1 /*
2 * Copyright (c) 2018, 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/classLoaderData.hpp"
28 #include "classfile/classLoaderDataGraph.hpp"
29 #include "gc/shared/referenceProcessor.hpp"
30 #include "gc/shared/referenceProcessorPhaseTimes.hpp"
31 #include "gc/shared/workgroup.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/shenandoahPhaseTimings.hpp"
39 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
40 #include "gc/shenandoah/shenandoahHeapRegionSet.inline.hpp"
41 #include "gc/shenandoah/shenandoahHeuristics.hpp"
42 #include "gc/shenandoah/shenandoahMarkingContext.inline.hpp"
43 #include "gc/shenandoah/shenandoahOopClosures.inline.hpp"
44 #include "gc/shenandoah/shenandoahRootProcessor.inline.hpp"
45 #include "gc/shenandoah/shenandoahStringDedup.hpp"
46 #include "gc/shenandoah/shenandoahTaskqueue.inline.hpp"
47 #include "gc/shenandoah/shenandoahTimingTracker.hpp"
48 #include "gc/shenandoah/shenandoahTraversalGC.hpp"
49 #include "gc/shenandoah/shenandoahUtils.hpp"
50 #include "gc/shenandoah/shenandoahVerifier.hpp"
51
52 #include "memory/iterator.hpp"
53 #include "memory/metaspace.hpp"
54 #include "memory/resourceArea.hpp"
55 #include "memory/universe.hpp"
56
57 /**
58 * NOTE: We are using the SATB buffer in thread.hpp and satbMarkQueue.hpp, however, it is not an SATB algorithm.
59 * We're using the buffer as generic oop buffer to enqueue new values in concurrent oop stores, IOW, the algorithm
60 * is incremental-update-based.
61 *
62 * NOTE on interaction with TAMS: we want to avoid traversing new objects for
63 * several reasons:
64 * - We will not reclaim them in this cycle anyway, because they are not in the
65 * cset
66 * - It makes up for the bulk of work during final-pause
67 * - It also shortens the concurrent cycle because we don't need to
68 * pointlessly traverse through newly allocated objects.
69 * - As a nice side-effect, it solves the I-U termination problem (mutators
70 * cannot outrun the GC by allocating like crazy)
71 * - It is an easy way to achieve MWF. What MWF does is to also enqueue the
72 * target object of stores if it's new. Treating new objects live implicitely
73 * achieves the same, but without extra barriers. I think the effect of
74 * shortened final-pause (mentioned above) is the main advantage of MWF. In
75 * particular, we will not see the head of a completely new long linked list
76 * in final-pause and end up traversing huge chunks of the heap there.
77 * - We don't need to see/update the fields of new objects either, because they
78 * are either still null, or anything that's been stored into them has been
79 * evacuated+enqueued before (and will thus be treated later).
80 *
81 * We achieve this by setting TAMS for each region, and everything allocated
82 * beyond TAMS will be 'implicitely marked'.
83 *
84 * Gotchas:
85 * - While we want new objects to be implicitely marked, we don't want to count
86 * them alive. Otherwise the next cycle wouldn't pick them up and consider
87 * them for cset. This means that we need to protect such regions from
88 * getting accidentally thrashed at the end of traversal cycle. This is why I
89 * keep track of alloc-regions and check is_alloc_region() in the trashing
90 * code.
91 * - We *need* to traverse through evacuated objects. Those objects are
92 * pre-existing, and any references in them point to interesting objects that
93 * we need to see. We also want to count them as live, because we just
94 * determined that they are alive :-) I achieve this by upping TAMS
95 * concurrently for every gclab/gc-shared alloc before publishing the
96 * evacuated object. This way, the GC threads will not consider such objects
97 * implictely marked, and traverse through them as normal.
98 */
99 class ShenandoahTraversalSATBBufferClosure : public SATBBufferClosure {
100 private:
101 ShenandoahObjToScanQueue* _queue;
102 ShenandoahTraversalGC* _traversal_gc;
103 ShenandoahHeap* const _heap;
104
105 public:
106 ShenandoahTraversalSATBBufferClosure(ShenandoahObjToScanQueue* q) :
107 _queue(q),
108 _heap(ShenandoahHeap::heap())
109 { }
110
111 void do_buffer(void** buffer, size_t size) {
112 for (size_t i = 0; i < size; ++i) {
113 oop* p = (oop*) &buffer[i];
114 oop obj = RawAccess<>::oop_load(p);
115 shenandoah_assert_not_forwarded(p, obj);
116 if (_heap->marking_context()->mark(obj)) {
117 _queue->push(ShenandoahMarkTask(obj));
118 }
119 }
120 }
121 };
122
123 class ShenandoahTraversalSATBThreadsClosure : public ThreadClosure {
124 private:
125 ShenandoahTraversalSATBBufferClosure* _satb_cl;
126
127 public:
128 ShenandoahTraversalSATBThreadsClosure(ShenandoahTraversalSATBBufferClosure* satb_cl) :
129 _satb_cl(satb_cl) {}
130
131 void do_thread(Thread* thread) {
132 ShenandoahThreadLocalData::satb_mark_queue(thread).apply_closure_and_empty(_satb_cl);
133 }
134 };
135
136 // Like CLDToOopClosure, but clears has_modified_oops, so that we can record modified CLDs during traversal
137 // and remark them later during final-traversal.
