1 /*
2 * Copyright (c) 2013, 2020, Red Hat, Inc. 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
27 #include "classfile/symbolTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30
31 #include "gc/shared/weakProcessor.inline.hpp"
32 #include "gc/shared/gcTimer.hpp"
33 #include "gc/shared/gcTrace.hpp"
34 #include "gc/shared/referenceProcessor.hpp"
35 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
36 #include "gc/shared/strongRootsScope.hpp"
37
38 #include "gc/shenandoah/shenandoahBarrierSet.inline.hpp"
39 #include "gc/shenandoah/shenandoahClosures.inline.hpp"
40 #include "gc/shenandoah/shenandoahConcurrentMark.inline.hpp"
41 #include "gc/shenandoah/shenandoahMarkCompact.hpp"
42 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
43 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
44 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
45 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
46 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
47 #include "gc/shenandoah/shenandoahUtils.hpp"
48
49 #include "memory/iterator.inline.hpp"
50 #include "memory/metaspace.hpp"
51 #include "memory/resourceArea.hpp"
52 #include "oops/oop.inline.hpp"
53 #include "runtime/handles.inline.hpp"
54
55 template<UpdateRefsMode UPDATE_REFS>
56 class ShenandoahInitMarkRootsClosure : public OopClosure {
57 private:
58 ShenandoahObjToScanQueue* _queue;
59 ShenandoahHeap* _heap;
60 ShenandoahMarkingContext* const _mark_context;
61
62 template <class T>
63 inline void do_oop_work(T* p) {
64 ShenandoahConcurrentMark::mark_through_ref<T, UPDATE_REFS, NO_DEDUP>(p, _heap, _queue, _mark_context);
65 }
66
67 public:
68 ShenandoahInitMarkRootsClosure(ShenandoahObjToScanQueue* q) :
69 _queue(q),
70 _heap(ShenandoahHeap::heap()),
71 _mark_context(_heap->marking_context()) {};
72
73 void do_oop(narrowOop* p) { do_oop_work(p); }
74 void do_oop(oop* p) { do_oop_work(p); }
75 };
76
77 ShenandoahMarkRefsSuperClosure::ShenandoahMarkRefsSuperClosure(ShenandoahObjToScanQueue* q, ReferenceProcessor* rp) :
78 MetadataVisitingOopIterateClosure(rp),
79 _queue(q),
80 _heap(ShenandoahHeap::heap()),
81 _mark_context(_heap->marking_context())
82 { }
83
84 template<UpdateRefsMode UPDATE_REFS>
85 class ShenandoahInitMarkRootsTask : public AbstractGangTask {
86 private:
87 ShenandoahRootScanner* _rp;
88 public:
89 ShenandoahInitMarkRootsTask(ShenandoahRootScanner* rp) :
90 AbstractGangTask("Shenandoah init mark roots task"),
91 _rp(rp) {
92 }
93
94 void work(uint worker_id) {
95 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
96 ShenandoahParallelWorkerSession worker_session(worker_id);
97
98 ShenandoahHeap* heap = ShenandoahHeap::heap();
99 ShenandoahObjToScanQueueSet* queues = heap->concurrent_mark()->task_queues();
100 assert(queues->get_reserved() > worker_id, "Queue has not been reserved for worker id: %d", worker_id);
101
102 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
103
104 ShenandoahInitMarkRootsClosure<UPDATE_REFS> mark_cl(q);
105 do_work(heap, &mark_cl, worker_id);
106 }
107
108 private:
109 void do_work(ShenandoahHeap* heap, OopClosure* oops, uint worker_id) {
110 // The rationale for selecting the roots to scan is as follows:
111 // a. With unload_classes = true, we only want to scan the actual strong roots from the
112 // code cache. This will allow us to identify the dead classes, unload them, *and*
113 // invalidate the relevant code cache blobs. This could be only done together with
114 // class unloading.
115 // b. With unload_classes = false, we have to nominally retain all the references from code
116 // cache, because there could be the case of embedded class/oop in the generated code,
117 // which we will never visit during mark. Without code cache invalidation, as in (a),
118 // we risk executing that code cache blob, and crashing.
