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/mode/shenandoahMode.hpp"
29 #include "gc/shenandoah/shenandoahAsserts.hpp"
30 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
31 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
32 #include "gc/shenandoah/shenandoahGenerationalControlThread.hpp"
33 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
34 #include "gc/shenandoah/shenandoahFreeSet.hpp"
35 #include "gc/shenandoah/shenandoahFullGC.hpp"
36 #include "gc/shenandoah/shenandoahGeneration.hpp"
37 #include "gc/shenandoah/shenandoahGenerationalHeap.hpp"
38 #include "gc/shenandoah/shenandoahOldGC.hpp"
39 #include "gc/shenandoah/shenandoahOldGeneration.hpp"
40 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
41 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
42 #include "gc/shenandoah/shenandoahPacer.inline.hpp"
43 #include "gc/shenandoah/shenandoahUtils.hpp"
44 #include "gc/shenandoah/shenandoahYoungGeneration.hpp"
45 #include "logging/log.hpp"
46 #include "memory/metaspaceUtils.hpp"
47 #include "memory/metaspaceStats.hpp"
48 #include "runtime/atomic.hpp"
49
50 ShenandoahGenerationalControlThread::ShenandoahGenerationalControlThread() :
51 ShenandoahController(),
52 _control_lock(Mutex::nosafepoint - 2, "ShenandoahControlGC_lock", true),
53 _regulator_lock(Mutex::nosafepoint - 2, "ShenandoahRegulatorGC_lock", true),
54 _requested_gc_cause(GCCause::_no_gc),
55 _requested_generation(GLOBAL),
56 _degen_point(ShenandoahGC::_degenerated_outside_cycle),
57 _degen_generation(nullptr),
58 _mode(none) {
59 shenandoah_assert_generational();
60 set_name("Shenandoah Control Thread");
61 create_and_start();
62 }
63
64 void ShenandoahGenerationalControlThread::run_service() {
65 ShenandoahGenerationalHeap* const heap = ShenandoahGenerationalHeap::heap();
66
67 const GCMode default_mode = concurrent_normal;
68 ShenandoahGenerationType generation = GLOBAL;
69
70 double last_shrink_time = os::elapsedTime();
71 uint age_period = 0;
72
73 // Shrink period avoids constantly polling regions for shrinking.
74 // Having a period 10x lower than the delay would mean we hit the
75 // shrinking with lag of less than 1/10-th of true delay.
76 // ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
77 const double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
78
79 ShenandoahCollectorPolicy* const policy = heap->shenandoah_policy();
80
81 // Heuristics are notified of allocation failures here and other outcomes
82 // of the cycle. They're also used here to control whether the Nth consecutive
83 // degenerated cycle should be 'promoted' to a full cycle. The decision to
84 // trigger a cycle or not is evaluated on the regulator thread.
85 ShenandoahHeuristics* global_heuristics = heap->global_generation()->heuristics();
86 while (!in_graceful_shutdown() && !should_terminate()) {
87 // Figure out if we have pending requests.
88 const bool alloc_failure_pending = _alloc_failure_gc.is_set();
89 const bool humongous_alloc_failure_pending = _humongous_alloc_failure_gc.is_set();
90
91 GCCause::Cause cause = Atomic::xchg(&_requested_gc_cause, GCCause::_no_gc);
92
93 const bool is_gc_requested = ShenandoahCollectorPolicy::is_requested_gc(cause);
94
95 // This control loop iteration has seen this much allocation.
96 const size_t allocs_seen = reset_allocs_seen();
97
98 // Check if we have seen a new target for soft max heap size.
99 const bool soft_max_changed = heap->check_soft_max_changed();
100
101 // Choose which GC mode to run in. The block below should select a single mode.