138 class ShenandoahMarkCLDClosure : public CLDClosure {
139 private:
140 OopClosure* _cl;
141 public:
142 ShenandoahMarkCLDClosure(OopClosure* cl) : _cl(cl) {}
143 void do_cld(ClassLoaderData* cld) {
144 cld->oops_do(_cl, ClassLoaderData::_claim_strong, true);
145 }
146 };
147
148 // Like CLDToOopClosure, but only process modified CLDs
149 class ShenandoahRemarkCLDClosure : public CLDClosure {
150 private:
151 OopClosure* _cl;
152 public:
153 ShenandoahRemarkCLDClosure(OopClosure* cl) : _cl(cl) {}
154 void do_cld(ClassLoaderData* cld) {
155 if (cld->has_modified_oops()) {
156 cld->oops_do(_cl, ClassLoaderData::_claim_strong, true);
157 }
158 }
159 };
160
161 class ShenandoahInitTraversalCollectionTask : public AbstractGangTask {
162 private:
163 ShenandoahCSetRootScanner* _rp;
164 ShenandoahHeap* _heap;
165 ShenandoahCsetCodeRootsIterator* _cset_coderoots;
166 ShenandoahStringDedupRoots _dedup_roots;
167
168 public:
169 ShenandoahInitTraversalCollectionTask(ShenandoahCSetRootScanner* rp) :
170 AbstractGangTask("Shenandoah Init Traversal Collection"),
171 _rp(rp),
172 _heap(ShenandoahHeap::heap()) {}
173
174 void work(uint worker_id) {
175 ShenandoahParallelWorkerSession worker_session(worker_id);
176
177 ShenandoahObjToScanQueueSet* queues = _heap->traversal_gc()->task_queues();
178 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
179
180 bool process_refs = _heap->process_references();
181 bool unload_classes = _heap->unload_classes();
182 ReferenceProcessor* rp = NULL;
183 if (process_refs) {
184 rp = _heap->ref_processor();
185 }
186
187 // Step 1: Process ordinary GC roots.
188 {
189 ShenandoahTraversalRootsClosure roots_cl(q, rp);
190 ShenandoahMarkCLDClosure cld_cl(&roots_cl);
191 MarkingCodeBlobClosure code_cl(&roots_cl, CodeBlobToOopClosure::FixRelocations);
192 if (unload_classes) {
193 _rp->roots_do(worker_id, &roots_cl, NULL, &code_cl);
194 } else {
195 _rp->roots_do(worker_id, &roots_cl, &cld_cl, &code_cl);
196 }
197 }
198 }
199 };
200
201 class ShenandoahConcurrentTraversalCollectionTask : public AbstractGangTask {
202 private:
203 TaskTerminator* _terminator;
204 ShenandoahHeap* _heap;
205 public:
206 ShenandoahConcurrentTraversalCollectionTask(TaskTerminator* terminator) :
207 AbstractGangTask("Shenandoah Concurrent Traversal Collection"),
208 _terminator(terminator),
209 _heap(ShenandoahHeap::heap()) {}
210
211 void work(uint worker_id) {
212 ShenandoahConcurrentWorkerSession worker_session(worker_id);
213 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
214 ShenandoahTraversalGC* traversal_gc = _heap->traversal_gc();
215
216 // Drain all outstanding work in queues.
217 traversal_gc->main_loop(worker_id, _terminator, true);
218 }
219 };
220
221 class ShenandoahFinalTraversalCollectionTask : public AbstractGangTask {
222 private:
223 ShenandoahAllRootScanner* _rp;
224 TaskTerminator* _terminator;
225 ShenandoahHeap* _heap;
226 public:
227 ShenandoahFinalTraversalCollectionTask(ShenandoahAllRootScanner* rp, TaskTerminator* terminator) :
228 AbstractGangTask("Shenandoah Final Traversal Collection"),
229 _rp(rp),
230 _terminator(terminator),
231 _heap(ShenandoahHeap::heap()) {}
232
233 void work(uint worker_id) {
234 ShenandoahParallelWorkerSession worker_session(worker_id);
235
236 ShenandoahTraversalGC* traversal_gc = _heap->traversal_gc();
237
238 ShenandoahObjToScanQueueSet* queues = traversal_gc->task_queues();
239 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
240
241 bool process_refs = _heap->process_references();
242 bool unload_classes = _heap->unload_classes();
243 ReferenceProcessor* rp = NULL;
244 if (process_refs) {
245 rp = _heap->ref_processor();
246 }
247
248 // Step 0: Drain outstanding SATB queues.
249 // NOTE: we piggy-back draining of remaining thread SATB buffers on the final root scan below.
250 ShenandoahTraversalSATBBufferClosure satb_cl(q);
251 {
252 // Process remaining finished SATB buffers.
253 SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
254 while (satb_mq_set.apply_closure_to_completed_buffer(&satb_cl));
255 // Process remaining threads SATB buffers below.
256 }
257
258 // Step 1: Process GC roots.
259 // For oops in code roots, they are marked, evacuated, enqueued for further traversal,
260 // and the references to the oops are updated during init pause. New nmethods are handled
261 // in similar way during nmethod-register process. Therefore, we don't need to rescan code
262 // roots here.
263 if (!_heap->is_degenerated_gc_in_progress()) {
264 ShenandoahTraversalRootsClosure roots_cl(q, rp);
265 ShenandoahTraversalSATBThreadsClosure tc(&satb_cl);
266 if (unload_classes) {
267 ShenandoahRemarkCLDClosure remark_cld_cl(&roots_cl);
268 _rp->strong_roots_do(worker_id, &roots_cl, &remark_cld_cl, NULL, &tc);
269 } else {
270 CLDToOopClosure cld_cl(&roots_cl, ClassLoaderData::_claim_strong);
271 _rp->roots_do(worker_id, &roots_cl, &cld_cl, NULL, &tc);
272 }
273 } else {
274 ShenandoahTraversalDegenClosure roots_cl(q, rp);
275 ShenandoahTraversalSATBThreadsClosure tc(&satb_cl);
276 if (unload_classes) {
277 ShenandoahRemarkCLDClosure remark_cld_cl(&roots_cl);
278 _rp->strong_roots_do(worker_id, &roots_cl, &remark_cld_cl, NULL, &tc);
279 } else {
280 CLDToOopClosure cld_cl(&roots_cl, ClassLoaderData::_claim_strong);
281 _rp->roots_do(worker_id, &roots_cl, &cld_cl, NULL, &tc);
282 }
283 }
284
285 {
286 ShenandoahWorkerTimings *worker_times = _heap->phase_timings()->worker_times();
287 ShenandoahWorkerTimingsTracker timer(worker_times, ShenandoahPhaseTimings::FinishQueues, worker_id);
288
289 // Step 3: Finally drain all outstanding work in queues.