119 if (heap->unload_classes()) {
120 _rp->strong_roots_do(worker_id, oops);
121 } else {
122 _rp->roots_do(worker_id, oops);
123 }
124 }
125 };
126
127 class ShenandoahUpdateRootsTask : public AbstractGangTask {
128 private:
129 ShenandoahRootUpdater* _root_updater;
130 bool _check_alive;
131 public:
132 ShenandoahUpdateRootsTask(ShenandoahRootUpdater* root_updater, bool check_alive) :
133 AbstractGangTask("Shenandoah update roots task"),
134 _root_updater(root_updater),
135 _check_alive(check_alive){
136 }
137
138 void work(uint worker_id) {
139 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
140 ShenandoahParallelWorkerSession worker_session(worker_id);
141
142 ShenandoahHeap* heap = ShenandoahHeap::heap();
143 ShenandoahUpdateRefsClosure cl;
144 if (_check_alive) {
145 ShenandoahForwardedIsAliveClosure is_alive;
146 _root_updater->roots_do<ShenandoahForwardedIsAliveClosure, ShenandoahUpdateRefsClosure>(worker_id, &is_alive, &cl);
147 } else {
148 AlwaysTrueClosure always_true;;
149 _root_updater->roots_do<AlwaysTrueClosure, ShenandoahUpdateRefsClosure>(worker_id, &always_true, &cl);
150 }
151 }
152 };
153
154 class ShenandoahConcurrentMarkingTask : public AbstractGangTask {
155 private:
156 ShenandoahConcurrentMark* _cm;
157 TaskTerminator* _terminator;
158
159 public:
160 ShenandoahConcurrentMarkingTask(ShenandoahConcurrentMark* cm, TaskTerminator* terminator) :
161 AbstractGangTask("Root Region Scan"), _cm(cm), _terminator(terminator) {
162 }
163
164 void work(uint worker_id) {
165 ShenandoahHeap* heap = ShenandoahHeap::heap();
166 ShenandoahConcurrentWorkerSession worker_session(worker_id);
167 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
168 ShenandoahObjToScanQueue* q = _cm->get_queue(worker_id);
169 ReferenceProcessor* rp;
170 if (heap->process_references()) {
171 rp = heap->ref_processor();
172 shenandoah_assert_rp_isalive_installed();
173 } else {
174 rp = NULL;
175 }
176
177 _cm->concurrent_scan_code_roots(worker_id, rp);
178 _cm->mark_loop(worker_id, _terminator, rp,
179 true, // cancellable
180 ShenandoahStringDedup::is_enabled()); // perform string dedup
181 }
182 };
183
184 class ShenandoahSATBAndRemarkCodeRootsThreadsClosure : public ThreadClosure {
185 private:
186 ShenandoahSATBBufferClosure* _satb_cl;
187 OopClosure* const _cl;
188 MarkingCodeBlobClosure* _code_cl;
189 uintx _claim_token;
190
191 public:
192 ShenandoahSATBAndRemarkCodeRootsThreadsClosure(ShenandoahSATBBufferClosure* satb_cl, OopClosure* cl, MarkingCodeBlobClosure* code_cl) :
193 _satb_cl(satb_cl), _cl(cl), _code_cl(code_cl),
194 _claim_token(Threads::thread_claim_token()) {}
195
196 void do_thread(Thread* thread) {
197 if (thread->claim_threads_do(true, _claim_token)) {
198 ShenandoahThreadLocalData::satb_mark_queue(thread).apply_closure_and_empty(_satb_cl);
199 if (thread->is_Java_thread()) {
200 if (_cl != NULL) {
201 ResourceMark rm;
202 thread->oops_do(_cl, _code_cl);
203 } else if (_code_cl != NULL) {
204 // In theory it should not be neccessary to explicitly walk the nmethods to find roots for concurrent marking
205 // however the liveness of oops reachable from nmethods have very complex lifecycles:
206 // * Alive if on the stack of an executing method
207 // * Weakly reachable otherwise
208 // Some objects reachable from nmethods, such as the class loader (or klass_holder) of the receiver should be
209 // live by the SATB invariant but other oops recorded in nmethods may behave differently.
210 JavaThread* jt = (JavaThread*)thread;
211 jt->nmethods_do(_code_cl);
212 }
213 }
214 }
215 }
216 };
217
218 class ShenandoahFinalMarkingTask : public AbstractGangTask {
219 private:
220 ShenandoahConcurrentMark* _cm;
221 TaskTerminator* _terminator;
222 bool _dedup_string;
223
224 public:
225 ShenandoahFinalMarkingTask(ShenandoahConcurrentMark* cm, TaskTerminator* terminator, bool dedup_string) :
226 AbstractGangTask("Shenandoah Final Marking"), _cm(cm), _terminator(terminator), _dedup_string(dedup_string) {
227 }
228
229 void work(uint worker_id) {
230 ShenandoahHeap* heap = ShenandoahHeap::heap();
231
232 ShenandoahParallelWorkerSession worker_session(worker_id);
233 ReferenceProcessor* rp;
234 if (heap->process_references()) {
235 rp = heap->ref_processor();
236 shenandoah_assert_rp_isalive_installed();
237 } else {
238 rp = NULL;
239 }
240
241 // First drain remaining SATB buffers.
242 // Notice that this is not strictly necessary for mark-compact. But since
243 // it requires a StrongRootsScope around the task, we need to claim the
244 // threads, and performance-wise it doesn't really matter. Adds about 1ms to
245 // full-gc.
