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