1 /*
2 * Copyright (c) 2013, 2021, Red Hat, Inc. All rights reserved.
3 * Copyright (C) 2022 THL A29 Limited, a Tencent company. All rights reserved.
4 * Copyright Amazon.com Inc. or its affiliates. All Rights Reserved.
5 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
6 *
7 * This code is free software; you can redistribute it and/or modify it
8 * under the terms of the GNU General Public License version 2 only, as
9 * published by the Free Software Foundation.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 *
25 */
26
27 #include "precompiled.hpp"
28 #include "gc/shenandoah/shenandoahAsserts.hpp"
29 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
30 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
31 #include "gc/shenandoah/shenandoahGenerationalControlThread.hpp"
32 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
33 #include "gc/shenandoah/shenandoahFreeSet.hpp"
34 #include "gc/shenandoah/shenandoahFullGC.hpp"
35 #include "gc/shenandoah/shenandoahGeneration.hpp"
36 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
37 #include "gc/shenandoah/shenandoahOldGC.hpp"
38 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
39 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
40 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
41 #include "gc/shenandoah/shenandoahPacer.inline.hpp"
42 #include "gc/shenandoah/shenandoahUtils.hpp"
43 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
44 #include "logging/log.hpp"
45 #include "memory/metaspaceUtils.hpp"
46 #include "memory/metaspaceStats.hpp"
47 #include "runtime/atomic.hpp"
48 #include "utilities/events.hpp"
49
50 ShenandoahGenerationalControlThread::ShenandoahGenerationalControlThread() :
51 _control_lock(Mutex::nosafepoint - 2, "ShenandoahGCRequest_lock", true),
52 _requested_gc_cause(GCCause::_no_gc),
53 _requested_generation(nullptr),
54 _gc_mode(none),
55 _degen_point(ShenandoahGC::_degenerated_unset),
56 _heap(ShenandoahGenerationalHeap::heap()),
57 _age_period(0) {
58 shenandoah_assert_generational();
59 set_name("Shenandoah Control Thread");
60 create_and_start();
61 }
62
63 void ShenandoahGenerationalControlThread::run_service() {
64
65 const int64_t wait_ms = ShenandoahPacing ? ShenandoahControlIntervalMin : 0;
66 ShenandoahGCRequest request;
67 while (!should_terminate()) {
68
69 // This control loop iteration has seen this much allocation.
70 const size_t allocs_seen = reset_allocs_seen();
71
72 // Figure out if we have pending requests.
73 check_for_request(request);
74
75 if (request.cause == GCCause::_shenandoah_stop_vm) {
76 break;
77 }
78
79 if (request.cause != GCCause::_no_gc) {
80 run_gc_cycle(request);
81 } else {
82 // Report to pacer that we have seen this many words allocated
83 if (ShenandoahPacing && (allocs_seen > 0)) {
84 _heap->pacer()->report_alloc(allocs_seen);
85 }
86 }
87
88 // If the cycle was cancelled, continue the next iteration to deal with it. Otherwise,
89 // if there was no other cycle requested, cleanup and wait for the next request.
90 if (!_heap->cancelled_gc()) {
91 MonitorLocker ml(&_control_lock, Mutex::_no_safepoint_check_flag);
92 if (_requested_gc_cause == GCCause::_no_gc) {
93 set_gc_mode(ml, none);
94 ml.wait(wait_ms);
95 }
96 }
97 }
98
99 // In case any threads are waiting for a cycle to happen, notify them so they observe the shutdown.
100 notify_gc_waiters();
101 notify_alloc_failure_waiters();
102 set_gc_mode(stopped);
103 }
104
105 void ShenandoahGenerationalControlThread::stop_service() {
106 log_debug(gc, thread)("Stopping control thread");
107 MonitorLocker ml(&_control_lock, Mutex::_no_safepoint_check_flag);
108 _heap->cancel_gc(GCCause::_shenandoah_stop_vm);
109 _requested_gc_cause = GCCause::_shenandoah_stop_vm;
110 notify_cancellation(ml, GCCause::_shenandoah_stop_vm);
111 // We can't wait here because it may interfere with the active cycle's ability
112 // to reach a safepoint (this runs on a java thread).