290 traversal_gc->main_loop(worker_id, _terminator, false);
291 }
292
293 }
294 };
295
296 ShenandoahTraversalGC::ShenandoahTraversalGC(ShenandoahHeap* heap, size_t num_regions) :
297 _heap(heap),
298 _task_queues(new ShenandoahObjToScanQueueSet(heap->max_workers())),
299 _traversal_set(ShenandoahHeapRegionSet()) {
300
301 // Traversal does not support concurrent code root scanning
302 FLAG_SET_DEFAULT(ShenandoahConcurrentScanCodeRoots, false);
303
304 uint num_queues = heap->max_workers();
305 for (uint i = 0; i < num_queues; ++i) {
306 ShenandoahObjToScanQueue* task_queue = new ShenandoahObjToScanQueue();
307 task_queue->initialize();
308 _task_queues->register_queue(i, task_queue);
309 }
310 }
311
312 ShenandoahTraversalGC::~ShenandoahTraversalGC() {
313 }
314
315 void ShenandoahTraversalGC::prepare_regions() {
316 size_t num_regions = _heap->num_regions();
317 ShenandoahMarkingContext* const ctx = _heap->marking_context();
318 for (size_t i = 0; i < num_regions; i++) {
319 ShenandoahHeapRegion* region = _heap->get_region(i);
320 if (_heap->is_bitmap_slice_committed(region)) {
321 if (_traversal_set.is_in(i)) {
322 ctx->capture_top_at_mark_start(region);
323 region->clear_live_data();
324 assert(ctx->is_bitmap_clear_range(region->bottom(), region->end()), "bitmap for traversal regions must be cleared");
325 } else {
326 // Everything outside the traversal set is always considered live.
327 ctx->reset_top_at_mark_start(region);
328 }
329 } else {
330 // FreeSet may contain uncommitted empty regions, once they are recommitted,
331 // their TAMS may have old values, so reset them here.
332 ctx->reset_top_at_mark_start(region);
333 }
334 }
335 }
336
337 void ShenandoahTraversalGC::prepare() {
338 {
339 ShenandoahGCPhase phase(ShenandoahPhaseTimings::traversal_gc_make_parsable);
340 _heap->make_parsable(true);
341 }
342
343 if (UseTLAB) {
344 ShenandoahGCPhase phase(ShenandoahPhaseTimings::traversal_gc_resize_tlabs);
345 _heap->resize_tlabs();
346 }
347
348 assert(_heap->marking_context()->is_bitmap_clear(), "need clean mark bitmap");
349 assert(!_heap->marking_context()->is_complete(), "should not be complete");
350
351 // About to choose the collection set, make sure we know which regions are pinned.
352 {
353 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_prepare_sync_pinned);
354 _heap->sync_pinned_region_status();
355 }
356
357 ShenandoahCollectionSet* collection_set = _heap->collection_set();
358 {
359 ShenandoahHeapLocker lock(_heap->lock());
360
361 collection_set->clear();
362 assert(collection_set->count() == 0, "collection set not clear");
363
364 // Find collection set
365 _heap->heuristics()->choose_collection_set(collection_set);
366 prepare_regions();
367
368 // Rebuild free set
369 _heap->free_set()->rebuild();
370 }
371
372 log_info(gc, ergo)("Collectable Garbage: " SIZE_FORMAT "%s, " SIZE_FORMAT "%s CSet, " SIZE_FORMAT " CSet regions",
373 byte_size_in_proper_unit(collection_set->garbage()), proper_unit_for_byte_size(collection_set->garbage()),
374 byte_size_in_proper_unit(collection_set->live_data()), proper_unit_for_byte_size(collection_set->live_data()),
375 collection_set->count());
376 }
377
378 void ShenandoahTraversalGC::init_traversal_collection() {
379 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "STW traversal GC");
380
381 if (ShenandoahVerify) {
382 _heap->verifier()->verify_before_traversal();
383 }
384
385 if (VerifyBeforeGC) {
386 Universe::verify();
387 }
388
389 {
390 ShenandoahGCPhase phase_prepare(ShenandoahPhaseTimings::traversal_gc_prepare);
391 prepare();
392 }
393
394 _heap->set_concurrent_traversal_in_progress(true);
395 _heap->set_has_forwarded_objects(true);
396
397 bool process_refs = _heap->process_references();
398 if (process_refs) {
399 ReferenceProcessor* rp = _heap->ref_processor();
400 rp->enable_discovery(true /*verify_no_refs*/);
401 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
402 }
403
404 {
405 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::init_traversal_gc_work);
406 assert(_task_queues->is_empty(), "queues must be empty before traversal GC");
407 TASKQUEUE_STATS_ONLY(_task_queues->reset_taskqueue_stats());
408
409 #if COMPILER2_OR_JVMCI
410 DerivedPointerTable::clear();
411 #endif
412
413 {
414 uint nworkers = _heap->workers()->active_workers();
415 task_queues()->reserve(nworkers);
416 ShenandoahCSetRootScanner rp(nworkers, ShenandoahPhaseTimings::init_traversal_gc_work);
417 ShenandoahInitTraversalCollectionTask traversal_task(&rp);
418 _heap->workers()->run_task(&traversal_task);
419 }
420
421 #if COMPILER2_OR_JVMCI
422 DerivedPointerTable::update_pointers();
423 #endif
424 }
425
426 if (ShenandoahPacing) {
427 _heap->pacer()->setup_for_traversal();
428 }
429 }
430
431 void ShenandoahTraversalGC::main_loop(uint w, TaskTerminator* t, bool sts_yield) {
432 ShenandoahObjToScanQueue* q = task_queues()->queue(w);
433
434 // Initialize live data.