246 {
247 ShenandoahObjToScanQueue* q = _cm->get_queue(worker_id);
248
249 ShenandoahSATBBufferClosure cl(q);
250 SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
251 while (satb_mq_set.apply_closure_to_completed_buffer(&cl));
252 bool do_nmethods = heap->unload_classes() && !ShenandoahConcurrentRoots::can_do_concurrent_class_unloading();
253 if (heap->has_forwarded_objects()) {
254 ShenandoahMarkResolveRefsClosure resolve_mark_cl(q, rp);
255 MarkingCodeBlobClosure blobsCl(&resolve_mark_cl, !CodeBlobToOopClosure::FixRelocations);
256 ShenandoahSATBAndRemarkCodeRootsThreadsClosure tc(&cl,
257 ShenandoahStoreValEnqueueBarrier ? &resolve_mark_cl : NULL,
258 do_nmethods ? &blobsCl : NULL);
259 Threads::threads_do(&tc);
260 } else {
261 ShenandoahMarkRefsClosure mark_cl(q, rp);
262 MarkingCodeBlobClosure blobsCl(&mark_cl, !CodeBlobToOopClosure::FixRelocations);
263 ShenandoahSATBAndRemarkCodeRootsThreadsClosure tc(&cl,
264 ShenandoahStoreValEnqueueBarrier ? &mark_cl : NULL,
265 do_nmethods ? &blobsCl : NULL);
266 Threads::threads_do(&tc);
267 }
268 }
269
270 if (heap->is_degenerated_gc_in_progress()) {
271 // Degenerated cycle may bypass concurrent cycle, so code roots might not be scanned,
272 // let's check here.
273 _cm->concurrent_scan_code_roots(worker_id, rp);
274 }
275
276 _cm->mark_loop(worker_id, _terminator, rp,
277 false, // not cancellable
278 _dedup_string);
279
280 assert(_cm->task_queues()->is_empty(), "Should be empty");
281 }
282 };
283
284 void ShenandoahConcurrentMark::mark_roots(ShenandoahPhaseTimings::Phase root_phase) {
285 assert(Thread::current()->is_VM_thread(), "can only do this in VMThread");
286 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
287
288 ShenandoahHeap* heap = ShenandoahHeap::heap();
289
290 ShenandoahGCPhase phase(root_phase);
291
292 WorkGang* workers = heap->workers();
293 uint nworkers = workers->active_workers();
294
295 assert(nworkers <= task_queues()->size(), "Just check");
296
297 ShenandoahRootScanner root_proc(nworkers, root_phase);
298 TASKQUEUE_STATS_ONLY(task_queues()->reset_taskqueue_stats());
299 task_queues()->reserve(nworkers);
300
301 if (heap->has_forwarded_objects()) {
302 ShenandoahInitMarkRootsTask<RESOLVE> mark_roots(&root_proc);
303 workers->run_task(&mark_roots);
304 } else {
305 // No need to update references, which means the heap is stable.
306 // Can save time not walking through forwarding pointers.
307 ShenandoahInitMarkRootsTask<NONE> mark_roots(&root_proc);
308 workers->run_task(&mark_roots);
309 }
310
311 clear_claim_codecache();
312 }
313
314 void ShenandoahConcurrentMark::update_roots(ShenandoahPhaseTimings::Phase root_phase) {
315 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
316 assert(root_phase == ShenandoahPhaseTimings::full_gc_update_roots ||
317 root_phase == ShenandoahPhaseTimings::degen_gc_update_roots,
318 "Only for these phases");
319
320 ShenandoahGCPhase phase(root_phase);
321
322 bool check_alive = root_phase == ShenandoahPhaseTimings::degen_gc_update_roots;
323
324 #if COMPILER2_OR_JVMCI
325 DerivedPointerTable::clear();
326 #endif
327
328 uint nworkers = _heap->workers()->active_workers();
329
330 ShenandoahRootUpdater root_updater(nworkers, root_phase);
331 ShenandoahUpdateRootsTask update_roots(&root_updater, check_alive);
332 _heap->workers()->run_task(&update_roots);
333
334 #if COMPILER2_OR_JVMCI
335 DerivedPointerTable::update_pointers();
336 #endif
337 }
338
339 class ShenandoahUpdateThreadRootsTask : public AbstractGangTask {
340 private:
341 ShenandoahThreadRoots _thread_roots;
342 ShenandoahPhaseTimings::Phase _phase;
343 ShenandoahGCWorkerPhase _worker_phase;
344 public:
345 ShenandoahUpdateThreadRootsTask(bool is_par, ShenandoahPhaseTimings::Phase phase) :
346 AbstractGangTask("Shenandoah Update Thread Roots"),
347 _thread_roots(phase, is_par),
348 _phase(phase),
349 _worker_phase(phase) {}
350
351 void work(uint worker_id) {
352 ShenandoahParallelWorkerSession worker_session(worker_id);
353 ShenandoahUpdateRefsClosure cl;
354 _thread_roots.oops_do(&cl, NULL, worker_id);
355 }
356 };
357
358 void ShenandoahConcurrentMark::update_thread_roots(ShenandoahPhaseTimings::Phase root_phase) {