113 }
114
115 void ShenandoahGenerationalControlThread::check_for_request(ShenandoahGCRequest& request) {
116 // Hold the lock while we read request cause and generation
117 MonitorLocker ml(&_control_lock, Mutex::_no_safepoint_check_flag);
118 if (_heap->cancelled_gc()) {
119 // The previous request was cancelled. Either it was cancelled for an allocation
120 // failure (degenerated cycle), or old marking was cancelled to run a young collection.
121 // In either case, the correct generation for the next cycle can be determined by
122 // the cancellation cause.
123 request.cause = _heap->cancelled_cause();
124 if (request.cause == GCCause::_shenandoah_concurrent_gc) {
125 request.generation = _heap->young_generation();
126 _heap->clear_cancelled_gc(false);
127 }
128 } else {
129 request.cause = _requested_gc_cause;
130 request.generation = _requested_generation;
131
132 // Only clear these if we made a request from them. In the case of a cancelled gc,
133 // we do not want to inadvertently lose this pending request.
134 _requested_gc_cause = GCCause::_no_gc;
135 _requested_generation = nullptr;
136 }
137
138 if (request.cause == GCCause::_no_gc || request.cause == GCCause::_shenandoah_stop_vm) {
139 return;
140 }
141
142 GCMode mode;
143 if (ShenandoahCollectorPolicy::is_allocation_failure(request.cause)) {
144 mode = prepare_for_allocation_failure_gc(request);
145 } else if (ShenandoahCollectorPolicy::is_explicit_gc(request.cause)) {
146 mode = prepare_for_explicit_gc(request);
147 } else {
148 mode = prepare_for_concurrent_gc(request);
149 }
150 set_gc_mode(ml, mode);
151 }
152
153 ShenandoahGenerationalControlThread::GCMode ShenandoahGenerationalControlThread::prepare_for_allocation_failure_gc(ShenandoahGCRequest &request) {
154
155 if (_degen_point == ShenandoahGC::_degenerated_unset) {
156 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
157 request.generation = _heap->young_generation();
158 } else if (request.generation->is_old()) {
159 // This means we degenerated during the young bootstrap for the old generation
160 // cycle. The following degenerated cycle should therefore also be young.
161 request.generation = _heap->young_generation();
162 }
163
164 ShenandoahHeuristics* heuristics = request.generation->heuristics();
165 bool old_gen_evacuation_failed = _heap->old_generation()->clear_failed_evacuation();
166
167 heuristics->log_trigger("Handle Allocation Failure");
168
169 // Do not bother with degenerated cycle if old generation evacuation failed or if humongous allocation failed
170 if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle() &&
171 !old_gen_evacuation_failed && request.cause != GCCause::_shenandoah_humongous_allocation_failure) {
172 heuristics->record_allocation_failure_gc();
173 _heap->shenandoah_policy()->record_alloc_failure_to_degenerated(_degen_point);
174 return stw_degenerated;
175 } else {
176 heuristics->record_allocation_failure_gc();
177 _heap->shenandoah_policy()->record_alloc_failure_to_full();
178 request.generation = _heap->global_generation();
179 return stw_full;
180 }
181 }
182
183 ShenandoahGenerationalControlThread::GCMode ShenandoahGenerationalControlThread::prepare_for_explicit_gc(ShenandoahGCRequest &request) const {
184 ShenandoahHeuristics* global_heuristics = _heap->global_generation()->heuristics();
185 request.generation = _heap->global_generation();
186 global_heuristics->log_trigger("GC request (%s)", GCCause::to_string(request.cause));
187 global_heuristics->record_requested_gc();
188
189 if (ShenandoahCollectorPolicy::should_run_full_gc(request.cause)) {
190 return stw_full;;
191 } else {
192 // Unload and clean up everything. Note that this is an _explicit_ request and so does not use
193 // the same `should_unload_classes` call as the regulator's concurrent gc request.
