1 /*
2 * Copyright (c) 2018, 2019, Red Hat, Inc. All rights reserved.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation.
7 *
8 * This code is distributed in the hope that it will be useful, but WITHOUT
9 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
10 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
11 * version 2 for more details (a copy is included in the LICENSE file that
12 * accompanied this code).
13 *
14 * You should have received a copy of the GNU General Public License version
15 * 2 along with this work; if not, write to the Free Software Foundation,
16 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
17 *
18 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
19 * or visit www.oracle.com if you need additional information or have any
20 * questions.
21 *
22 */
23
24 #include "precompiled.hpp"
25
26 #include "classfile/classLoaderData.hpp"
27 #include "classfile/classLoaderDataGraph.hpp"
28 #include "gc/shared/referenceProcessor.hpp"
29 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
30 #include "gc/shared/workgroup.hpp"
31 #include "gc/shared/weakProcessor.inline.hpp"
32 #include "gc/shenandoah/shenandoahBarrierSet.hpp"
33 #include "gc/shenandoah/shenandoahClosures.inline.hpp"
34 #include "gc/shenandoah/shenandoahCodeRoots.hpp"
35 #include "gc/shenandoah/shenandoahCollectionSet.hpp"
36 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
37 #include "gc/shenandoah/shenandoahFreeSet.hpp"
38 #include "gc/shenandoah/shenandoahForwarding.hpp"
39 #include "gc/shenandoah/shenandoahPhaseTimings.hpp"
40 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
41 #include "gc/shenandoah/shenandoahHeapRegionSet.inline.hpp"
42 #include "gc/shenandoah/shenandoahHeuristics.hpp"
43 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
44 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
45 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
46 #include "gc/shenandoah/shenandoahStringDedup.hpp"
47 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
48 #include "gc/shenandoah/shenandoahTimingTracker.hpp"
49 #include "gc/shenandoah/shenandoahTraversalGC.hpp"
50 #include "gc/shenandoah/shenandoahUtils.hpp"
51 #include "gc/shenandoah/shenandoahVerifier.hpp"
52
53 #include "memory/iterator.hpp"
54 #include "memory/metaspace.hpp"
55 #include "memory/resourceArea.hpp"
56 #include "memory/universe.hpp"
57
58 /**
59 * NOTE: We are using the SATB buffer in thread.hpp and satbMarkQueue.hpp, however, it is not an SATB algorithm.
60 * We're using the buffer as generic oop buffer to enqueue new values in concurrent oop stores, IOW, the algorithm
61 * is incremental-update-based.
62 *
63 * NOTE on interaction with TAMS: we want to avoid traversing new objects for
64 * several reasons:
65 * - We will not reclaim them in this cycle anyway, because they are not in the
66 * cset
67 * - It makes up for the bulk of work during final-pause
68 * - It also shortens the concurrent cycle because we don't need to
69 * pointlessly traverse through newly allocated objects.
70 * - As a nice side-effect, it solves the I-U termination problem (mutators
71 * cannot outrun the GC by allocating like crazy)
72 * - It is an easy way to achieve MWF. What MWF does is to also enqueue the
73 * target object of stores if it's new. Treating new objects live implicitely
74 * achieves the same, but without extra barriers. I think the effect of
75 * shortened final-pause (mentioned above) is the main advantage of MWF. In
76 * particular, we will not see the head of a completely new long linked list
77 * in final-pause and end up traversing huge chunks of the heap there.
78 * - We don't need to see/update the fields of new objects either, because they
79 * are either still null, or anything that's been stored into them has been
80 * evacuated+enqueued before (and will thus be treated later).
81 *
82 * We achieve this by setting TAMS for each region, and everything allocated
83 * beyond TAMS will be 'implicitely marked'.
84 *
85 * Gotchas:
86 * - While we want new objects to be implicitely marked, we don't want to count
87 * them alive. Otherwise the next cycle wouldn't pick them up and consider
88 * them for cset. This means that we need to protect such regions from
89 * getting accidentally thrashed at the end of traversal cycle. This is why I
90 * keep track of alloc-regions and check is_alloc_region() in the trashing
91 * code.
92 * - We *need* to traverse through evacuated objects. Those objects are
93 * pre-existing, and any references in them point to interesting objects that
94 * we need to see. We also want to count them as live, because we just
95 * determined that they are alive :-) I achieve this by upping TAMS
96 * concurrently for every gclab/gc-shared alloc before publishing the
97 * evacuated object. This way, the GC threads will not consider such objects
98 * implictely marked, and traverse through them as normal.
99 */
100 class ShenandoahTraversalSATBBufferClosure : public SATBBufferClosure {
101 private:
102 ShenandoahObjToScanQueue* _queue;
103 ShenandoahTraversalGC* _traversal_gc;
104 ShenandoahHeap* const _heap;
105
106 public:
107 ShenandoahTraversalSATBBufferClosure(ShenandoahObjToScanQueue* q) :
108 _queue(q),
109 _heap(ShenandoahHeap::heap())
110 { }
111
112 void do_buffer(void** buffer, size_t size) {
113 for (size_t i = 0; i < size; ++i) {
114 oop* p = (oop*) &buffer[i];
115 oop obj = RawAccess<>::oop_load(p);
116 shenandoah_assert_not_forwarded(p, obj);
117 if (_heap->marking_context()->mark(obj)) {
118 _queue->push(ShenandoahMarkTask(obj));
119 }
120 }
121 }
122 };
123
124 class ShenandoahTraversalSATBThreadsClosure : public ThreadClosure {
125 private:
126 ShenandoahTraversalSATBBufferClosure* _satb_cl;
127
128 public:
129 ShenandoahTraversalSATBThreadsClosure(ShenandoahTraversalSATBBufferClosure* satb_cl) :
130 _satb_cl(satb_cl) {}
131
132 void do_thread(Thread* thread) {
133 ShenandoahThreadLocalData::satb_mark_queue(thread).apply_closure_and_empty(_satb_cl);
134 }
135 };
136
137 // Like CLDToOopClosure, but clears has_modified_oops, so that we can record modified CLDs during traversal
138 // and remark them later during final-traversal.