435 jushort* ld = _heap->get_liveness_cache(w);
436
437 ReferenceProcessor* rp = NULL;
438 if (_heap->process_references()) {
439 rp = _heap->ref_processor();
440 }
441 {
442 if (!_heap->is_degenerated_gc_in_progress()) {
443 if (_heap->unload_classes()) {
444 if (ShenandoahStringDedup::is_enabled()) {
445 ShenandoahTraversalMetadataDedupClosure cl(q, rp);
446 main_loop_work<ShenandoahTraversalMetadataDedupClosure>(&cl, ld, w, t, sts_yield);
447 } else {
448 ShenandoahTraversalMetadataClosure cl(q, rp);
449 main_loop_work<ShenandoahTraversalMetadataClosure>(&cl, ld, w, t, sts_yield);
450 }
451 } else {
452 if (ShenandoahStringDedup::is_enabled()) {
453 ShenandoahTraversalDedupClosure cl(q, rp);
454 main_loop_work<ShenandoahTraversalDedupClosure>(&cl, ld, w, t, sts_yield);
455 } else {
456 ShenandoahTraversalClosure cl(q, rp);
457 main_loop_work<ShenandoahTraversalClosure>(&cl, ld, w, t, sts_yield);
458 }
459 }
460 } else {
461 if (_heap->unload_classes()) {
462 if (ShenandoahStringDedup::is_enabled()) {
463 ShenandoahTraversalMetadataDedupDegenClosure cl(q, rp);
464 main_loop_work<ShenandoahTraversalMetadataDedupDegenClosure>(&cl, ld, w, t, sts_yield);
465 } else {
466 ShenandoahTraversalMetadataDegenClosure cl(q, rp);
467 main_loop_work<ShenandoahTraversalMetadataDegenClosure>(&cl, ld, w, t, sts_yield);
468 }
469 } else {
470 if (ShenandoahStringDedup::is_enabled()) {
471 ShenandoahTraversalDedupDegenClosure cl(q, rp);
472 main_loop_work<ShenandoahTraversalDedupDegenClosure>(&cl, ld, w, t, sts_yield);
473 } else {
474 ShenandoahTraversalDegenClosure cl(q, rp);
475 main_loop_work<ShenandoahTraversalDegenClosure>(&cl, ld, w, t, sts_yield);
476 }
477 }
478 }
479 }
480
481 _heap->flush_liveness_cache(w);
482 }
483
484 template <class T>
485 void ShenandoahTraversalGC::main_loop_work(T* cl, jushort* live_data, uint worker_id, TaskTerminator* terminator, bool sts_yield) {
486 ShenandoahObjToScanQueueSet* queues = task_queues();
487 ShenandoahObjToScanQueue* q = queues->queue(worker_id);
488 ShenandoahConcurrentMark* conc_mark = _heap->concurrent_mark();
489
490 uintx stride = ShenandoahMarkLoopStride;
491
492 ShenandoahMarkTask task;
493
494 // Process outstanding queues, if any.
495 q = queues->claim_next();
496 while (q != NULL) {
497 if (_heap->check_cancelled_gc_and_yield(sts_yield)) {
498 return;
499 }
500
501 for (uint i = 0; i < stride; i++) {
502 if (q->pop(task)) {
503 conc_mark->do_task<T>(q, cl, live_data, &task);
504 } else {
505 assert(q->is_empty(), "Must be empty");
506 q = queues->claim_next();
507 break;
508 }
509 }
510 }
511
512 if (check_and_handle_cancelled_gc(terminator, sts_yield)) return;
513
514 // Normal loop.