102 set_gc_mode(none);
103 ShenandoahGC::ShenandoahDegenPoint degen_point = ShenandoahGC::_degenerated_unset;
104
105 if (alloc_failure_pending) {
106 // Allocation failure takes precedence: we have to deal with it first thing
107 cause = GCCause::_allocation_failure;
108
109 // Consume the degen point, and seed it with default value
110 degen_point = _degen_point;
111 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
112
113 if (degen_point == ShenandoahGC::_degenerated_outside_cycle) {
114 _degen_generation = heap->young_generation();
115 } else {
116 assert(_degen_generation != nullptr, "Need to know which generation to resume");
117 }
118
119 ShenandoahHeuristics* heuristics = _degen_generation->heuristics();
120 generation = _degen_generation->type();
121 bool old_gen_evacuation_failed = heap->old_generation()->clear_failed_evacuation();
122
123 heuristics->log_trigger("Handle Allocation Failure");
124
125 // Do not bother with degenerated cycle if old generation evacuation failed or if humongous allocation failed
126 if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle() &&
127 !old_gen_evacuation_failed && !humongous_alloc_failure_pending) {
128 heuristics->record_allocation_failure_gc();
129 policy->record_alloc_failure_to_degenerated(degen_point);
130 set_gc_mode(stw_degenerated);
131 } else {
132 heuristics->record_allocation_failure_gc();
133 policy->record_alloc_failure_to_full();
134 generation = GLOBAL;
135 set_gc_mode(stw_full);
136 }
137 } else if (is_gc_requested) {
138 generation = GLOBAL;
139 global_heuristics->log_trigger("GC request (%s)", GCCause::to_string(cause));
140 global_heuristics->record_requested_gc();
141
142 if (ShenandoahCollectorPolicy::should_run_full_gc(cause)) {
143 set_gc_mode(stw_full);
144 } else {
145 set_gc_mode(default_mode);
146 // Unload and clean up everything
147 heap->set_unload_classes(global_heuristics->can_unload_classes());
148 }
149 } else {
150 // We should only be here if the regulator requested a cycle or if
151 // there is an old generation mark in progress.
152 if (cause == GCCause::_shenandoah_concurrent_gc) {
153 if (_requested_generation == OLD && heap->old_generation()->is_doing_mixed_evacuations()) {
154 // If a request to start an old cycle arrived while an old cycle was running, but _before_
155 // it chose any regions for evacuation we don't want to start a new old cycle. Rather, we want
156 // the heuristic to run a young collection so that we can evacuate some old regions.
157 assert(!heap->is_concurrent_old_mark_in_progress(), "Should not be running mixed collections and concurrent marking");
158 generation = YOUNG;
159 } else {
160 generation = _requested_generation;
161 }
162
163 // preemption was requested or this is a regular cycle
164 set_gc_mode(default_mode);
165
166 // Don't start a new old marking if there is one already in progress
167 if (generation == OLD && heap->is_concurrent_old_mark_in_progress()) {
168 set_gc_mode(servicing_old);
169 }
170
171 if (generation == GLOBAL) {
172 heap->set_unload_classes(global_heuristics->should_unload_classes());
173 } else {
174 heap->set_unload_classes(false);
175 }
176 } else if (heap->is_concurrent_old_mark_in_progress() || heap->is_prepare_for_old_mark_in_progress()) {
177 // Nobody asked us to do anything, but we have an old-generation mark or old-generation preparation for
178 // mixed evacuation in progress, so resume working on that.
179 log_info(gc)("Resume old GC: marking is%s in progress, preparing is%s in progress",
180 heap->is_concurrent_old_mark_in_progress() ? "" : " NOT",
181 heap->is_prepare_for_old_mark_in_progress() ? "" : " NOT");
182
183 cause = GCCause::_shenandoah_concurrent_gc;
184 generation = OLD;
185 set_gc_mode(servicing_old);
186 heap->set_unload_classes(false);
187 }
188 }
189
190 const bool gc_requested = (gc_mode() != none);
191 assert (!gc_requested || cause != GCCause::_no_gc, "GC cause should be set");
192
193 if (gc_requested) {
194 // Blow away all soft references on this cycle, if handling allocation failure,
195 // either implicit or explicit GC request, or we are requested to do so unconditionally.