139 class ShenandoahMarkCLDClosure : public CLDClosure {
140 private:
141 OopClosure* _cl;
142 public:
143 ShenandoahMarkCLDClosure(OopClosure* cl) : _cl(cl) {}
144 void do_cld(ClassLoaderData* cld) {
145 cld->oops_do(_cl, true, true);
146 }
147 };
148
149 // Like CLDToOopClosure, but only process modified CLDs
150 class ShenandoahRemarkCLDClosure : public CLDClosure {
151 private:
152 OopClosure* _cl;
153 public:
154 ShenandoahRemarkCLDClosure(OopClosure* cl) : _cl(cl) {}
155 void do_cld(ClassLoaderData* cld) {
156 if (cld->has_modified_oops()) {
157 cld->oops_do(_cl, true, true);
158 }
159 }
160 };
161
162 class ShenandoahInitTraversalCollectionTask : public AbstractGangTask {
163 private:
164 ShenandoahRootProcessor* _rp;
165 ShenandoahHeap* _heap;
166 ShenandoahCsetCodeRootsIterator* _cset_coderoots;
167 ShenandoahStringDedupRoot _dedup_roots;
168
169 public:
170 ShenandoahInitTraversalCollectionTask(ShenandoahRootProcessor* rp, ShenandoahCsetCodeRootsIterator* cset_coderoots) :
171 AbstractGangTask("Shenandoah Init Traversal Collection"),
172 _rp(rp),
173 _heap(ShenandoahHeap::heap()),
174 _cset_coderoots(cset_coderoots) {}
175
176 void work(uint worker_id) {
177 ShenandoahParallelWorkerSession worker_session(worker_id);
178
179 ShenandoahEvacOOMScope oom_evac_scope;
180 ShenandoahObjToScanQueueSet* queues = _heap->traversal_gc()->task_queues();
181 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
182
183 bool process_refs = _heap->process_references();
184 bool unload_classes = _heap->unload_classes();
185 ReferenceProcessor* rp = NULL;
186 if (process_refs) {
187 rp = _heap->ref_processor();
188 }
189
190 // Step 1: Process ordinary GC roots.
191 {
192 ShenandoahTraversalClosure roots_cl(q, rp);
193 ShenandoahMarkCLDClosure cld_cl(&roots_cl);
194 MarkingCodeBlobClosure code_cl(&roots_cl, CodeBlobToOopClosure::FixRelocations);
195 if (unload_classes) {
196 _rp->strong_roots_do(worker_id, &roots_cl);
197 // Need to pre-evac code roots here. Otherwise we might see from-space constants.
198 ShenandoahWorkerTimings* worker_times = _heap->phase_timings()->worker_times();
199 ShenandoahWorkerTimingsTracker timer(worker_times, ShenandoahPhaseTimings::CodeCacheRoots, worker_id);
200 _cset_coderoots->possibly_parallel_blobs_do(&code_cl);
201 } else {
202 _rp->roots_do(worker_id, &roots_cl, &cld_cl, &code_cl);
203 }
204
205 AlwaysTrueClosure is_alive;
206 _dedup_roots.oops_do(&is_alive, &roots_cl, worker_id);
207 }
208 }
209 };
210
211 class ShenandoahConcurrentTraversalCollectionTask : public AbstractGangTask {
212 private:
213 ShenandoahTaskTerminator* _terminator;
214 ShenandoahHeap* _heap;
215 public:
216 ShenandoahConcurrentTraversalCollectionTask(ShenandoahTaskTerminator* terminator) :
217 AbstractGangTask("Shenandoah Concurrent Traversal Collection"),
218 _terminator(terminator),
219 _heap(ShenandoahHeap::heap()) {}
220
221 void work(uint worker_id) {
222 ShenandoahConcurrentWorkerSession worker_session(worker_id);
223 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
224 ShenandoahEvacOOMScope oom_evac_scope;
225 ShenandoahTraversalGC* traversal_gc = _heap->traversal_gc();
226
227 // Drain all outstanding work in queues.
228 traversal_gc->main_loop(worker_id, _terminator, true);
229 }
230 };
231
232 class ShenandoahFinalTraversalCollectionTask : public AbstractGangTask {
233 private:
234 ShenandoahRootProcessor* _rp;
235 ShenandoahTaskTerminator* _terminator;
236 ShenandoahHeap* _heap;
237 public:
238 ShenandoahFinalTraversalCollectionTask(ShenandoahRootProcessor* rp, ShenandoahTaskTerminator* terminator) :
239 AbstractGangTask("Shenandoah Final Traversal Collection"),
240 _rp(rp),
241 _terminator(terminator),
242 _heap(ShenandoahHeap::heap()) {}
243
244 void work(uint worker_id) {
245 ShenandoahParallelWorkerSession worker_session(worker_id);
246
247 ShenandoahEvacOOMScope oom_evac_scope;
248 ShenandoahTraversalGC* traversal_gc = _heap->traversal_gc();
249
250 ShenandoahObjToScanQueueSet* queues = traversal_gc->task_queues();
251 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
252
253 bool process_refs = _heap->process_references();
254 bool unload_classes = _heap->unload_classes();
255 ReferenceProcessor* rp = NULL;
256 if (process_refs) {
257 rp = _heap->ref_processor();
258 }
259
260 // Step 0: Drain outstanding SATB queues.