359 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
360
361 ShenandoahGCPhase phase(root_phase);
362
363 #if COMPILER2_OR_JVMCI
364 DerivedPointerTable::clear();
365 #endif
366
367 WorkGang* workers = _heap->workers();
368 bool is_par = workers->active_workers() > 1;
369
370 ShenandoahUpdateThreadRootsTask task(is_par, root_phase);
371 workers->run_task(&task);
372
373 #if COMPILER2_OR_JVMCI
374 DerivedPointerTable::update_pointers();
375 #endif
376 }
377
378 void ShenandoahConcurrentMark::initialize(uint workers) {
379 _heap = ShenandoahHeap::heap();
380
381 uint num_queues = MAX2(workers, 1U);
382
383 _task_queues = new ShenandoahObjToScanQueueSet((int) num_queues);
384
385 for (uint i = 0; i < num_queues; ++i) {
386 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
387 task_queue->initialize();
388 _task_queues->register_queue(i, task_queue);
389 }
390 }
391
392 void ShenandoahConcurrentMark::concurrent_scan_code_roots(uint worker_id, ReferenceProcessor* rp) {
393 if (claim_codecache()) {
394 ShenandoahObjToScanQueue* q = task_queues()->queue(worker_id);
395 if (!_heap->unload_classes()) {
396 MutexLocker mu(CodeCache_lock, Mutex::_no_safepoint_check_flag);
397 // TODO: We can not honor StringDeduplication here, due to lock ranking
398 // inversion. So, we may miss some deduplication candidates.
399 if (_heap->has_forwarded_objects()) {
400 ShenandoahMarkResolveRefsClosure cl(q, rp);
401 CodeBlobToOopClosure blobs(&cl, !CodeBlobToOopClosure::FixRelocations);
402 CodeCache::blobs_do(&blobs);
403 } else {
404 ShenandoahMarkRefsClosure cl(q, rp);
405 CodeBlobToOopClosure blobs(&cl, !CodeBlobToOopClosure::FixRelocations);
406 CodeCache::blobs_do(&blobs);
407 }
408 }
409 }
410 }
411
412 void ShenandoahConcurrentMark::mark_from_roots() {
413 WorkGang* workers = _heap->workers();
414 uint nworkers = workers->active_workers();
415
416 if (_heap->process_references()) {
417 ReferenceProcessor* rp = _heap->ref_processor();
418 rp->set_active_mt_degree(nworkers);
419
420 // enable ("weak") refs discovery
421 rp->enable_discovery(true /*verify_no_refs*/);
422 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
423 }
424
425 shenandoah_assert_rp_isalive_not_installed();
426 ShenandoahIsAliveSelector is_alive;
427 ReferenceProcessorIsAliveMutator fix_isalive(_heap->ref_processor(), is_alive.is_alive_closure());
428
429 task_queues()->reserve(nworkers);
430
431 {
432 TaskTerminator terminator(nworkers, task_queues());
433 ShenandoahConcurrentMarkingTask task(this, &terminator);
434 workers->run_task(&task);
435 }
436
437 assert(task_queues()->is_empty() || _heap->cancelled_gc(), "Should be empty when not cancelled");
438 }
439
440 void ShenandoahConcurrentMark::finish_mark_from_roots(bool full_gc) {
441 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
442
443 uint nworkers = _heap->workers()->active_workers();
444
445 // Finally mark everything else we've got in our queues during the previous steps.
446 // It does two different things for concurrent vs. mark-compact GC:
447 // - For concurrent GC, it starts with empty task queues, drains the remaining
448 // SATB buffers, and then completes the marking closure.
449 // - For mark-compact GC, it starts out with the task queues seeded by initial
450 // root scan, and completes the closure, thus marking through all live objects
451 // The implementation is the same, so it's shared here.
452 {
453 ShenandoahGCPhase phase(full_gc ?
454 ShenandoahPhaseTimings::full_gc_mark_finish_queues :
455 ShenandoahPhaseTimings::finish_queues);
456 task_queues()->reserve(nworkers);
457
458 shenandoah_assert_rp_isalive_not_installed();
459 ShenandoahIsAliveSelector is_alive;
460 ReferenceProcessorIsAliveMutator fix_isalive(_heap->ref_processor(), is_alive.is_alive_closure());
461
462 StrongRootsScope scope(nworkers);
463 TaskTerminator terminator(nworkers, task_queues());
464 ShenandoahFinalMarkingTask task(this, &terminator, ShenandoahStringDedup::is_enabled());
465 _heap->workers()->run_task(&task);
466 }
467
468 assert(task_queues()->is_empty(), "Should be empty");
469
470 // When we're done marking everything, we process weak references.