196 if (generation == GLOBAL && (alloc_failure_pending || is_gc_requested || ShenandoahAlwaysClearSoftRefs)) {
197 heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
198 }
199
200 // GC is starting, bump the internal ID
201 update_gc_id();
202
203 heap->reset_bytes_allocated_since_gc_start();
204
205 MetaspaceCombinedStats meta_sizes = MetaspaceUtils::get_combined_statistics();
206
207 // If GC was requested, we are sampling the counters even without actual triggers
208 // from allocation machinery. This captures GC phases more accurately.
209 heap->set_forced_counters_update(true);
210
211 // If GC was requested, we better dump freeset data for performance debugging
212 heap->free_set()->log_status_under_lock();
213
214 // In case this is a degenerated cycle, remember whether original cycle was aging.
215 const bool was_aging_cycle = heap->is_aging_cycle();
216 heap->set_aging_cycle(false);
217
218 switch (gc_mode()) {
219 case concurrent_normal: {
220 // At this point:
221 // if (generation == YOUNG), this is a normal YOUNG cycle
222 // if (generation == OLD), this is a bootstrap OLD cycle
223 // if (generation == GLOBAL), this is a GLOBAL cycle triggered by System.gc()
224 // In all three cases, we want to age old objects if this is an aging cycle
225 if (age_period-- == 0) {
226 heap->set_aging_cycle(true);
227 age_period = ShenandoahAgingCyclePeriod - 1;
228 }
229 service_concurrent_normal_cycle(heap, generation, cause);
230 break;
231 }
232 case stw_degenerated: {
233 heap->set_aging_cycle(was_aging_cycle);
234 service_stw_degenerated_cycle(cause, degen_point);
235 break;
236 }
237 case stw_full: {
238 if (age_period-- == 0) {
239 heap->set_aging_cycle(true);
240 age_period = ShenandoahAgingCyclePeriod - 1;
241 }
242 service_stw_full_cycle(cause);
243 break;
244 }
245 case servicing_old: {
246 assert(generation == OLD, "Expected old generation here");
247 GCIdMark gc_id_mark;
248 service_concurrent_old_cycle(heap, cause);
249 break;
250 }
251 default:
252 ShouldNotReachHere();
253 }
254
255 // If this was the requested GC cycle, notify waiters about it
256 if (is_gc_requested) {
257 notify_gc_waiters();
258 }
259
260 // If this was the allocation failure GC cycle, notify waiters about it
261 if (alloc_failure_pending) {
262 notify_alloc_failure_waiters();
263 }
264
265 // Report current free set state at the end of cycle, whether
266 // it is a normal completion, or the abort.
267 heap->free_set()->log_status_under_lock();
268
269 // Notify Universe about new heap usage. This has implications for
270 // global soft refs policy, and we better report it every time heap
271 // usage goes down.
272 heap->update_capacity_and_used_at_gc();
273
274 // Signal that we have completed a visit to all live objects.
275 heap->record_whole_heap_examined_timestamp();
276
277 // Disable forced counters update, and update counters one more time
278 // to capture the state at the end of GC session.
279 heap->handle_force_counters_update();
280 heap->set_forced_counters_update(false);
281
282 // Retract forceful part of soft refs policy
283 heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
284
285 // Clear metaspace oom flag, if current cycle unloaded classes
286 if (heap->unload_classes()) {
287 global_heuristics->clear_metaspace_oom();
288 }
289
290 process_phase_timings(heap);
291
292 // Print Metaspace change following GC (if logging is enabled).
293 MetaspaceUtils::print_metaspace_change(meta_sizes);
294
295 // GC is over, we are at idle now
296 if (ShenandoahPacing) {
297 heap->pacer()->setup_for_idle();
298 }
299 } else {
300 // Report to pacer that we have seen this many words allocated
301 if (ShenandoahPacing && (allocs_seen > 0)) {
302 heap->pacer()->report_alloc(allocs_seen);
303 }
304 }
305
306 const double current = os::elapsedTime();
307
308 if (ShenandoahUncommit && (is_gc_requested || soft_max_changed || (current - last_shrink_time > shrink_period))) {
309 // Explicit GC tries to uncommit everything down to min capacity.