515 q = queues->queue(worker_id);
516
517 ShenandoahTraversalSATBBufferClosure drain_satb(q);
518 SATBMarkQueueSet& satb_mq_set = ShenandoahBarrierSet::satb_mark_queue_set();
519
520 while (true) {
521 if (check_and_handle_cancelled_gc(terminator, sts_yield)) return;
522
523 while (satb_mq_set.completed_buffers_num() > 0) {
524 satb_mq_set.apply_closure_to_completed_buffer(&drain_satb);
525 }
526
527 uint work = 0;
528 for (uint i = 0; i < stride; i++) {
529 if (q->pop(task) ||
530 queues->steal(worker_id, task)) {
531 conc_mark->do_task<T>(q, cl, live_data, &task);
532 work++;
533 } else {
534 break;
535 }
536 }
537
538 if (work == 0) {
539 // No more work, try to terminate
540 ShenandoahSuspendibleThreadSetLeaver stsl(sts_yield && ShenandoahSuspendibleWorkers);
541 ShenandoahTerminatorTerminator tt(_heap);
542
543 if (terminator->offer_termination(&tt)) return;
544 }
545 }
546 }
547
548 bool ShenandoahTraversalGC::check_and_handle_cancelled_gc(TaskTerminator* terminator, bool sts_yield) {
549 if (_heap->cancelled_gc()) {
550 return true;
551 }
552 return false;
553 }
554
555 void ShenandoahTraversalGC::concurrent_traversal_collection() {
556 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::conc_traversal);
557 if (!_heap->cancelled_gc()) {
558 uint nworkers = _heap->workers()->active_workers();
559 task_queues()->reserve(nworkers);
560
561 TaskTerminator terminator(nworkers, task_queues());
562 ShenandoahConcurrentTraversalCollectionTask task(&terminator);
563 _heap->workers()->run_task(&task);
564 }
565
566 if (!_heap->cancelled_gc() && ShenandoahPreclean && _heap->process_references()) {
567 preclean_weak_refs();
568 }
569 }
570
571 void ShenandoahTraversalGC::final_traversal_collection() {
572 if (!_heap->cancelled_gc()) {
573 #if COMPILER2_OR_JVMCI
574 DerivedPointerTable::clear();
575 #endif
576 ShenandoahGCPhase phase_work(ShenandoahPhaseTimings::final_traversal_gc_work);
577 uint nworkers = _heap->workers()->active_workers();
578 task_queues()->reserve(nworkers);
579
580 // Finish traversal
581 ShenandoahAllRootScanner rp(nworkers, ShenandoahPhaseTimings::final_traversal_gc_work);
582 TaskTerminator terminator(nworkers, task_queues());
583 ShenandoahFinalTraversalCollectionTask task(&rp, &terminator);
584 _heap->workers()->run_task(&task);
585 #if COMPILER2_OR_JVMCI
586 DerivedPointerTable::update_pointers();
587 #endif
588 }
589
590 if (!_heap->cancelled_gc() && _heap->process_references()) {
591 weak_refs_work();
592 }
593
594 if (!_heap->cancelled_gc()) {
595 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
596 TASKQUEUE_STATS_ONLY(_task_queues->print_taskqueue_stats());
597 TASKQUEUE_STATS_ONLY(_task_queues->reset_taskqueue_stats());
598
599 // No more marking expected
600 _heap->set_concurrent_traversal_in_progress(false);
601 _heap->mark_complete_marking_context();
602
603 // A rare case, TLAB/GCLAB is initialized from an empty region without
604 // any live data, the region can be trashed and may be uncommitted in later code,
605 // that results the TLAB/GCLAB not usable. Retire them here.
606 _heap->make_parsable(true);
607
608 _heap->parallel_cleaning(false);
609 fixup_roots();
610
611 _heap->set_has_forwarded_objects(false);
612
613 // Resize metaspace
614 MetaspaceGC::compute_new_size();
615
616 // Need to see that pinned region status is updated: newly pinned regions must not
617 // be trashed. New unpinned regions should be trashed.
618 {
619 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_sync_pinned);
620 _heap->sync_pinned_region_status();
621 }
622
623 // Still good? We can now trash the cset, and make final verification
624 {
625 ShenandoahGCPhase phase_cleanup(ShenandoahPhaseTimings::traversal_gc_cleanup);
626 ShenandoahHeapLocker lock(_heap->lock());
627
628 // Trash everything
629 // Clear immediate garbage regions.
630 size_t num_regions = _heap->num_regions();
631
632 ShenandoahHeapRegionSet* traversal_regions = traversal_set();
633 ShenandoahFreeSet* free_regions = _heap->free_set();
634 ShenandoahMarkingContext* const ctx = _heap->marking_context();
635 free_regions->clear();
636 for (size_t i = 0; i < num_regions; i++) {
637 ShenandoahHeapRegion* r = _heap->get_region(i);
638 bool not_allocated = ctx->top_at_mark_start(r) == r->top();
639
640 bool candidate = traversal_regions->is_in(r) && !r->has_live() && not_allocated;
641 if (r->is_humongous_start() && candidate) {
642 // Trash humongous.
643 HeapWord* humongous_obj = r->bottom();
644 assert(!ctx->is_marked(oop(humongous_obj)), "must not be marked");
645 r->make_trash_immediate();
646 while (i + 1 < num_regions && _heap->get_region(i + 1)->is_humongous_continuation()) {
647 i++;
648 r = _heap->get_region(i);
649 assert(r->is_humongous_continuation(), "must be humongous continuation");
650 r->make_trash_immediate();
651 }
652 } else if (!r->is_empty() && candidate) {
653 // Trash regular.