194 _heap->set_unload_classes(global_heuristics->can_unload_classes());
195 return concurrent_normal;
196 }
197 }
198
199 ShenandoahGenerationalControlThread::GCMode ShenandoahGenerationalControlThread::prepare_for_concurrent_gc(const ShenandoahGCRequest &request) const {
200 assert(!(request.generation->is_old() && _heap->old_generation()->is_doing_mixed_evacuations()),
201 "Old heuristic should not request cycles while it waits for mixed evacuations");
202
203 if (request.generation->is_global()) {
204 ShenandoahHeuristics* global_heuristics = _heap->global_generation()->heuristics();
205 _heap->set_unload_classes(global_heuristics->should_unload_classes());
206 } else {
207 _heap->set_unload_classes(false);
208 }
209
210 // preemption was requested or this is a regular cycle
211 return request.generation->is_old() ? servicing_old : concurrent_normal;
212 }
213
214 void ShenandoahGenerationalControlThread::maybe_set_aging_cycle() {
215 if (_age_period-- == 0) {
216 _heap->set_aging_cycle(true);
217 _age_period = ShenandoahAgingCyclePeriod - 1;
218 } else {
219 _heap->set_aging_cycle(false);
220 }
221 }
222
223 void ShenandoahGenerationalControlThread::run_gc_cycle(const ShenandoahGCRequest& request) {
224
225 log_debug(gc, thread)("Starting GC (%s): %s, %s", gc_mode_name(gc_mode()), GCCause::to_string(request.cause), request.generation->name());
226 assert(gc_mode() != none, "GC mode cannot be none here");
227
228 // Blow away all soft references on this cycle, if handling allocation failure,
229 // either implicit or explicit GC request, or we are requested to do so unconditionally.
230 if (request.generation->is_global() && (ShenandoahCollectorPolicy::is_allocation_failure(request.cause) || ShenandoahCollectorPolicy::is_explicit_gc(request.cause) || ShenandoahAlwaysClearSoftRefs)) {
231 _heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
232 }
233
234 // GC is starting, bump the internal ID
235 update_gc_id();
236
237 GCIdMark gc_id_mark;
238
239 _heap->reset_bytes_allocated_since_gc_start();
240
241 MetaspaceCombinedStats meta_sizes = MetaspaceUtils::get_combined_statistics();
242
243 // If GC was requested, we are sampling the counters even without actual triggers
244 // from allocation machinery. This captures GC phases more accurately.
245 _heap->set_forced_counters_update(true);
246
247 // If GC was requested, we better dump freeset data for performance debugging
248 _heap->free_set()->log_status_under_lock();
249
250 {
251 // Cannot uncommit bitmap slices during concurrent reset
252 ShenandoahNoUncommitMark forbid_region_uncommit(_heap);
253
254 switch (gc_mode()) {
255 case concurrent_normal: {
256 service_concurrent_normal_cycle(request);
257 break;
258 }
259 case stw_degenerated: {
260 service_stw_degenerated_cycle(request);
261 break;
262 }
263 case stw_full: {
264 service_stw_full_cycle(request.cause);
265 break;
266 }
267 case servicing_old: {
268 assert(request.generation->is_old(), "Expected old generation here");
269 service_concurrent_old_cycle(request);
270 break;
271 }
272 default:
273 ShouldNotReachHere();
274 }
275 }
276
277 // If this cycle completed successfully, notify threads waiting for gc
278 if (!_heap->cancelled_gc()) {
279 notify_gc_waiters();
280 notify_alloc_failure_waiters();
281 }
282
283 // Report current free set state at the end of cycle, whether
284 // it is a normal completion, or the abort.
285 _heap->free_set()->log_status_under_lock();
286
287 // Notify Universe about new heap usage. This has implications for
288 // global soft refs policy, and we better report it every time heap
289 // usage goes down.
290 _heap->update_capacity_and_used_at_gc();
291
292 // Signal that we have completed a visit to all live objects.
293 _heap->record_whole_heap_examined_timestamp();
294
295 // Disable forced counters update, and update counters one more time
296 // to capture the state at the end of GC session.
297 _heap->handle_force_counters_update();
298 _heap->set_forced_counters_update(false);
299
300 // Retract forceful part of soft refs policy
301 _heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
302
303 // Clear metaspace oom flag, if current cycle unloaded classes
304 if (_heap->unload_classes()) {
305 _heap->global_generation()->heuristics()->clear_metaspace_oom();
306 }
307
308 process_phase_timings();
309
310 // Print Metaspace change following GC (if logging is enabled).
311 MetaspaceUtils::print_metaspace_change(meta_sizes);
312
313 // GC is over, we are at idle now
314 if (ShenandoahPacing) {
315 _heap->pacer()->setup_for_idle();
316 }
317
318 // Check if we have seen a new target for soft max heap size or if a gc was requested.
319 // Either of these conditions will attempt to uncommit regions.