261 // NOTE: we piggy-back draining of remaining thread SATB buffers on the final root scan below.
262 ShenandoahTraversalSATBBufferClosure satb_cl(q);
263 {
264 // Process remaining finished SATB buffers.
265 SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
266 while (satb_mq_set.apply_closure_to_completed_buffer(&satb_cl));
267 // Process remaining threads SATB buffers below.
268 }
269
270 // Step 1: Process GC roots.
271 // For oops in code roots, they are marked, evacuated, enqueued for further traversal,
272 // and the references to the oops are updated during init pause. New nmethods are handled
273 // in similar way during nmethod-register process. Therefore, we don't need to rescan code
274 // roots here.
275 if (!_heap->is_degenerated_gc_in_progress()) {
276 ShenandoahTraversalClosure roots_cl(q, rp);
277 ShenandoahTraversalSATBThreadsClosure tc(&satb_cl);
278 if (unload_classes) {
279 ShenandoahRemarkCLDClosure remark_cld_cl(&roots_cl);
280 _rp->strong_roots_do(worker_id, &roots_cl, &remark_cld_cl, NULL, &tc);
281 } else {
282 CLDToOopClosure cld_cl(&roots_cl, ClassLoaderData::_claim_strong);
283 _rp->roots_do(worker_id, &roots_cl, &cld_cl, NULL, &tc);
284 }
285 } else {
286 ShenandoahTraversalDegenClosure roots_cl(q, rp);
287 ShenandoahTraversalSATBThreadsClosure tc(&satb_cl);
288 if (unload_classes) {
289 ShenandoahRemarkCLDClosure remark_cld_cl(&roots_cl);
290 _rp->strong_roots_do(worker_id, &roots_cl, &remark_cld_cl, NULL, &tc);
291 } else {
292 CLDToOopClosure cld_cl(&roots_cl, ClassLoaderData::_claim_strong);
293 _rp->roots_do(worker_id, &roots_cl, &cld_cl, NULL, &tc);
294 }
295 }
296
297 {
298 ShenandoahWorkerTimings *worker_times = _heap->phase_timings()->worker_times();
299 ShenandoahWorkerTimingsTracker timer(worker_times, ShenandoahPhaseTimings::FinishQueues, worker_id);
300
301 // Step 3: Finally drain all outstanding work in queues.
302 traversal_gc->main_loop(worker_id, _terminator, false);
303 }
304
305 }
306 };
307
308 ShenandoahTraversalGC::ShenandoahTraversalGC(ShenandoahHeap* heap, size_t num_regions) :
309 _heap(heap),
310 _task_queues(new ShenandoahObjToScanQueueSet(heap->max_workers())),
311 _traversal_set(ShenandoahHeapRegionSet()) {
312
313 uint num_queues = heap->max_workers();
314 for (uint i = 0; i < num_queues; ++i) {
315 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
316 task_queue->initialize();
317 _task_queues->register_queue(i, task_queue);
318 }
319 }
320
321 ShenandoahTraversalGC::~ShenandoahTraversalGC() {
322 }
323
324 void ShenandoahTraversalGC::prepare_regions() {
325 size_t num_regions = _heap->num_regions();
326 ShenandoahMarkingContext* const ctx = _heap->marking_context();
327 for (size_t i = 0; i < num_regions; i++) {
328 ShenandoahHeapRegion* region = _heap->get_region(i);
329 if (_heap->is_bitmap_slice_committed(region)) {
330 if (_traversal_set.is_in(i)) {
331 ctx->capture_top_at_mark_start(region);
332 region->clear_live_data();
333 assert(ctx->is_bitmap_clear_range(region->bottom(), region->end()), "bitmap for traversal regions must be cleared");
334 } else {
335 // Everything outside the traversal set is always considered live.
336 ctx->reset_top_at_mark_start(region);
337 }
338 } else {
339 // FreeSet may contain uncommitted empty regions, once they are recommitted,
340 // their TAMS may have old values, so reset them here.