310 // Soft max change tries to uncommit everything down to target capacity.
311 // Periodic uncommit tries to uncommit suitable regions down to min capacity.
312
313 double shrink_before = (is_gc_requested || soft_max_changed) ?
314 current :
315 current - (ShenandoahUncommitDelay / 1000.0);
316
317 size_t shrink_until = soft_max_changed ?
318 heap->soft_max_capacity() :
319 heap->min_capacity();
320
321 heap->maybe_uncommit(shrink_before, shrink_until);
322 heap->phase_timings()->flush_cycle_to_global();
323 last_shrink_time = current;
324 }
325
326 // Wait for ShenandoahControlIntervalMax unless there was an allocation failure or another request was made mid-cycle.
327 if (!is_alloc_failure_gc() && _requested_gc_cause == GCCause::_no_gc) {
328 // The timed wait is necessary because this thread has a responsibility to send
329 // 'alloc_words' to the pacer when it does not perform a GC.
330 MonitorLocker lock(&_control_lock, Mutex::_no_safepoint_check_flag);
331 lock.wait(ShenandoahControlIntervalMax);
332 }
333 }
334
335 // Wait for the actual stop(), can't leave run_service() earlier.
336 while (!should_terminate()) {
337 os::naked_short_sleep(ShenandoahControlIntervalMin);
338 }
339 }
340
341 void ShenandoahGenerationalControlThread::process_phase_timings(const ShenandoahGenerationalHeap* heap) {
342 // Commit worker statistics to cycle data
343 heap->phase_timings()->flush_par_workers_to_cycle();
344 if (ShenandoahPacing) {
345 heap->pacer()->flush_stats_to_cycle();
346 }
347
348 ShenandoahEvacuationTracker* evac_tracker = heap->evac_tracker();
349 ShenandoahCycleStats evac_stats = evac_tracker->flush_cycle_to_global();
350
351 // Print GC stats for current cycle
352 {
353 LogTarget(Info, gc, stats) lt;
354 if (lt.is_enabled()) {
355 ResourceMark rm;
356 LogStream ls(lt);
357 heap->phase_timings()->print_cycle_on(&ls);
358 evac_tracker->print_evacuations_on(&ls, &evac_stats.workers,
359 &evac_stats.mutators);
360 if (ShenandoahPacing) {
361 heap->pacer()->print_cycle_on(&ls);
362 }
363 }
364 }
365
366 // Commit statistics to globals
367 heap->phase_timings()->flush_cycle_to_global();
368 }
369
370 // Young and old concurrent cycles are initiated by the regulator. Implicit
371 // and explicit GC requests are handled by the controller thread and always
372 // run a global cycle (which is concurrent by default, but may be overridden
373 // by command line options). Old cycles always degenerate to a global cycle.
374 // Young cycles are degenerated to complete the young cycle. Young
375 // and old degen may upgrade to Full GC. Full GC may also be
376 // triggered directly by a System.gc() invocation.
377 //
378 //
379 // +-----+ Idle +-----+-----------+---------------------+
380 // | + | | |
381 // | | | | |
382 // | | v | |
383 // | | Bootstrap Old +-- | ------------+ |
384 // | | + | | |
385 // | | | | | |
386 // | v v v v |
387 // | Resume Old <----------+ Young +--> Young Degen |
388 // | + + ^ + + |
389 // v | | | | | |
390 // Global <-+ | +----------------------------+ | |
391 // + | | |
392 // | v v |
393 // +---> Global Degen +--------------------> Full <----+
394 //
395 void ShenandoahGenerationalControlThread::service_concurrent_normal_cycle(ShenandoahGenerationalHeap* heap,
396 const ShenandoahGenerationType generation,
397 GCCause::Cause cause) {
398 GCIdMark gc_id_mark;
399 switch (generation) {
400 case YOUNG: {
401 // Run a young cycle. This might or might not, have interrupted an ongoing
402 // concurrent mark in the old generation. We need to think about promotions
403 // in this case. Promoted objects should be above the TAMS in the old regions
404 // they end up in, but we have to be sure we don't promote into any regions
405 // that are in the cset.