320 if (ShenandoahUncommit) {
321 if (_heap->check_soft_max_changed()) {
322 _heap->notify_soft_max_changed();
323 } else if (ShenandoahCollectorPolicy::is_explicit_gc(request.cause)) {
324 _heap->notify_explicit_gc_requested();
325 }
326 }
327
328 log_debug(gc, thread)("Completed GC (%s): %s, %s, cancelled: %s",
329 gc_mode_name(gc_mode()), GCCause::to_string(request.cause), request.generation->name(), GCCause::to_string(_heap->cancelled_cause()));
330 }
331
332 void ShenandoahGenerationalControlThread::process_phase_timings() const {
333 // Commit worker statistics to cycle data
334 _heap->phase_timings()->flush_par_workers_to_cycle();
335 if (ShenandoahPacing) {
336 _heap->pacer()->flush_stats_to_cycle();
337 }
338
339 ShenandoahEvacuationTracker* evac_tracker = _heap->evac_tracker();
340 ShenandoahCycleStats evac_stats = evac_tracker->flush_cycle_to_global();
341
342 // Print GC stats for current cycle
343 {
344 LogTarget(Info, gc, stats) lt;
345 if (lt.is_enabled()) {
346 ResourceMark rm;
347 LogStream ls(lt);
348 _heap->phase_timings()->print_cycle_on(&ls);
349 evac_tracker->print_evacuations_on(&ls, &evac_stats.workers,
350 &evac_stats.mutators);
351 if (ShenandoahPacing) {
352 _heap->pacer()->print_cycle_on(&ls);
353 }
354 }
355 }
356
357 // Commit statistics to globals
358 _heap->phase_timings()->flush_cycle_to_global();
359 }
360
361 // Young and old concurrent cycles are initiated by the regulator. Implicit
362 // and explicit GC requests are handled by the controller thread and always
363 // run a global cycle (which is concurrent by default, but may be overridden
364 // by command line options). Old cycles always degenerate to a global cycle.
365 // Young cycles are degenerated to complete the young cycle. Young
366 // and old degen may upgrade to Full GC. Full GC may also be
367 // triggered directly by a System.gc() invocation.
368 //
369 //
370 // +-----+ Idle +-----+-----------+---------------------+
371 // | + | | |
372 // | | | | |
373 // | | v | |
374 // | | Bootstrap Old +-- | ------------+ |
375 // | | + | | |
376 // | | | | | |
377 // | v v v v |
378 // | Resume Old <----------+ Young +--> Young Degen |
379 // | + + ^ + + |
380 // v | | | | | |
381 // Global <-+ | +----------------------------+ | |
382 // + | | |
383 // | v v |
384 // +---> Global Degen +--------------------> Full <----+
385 //
386 void ShenandoahGenerationalControlThread::service_concurrent_normal_cycle(const ShenandoahGCRequest& request) {
387 log_info(gc, ergo)("Start GC cycle (%s)", request.generation->name());
388 if (request.generation->is_old()) {
389 service_concurrent_old_cycle(request);
390 } else {
391 service_concurrent_cycle(request.generation, request.cause, false);
392 }
393 }
394
395 void ShenandoahGenerationalControlThread::service_concurrent_old_cycle(const ShenandoahGCRequest& request) {
396 ShenandoahOldGeneration* old_generation = _heap->old_generation();
397 ShenandoahYoungGeneration* young_generation = _heap->young_generation();
398 ShenandoahOldGeneration::State original_state = old_generation->state();
399
400 TraceCollectorStats tcs(_heap->monitoring_support()->concurrent_collection_counters());
401
402 switch (original_state) {
403 case ShenandoahOldGeneration::FILLING: {
404 ShenandoahGCSession session(request.cause, old_generation);
405 assert(gc_mode() == servicing_old, "Filling should be servicing old");
406 _allow_old_preemption.set();
407 old_generation->entry_coalesce_and_fill();
408 _allow_old_preemption.unset();
409
410 // Before bootstrapping begins, we must acknowledge any cancellation request.
411 // If the gc has not been cancelled, this does nothing. If it has been cancelled,
412 // this will clear the cancellation request and exit before starting the bootstrap
413 // phase. This will allow the young GC cycle to proceed normally. If we do not
414 // acknowledge the cancellation request, the subsequent young cycle will observe
415 // the request and essentially cancel itself.
416 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) {
417 log_info(gc, thread)("Preparation for old generation cycle was cancelled");
418 return;
419 }
420
421 // Coalescing threads completed and nothing was cancelled. it is safe to transition from this state.