341 ctx->reset_top_at_mark_start(region);
342 }
343 }
344 }
345
346 void ShenandoahTraversalGC::prepare() {
347 _heap->collection_set()->clear();
348 assert(_heap->collection_set()->count() == 0, "collection set not clear");
349
350 {
351 ShenandoahGCPhase phase(ShenandoahPhaseTimings::traversal_gc_make_parsable);
352 _heap->make_parsable(true);
353 }
354
355 if (UseTLAB) {
356 ShenandoahGCPhase phase(ShenandoahPhaseTimings::traversal_gc_resize_tlabs);
357 _heap->resize_tlabs();
358 }
359
360 assert(_heap->marking_context()->is_bitmap_clear(), "need clean mark bitmap");
361 assert(!_heap->marking_context()->is_complete(), "should not be complete");
362
363 ShenandoahFreeSet* free_set = _heap->free_set();
364 ShenandoahCollectionSet* collection_set = _heap->collection_set();
365
366 // Find collection set
367 _heap->heuristics()->choose_collection_set(collection_set);
368 prepare_regions();
369
370 // Rebuild free set
371 free_set->rebuild();
372
373 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "M, " SIZE_FORMAT "M CSet, " SIZE_FORMAT " CSet regions",
374 collection_set->garbage() / M, collection_set->live_data() / M, collection_set->count());
375 }
376
377 void ShenandoahTraversalGC::init_traversal_collection() {
378 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "STW traversal GC");
379
380 if (ShenandoahVerify) {
381 _heap->verifier()->verify_before_traversal();
382 }
383
384 if (VerifyBeforeGC) {
385 Universe::verify();
386 }
387
388 {
389 ShenandoahGCPhase phase_prepare(ShenandoahPhaseTimings::traversal_gc_prepare);
390 ShenandoahHeapLocker lock(_heap->lock());
391 prepare();
392 }
393
394 _heap->set_concurrent_traversal_in_progress(true);
395
396 bool process_refs = _heap->process_references();
397 if (process_refs) {
398 ReferenceProcessor* rp = _heap->ref_processor();
399 rp->enable_discovery(true /*verify_no_refs*/);
400 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
401 }
402
403 {
404 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::init_traversal_gc_work);
405 assert(_task_queues->is_empty(), "queues must be empty before traversal GC");
406 TASKQUEUE_STATS_ONLY(_task_queues->reset_taskqueue_stats());
407
408 #if defined(COMPILER2) || INCLUDE_JVMCI
409 DerivedPointerTable::clear();
410 #endif
411
412 {
413 uint nworkers = _heap->workers()->active_workers();
414 task_queues()->reserve(nworkers);
415 ShenandoahRootProcessor rp(nworkers, ShenandoahPhaseTimings::init_traversal_gc_work);
416
417 ShenandoahCsetCodeRootsIterator cset_coderoots = ShenandoahCodeRoots::cset_iterator();
418
419 ShenandoahInitTraversalCollectionTask traversal_task(&rp, &cset_coderoots);
420 _heap->workers()->run_task(&traversal_task);
421 }
422
423 #if defined(COMPILER2) || INCLUDE_JVMCI
424 DerivedPointerTable::update_pointers();
425 #endif
426 }
427
428 if (ShenandoahPacing) {
429 _heap->pacer()->setup_for_traversal();
430 }
431 }
432
433 void ShenandoahTraversalGC::main_loop(uint w, ShenandoahTaskTerminator* t, bool sts_yield) {
434 ShenandoahObjToScanQueue* q = task_queues()->queue(w);
435
436 // Initialize live data.
437 jushort* ld = _heap->get_liveness_cache(w);
438
439 ReferenceProcessor* rp = NULL;
440 if (_heap->process_references()) {
441 rp = _heap->ref_processor();
442 }
443 {
444 if (!_heap->is_degenerated_gc_in_progress()) {
445 if (_heap->unload_classes()) {
446 if (ShenandoahStringDedup::is_enabled()) {
447 ShenandoahTraversalMetadataDedupClosure cl(q, rp);
448 main_loop_work<ShenandoahTraversalMetadataDedupClosure>(&cl, ld, w, t, sts_yield);
449 } else {
450 ShenandoahTraversalMetadataClosure cl(q, rp);
451 main_loop_work<ShenandoahTraversalMetadataClosure>(&cl, ld, w, t, sts_yield);
452 }
453 } else {
454 if (ShenandoahStringDedup::is_enabled()) {
455 ShenandoahTraversalDedupClosure cl(q, rp);
456 main_loop_work<ShenandoahTraversalDedupClosure>(&cl, ld, w, t, sts_yield);
457 } else {
458 ShenandoahTraversalClosure cl(q, rp);
459 main_loop_work<ShenandoahTraversalClosure>(&cl, ld, w, t, sts_yield);
460 }
461 }
462 } else {
463 if (_heap->unload_classes()) {
464 if (ShenandoahStringDedup::is_enabled()) {
465 ShenandoahTraversalMetadataDedupDegenClosure cl(q, rp);
466 main_loop_work<ShenandoahTraversalMetadataDedupDegenClosure>(&cl, ld, w, t, sts_yield);
467 } else {
468 ShenandoahTraversalMetadataDegenClosure cl(q, rp);
469 main_loop_work<ShenandoahTraversalMetadataDegenClosure>(&cl, ld, w, t, sts_yield);
470 }
471 } else {
472 if (ShenandoahStringDedup::is_enabled()) {
473 ShenandoahTraversalDedupDegenClosure cl(q, rp);
474 main_loop_work<ShenandoahTraversalDedupDegenClosure>(&cl, ld, w, t, sts_yield);
475 } else {
476 ShenandoahTraversalDegenClosure cl(q, rp);
477 main_loop_work<ShenandoahTraversalDegenClosure>(&cl, ld, w, t, sts_yield);
478 }
479 }
480 }
481 }
482
483 _heap->flush_liveness_cache(w);
484 }
485
486 template <class T>
487 void ShenandoahTraversalGC::main_loop_work(T* cl, jushort* live_data, uint worker_id, ShenandoahTaskTerminator* terminator, bool sts_yield) {
488 ShenandoahObjToScanQueueSet* queues = task_queues();
489 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
490 ShenandoahConcurrentMark* conc_mark = _heap->concurrent_mark();
491
492 uintx stride = ShenandoahMarkLoopStride;
493
494 ShenandoahMarkTask task;
495
496 // Process outstanding queues, if any.
497 q = queues->claim_next();
498 while (q != NULL) {
499 if (_heap->check_cancelled_gc_and_yield(sts_yield)) {
500 return;
501 }
502
503 for (uint i = 0; i < stride; i++) {
504 if (q->pop(task)) {
505 conc_mark->do_task<T>(q, cl, live_data, &task);
506 } else {
507 assert(q->is_empty(), "Must be empty");
508 q = queues->claim_next();
509 break;
510 }
511 }
512 }
513
514 if (check_and_handle_cancelled_gc(terminator, sts_yield)) return;
515
516 // Normal loop.