406 log_info(gc, ergo)("Start GC cycle (Young)");
407 service_concurrent_cycle(heap->young_generation(), cause, false);
408 break;
409 }
410 case OLD: {
411 log_info(gc, ergo)("Start GC cycle (Old)");
412 service_concurrent_old_cycle(heap, cause);
413 break;
414 }
415 case GLOBAL: {
416 log_info(gc, ergo)("Start GC cycle (Global)");
417 service_concurrent_cycle(heap->global_generation(), cause, false);
418 break;
419 }
420 default:
421 ShouldNotReachHere();
422 }
423 }
424
425 void ShenandoahGenerationalControlThread::service_concurrent_old_cycle(ShenandoahGenerationalHeap* heap, GCCause::Cause &cause) {
426 ShenandoahOldGeneration* old_generation = heap->old_generation();
427 ShenandoahYoungGeneration* young_generation = heap->young_generation();
428 ShenandoahOldGeneration::State original_state = old_generation->state();
429
430 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
431
432 switch (original_state) {
433 case ShenandoahOldGeneration::FILLING: {
434 ShenandoahGCSession session(cause, old_generation);
435 _allow_old_preemption.set();
436 old_generation->entry_coalesce_and_fill();
437 _allow_old_preemption.unset();
438
439 // Before bootstrapping begins, we must acknowledge any cancellation request.
440 // If the gc has not been cancelled, this does nothing. If it has been cancelled,
441 // this will clear the cancellation request and exit before starting the bootstrap
442 // phase. This will allow the young GC cycle to proceed normally. If we do not
443 // acknowledge the cancellation request, the subsequent young cycle will observe
444 // the request and essentially cancel itself.
445 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) {
446 log_info(gc)("Preparation for old generation cycle was cancelled");
447 return;
448 }
449
450 // Coalescing threads completed and nothing was cancelled. it is safe to transition from this state.
451 old_generation->transition_to(ShenandoahOldGeneration::WAITING_FOR_BOOTSTRAP);
452 return;
453 }
454 case ShenandoahOldGeneration::WAITING_FOR_BOOTSTRAP:
455 old_generation->transition_to(ShenandoahOldGeneration::BOOTSTRAPPING);
456 case ShenandoahOldGeneration::BOOTSTRAPPING: {
457 // Configure the young generation's concurrent mark to put objects in
458 // old regions into the concurrent mark queues associated with the old
459 // generation. The young cycle will run as normal except that rather than
460 // ignore old references it will mark and enqueue them in the old concurrent
461 // task queues but it will not traverse them.
462 set_gc_mode(bootstrapping_old);
463 young_generation->set_old_gen_task_queues(old_generation->task_queues());
464 ShenandoahGCSession session(cause, young_generation);
465 service_concurrent_cycle(heap, young_generation, cause, true);
466 process_phase_timings(heap);
467 if (heap->cancelled_gc()) {
468 // Young generation bootstrap cycle has failed. Concurrent mark for old generation
469 // is going to resume after degenerated bootstrap cycle completes.
470 log_info(gc)("Bootstrap cycle for old generation was cancelled");
471 return;
472 }
473
474 // Reset the degenerated point. Normally this would happen at the top
475 // of the control loop, but here we have just completed a young cycle
476 // which has bootstrapped the old concurrent marking.
477 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
478
479 // From here we will 'resume' the old concurrent mark. This will skip reset
480 // and init mark for the concurrent mark. All of that work will have been
481 // done by the bootstrapping young cycle.