422 old_generation->transition_to(ShenandoahOldGeneration::WAITING_FOR_BOOTSTRAP);
423 return;
424 }
425 case ShenandoahOldGeneration::WAITING_FOR_BOOTSTRAP:
426 old_generation->transition_to(ShenandoahOldGeneration::BOOTSTRAPPING);
427 case ShenandoahOldGeneration::BOOTSTRAPPING: {
428 // Configure the young generation's concurrent mark to put objects in
429 // old regions into the concurrent mark queues associated with the old
430 // generation. The young cycle will run as normal except that rather than
431 // ignore old references it will mark and enqueue them in the old concurrent
432 // task queues but it will not traverse them.
433 set_gc_mode(bootstrapping_old);
434 young_generation->set_old_gen_task_queues(old_generation->task_queues());
435 service_concurrent_cycle(young_generation, request.cause, true);
436 process_phase_timings();
437 if (_heap->cancelled_gc()) {
438 // Young generation bootstrap cycle has failed. Concurrent mark for old generation
439 // is going to resume after degenerated bootstrap cycle completes.
440 log_info(gc)("Bootstrap cycle for old generation was cancelled");
441 return;
442 }
443
444 assert(_degen_point == ShenandoahGC::_degenerated_unset, "Degen point should not be set if gc wasn't cancelled");
445
446 // From here we will 'resume' the old concurrent mark. This will skip reset
447 // and init mark for the concurrent mark. All of that work will have been
448 // done by the bootstrapping young cycle.
449 set_gc_mode(servicing_old);
450 old_generation->transition_to(ShenandoahOldGeneration::MARKING);
451 }
452 case ShenandoahOldGeneration::MARKING: {
453 ShenandoahGCSession session(request.cause, old_generation);
454 bool marking_complete = resume_concurrent_old_cycle(old_generation, request.cause);
455 if (marking_complete) {
456 assert(old_generation->state() != ShenandoahOldGeneration::MARKING, "Should not still be marking");
457 if (original_state == ShenandoahOldGeneration::MARKING) {
458 _heap->mmu_tracker()->record_old_marking_increment(true);
459 _heap->log_heap_status("At end of Concurrent Old Marking finishing increment");
460 }
461 } else if (original_state == ShenandoahOldGeneration::MARKING) {
462 _heap->mmu_tracker()->record_old_marking_increment(false);
463 _heap->log_heap_status("At end of Concurrent Old Marking increment");
464 }
465 break;
466 }
467 default:
468 fatal("Unexpected state for old GC: %s", ShenandoahOldGeneration::state_name(old_generation->state()));
469 }
470 }
471
472 bool ShenandoahGenerationalControlThread::resume_concurrent_old_cycle(ShenandoahOldGeneration* generation, GCCause::Cause cause) {
473 assert(_heap->is_concurrent_old_mark_in_progress(), "Old mark should be in progress");
474 log_debug(gc)("Resuming old generation with " UINT32_FORMAT " marking tasks queued", generation->task_queues()->tasks());
475
476 // We can only tolerate being cancelled during concurrent marking or during preparation for mixed
477 // evacuation. This flag here (passed by reference) is used to control precisely where the regulator
478 // is allowed to cancel a GC.
479 ShenandoahOldGC gc(generation, _allow_old_preemption);
480 if (gc.collect(cause)) {
481 _heap->notify_gc_progress();
482 generation->record_success_concurrent(false);
483 }
484
485 if (_heap->cancelled_gc()) {
486 // It's possible the gc cycle was cancelled after the last time
487 // the collection checked for cancellation. In which case, the
488 // old gc cycle is still completed, and we have to deal with this
489 // cancellation. We set the degeneration point to be outside
490 // the cycle because if this is an allocation failure, that is
491 // what must be done (there is no degenerated old cycle). If the
492 // cancellation was due to a heuristic wanting to start a young
493 // cycle, then we are not actually going to a degenerated cycle,
494 // so the degenerated point doesn't matter here.
495 check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle);
496 if (cause == GCCause::_shenandoah_concurrent_gc) {
497 _heap->shenandoah_policy()->record_interrupted_old();
498 }
499 return false;
500 }
501 return true;
502 }
503
504 // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
505 // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
506 // If second allocation failure happens during Degenerated GC cycle (for example, when GC
507 // tries to evac something and no memory is available), cycle degrades to Full GC.