654 assert(!r->is_humongous(), "handled above");
655 assert(!r->is_trash(), "must not already be trashed");
656 r->make_trash_immediate();
657 }
658 }
659 _heap->collection_set()->clear();
660 _heap->free_set()->rebuild();
661 reset();
662 }
663
664 assert(_task_queues->is_empty(), "queues must be empty after traversal GC");
665 assert(!_heap->cancelled_gc(), "must not be cancelled when getting out here");
666
667 if (ShenandoahVerify) {
668 _heap->verifier()->verify_after_traversal();
669 }
670 #ifdef ASSERT
671 else {
672 verify_roots_after_gc();
673 }
674 #endif
675
676 if (VerifyAfterGC) {
677 Universe::verify();
678 }
679 }
680 }
681
682 class ShenandoahVerifyAfterGC : public OopClosure {
683 private:
684 template <class T>
685 void do_oop_work(T* p) {
686 T o = RawAccess<>::oop_load(p);
687 if (!CompressedOops::is_null(o)) {
688 oop obj = CompressedOops::decode_not_null(o);
689 shenandoah_assert_correct(p, obj);
690 shenandoah_assert_not_in_cset_except(p, obj, ShenandoahHeap::heap()->cancelled_gc());
691 shenandoah_assert_not_forwarded(p, obj);
692 }
693 }
694
695 public:
696 void do_oop(narrowOop* p) { do_oop_work(p); }
697 void do_oop(oop* p) { do_oop_work(p); }
698 };
699
700 void ShenandoahTraversalGC::verify_roots_after_gc() {
701 ShenandoahRootVerifier verifier;
702 ShenandoahVerifyAfterGC cl;
703 verifier.oops_do(&cl);
704 }
705
706 class ShenandoahTraversalFixRootsClosure : public OopClosure {
707 private:
708 template <class T>
709 inline void do_oop_work(T* p) {
710 T o = RawAccess<>::oop_load(p);
711 if (!CompressedOops::is_null(o)) {
712 oop obj = CompressedOops::decode_not_null(o);
713 oop forw = ShenandoahBarrierSet::resolve_forwarded_not_null(obj);
714 if (obj != forw) {
715 RawAccess<IS_NOT_NULL>::oop_store(p, forw);
716 }
717 }
718 }
719
720 public:
721 inline void do_oop(oop* p) { do_oop_work(p); }
722 inline void do_oop(narrowOop* p) { do_oop_work(p); }
723 };
724
725 class ShenandoahTraversalFixRootsTask : public AbstractGangTask {
726 private:
727 ShenandoahRootUpdater* _rp;
728
729 public:
730 ShenandoahTraversalFixRootsTask(ShenandoahRootUpdater* rp) :
731 AbstractGangTask("Shenandoah traversal fix roots"),
732 _rp(rp) {
733 assert(ShenandoahHeap::heap()->has_forwarded_objects(), "Must be");
734 }
735
736 void work(uint worker_id) {
737 ShenandoahParallelWorkerSession worker_session(worker_id);
738 ShenandoahTraversalFixRootsClosure cl;
739 ShenandoahForwardedIsAliveClosure is_alive;
740 _rp->roots_do(worker_id, &is_alive, &cl);
741 }
742 };
743
744 void ShenandoahTraversalGC::fixup_roots() {
745 #if COMPILER2_OR_JVMCI
746 DerivedPointerTable::clear();
747 #endif
748 ShenandoahRootUpdater rp(_heap->workers()->active_workers(), ShenandoahPhaseTimings::final_traversal_update_roots);
749 ShenandoahTraversalFixRootsTask update_roots_task(&rp);
750 _heap->workers()->run_task(&update_roots_task);
751 #if COMPILER2_OR_JVMCI
752 DerivedPointerTable::update_pointers();
753 #endif
754 }
755
756 void ShenandoahTraversalGC::reset() {
757 _task_queues->clear();
758 }
759
760 ShenandoahObjToScanQueueSet* ShenandoahTraversalGC::task_queues() {
761 return _task_queues;
762 }
763
764 class ShenandoahTraversalCancelledGCYieldClosure : public YieldClosure {
765 private:
766 ShenandoahHeap* const _heap;
767 public:
768 ShenandoahTraversalCancelledGCYieldClosure() : _heap(ShenandoahHeap::heap()) {};
769 virtual bool should_return() { return _heap->cancelled_gc(); }
770 };
771
772 class ShenandoahTraversalPrecleanCompleteGCClosure : public VoidClosure {
773 public:
774 void do_void() {
775 ShenandoahHeap* sh = ShenandoahHeap::heap();
776 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
777 assert(sh->process_references(), "why else would we be here?");
778 TaskTerminator terminator(1, traversal_gc->task_queues());
779 shenandoah_assert_rp_isalive_installed();
780 traversal_gc->main_loop((uint) 0, &terminator, true);
781 }
782 };
783
784 class ShenandoahTraversalKeepAliveUpdateClosure : public OopClosure {
785 private:
786 ShenandoahObjToScanQueue* _queue;
787 Thread* _thread;
788 ShenandoahTraversalGC* _traversal_gc;
789 ShenandoahMarkingContext* const _mark_context;
790
791 template <class T>
792 inline void do_oop_work(T* p) {
793 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */, true /* atomic update */>(p, _thread, _queue, _mark_context);
794 }
795
796 public:
797 ShenandoahTraversalKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
798 _queue(q), _thread(Thread::current()),
799 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
800 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
801
802 void do_oop(narrowOop* p) { do_oop_work(p); }
803 void do_oop(oop* p) { do_oop_work(p); }
804 };
805
806 class ShenandoahTraversalKeepAliveUpdateDegenClosure : public OopClosure {
807 private:
808 ShenandoahObjToScanQueue* _queue;
809 Thread* _thread;
810 ShenandoahTraversalGC* _traversal_gc;
811 ShenandoahMarkingContext* const _mark_context;
812
813 template <class T>
814 inline void do_oop_work(T* p) {
815 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */, false /* atomic update */>(p, _thread, _queue, _mark_context);
816 }
817
818 public:
819 ShenandoahTraversalKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
820 _queue(q), _thread(Thread::current()),
821 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
822 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
823
824 void do_oop(narrowOop* p) { do_oop_work(p); }
825 void do_oop(oop* p) { do_oop_work(p); }
826 };
827
828 class ShenandoahTraversalSingleThreadKeepAliveUpdateClosure : public OopClosure {
829 private:
830 ShenandoahObjToScanQueue* _queue;
831 Thread* _thread;
832 ShenandoahTraversalGC* _traversal_gc;
833 ShenandoahMarkingContext* const _mark_context;
834
835 template <class T>
836 inline void do_oop_work(T* p) {
837 _traversal_gc->process_oop<T, false /* string dedup */, false /* degen */, true /* atomic update */>(p, _thread, _queue, _mark_context);
838 }
839
840 public:
841 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure(ShenandoahObjToScanQueue* q) :
842 _queue(q), _thread(Thread::current()),
843 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