482 set_gc_mode(servicing_old);
483 old_generation->transition_to(ShenandoahOldGeneration::MARKING);
484 }
485 case ShenandoahOldGeneration::MARKING: {
486 ShenandoahGCSession session(cause, old_generation);
487 bool marking_complete = resume_concurrent_old_cycle(old_generation, cause);
488 if (marking_complete) {
489 assert(old_generation->state() != ShenandoahOldGeneration::MARKING, "Should not still be marking");
490 if (original_state == ShenandoahOldGeneration::MARKING) {
491 heap->mmu_tracker()->record_old_marking_increment(true);
492 heap->log_heap_status("At end of Concurrent Old Marking finishing increment");
493 }
494 } else if (original_state == ShenandoahOldGeneration::MARKING) {
495 heap->mmu_tracker()->record_old_marking_increment(false);
496 heap->log_heap_status("At end of Concurrent Old Marking increment");
497 }
498 break;
499 }
500 default:
501 fatal("Unexpected state for old GC: %s", ShenandoahOldGeneration::state_name(old_generation->state()));
502 }
503 }
504
505 bool ShenandoahGenerationalControlThread::resume_concurrent_old_cycle(ShenandoahOldGeneration* generation, GCCause::Cause cause) {
506 assert(ShenandoahHeap::heap()->is_concurrent_old_mark_in_progress(), "Old mark should be in progress");
507 log_debug(gc)("Resuming old generation with " UINT32_FORMAT " marking tasks queued", generation->task_queues()->tasks());
508
509 ShenandoahHeap* heap = ShenandoahHeap::heap();
510
511 // We can only tolerate being cancelled during concurrent marking or during preparation for mixed
512 // evacuation. This flag here (passed by reference) is used to control precisely where the regulator
513 // is allowed to cancel a GC.
514 ShenandoahOldGC gc(generation, _allow_old_preemption);
515 if (gc.collect(cause)) {
516 heap->notify_gc_progress();
517 generation->record_success_concurrent(false);
518 }
519
520 if (heap->cancelled_gc()) {
521 // It's possible the gc cycle was cancelled after the last time
522 // the collection checked for cancellation. In which case, the
523 // old gc cycle is still completed, and we have to deal with this
524 // cancellation. We set the degeneration point to be outside
525 // the cycle because if this is an allocation failure, that is
526 // what must be done (there is no degenerated old cycle). If the
527 // cancellation was due to a heuristic wanting to start a young
528 // cycle, then we are not actually going to a degenerated cycle,
529 // so the degenerated point doesn't matter here.
530 check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle);
531 if (_requested_gc_cause == GCCause::_shenandoah_concurrent_gc) {
532 heap->shenandoah_policy()->record_interrupted_old();
533 }
534 return false;
535 }
536 return true;
537 }
538
539 void ShenandoahGenerationalControlThread::service_concurrent_cycle(ShenandoahGeneration* generation, GCCause::Cause cause, bool do_old_gc_bootstrap) {
540 // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
541 // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
542 // If second allocation failure happens during Degenerated GC cycle (for example, when GC
543 // tries to evac something and no memory is available), cycle degrades to Full GC.
544 //
545 // There are also a shortcut through the normal cycle: immediate garbage shortcut, when
546 // heuristics says there are no regions to compact, and all the collection comes from immediately
547 // reclaimable regions.
548 //
549 // ................................................................................................
550 //
551 // (immediate garbage shortcut) Concurrent GC
552 // /-------------------------------------------\
553 // | |
554 // | |
555 // | |
556 // | v
557 // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
558 // | | | ^
559 // | (af) | (af) | (af) |
560 // ..................|....................|.................|..............|.......................
561 // | | | |
562 // | | | | Degenerated GC
563 // v v v |
564 // STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
565 // | | | ^
566 // | (af) | (af) | (af) |
567 // ..................|....................|.................|..............|.......................