508 //
509 // There are also a shortcut through the normal cycle: immediate garbage shortcut, when
510 // heuristics says there are no regions to compact, and all the collection comes from immediately
511 // reclaimable regions.
512 //
513 // ................................................................................................
514 //
515 // (immediate garbage shortcut) Concurrent GC
516 // /-------------------------------------------\
517 // | |
518 // | |
519 // | |
520 // | v
521 // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
522 // | | | ^
523 // | (af) | (af) | (af) |
524 // ..................|....................|.................|..............|.......................
525 // | | | |
526 // | | | | Degenerated GC
527 // v v v |
528 // STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
529 // | | | ^
530 // | (af) | (af) | (af) |
531 // ..................|....................|.................|..............|.......................
532 // | | | |
533 // | v | | Full GC
534 // \------------------->o<----------------/ |
535 // | |
536 // v |
537 // Full GC --------------------------/
538 //
539 void ShenandoahGenerationalControlThread::service_concurrent_cycle(ShenandoahGeneration* generation,
540 GCCause::Cause cause,
541 bool do_old_gc_bootstrap) {
542 // At this point:
543 // if (generation == YOUNG), this is a normal young cycle or a bootstrap cycle
544 // if (generation == GLOBAL), this is a GLOBAL cycle
545 // In either case, we want to age old objects if this is an aging cycle
546 maybe_set_aging_cycle();
547
548 ShenandoahGCSession session(cause, generation);
549 TraceCollectorStats tcs(_heap->monitoring_support()->concurrent_collection_counters());
550
551 assert(!generation->is_old(), "Old GC takes a different control path");
552
553 ShenandoahConcurrentGC gc(generation, do_old_gc_bootstrap);
554 if (gc.collect(cause)) {
555 // Cycle is complete
556 _heap->notify_gc_progress();
557 generation->record_success_concurrent(gc.abbreviated());
558 } else {
559 assert(_heap->cancelled_gc(), "Must have been cancelled");
560 check_cancellation_or_degen(gc.degen_point());
561 }
562
563 const char* msg;
564 ShenandoahMmuTracker* mmu_tracker = _heap->mmu_tracker();
565 if (generation->is_young()) {
566 if (_heap->cancelled_gc()) {
567 msg = (do_old_gc_bootstrap) ? "At end of Interrupted Concurrent Bootstrap GC" :
568 "At end of Interrupted Concurrent Young GC";
569 } else {
570 // We only record GC results if GC was successful
571 msg = (do_old_gc_bootstrap) ? "At end of Concurrent Bootstrap GC" :
572 "At end of Concurrent Young GC";
573 if (_heap->collection_set()->has_old_regions()) {
574 mmu_tracker->record_mixed(get_gc_id());
575 } else if (do_old_gc_bootstrap) {
576 mmu_tracker->record_bootstrap(get_gc_id());
577 } else {
578 mmu_tracker->record_young(get_gc_id());
579 }
580 }
581 } else {
582 assert(generation->is_global(), "If not young, must be GLOBAL");
583 assert(!do_old_gc_bootstrap, "Do not bootstrap with GLOBAL GC");
584 if (_heap->cancelled_gc()) {
585 msg = "At end of Interrupted Concurrent GLOBAL GC";
586 } else {
587 // We only record GC results if GC was successful
588 msg = "At end of Concurrent Global GC";
589 mmu_tracker->record_global(get_gc_id());
590 }
591 }
592 _heap->log_heap_status(msg);
593 }
594
595 bool ShenandoahGenerationalControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
596 if (!_heap->cancelled_gc()) {
597 return false;
598 }
599
