop(Atomic::xchg_ptr(BUSY, &_overflow_list));
1398 }
1399 }
1400 if (prefix == NULL || prefix == BUSY) {
1401 // Nothing to take or waited long enough
1402 if (prefix == NULL) {
1403 // Write back the NULL in case we overwrote it with BUSY above
1404 // and it is still the same value.
1405 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1406 }
1407 return false;
1408 }
1409 assert(prefix != NULL && prefix != BUSY, "Error");
1410 size_t i = 1;
1411 oop cur = prefix;
1412 while (i < objsFromOverflow && cur->klass_or_null() != NULL) {
1413 i++; cur = cur->list_ptr_from_klass();
1414 }
1415
1416 // Reattach remaining (suffix) to overflow list
1417 if (cur->klass_or_null() == NULL) {
1418 // Write back the NULL in lieu of the BUSY we wrote
1419 // above and it is still the same value.
1420 if (_overflow_list == BUSY) {
1421 (void) Atomic::cmpxchg_ptr(NULL, &_overflow_list, BUSY);
1422 }
1423 } else {
1424 assert(cur->klass_or_null() != (Klass*)(address)BUSY, "Error");
1425 oop suffix = cur->list_ptr_from_klass(); // suffix will be put back on global list
1426 cur->set_klass_to_list_ptr(NULL); // break off suffix
1427 // It's possible that the list is still in the empty(busy) state
1428 // we left it in a short while ago; in that case we may be
1429 // able to place back the suffix.
1430 oop observed_overflow_list = _overflow_list;
1431 oop cur_overflow_list = observed_overflow_list;
1432 bool attached = false;
1433 while (observed_overflow_list == BUSY || observed_overflow_list == NULL) {
1434 observed_overflow_list =
1435 (oop) Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1436 if (cur_overflow_list == observed_overflow_list) {
1437 attached = true;
1438 break;
1439 } else cur_overflow_list = observed_overflow_list;
1440 }
1441 if (!attached) {
1442 // Too bad, someone else got in in between; we'll need to do a splice.
1443 // Find the last item of suffix list
1444 oop last = suffix;
1445 while (last->klass_or_null() != NULL) {
1446 last = last->list_ptr_from_klass();
1447 }
1448 // Atomically prepend suffix to current overflow list
1449 observed_overflow_list = _overflow_list;
1450 do {
1451 cur_overflow_list = observed_overflow_list;
1452 if (cur_overflow_list != BUSY) {
1453 // Do the splice ...
1454 last->set_klass_to_list_ptr(cur_overflow_list);
1455 } else { // cur_overflow_list == BUSY
1456 last->set_klass_to_list_ptr(NULL);
1457 }
1458 observed_overflow_list =
1459 (oop)Atomic::cmpxchg_ptr(suffix, &_overflow_list, cur_overflow_list);
1460 } while (cur_overflow_list != observed_overflow_list);
1461 }
1462 }
1463
1464 // Push objects on prefix list onto this thread's work queue
1465 assert(prefix != NULL && prefix != BUSY, "program logic");
1466 cur = prefix;
1467 ssize_t n = 0;
1468 while (cur != NULL) {
1469 oop obj_to_push = cur->forwardee();
1470 oop next = cur->list_ptr_from_klass();
1471 cur->set_klass(obj_to_push->klass());
1472 // This may be an array object that is self-forwarded. In that case, the list pointer
1473 // space, cur, is not in the Java heap, but rather in the C-heap and should be freed.
1474 if (!is_in_reserved(cur)) {
1475 // This can become a scaling bottleneck when there is work queue overflow coincident
1476 // with promotion failure.
1477 oopDesc* f = cur;
1478 FREE_C_HEAP_ARRAY(oopDesc, f);
1479 } else if (par_scan_state->should_be_partially_scanned(obj_to_push, cur)) {
1480 assert(arrayOop(cur)->length() == 0, "entire array remaining to be scanned");
1481 obj_to_push = cur;
1482 }
1483 bool ok = work_q->push(obj_to_push);
1484 assert(ok, "Should have succeeded");
1485 cur = next;
1486 n++;
1487 }
1488 TASKQUEUE_STATS_ONLY(par_scan_state->note_overflow_refill(n));
1489 #ifndef PRODUCT
1490 assert(_num_par_pushes >= n, "Too many pops?");
1491 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes);
1492 #endif
1493 return true;
1494 }
1495 #undef BUSY
1496
1497 void ParNewGeneration::ref_processor_init() {
1498 if (_ref_processor == NULL) {
1499 // Allocate and initialize a reference processor
1500 _ref_processor =
1501 new ReferenceProcessor(_reserved, // span
1502 ParallelRefProcEnabled && (ParallelGCThreads > 1), // mt processing
1503 (int) ParallelGCThreads, // mt processing degree
1504 refs_discovery_is_mt(), // mt discovery
1505 (int) ParallelGCThreads, // mt discovery degree
1506 refs_discovery_is_atomic(), // atomic_discovery
1507 NULL); // is_alive_non_header
1508 }
1509 }
1510
1511 const char* ParNewGeneration::name() const {
1512 return "par new generation";
1513 }