517 q = queues->queue(worker_id);
518
519 ShenandoahTraversalSATBBufferClosure drain_satb(q);
520 SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
521
522 while (true) {
523 if (check_and_handle_cancelled_gc(terminator, sts_yield)) return;
524
525 while (satb_mq_set.completed_buffers_num() > 0) {
526 satb_mq_set.apply_closure_to_completed_buffer(&drain_satb);
527 }
528
529 uint work = 0;
530 for (uint i = 0; i < stride; i++) {
531 if (q->pop(task) ||
532 queues->steal(worker_id, task)) {
533 conc_mark->do_task<T>(q, cl, live_data, &task);
534 work++;
535 } else {
536 break;
537 }
538 }
539
540 if (work == 0) {
541 // No more work, try to terminate
542 ShenandoahEvacOOMScopeLeaver oom_scope_leaver;
543 ShenandoahSuspendibleThreadSetLeaver stsl(sts_yield && ShenandoahSuspendibleWorkers);
544 ShenandoahTerminationTimingsTracker term_tracker(worker_id);
545 ShenandoahTerminatorTerminator tt(_heap);
546
547 if (terminator->offer_termination(&tt)) return;
548 }
549 }
550 }
551
552 bool ShenandoahTraversalGC::check_and_handle_cancelled_gc(ShenandoahTaskTerminator* terminator, bool sts_yield) {
553 if (_heap->cancelled_gc()) {
554 return true;
555 }
556 return false;
557 }
558
559 void ShenandoahTraversalGC::concurrent_traversal_collection() {
560 {
561 MutexLocker ml(ClassLoaderDataGraph_lock);
562 ClassLoaderDataGraph::clear_claimed_marks();
563 }
564
565 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::conc_traversal);
566 if (!_heap->cancelled_gc()) {
567 uint nworkers = _heap->workers()->active_workers();
568 task_queues()->reserve(nworkers);
569 ShenandoahTerminationTracker tracker(ShenandoahPhaseTimings::conc_traversal_termination);
570
571 ShenandoahTaskTerminator terminator(nworkers, task_queues());
572 ShenandoahConcurrentTraversalCollectionTask task(&terminator);
573 _heap->workers()->run_task(&task);
574 }
575
576 if (!_heap->cancelled_gc() && ShenandoahPreclean && _heap->process_references()) {
577 preclean_weak_refs();
578 }
579 }
580
581 void ShenandoahTraversalGC::final_traversal_collection() {
582 _heap->make_parsable(true);
583
584 if (!_heap->cancelled_gc()) {
585 #if defined(COMPILER2) || INCLUDE_JVMCI
586 DerivedPointerTable::clear();
587 #endif
588 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::final_traversal_gc_work);
589 uint nworkers = _heap->workers()->active_workers();
590 task_queues()->reserve(nworkers);
591
592 // Finish traversal
593 ShenandoahRootProcessor rp(nworkers, ShenandoahPhaseTimings::final_traversal_gc_work);
594 ShenandoahTerminationTracker term(ShenandoahPhaseTimings::final_traversal_gc_termination);
595
596 ShenandoahTaskTerminator terminator(nworkers, task_queues());
597 ShenandoahFinalTraversalCollectionTask task(&rp, &terminator);
598 _heap->workers()->run_task(&task);
599 #if defined(COMPILER2) || INCLUDE_JVMCI
600 DerivedPointerTable::update_pointers();
601 #endif
602 }
603
604 if (!_heap->cancelled_gc() && _heap->process_references()) {
605 weak_refs_work();
606 }
607
608 if (!_heap->cancelled_gc()) {
609 fixup_roots();
610 if (_heap->unload_classes()) {
611 _heap->unload_classes_and_cleanup_tables(false);
612 }
613 }
614
615 if (!_heap->cancelled_gc()) {
616 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
617 TASKQUEUE_STATS_ONLY(_task_queues->print_taskqueue_stats());
618 TASKQUEUE_STATS_ONLY(_task_queues->reset_taskqueue_stats());
619
620 // No more marking expected
621 _heap->mark_complete_marking_context();
622
623 // Resize metaspace
624 MetaspaceGC::compute_new_size();
625
626 // Still good? We can now trash the cset, and make final verification
627 {
628 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_cleanup);
629 ShenandoahHeapLocker lock(_heap->lock());
630
631 // Trash everything
632 // Clear immediate garbage regions.
633 size_t num_regions = _heap->num_regions();
634
635 ShenandoahHeapRegionSet* traversal_regions = traversal_set();
636 ShenandoahFreeSet* free_regions = _heap->free_set();
637 ShenandoahMarkingContext* const ctx = _heap->marking_context();
638 free_regions->clear();
639 for (size_t i = 0; i < num_regions; i++) {
640 ShenandoahHeapRegion* r = _heap->get_region(i);
641 bool not_allocated = ctx->top_at_mark_start(r) == r->top();
642
643 bool candidate = traversal_regions->is_in(r) && !r->has_live() && not_allocated;
644 if (r->is_humongous_start() && candidate) {
645 // Trash humongous.
646 HeapWord* humongous_obj = r->bottom() + ShenandoahForwarding::word_size();
647 assert(!ctx->is_marked(oop(humongous_obj)), "must not be marked");
648 r->make_trash_immediate();
649 while (i + 1 < num_regions && _heap->get_region(i + 1)->is_humongous_continuation()) {
650 i++;
651 r = _heap->get_region(i);
652 assert(r->is_humongous_continuation(), "must be humongous continuation");
653 r->make_trash_immediate();
654 }
655 } else if (!r->is_empty() && candidate) {
656 // Trash regular.