600 if (_heap->cancelled_cause() == GCCause::_shenandoah_stop_vm
601 || _heap->cancelled_cause() == GCCause::_shenandoah_concurrent_gc) {
602 log_debug(gc, thread)("Cancellation detected, reason: %s", GCCause::to_string(_heap->cancelled_cause()));
603 return true;
604 }
605
606 if (ShenandoahCollectorPolicy::is_allocation_failure(_heap->cancelled_cause())) {
607 assert(_degen_point == ShenandoahGC::_degenerated_unset,
608 "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
609 _degen_point = point;
610 log_debug(gc, thread)("Cancellation detected:, reason: %s, degen point: %s",
611 GCCause::to_string(_heap->cancelled_cause()),
612 ShenandoahGC::degen_point_to_string(_degen_point));
613 return true;
614 }
615
616 fatal("Cancel GC either for alloc failure GC, or gracefully exiting, or to pause old generation marking");
617 return false;
618 }
619
620 void ShenandoahGenerationalControlThread::service_stw_full_cycle(GCCause::Cause cause) {
621 ShenandoahGCSession session(cause, _heap->global_generation());
622 maybe_set_aging_cycle();
623 ShenandoahFullGC gc;
624 gc.collect(cause);
625 _degen_point = ShenandoahGC::_degenerated_unset;
626 }
627
628 void ShenandoahGenerationalControlThread::service_stw_degenerated_cycle(const ShenandoahGCRequest& request) {
629 assert(_degen_point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
630
631 ShenandoahGCSession session(request.cause, request.generation);
632
633 ShenandoahDegenGC gc(_degen_point, request.generation);
634 gc.collect(request.cause);
635 _degen_point = ShenandoahGC::_degenerated_unset;
636
637 assert(_heap->young_generation()->task_queues()->is_empty(), "Unexpected young generation marking tasks");
638 if (request.generation->is_global()) {
639 assert(_heap->old_generation()->task_queues()->is_empty(), "Unexpected old generation marking tasks");
640 assert(_heap->global_generation()->task_queues()->is_empty(), "Unexpected global generation marking tasks");
641 } else {
642 assert(request.generation->is_young(), "Expected degenerated young cycle, if not global.");
643 ShenandoahOldGeneration* old = _heap->old_generation();
644 if (old->is_bootstrapping()) {
645 old->transition_to(ShenandoahOldGeneration::MARKING);
646 }
647 }
648 }
649
650 void ShenandoahGenerationalControlThread::request_gc(GCCause::Cause cause) {
651 if (ShenandoahCollectorPolicy::is_allocation_failure(cause)) {
652 // GC should already be cancelled. Here we are just notifying the control thread to
653 // wake up and handle the cancellation request, so we don't need to set _requested_gc_cause.
654 notify_cancellation(cause);
655 } else if (ShenandoahCollectorPolicy::should_handle_requested_gc(cause)) {
656 handle_requested_gc(cause);
657 }
658 }
659
660 bool ShenandoahGenerationalControlThread::request_concurrent_gc(ShenandoahGeneration* generation) {
661 if (_heap->cancelled_gc()) {
662 // Ignore subsequent requests from the heuristics
663 log_debug(gc, thread)("Reject request for concurrent gc: gc_requested: %s, gc_cancelled: %s",
664 GCCause::to_string(_requested_gc_cause),
665 BOOL_TO_STR(_heap->cancelled_gc()));
666 return false;
667 }
668
669 MonitorLocker ml(&_control_lock, Mutex::_no_safepoint_check_flag);
670 if (gc_mode() == servicing_old) {
671 if (!preempt_old_marking(generation)) {
672 log_debug(gc, thread)("Cannot start young, old collection is not preemptible");
673 return false;
674 }
675
676 // Cancel the old GC and wait for the control thread to start servicing the new request.