844 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
845
846 void do_oop(narrowOop* p) { do_oop_work(p); }
847 void do_oop(oop* p) { do_oop_work(p); }
848 };
849
850 class ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure : public OopClosure {
851 private:
852 ShenandoahObjToScanQueue* _queue;
853 Thread* _thread;
854 ShenandoahTraversalGC* _traversal_gc;
855 ShenandoahMarkingContext* const _mark_context;
856
857 template <class T>
858 inline void do_oop_work(T* p) {
859 _traversal_gc->process_oop<T, false /* string dedup */, true /* degen */, false /* atomic update */>(p, _thread, _queue, _mark_context);
860 }
861
862 public:
863 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure(ShenandoahObjToScanQueue* q) :
864 _queue(q), _thread(Thread::current()),
865 _traversal_gc(ShenandoahHeap::heap()->traversal_gc()),
866 _mark_context(ShenandoahHeap::heap()->marking_context()) {}
867
868 void do_oop(narrowOop* p) { do_oop_work(p); }
869 void do_oop(oop* p) { do_oop_work(p); }
870 };
871
872 class ShenandoahTraversalPrecleanTask : public AbstractGangTask {
873 private:
874 ReferenceProcessor* _rp;
875
876 public:
877 ShenandoahTraversalPrecleanTask(ReferenceProcessor* rp) :
878 AbstractGangTask("Precleaning task"),
879 _rp(rp) {}
880
881 void work(uint worker_id) {
882 assert(worker_id == 0, "The code below is single-threaded, only one worker is expected");
883 ShenandoahParallelWorkerSession worker_session(worker_id);
884 ShenandoahSuspendibleThreadSetJoiner stsj(ShenandoahSuspendibleWorkers);
885
886 ShenandoahHeap* sh = ShenandoahHeap::heap();
887
888 ShenandoahObjToScanQueue* q = sh->traversal_gc()->task_queues()->queue(worker_id);
889
890 ShenandoahForwardedIsAliveClosure is_alive;
891 ShenandoahTraversalCancelledGCYieldClosure yield;
892 ShenandoahTraversalPrecleanCompleteGCClosure complete_gc;
893 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(q);
894 ResourceMark rm;
895 _rp->preclean_discovered_references(&is_alive, &keep_alive,
896 &complete_gc, &yield,
897 NULL);
898 }
899 };
900
901 void ShenandoahTraversalGC::preclean_weak_refs() {
902 // Pre-cleaning weak references before diving into STW makes sense at the
903 // end of concurrent mark. This will filter out the references which referents
904 // are alive. Note that ReferenceProcessor already filters out these on reference
905 // discovery, and the bulk of work is done here. This phase processes leftovers
906 // that missed the initial filtering, i.e. when referent was marked alive after
907 // reference was discovered by RP.
908
909 assert(_heap->process_references(), "sanity");
910 assert(!_heap->is_degenerated_gc_in_progress(), "must be in concurrent non-degenerated phase");
911
912 // Shortcut if no references were discovered to avoid winding up threads.
913 ReferenceProcessor* rp = _heap->ref_processor();
914 if (!rp->has_discovered_references()) {
915 return;
916 }
917
918 ReferenceProcessorMTDiscoveryMutator fix_mt_discovery(rp, false);
919
920 shenandoah_assert_rp_isalive_not_installed();
921 ShenandoahForwardedIsAliveClosure is_alive;
922 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
923
924 assert(task_queues()->is_empty(), "Should be empty");
925
926 // Execute precleaning in the worker thread: it will give us GCLABs, String dedup
927 // queues and other goodies. When upstream ReferenceProcessor starts supporting
928 // parallel precleans, we can extend this to more threads.
929 ShenandoahPushWorkerScope scope(_heap->workers(), 1, /* check_workers = */ false);
930
931 WorkGang* workers = _heap->workers();
932 uint nworkers = workers->active_workers();
933 assert(nworkers == 1, "This code uses only a single worker");
934 task_queues()->reserve(nworkers);
935
936 ShenandoahTraversalPrecleanTask task(rp);
937 workers->run_task(&task);
938
939 assert(_heap->cancelled_gc() || task_queues()->is_empty(), "Should be empty");
940 }
941
942 // Weak Reference Closures
943 class ShenandoahTraversalDrainMarkingStackClosure: public VoidClosure {
944 uint _worker_id;
945 TaskTerminator* _terminator;
946 bool _reset_terminator;
947
948 public:
949 ShenandoahTraversalDrainMarkingStackClosure(uint worker_id, TaskTerminator* t, bool reset_terminator = false):
950 _worker_id(worker_id),
951 _terminator(t),
952 _reset_terminator(reset_terminator) {
953 }
954
955 void do_void() {
956 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
957
958 ShenandoahHeap* sh = ShenandoahHeap::heap();
959 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
960 assert(sh->process_references(), "why else would we be here?");
961 shenandoah_assert_rp_isalive_installed();
962
963 traversal_gc->main_loop(_worker_id, _terminator, false);
964
965 if (_reset_terminator) {
966 _terminator->reset_for_reuse();
967 }
968 }
969 };
970
971 class ShenandoahTraversalSingleThreadedDrainMarkingStackClosure: public VoidClosure {
972 uint _worker_id;
973 TaskTerminator* _terminator;
974 bool _reset_terminator;
975
976 public:
977 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure(uint worker_id, TaskTerminator* t, bool reset_terminator = false):
978 _worker_id(worker_id),
979 _terminator(t),
980 _reset_terminator(reset_terminator) {
981 }
982
983 void do_void() {
984 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
985
986 ShenandoahHeap* sh = ShenandoahHeap::heap();
987 ShenandoahTraversalGC* traversal_gc = sh->traversal_gc();
988 assert(sh->process_references(), "why else would we be here?");
989 shenandoah_assert_rp_isalive_installed();
990
991 traversal_gc->main_loop(_worker_id, _terminator, false);
992
993 if (_reset_terminator) {
994 _terminator->reset_for_reuse();
995 }
996 }
997 };
998
999 void ShenandoahTraversalGC::weak_refs_work() {
1000 assert(_heap->process_references(), "sanity");
1001
1002 ShenandoahPhaseTimings::Phase phase_root = ShenandoahPhaseTimings::weakrefs;
1003
1004 ShenandoahGCPhase phase(phase_root);
1005
1006 ReferenceProcessor* rp = _heap->ref_processor();
1007
1008 // NOTE: We cannot shortcut on has_discovered_references() here, because
1009 // we will miss marking JNI Weak refs then, see implementation in
1010 // ReferenceProcessor::process_discovered_references.