471 if (_heap->process_references()) {
472 weak_refs_work(full_gc);
473 }
474
475 assert(task_queues()->is_empty(), "Should be empty");
476 TASKQUEUE_STATS_ONLY(task_queues()->print_taskqueue_stats());
477 TASKQUEUE_STATS_ONLY(task_queues()->reset_taskqueue_stats());
478 }
479
480 // Weak Reference Closures
481 class ShenandoahCMDrainMarkingStackClosure: public VoidClosure {
482 uint _worker_id;
483 TaskTerminator* _terminator;
484 bool _reset_terminator;
485
486 public:
487 ShenandoahCMDrainMarkingStackClosure(uint worker_id, TaskTerminator* t, bool reset_terminator = false):
488 _worker_id(worker_id),
489 _terminator(t),
490 _reset_terminator(reset_terminator) {
491 }
492
493 void do_void() {
494 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
495
496 ShenandoahHeap* sh = ShenandoahHeap::heap();
497 ShenandoahConcurrentMark* scm = sh->concurrent_mark();
498 assert(sh->process_references(), "why else would we be here?");
499 ReferenceProcessor* rp = sh->ref_processor();
500
501 shenandoah_assert_rp_isalive_installed();
502
503 scm->mark_loop(_worker_id, _terminator, rp,
504 false, // not cancellable
505 false); // do not do strdedup
506
507 if (_reset_terminator) {
508 _terminator->reset_for_reuse();
509 }
510 }
511 };
512
513 class ShenandoahCMKeepAliveClosure : public OopClosure {
514 private:
515 ShenandoahObjToScanQueue* _queue;
516 ShenandoahHeap* _heap;
517 ShenandoahMarkingContext* const _mark_context;
518
519 template <class T>
520 inline void do_oop_work(T* p) {
521 ShenandoahConcurrentMark::mark_through_ref<T, NONE, NO_DEDUP>(p, _heap, _queue, _mark_context);
522 }
523
524 public:
525 ShenandoahCMKeepAliveClosure(ShenandoahObjToScanQueue* q) :
526 _queue(q),
527 _heap(ShenandoahHeap::heap()),
528 _mark_context(_heap->marking_context()) {}
529
530 void do_oop(narrowOop* p) { do_oop_work(p); }
531 void do_oop(oop* p) { do_oop_work(p); }
532 };
533
534 class ShenandoahCMKeepAliveUpdateClosure : public OopClosure {
535 private:
536 ShenandoahObjToScanQueue* _queue;
537 ShenandoahHeap* _heap;
538 ShenandoahMarkingContext* const _mark_context;
539
540 template <class T>
541 inline void do_oop_work(T* p) {
542 ShenandoahConcurrentMark::mark_through_ref<T, SIMPLE, NO_DEDUP>(p, _heap, _queue, _mark_context);
543 }
544
545 public:
546 ShenandoahCMKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
547 _queue(q),
548 _heap(ShenandoahHeap::heap()),
549 _mark_context(_heap->marking_context()) {}
550
551 void do_oop(narrowOop* p) { do_oop_work(p); }
552 void do_oop(oop* p) { do_oop_work(p); }
553 };
554
555 class ShenandoahWeakUpdateClosure : public OopClosure {
556 private:
557 ShenandoahHeap* const _heap;
558
559 template <class T>
560 inline void do_oop_work(T* p) {
561 oop o = _heap->maybe_update_with_forwarded(p);
562 shenandoah_assert_marked_except(p, o, o == NULL);
563 }
564
565 public:
566 ShenandoahWeakUpdateClosure() : _heap(ShenandoahHeap::heap()) {}
567
568 void do_oop(narrowOop* p) { do_oop_work(p); }
569 void do_oop(oop* p) { do_oop_work(p); }
570 };
571
572 class ShenandoahRefProcTaskProxy : public AbstractGangTask {
573 private:
574 AbstractRefProcTaskExecutor::ProcessTask& _proc_task;
575 TaskTerminator* _terminator;
576
577 public:
578 ShenandoahRefProcTaskProxy(AbstractRefProcTaskExecutor::ProcessTask& proc_task,
579 TaskTerminator* t) :
580 AbstractGangTask("Process reference objects in parallel"),
581 _proc_task(proc_task),
582 _terminator(t) {
583 }
584
585 void work(uint worker_id) {
586 ResourceMark rm;
587 HandleMark hm;
588 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
589 ShenandoahHeap* heap = ShenandoahHeap::heap();
590 ShenandoahParallelWorkerSession worker_session(worker_id);
591 ShenandoahCMDrainMarkingStackClosure complete_gc(worker_id, _terminator);
592 if (heap->has_forwarded_objects()) {
593 ShenandoahForwardedIsAliveClosure is_alive;
594 ShenandoahCMKeepAliveUpdateClosure keep_alive(heap->concurrent_mark()->get_queue(worker_id));
595 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
596 } else {
597 ShenandoahIsAliveClosure is_alive;
598 ShenandoahCMKeepAliveClosure keep_alive(heap->concurrent_mark()->get_queue(worker_id));
599 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
600 }
601 }
602 };
603
604 class ShenandoahRefProcTaskExecutor : public AbstractRefProcTaskExecutor {
605 private:
606 WorkGang* _workers;
607
608 public:
609 ShenandoahRefProcTaskExecutor(WorkGang* workers) :
610 _workers(workers) {
611 }
612
613 // Executes a task using worker threads.