657 assert(!r->is_humongous(), "handled above");
658 assert(!r->is_trash(), "must not already be trashed");
659 r->make_trash_immediate();
660 }
661 }
662 _heap->collection_set()->clear();
663 _heap->free_set()->rebuild();
664 reset();
665 }
666
667 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
668 _heap->set_concurrent_traversal_in_progress(false);
669 assert(!_heap->cancelled_gc(), "must not be cancelled when getting out here");
670
671 if (ShenandoahVerify) {
672 _heap->verifier()->verify_after_traversal();
673 }
674
675 if (VerifyAfterGC) {
676 Universe::verify();
677 }
678 }
679 }
680
681 class ShenandoahTraversalFixRootsClosure : public OopClosure {
682 private:
683 template <class T>
684 inline void do_oop_work(T* p) {
685 T o = RawAccess<>::oop_load(p);
686 if (!CompressedOops::is_null(o)) {
687 oop obj = CompressedOops::decode_not_null(o);
688 oop forw = ShenandoahBarrierSet::resolve_forwarded_not_null(obj);
689 if (!oopDesc::equals_raw(obj, forw)) {
690 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
691 }
692 }
693 }
694
695 public:
696 inline void do_oop(oop* p) { do_oop_work(p); }
697 inline void do_oop(narrowOop* p) { do_oop_work(p); }
698 };
699
700 class ShenandoahTraversalFixRootsTask : public AbstractGangTask {
701 private:
702 ShenandoahRootUpdater* _rp;
703
704 public:
705 ShenandoahTraversalFixRootsTask(ShenandoahRootUpdater* rp) :
706 AbstractGangTask("Shenandoah traversal fix roots"),
707 _rp(rp) {
708 assert(ShenandoahHeap::heap()->has_forwarded_objects(), "Must be");
709 }
710
711 void work(uint worker_id) {
712 ShenandoahParallelWorkerSession worker_session(worker_id);
713 ShenandoahTraversalFixRootsClosure cl;
714 ShenandoahForwardedIsAliveClosure is_alive;
715 _rp->roots_do<ShenandoahForwardedIsAliveClosure, ShenandoahTraversalFixRootsClosure>(worker_id, &is_alive, &cl);
716 }
717 };
718
719 void ShenandoahTraversalGC::fixup_roots() {
720 #if defined(COMPILER2) || INCLUDE_JVMCI
721 DerivedPointerTable::clear();
722 #endif
723 ShenandoahRootUpdater rp(_heap->workers()->active_workers(), ShenandoahPhaseTimings::final_traversal_update_roots, true /* update code cache */);
724 ShenandoahTraversalFixRootsTask update_roots_task(&rp);
725 _heap->workers()->run_task(&update_roots_task);
726 #if defined(COMPILER2) || INCLUDE_JVMCI
727 DerivedPointerTable::update_pointers();
728 #endif
729 }
730
731 void ShenandoahTraversalGC::reset() {
732 _task_queues->clear();
733 }
734
735 ShenandoahObjToScanQueueSet* ShenandoahTraversalGC::task_queues() {
736 return _task_queues;
737 }
738
739 class ShenandoahTraversalCancelledGCYieldClosure : public YieldClosure {
740 private:
741 ShenandoahHeap* const _heap;
742 public:
743 ShenandoahTraversalCancelledGCYieldClosure() : _heap(ShenandoahHeap::heap()) {};
744 virtual bool should_return() { return _heap->cancelled_gc(); }
745 };
746
747 class ShenandoahTraversalPrecleanCompleteGCClosure : public VoidClosure {
748 public:
749 void do_void() {
750 ShenandoahHeap* sh = ShenandoahHeap::heap();
751 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
752 assert(sh->process_references(), "why else would we be here?");
753 ShenandoahTaskTerminator terminator(1, traversal_gc->task_queues());
754 shenandoah_assert_rp_isalive_installed();
755 traversal_gc->main_loop((uint) 0, &terminator, true);
756 }
757 };
758
759 class ShenandoahTraversalKeepAliveUpdateClosure : public OopClosure {
760 private:
761 ShenandoahObjToScanQueue* _queue;
762 Thread* _thread;
763 ShenandoahTraversalGC* _traversal_gc;
764 ShenandoahMarkingContext* const _mark_context;
765
766 template <class T>
767 inline void do_oop_work(T* p) {
768 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */>(p, _thread, _queue, _mark_context);
769 }
770
771 public:
772 ShenandoahTraversalKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
773 _queue(q), _thread(Thread::current()),
774 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
775 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
776
777 void do_oop(narrowOop* p) { do_oop_work(p); }
778 void do_oop(oop* p) { do_oop_work(p); }
779 };
780
781 class ShenandoahTraversalKeepAliveUpdateDegenClosure : public OopClosure {
782 private:
783 ShenandoahObjToScanQueue* _queue;
784 Thread* _thread;
785 ShenandoahTraversalGC* _traversal_gc;
786 ShenandoahMarkingContext* const _mark_context;
787
788 template <class T>
789 inline void do_oop_work(T* p) {
790 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */>(p, _thread, _queue, _mark_context);
791 }
792
793 public:
794 ShenandoahTraversalKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
795 _queue(q), _thread(Thread::current()),
796 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
797 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
798
799 void do_oop(narrowOop* p) { do_oop_work(p); }
800 void do_oop(oop* p) { do_oop_work(p); }
801 };
802
803 class ShenandoahTraversalSingleThreadKeepAliveUpdateClosure : public OopClosure {
804 private:
805 ShenandoahObjToScanQueue* _queue;
806 Thread* _thread;
807 ShenandoahTraversalGC* _traversal_gc;
808 ShenandoahMarkingContext* const _mark_context;
809
810 template <class T>
811 inline void do_oop_work(T* p) {
812 ShenandoahEvacOOMScope evac_scope;
813 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */>(p, _thread, _queue, _mark_context);
814 }
815
816 public:
817 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
818 _queue(q), _thread(Thread::current()),
819 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
820 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
821
822 void do_oop(narrowOop* p) { do_oop_work(p); }
823 void do_oop(oop* p) { do_oop_work(p); }
824 };
825
826 class ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure : public OopClosure {
827 private:
828 ShenandoahObjToScanQueue* _queue;
829 Thread* _thread;
830 ShenandoahTraversalGC* _traversal_gc;
