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