614 void execute(ProcessTask& task, uint ergo_workers) {
615 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
616
617 ShenandoahHeap* heap = ShenandoahHeap::heap();
618 ShenandoahConcurrentMark* cm = heap->concurrent_mark();
619 ShenandoahPushWorkerQueuesScope scope(_workers, cm->task_queues(),
620 ergo_workers,
621 /* do_check = */ false);
622 uint nworkers = _workers->active_workers();
623 cm->task_queues()->reserve(nworkers);
624 TaskTerminator terminator(nworkers, cm->task_queues());
625 ShenandoahRefProcTaskProxy proc_task_proxy(task, &terminator);
626 _workers->run_task(&proc_task_proxy);
627 }
628 };
629
630 void ShenandoahConcurrentMark::weak_refs_work(bool full_gc) {
631 assert(_heap->process_references(), "sanity");
632
633 ShenandoahPhaseTimings::Phase phase_root =
634 full_gc ?
635 ShenandoahPhaseTimings::full_gc_weakrefs :
636 ShenandoahPhaseTimings::weakrefs;
637
638 ShenandoahGCPhase phase(phase_root);
639
640 ReferenceProcessor* rp = _heap->ref_processor();
641
642 // NOTE: We cannot shortcut on has_discovered_references() here, because
643 // we will miss marking JNI Weak refs then, see implementation in
644 // ReferenceProcessor::process_discovered_references.
645 weak_refs_work_doit(full_gc);
646
647 rp->verify_no_references_recorded();
648 assert(!rp->discovery_enabled(), "Post condition");
649
650 }
651
652 void ShenandoahConcurrentMark::weak_refs_work_doit(bool full_gc) {
653 ReferenceProcessor* rp = _heap->ref_processor();
654
655 ShenandoahPhaseTimings::Phase phase_process =
656 full_gc ?
657 ShenandoahPhaseTimings::full_gc_weakrefs_process :
658 ShenandoahPhaseTimings::weakrefs_process;
659
660 shenandoah_assert_rp_isalive_not_installed();
661 ShenandoahIsAliveSelector is_alive;
662 ReferenceProcessorIsAliveMutator fix_isalive(rp, is_alive.is_alive_closure());
663
664 WorkGang* workers = _heap->workers();
665 uint nworkers = workers->active_workers();
666
667 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
668 rp->set_active_mt_degree(nworkers);
669
670 assert(task_queues()->is_empty(), "Should be empty");
671
672 // complete_gc and keep_alive closures instantiated here are only needed for
673 // single-threaded path in RP. They share the queue 0 for tracking work, which
674 // simplifies implementation. Since RP may decide to call complete_gc several
675 // times, we need to be able to reuse the terminator.
676 uint serial_worker_id = 0;
677 TaskTerminator terminator(1, task_queues());
678 ShenandoahCMDrainMarkingStackClosure complete_gc(serial_worker_id, &terminator, /* reset_terminator = */ true);
679
680 ShenandoahRefProcTaskExecutor executor(workers);
681
682 ReferenceProcessorPhaseTimes pt(_heap->gc_timer(), rp->num_queues());
683
684 {
685 // Note: Don't emit JFR event for this phase, to avoid overflow nesting phase level.
686 // Reference Processor emits 2 levels JFR event, that can get us over the JFR
687 // event nesting level limits, in case of degenerated GC gets upgraded to
688 // full GC.