831 ShenandoahMarkingContext* const _mark_context;
832
833 template <class T>
834 inline void do_oop_work(T* p) {
835 ShenandoahEvacOOMScope evac_scope;
836 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */>(p, _thread, _queue, _mark_context);
837 }
838
839 public:
840 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
841 _queue(q), _thread(Thread::current()),
842 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
843 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
844
845 void do_oop(narrowOop* p) { do_oop_work(p); }
846 void do_oop(oop* p) { do_oop_work(p); }
847 };
848
849 class ShenandoahTraversalPrecleanTask : public AbstractGangTask {
850 private:
851 ReferenceProcessor* _rp;
852
853 public:
854 ShenandoahTraversalPrecleanTask(ReferenceProcessor* rp) :
855 AbstractGangTask("Precleaning task"),
856 _rp(rp) {}
857
858 void work(uint worker_id) {
859 assert(worker_id == 0, "The code below is single-threaded, only one worker is expected");
860 ShenandoahParallelWorkerSession worker_session(worker_id);
861 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
862 ShenandoahEvacOOMScope oom_evac_scope;
863
864 ShenandoahHeap* sh = ShenandoahHeap::heap();
865
866 ShenandoahObjToScanQueue* q = sh->traversal_gc()->task_queues()->queue(worker_id);
867
868 ShenandoahForwardedIsAliveClosure is_alive;
869 ShenandoahTraversalCancelledGCYieldClosure yield;
870 ShenandoahTraversalPrecleanCompleteGCClosure complete_gc;
871 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(q);
872 ResourceMark rm;
873 _rp->preclean_discovered_references(&is_alive, &keep_alive,
874 &complete_gc, &yield,
875 NULL);
876 }
877 };
878
879 void ShenandoahTraversalGC::preclean_weak_refs() {
880 // Pre-cleaning weak references before diving into STW makes sense at the
881 // end of concurrent mark. This will filter out the references which referents
882 // are alive. Note that ReferenceProcessor already filters out these on reference
883 // discovery, and the bulk of work is done here. This phase processes leftovers
884 // that missed the initial filtering, i.e. when referent was marked alive after
885 // reference was discovered by RP.
886
887 assert(_heap->process_references(), "sanity");
888 assert(!_heap->is_degenerated_gc_in_progress(), "must be in concurrent non-degenerated phase");
889
890 // Shortcut if no references were discovered to avoid winding up threads.
891 ReferenceProcessor* rp = _heap->ref_processor();
892 if (!rp->has_discovered_references()) {
893 return;
894 }
895
896 ReferenceProcessorMTDiscoveryMutator fix_mt_discovery(rp, false);
897
898 shenandoah_assert_rp_isalive_not_installed();
899 ShenandoahForwardedIsAliveClosure is_alive;
900 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
901
902 assert(task_queues()->is_empty(), "Should be empty");
903
904 // Execute precleaning in the worker thread: it will give us GCLABs, String dedup
905 // queues and other goodies. When upstream ReferenceProcessor starts supporting
906 // parallel precleans, we can extend this to more threads.
907 ShenandoahPushWorkerScope scope(_heap->workers(), 1, /* check_workers = */ false);
908
909 WorkGang* workers = _heap->workers();
910 uint nworkers = workers->active_workers();
911 assert(nworkers == 1, "This code uses only a single worker");
912 task_queues()->reserve(nworkers);
913
914 ShenandoahTraversalPrecleanTask task(rp);
915 workers->run_task(&task);
916
917 assert(_heap->cancelled_gc() || task_queues()->is_empty(), "Should be empty");
918 }
919
920 // Weak Reference Closures
921 class ShenandoahTraversalDrainMarkingStackClosure: public VoidClosure {
922 uint _worker_id;
923 ShenandoahTaskTerminator* _terminator;
924 bool _reset_terminator;
925
926 public:
927 ShenandoahTraversalDrainMarkingStackClosure(uint worker_id, ShenandoahTaskTerminator* t, bool reset_terminator = false):
928 _worker_id(worker_id),
929 _terminator(t),
930 _reset_terminator(reset_terminator) {
931 }
932
933 void do_void() {
934 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
935
936 ShenandoahHeap* sh = ShenandoahHeap::heap();
937 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
938 assert(sh->process_references(), "why else would we be here?");
939 shenandoah_assert_rp_isalive_installed();
940
941 traversal_gc->main_loop(_worker_id, _terminator, false);
942
943 if (_reset_terminator) {
944 _terminator->reset_for_reuse();
945 }
946 }
947 };
948
949 class ShenandoahTraversalSingleThreadedDrainMarkingStackClosure: public VoidClosure {
950 uint _worker_id;
951 ShenandoahTaskTerminator* _terminator;
952 bool _reset_terminator;
953
954 public:
955 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure(uint worker_id, ShenandoahTaskTerminator* t, bool reset_terminator = false):
956 _worker_id(worker_id),
957 _terminator(t),
958 _reset_terminator(reset_terminator) {
959 }
960
961 void do_void() {
962 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
963
964 ShenandoahHeap* sh = ShenandoahHeap::heap();
965 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
966 assert(sh->process_references(), "why else would we be here?");
967 shenandoah_assert_rp_isalive_installed();
968
969 ShenandoahEvacOOMScope evac_scope;
970 traversal_gc->main_loop(_worker_id, _terminator, false);
971
972 if (_reset_terminator) {
973 _terminator->reset_for_reuse();
974 }
975 }
976 };
977
978 void ShenandoahTraversalGC::weak_refs_work() {
979 assert(_heap->process_references(), "sanity");
980
981 ShenandoahPhaseTimings::Phase phase_root = ShenandoahPhaseTimings::weakrefs;
982
983 ShenandoahGCPhase phase(phase_root);
984
985 ReferenceProcessor* rp = _heap->ref_processor();
986
987 // NOTE: We cannot shortcut on has_discovered_references() here, because
988 // we will miss marking JNI Weak refs then, see implementation in
989 // ReferenceProcessor::process_discovered_references.