1011 weak_refs_work_doit();
1012
1013 rp->verify_no_references_recorded();
1014 assert(!rp->discovery_enabled(), "Post condition");
1015
1016 }
1017
1018 class ShenandoahTraversalRefProcTaskProxy : public AbstractGangTask {
1019 private:
1020 AbstractRefProcTaskExecutor::ProcessTask& _proc_task;
1021 TaskTerminator* _terminator;
1022
1023 public:
1024 ShenandoahTraversalRefProcTaskProxy(AbstractRefProcTaskExecutor::ProcessTask& proc_task,
1025 TaskTerminator* t) :
1026 AbstractGangTask("Process reference objects in parallel"),
1027 _proc_task(proc_task),
1028 _terminator(t) {
1029 }
1030
1031 void work(uint worker_id) {
1032 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1033 ShenandoahHeap* heap = ShenandoahHeap::heap();
1034 ShenandoahTraversalDrainMarkingStackClosure complete_gc(worker_id, _terminator);
1035
1036 ShenandoahForwardedIsAliveClosure is_alive;
1037 if (!heap->is_degenerated_gc_in_progress()) {
1038 ShenandoahTraversalKeepAliveUpdateClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1039 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1040 } else {
1041 ShenandoahTraversalKeepAliveUpdateDegenClosure keep_alive(heap->traversal_gc()->task_queues()->queue(worker_id));
1042 _proc_task.work(worker_id, is_alive, keep_alive, complete_gc);
1043 }
1044 }
1045 };
1046
1047 class ShenandoahTraversalRefProcTaskExecutor : public AbstractRefProcTaskExecutor {
1048 private:
1049 WorkGang* _workers;
1050
1051 public:
1052 ShenandoahTraversalRefProcTaskExecutor(WorkGang* workers) : _workers(workers) {}
1053
1054 // Executes a task using worker threads.
1055 void execute(ProcessTask& task, uint ergo_workers) {
1056 assert(ShenandoahSafepoint::is_at_shenandoah_safepoint(), "Must be at a safepoint");
1057
1058 ShenandoahHeap* heap = ShenandoahHeap::heap();
1059 ShenandoahTraversalGC* traversal_gc = heap->traversal_gc();
1060 ShenandoahPushWorkerQueuesScope scope(_workers,
1061 traversal_gc->task_queues(),
1062 ergo_workers,
1063 /* do_check = */ false);
1064 uint nworkers = _workers->active_workers();
1065 traversal_gc->task_queues()->reserve(nworkers);
1066 TaskTerminator terminator(nworkers, traversal_gc->task_queues());
1067 ShenandoahTraversalRefProcTaskProxy proc_task_proxy(task, &terminator);
1068 _workers->run_task(&proc_task_proxy);
1069 }
1070 };
1071
1072 void ShenandoahTraversalGC::weak_refs_work_doit() {
1073 ReferenceProcessor* rp = _heap->ref_processor();
1074
1075 ShenandoahPhaseTimings::Phase phase_process = ShenandoahPhaseTimings::weakrefs_process;
1076
1077 shenandoah_assert_rp_isalive_not_installed();
1078 ShenandoahForwardedIsAliveClosure is_alive;
1079 ReferenceProcessorIsAliveMutator fix_isalive(rp, &is_alive);
1080
1081 WorkGang* workers = _heap->workers();
1082 uint nworkers = workers->active_workers();
1083
1084 rp->setup_policy(_heap->soft_ref_policy()->should_clear_all_soft_refs());
1085 rp->set_active_mt_degree(nworkers);
1086
1087 assert(task_queues()->is_empty(), "Should be empty");
1088
1089 // complete_gc and keep_alive closures instantiated here are only needed for
1090 // single-threaded path in RP. They share the queue 0 for tracking work, which
1091 // simplifies implementation. Since RP may decide to call complete_gc several
1092 // times, we need to be able to reuse the terminator.
1093 uint serial_worker_id = 0;
1094 TaskTerminator terminator(1, task_queues());
1095 ShenandoahTraversalSingleThreadedDrainMarkingStackClosure complete_gc(serial_worker_id, &terminator, /* reset_terminator = */ true);
1096 ShenandoahPushWorkerQueuesScope scope(workers, task_queues(), 1, /* do_check = */ false);
1097
1098 ShenandoahTraversalRefProcTaskExecutor executor(workers);
1099
1100 ReferenceProcessorPhaseTimes pt(_heap->gc_timer(), rp->num_queues());
1101 if (!_heap->is_degenerated_gc_in_progress()) {
1102 ShenandoahTraversalSingleThreadKeepAliveUpdateClosure keep_alive(task_queues()->queue(serial_worker_id));
1103 rp->process_discovered_references(&is_alive, &keep_alive,
1104 &complete_gc, &executor,
1105 &pt);
1106 } else {
1107 ShenandoahTraversalSingleThreadKeepAliveUpdateDegenClosure keep_alive(task_queues()->queue(serial_worker_id));
1108 rp->process_discovered_references(&is_alive, &keep_alive,
1109 &complete_gc, &executor,
1110 &pt);
1111 }
1112
1113 pt.print_all_references();
1114 assert(task_queues()->is_empty() || _heap->cancelled_gc(), "Should be empty");
1115 }