689 ShenandoahTimingsTracker phase_timing(phase_process);
690
691 if (_heap->has_forwarded_objects()) {
692 ShenandoahCMKeepAliveUpdateClosure keep_alive(get_queue(serial_worker_id));
693 const ReferenceProcessorStats& stats =
694 rp->process_discovered_references(is_alive.is_alive_closure(), &keep_alive,
695 &complete_gc, &executor,
696 &pt);
697 _heap->tracer()->report_gc_reference_stats(stats);
698 } else {
699 ShenandoahCMKeepAliveClosure keep_alive(get_queue(serial_worker_id));
700 const ReferenceProcessorStats& stats =
701 rp->process_discovered_references(is_alive.is_alive_closure(), &keep_alive,
702 &complete_gc, &executor,
703 &pt);
704 _heap->tracer()->report_gc_reference_stats(stats);
705 }
706
707 pt.print_all_references();
708
709 assert(task_queues()->is_empty(), "Should be empty");
710 }
711 }
712
713 class ShenandoahCancelledGCYieldClosure : public YieldClosure {
714 private:
715 ShenandoahHeap* const _heap;
716 public:
717 ShenandoahCancelledGCYieldClosure() : _heap(ShenandoahHeap::heap()) {};
718 virtual bool should_return() { return _heap->cancelled_gc(); }
719 };
720
721 class ShenandoahPrecleanCompleteGCClosure : public VoidClosure {
722 public:
723 void do_void() {
724 ShenandoahHeap* sh = ShenandoahHeap::heap();
725 ShenandoahConcurrentMark* scm = sh->concurrent_mark();
726 assert(sh->process_references(), "why else would we be here?");
727 TaskTerminator terminator(1, scm->task_queues());
728
729 ReferenceProcessor* rp = sh->ref_processor();
730 shenandoah_assert_rp_isalive_installed();
731
732 scm->mark_loop(0, &terminator, rp,
733 false, // not cancellable
734 false); // do not do strdedup
735 }
736 };
737
738 class ShenandoahPrecleanTask : public AbstractGangTask {
739 private:
740 ReferenceProcessor* _rp;
741
742 public:
743 ShenandoahPrecleanTask(ReferenceProcessor* rp) :
744 AbstractGangTask("Precleaning task"),
745 _rp(rp) {}
746
747 void work(uint worker_id) {
748 assert(worker_id == 0, "The code below is single-threaded, only one worker is expected");
749 ShenandoahParallelWorkerSession worker_session(worker_id);
750
751 ShenandoahHeap* sh = ShenandoahHeap::heap();
752 assert(!sh->has_forwarded_objects(), "No forwarded objects expected here");
753
754 ShenandoahObjToScanQueue* q = sh->concurrent_mark()->get_queue(worker_id);
755
756 ShenandoahCancelledGCYieldClosure yield;
757 ShenandoahPrecleanCompleteGCClosure complete_gc;
758
759 ShenandoahIsAliveClosure is_alive;
760 ShenandoahCMKeepAliveClosure keep_alive(q);
761 ResourceMark rm;
762 _rp->preclean_discovered_references(&is_alive, &keep_alive,
763 &complete_gc, &yield,
764 NULL);
765 }
766 };
767
768 void ShenandoahConcurrentMark::preclean_weak_refs() {
769 // Pre-cleaning weak references before diving into STW makes sense at the
770 // end of concurrent mark. This will filter out the references which referents
771 // are alive. Note that ReferenceProcessor already filters out these on reference
772 // discovery, and the bulk of work is done here. This phase processes leftovers
773 // that missed the initial filtering, i.e. when referent was marked alive after
774 // reference was discovered by RP.
775
776 assert(_heap->process_references(), "sanity");
777
778 // Shortcut if no references were discovered to avoid winding up threads.
779 ReferenceProcessor* rp = _heap->ref_processor();
780 if (!rp->has_discovered_references()) {
781 return;
782 }
783
784 assert(task_queues()->is_empty(), "Should be empty");
785
786 ReferenceProcessorMTDiscoveryMutator fix_mt_discovery(rp, false);
787
788 shenandoah_assert_rp_isalive_not_installed();
789 ShenandoahIsAliveSelector is_alive;
790 ReferenceProcessorIsAliveMutator fix_isalive(rp, is_alive.is_alive_closure());
791
792 // Execute precleaning in the worker thread: it will give us GCLABs, String dedup
793 // queues and other goodies. When upstream ReferenceProcessor starts supporting
794 // parallel precleans, we can extend this to more threads.
795 WorkGang* workers = _heap->workers();
796 uint nworkers = workers->active_workers();
797 assert(nworkers == 1, "This code uses only a single worker");
798 task_queues()->reserve(nworkers);
799
800 ShenandoahPrecleanTask task(rp);
801 workers->run_task(&task);
802
803 assert(task_queues()->is_empty(), "Should be empty");
804 }
805
806 void ShenandoahConcurrentMark::cancel() {
807 // Clean up marking stacks.
808 ShenandoahObjToScanQueueSet* queues = task_queues();
809 queues->clear();
810
811 // Cancel SATB buffers.
812 ShenandoahBarrierSet::satb_mark_queue_set().abandon_partial_marking();
813 }
814
815 ShenandoahObjToScanQueue* ShenandoahConcurrentMark::get_queue(uint worker_id) {
816 assert(task_queues()->get_reserved() > worker_id, "No reserved queue for worker id: %d", worker_id);
817 return _task_queues->queue(worker_id);
818 }
819
820 template <bool CANCELLABLE>
821 void ShenandoahConcurrentMark::mark_loop_prework(uint w, TaskTerminator *t, ReferenceProcessor *rp,
822 bool strdedup) {
823 ShenandoahObjToScanQueue* q = get_queue(w);
824
825 ShenandoahLiveData* ld = _heap->get_liveness_cache(w);
826
827 // TODO: We can clean up this if we figure out how to do templated oop closures that
828 // play nice with specialized_oop_iterators.