990 weak_refs_work_doit();
991
992 rp->verify_no_references_recorded();
993 assert(!rp->discovery_enabled(), "Post condition");
994
995 }
996
997 class ShenandoahTraversalRefProcTaskProxy : public AbstractGangTask {
998 private:
999 AbstractRefProcTaskExecutor::ProcessTask& _proc_task;
1000 ShenandoahTaskTerminator* _terminator;
1001
1002 public:
1003 ShenandoahTraversalRefProcTaskProxy(AbstractRefProcTaskExecutor::ProcessTask& proc_task,
1004 ShenandoahTaskTerminator* t) :
1005 AbstractGangTask("Process reference objects in parallel"),
1006 _proc_task(proc_task),
1007 _terminator(t) {
1008 }
1009
1010 void work(uint worker_id) {
1011 ShenandoahEvacOOMScope oom_evac_scope;
1012 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1013 ShenandoahHeap* heap = ShenandoahHeap::heap();
1014 ShenandoahTraversalDrainMarkingStackClosure complete_gc(worker_id, _terminator);
1015
1016 ShenandoahForwardedIsAliveClosure is_alive;
1017 if (!heap->is_degenerated_gc_in_progress()) {
1018 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1019 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1020 } else {
1021 ShenandoahTraversalKeepAliveUpdateDegenClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1022 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1023 }
1024 }
1025 };
1026
1027 class ShenandoahTraversalRefProcTaskExecutor : public AbstractRefProcTaskExecutor {
1028 private:
1029 WorkGang* _workers;
1030
1031 public:
1032 ShenandoahTraversalRefProcTaskExecutor(WorkGang* workers) : _workers(workers) {}
1033
1034 // Executes a task using worker threads.
1035 void execute(ProcessTask& task, uint ergo_workers) {
1036 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1037
1038 ShenandoahHeap* heap = ShenandoahHeap::heap();
1039 ShenandoahTraversalGC* traversal_gc = heap->traversal_gc();
1040 ShenandoahPushWorkerQueuesScope scope(_workers,
1041 traversal_gc->task_queues(),
1042 ergo_workers,
1043 /* do_check = */ false);
1044 uint nworkers = _workers->active_workers();
1045 traversal_gc->task_queues()->reserve(nworkers);
1046 ShenandoahTaskTerminator terminator(nworkers, traversal_gc->task_queues());
1047 ShenandoahTraversalRefProcTaskProxy proc_task_proxy(task, &terminator);
1048 _workers->run_task(&proc_task_proxy);
1049 }
1050 };
1051
1052 void ShenandoahTraversalGC::weak_refs_work_doit() {
1053 ReferenceProcessor* rp = _heap->ref_processor();
1054
1055 ShenandoahPhaseTimings::Phase phase_process = ShenandoahPhaseTimings::weakrefs_process;
1056
1057 shenandoah_assert_rp_isalive_not_installed();
1058 ShenandoahForwardedIsAliveClosure is_alive;
1059 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
1060
1061 WorkGang* workers = _heap->workers();
1062 uint nworkers = workers->active_workers();
1063
1064 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
1065 rp->set_active_mt_degree(nworkers);
1066
1067 assert(task_queues()->is_empty(), "Should be empty");
1068
1069 // complete_gc and keep_alive closures instantiated here are only needed for
1070 // single-threaded path in RP. They share the queue 0 for tracking work, which
1071 // simplifies implementation. Since RP may decide to call complete_gc several
1072 // times, we need to be able to reuse the terminator.
1073 uint serial_worker_id = 0;
1074 ShenandoahTaskTerminator terminator(1, task_queues());
1075 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure complete_gc(serial_worker_id, &terminator, /* reset_terminator = */ true);
1076 ShenandoahPushWorkerQueuesScope scope(workers, task_queues(), 1, /* do_check = */ false);
1077
1078 ShenandoahTraversalRefProcTaskExecutor executor(workers);
1079
1080 ReferenceProcessorPhaseTimes pt(_heap->gc_timer(), rp->num_queues());
1081 if (!_heap->is_degenerated_gc_in_progress()) {
1082 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure keep_alive(task_queues()->queue(serial_worker_id));
1083 rp->process_discovered_references(&is_alive, &keep_alive,
1084 &complete_gc, &executor,
1085 &pt);
1086 } else {
1087 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure keep_alive(task_queues()->queue(serial_worker_id));
1088 rp->process_discovered_references(&is_alive, &keep_alive,
1089 &complete_gc, &executor,
1090 &pt);
1091 }
1092
1093 pt.print_all_references();
1094 assert(task_queues()->is_empty() || _heap->cancelled_gc(), "Should be empty");
1095 }