677 log_info(gc)("Preempting old generation mark to allow %s GC", generation->name());
678 while (gc_mode() == servicing_old) {
679 ShenandoahHeap::heap()->cancel_gc(GCCause::_shenandoah_concurrent_gc);
680 notify_cancellation(ml, GCCause::_shenandoah_concurrent_gc);
681 ml.wait();
682 }
683 return true;
684 }
685
686 if (gc_mode() == none) {
687 const size_t current_gc_id = get_gc_id();
688 while (gc_mode() == none && current_gc_id == get_gc_id()) {
689 if (_requested_gc_cause != GCCause::_no_gc) {
690 log_debug(gc, thread)("Reject request for concurrent gc because another gc is pending: %s", GCCause::to_string(_requested_gc_cause));
691 return false;
692 }
693
694 notify_control_thread(ml, GCCause::_shenandoah_concurrent_gc, generation);
695 ml.wait();
696 }
697 return true;
698 }
699
700
701 log_debug(gc, thread)("Reject request for concurrent gc: mode: %s, allow_old_preemption: %s",
702 gc_mode_name(gc_mode()),
703 BOOL_TO_STR(_allow_old_preemption.is_set()));
704 return false;
705 }
706
707 void ShenandoahGenerationalControlThread::notify_control_thread(GCCause::Cause cause, ShenandoahGeneration* generation) {
708 MonitorLocker ml(&_control_lock, Mutex::_no_safepoint_check_flag);
709 notify_control_thread(ml, cause, generation);
710 }
711
712 void ShenandoahGenerationalControlThread::notify_control_thread(MonitorLocker& ml, GCCause::Cause cause, ShenandoahGeneration* generation) {
713 assert(_control_lock.is_locked(), "Request lock must be held here");
714 log_debug(gc, thread)("Notify control (%s): %s, %s", gc_mode_name(gc_mode()), GCCause::to_string(cause), generation->name());
715 _requested_gc_cause = cause;
716 _requested_generation = generation;
717 ml.notify();
718 }
719
720 void ShenandoahGenerationalControlThread::notify_cancellation(GCCause::Cause cause) {
721 MonitorLocker ml(&_control_lock, Mutex::_no_safepoint_check_flag);
722 notify_cancellation(ml, cause);
723 }
724
725 void ShenandoahGenerationalControlThread::notify_cancellation(MonitorLocker& ml, GCCause::Cause cause) {
726 assert(_heap->cancelled_gc(), "GC should already be cancelled");
727 log_debug(gc,thread)("Notify control (%s): %s", gc_mode_name(gc_mode()), GCCause::to_string(cause));
728 ml.notify();
729 }
730
731 bool ShenandoahGenerationalControlThread::preempt_old_marking(ShenandoahGeneration* generation) {
732 return generation->is_young() && _allow_old_preemption.try_unset();
733 }
734
735 void ShenandoahGenerationalControlThread::handle_requested_gc(GCCause::Cause cause) {
736 // For normal requested GCs (System.gc) we want to block the caller. However,
737 // for whitebox requested GC, we want to initiate the GC and return immediately.
738 // The whitebox caller thread will arrange for itself to wait until the GC notifies
739 // it that has reached the requested breakpoint (phase in the GC).
740 if (cause == GCCause::_wb_breakpoint) {
741 notify_control_thread(cause, ShenandoahHeap::heap()->global_generation());
742 return;
743 }
744
745 // Make sure we have at least one complete GC cycle before unblocking
746 // from the explicit GC request.
747 //
748 // This is especially important for weak references cleanup and/or native
749 // resources (e.g. DirectByteBuffers) machinery: when explicit GC request
750 // comes very late in the already running cycle, it would miss lots of new
751 // opportunities for cleanup that were made available before the caller
752 // requested the GC.
753
754 MonitorLocker ml(&_gc_waiters_lock);
755 size_t current_gc_id = get_gc_id();
756 const size_t required_gc_id = current_gc_id + 1;
757 while (current_gc_id < required_gc_id && !should_terminate()) {
758 // Make requests to run a global cycle until at least one is completed
759 notify_control_thread(cause, ShenandoahHeap::heap()->global_generation());
760 ml.wait();
761 current_gc_id = get_gc_id();
762 }
763 }
764
765 void ShenandoahGenerationalControlThread::notify_gc_waiters() {
766 MonitorLocker ml(&_gc_waiters_lock);
767 ml.notify_all();
768 }
769
770 const char* ShenandoahGenerationalControlThread::gc_mode_name(GCMode mode) {
771 switch (mode) {
772 case none: return "idle";
773 case concurrent_normal: return "normal";
774 case stw_degenerated: return "degenerated";
775 case stw_full: return "full";
776 case servicing_old: return "old";
777 case bootstrapping_old: return "bootstrap";
778 case stopped: return "stopped";
779 default: return "unknown";
780 }
781 }
782
783 void ShenandoahGenerationalControlThread::set_gc_mode(GCMode new_mode) {
784 MonitorLocker ml(&_control_lock, Mutex::_no_safepoint_check_flag);
785 set_gc_mode(ml, new_mode);
786 }
787
788 void ShenandoahGenerationalControlThread::set_gc_mode(MonitorLocker& ml, GCMode new_mode) {
789 if (_gc_mode != new_mode) {
790 log_debug(gc, thread)("Transition from: %s to: %s", gc_mode_name(_gc_mode), gc_mode_name(new_mode));
791 EventMark event("Control thread transition from: %s, to %s", gc_mode_name(_gc_mode), gc_mode_name(new_mode));
792 _gc_mode = new_mode;
793 ml.notify_all();
794 }
795 }