829 if (_heap->unload_classes()) {
830 if (_heap->has_forwarded_objects()) {
831 if (strdedup) {
832 ShenandoahMarkUpdateRefsMetadataDedupClosure cl(q, rp);
833 mark_loop_work<ShenandoahMarkUpdateRefsMetadataDedupClosure, CANCELLABLE>(&cl, ld, w, t);
834 } else {
835 ShenandoahMarkUpdateRefsMetadataClosure cl(q, rp);
836 mark_loop_work<ShenandoahMarkUpdateRefsMetadataClosure, CANCELLABLE>(&cl, ld, w, t);
837 }
838 } else {
839 if (strdedup) {
840 ShenandoahMarkRefsMetadataDedupClosure cl(q, rp);
841 mark_loop_work<ShenandoahMarkRefsMetadataDedupClosure, CANCELLABLE>(&cl, ld, w, t);
842 } else {
843 ShenandoahMarkRefsMetadataClosure cl(q, rp);
844 mark_loop_work<ShenandoahMarkRefsMetadataClosure, CANCELLABLE>(&cl, ld, w, t);
845 }
846 }
847 } else {
848 if (_heap->has_forwarded_objects()) {
849 if (strdedup) {
850 ShenandoahMarkUpdateRefsDedupClosure cl(q, rp);
851 mark_loop_work<ShenandoahMarkUpdateRefsDedupClosure, CANCELLABLE>(&cl, ld, w, t);
852 } else {
853 ShenandoahMarkUpdateRefsClosure cl(q, rp);
854 mark_loop_work<ShenandoahMarkUpdateRefsClosure, CANCELLABLE>(&cl, ld, w, t);
855 }
856 } else {
857 if (strdedup) {
858 ShenandoahMarkRefsDedupClosure cl(q, rp);
859 mark_loop_work<ShenandoahMarkRefsDedupClosure, CANCELLABLE>(&cl, ld, w, t);
860 } else {
861 ShenandoahMarkRefsClosure cl(q, rp);
862 mark_loop_work<ShenandoahMarkRefsClosure, CANCELLABLE>(&cl, ld, w, t);
863 }
864 }
865 }
866
867 _heap->flush_liveness_cache(w);
868 }
869
870 template <class T, bool CANCELLABLE>
871 void ShenandoahConcurrentMark::mark_loop_work(T* cl, ShenandoahLiveData* live_data, uint worker_id, TaskTerminator *terminator) {
872 uintx stride = ShenandoahMarkLoopStride;
873
874 ShenandoahHeap* heap = ShenandoahHeap::heap();
875 ShenandoahObjToScanQueueSet* queues = task_queues();
876 ShenandoahObjToScanQueue* q;
877 ShenandoahMarkTask t;
878
879 /*
880 * Process outstanding queues, if any.
881 *
882 * There can be more queues than workers. To deal with the imbalance, we claim
883 * extra queues first. Since marking can push new tasks into the queue associated
884 * with this worker id, we come back to process this queue in the normal loop.
885 */
886 assert(queues->get_reserved() == heap->workers()->active_workers(),
887 "Need to reserve proper number of queues: reserved: %u, active: %u", queues->get_reserved(), heap->workers()->active_workers());
888
889 q = queues->claim_next();
890 while (q != NULL) {
891 if (CANCELLABLE && heap->check_cancelled_gc_and_yield()) {
892 return;
893 }
894
895 for (uint i = 0; i < stride; i++) {
896 if (q->pop(t)) {
897 do_task<T>(q, cl, live_data, &t);
898 } else {
899 assert(q->is_empty(), "Must be empty");
900 q = queues->claim_next();
901 break;
902 }
903 }
904 }
905 q = get_queue(worker_id);
906
907 ShenandoahSATBBufferClosure drain_satb(q);
908 SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
909
910 /*
911 * Normal marking loop:
912 */
913 while (true) {
914 if (CANCELLABLE && heap->check_cancelled_gc_and_yield()) {
915 return;
916 }
917
918 while (satb_mq_set.completed_buffers_num() > 0) {
919 satb_mq_set.apply_closure_to_completed_buffer(&drain_satb);
920 }
921
922 uint work = 0;
923 for (uint i = 0; i < stride; i++) {
924 if (q->pop(t) ||
925 queues->steal(worker_id, t)) {
926 do_task<T>(q, cl, live_data, &t);
927 work++;
928 } else {
929 break;
930 }
931 }
932
933 if (work == 0) {
934 // No work encountered in current stride, try to terminate.
935 // Need to leave the STS here otherwise it might block safepoints.
936 ShenandoahSuspendibleThreadSetLeaver stsl(CANCELLABLE && ShenandoahSuspendibleWorkers);
937 ShenandoahTerminatorTerminator tt(heap);
938 if (terminator->offer_termination(&tt)) return;
939 }
940 }
941 }
942
943 bool ShenandoahConcurrentMark::claim_codecache() {
944 return _claimed_codecache.try_set();
945 }
946
947 void ShenandoahConcurrentMark::clear_claim_codecache() {
948 _claimed_codecache.unset();
949 }