568 // | | | |
569 // | v | | Full GC
570 // \------------------->o<----------------/ |
571 // | |
572 // v |
573 // Full GC --------------------------/
574 //
575 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) return;
576
577 ShenandoahHeap* heap = ShenandoahHeap::heap();
578 ShenandoahGCSession session(cause, generation);
579 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
580
581 service_concurrent_cycle(heap, generation, cause, do_old_gc_bootstrap);
582 }
583
584 void ShenandoahGenerationalControlThread::service_concurrent_cycle(ShenandoahHeap* heap,
585 ShenandoahGeneration* generation,
586 GCCause::Cause& cause,
587 bool do_old_gc_bootstrap) {
588 assert(!generation->is_old(), "Old GC takes a different control path");
589
590 ShenandoahConcurrentGC gc(generation, do_old_gc_bootstrap);
591 if (gc.collect(cause)) {
592 // Cycle is complete
593 heap->notify_gc_progress();
594 generation->record_success_concurrent(gc.abbreviated());
595 } else {
596 assert(heap->cancelled_gc(), "Must have been cancelled");
597 check_cancellation_or_degen(gc.degen_point());
598
599 // Concurrent young-gen collection degenerates to young
600 // collection. Same for global collections.
601 _degen_generation = generation;
602 }
603 const char* msg;
604 ShenandoahMmuTracker* mmu_tracker = heap->mmu_tracker();
605 if (generation->is_young()) {
606 if (heap->cancelled_gc()) {
607 msg = (do_old_gc_bootstrap) ? "At end of Interrupted Concurrent Bootstrap GC" :
608 "At end of Interrupted Concurrent Young GC";
609 } else {
610 // We only record GC results if GC was successful
611 msg = (do_old_gc_bootstrap) ? "At end of Concurrent Bootstrap GC" :
612 "At end of Concurrent Young GC";
613 if (heap->collection_set()->has_old_regions()) {
614 mmu_tracker->record_mixed(get_gc_id());
615 } else if (do_old_gc_bootstrap) {
616 mmu_tracker->record_bootstrap(get_gc_id());
617 } else {
618 mmu_tracker->record_young(get_gc_id());
619 }
620 }
621 } else {
622 assert(generation->is_global(), "If not young, must be GLOBAL");
623 assert(!do_old_gc_bootstrap, "Do not bootstrap with GLOBAL GC");
624 if (heap->cancelled_gc()) {
625 msg = "At end of Interrupted Concurrent GLOBAL GC";
626 } else {
627 // We only record GC results if GC was successful
628 msg = "At end of Concurrent Global GC";
629 mmu_tracker->record_global(get_gc_id());
630 }
631 }
632 heap->log_heap_status(msg);
633 }
634
635 bool ShenandoahGenerationalControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
636 ShenandoahHeap* heap = ShenandoahHeap::heap();
637 if (!heap->cancelled_gc()) {
638 return false;
639 }
640
641 if (in_graceful_shutdown()) {
642 return true;
643 }
644
645 assert(_degen_point == ShenandoahGC::_degenerated_outside_cycle,
646 "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
647
648 if (is_alloc_failure_gc()) {
649 _degen_point = point;
650 _preemption_requested.unset();
651 return true;
652 }
653
654 if (_preemption_requested.is_set()) {
655 assert(_requested_generation == YOUNG, "Only young GCs may preempt old.");
656 _preemption_requested.unset();
657
658 // Old generation marking is only cancellable during concurrent marking.
659 // Once final mark is complete, the code does not check again for cancellation.
660 // If old generation was cancelled for an allocation failure, we wouldn't
661 // make it to this case. The calling code is responsible for forcing a
662 // cancellation due to allocation failure into a degenerated cycle.
663 _degen_point = point;
664 heap->clear_cancelled_gc(false /* clear oom handler */);
665 return true;
666 }
667
668 fatal("Cancel GC either for alloc failure GC, or gracefully exiting, or to pause old generation marking");
669 return false;
670 }
671
672 void ShenandoahGenerationalControlThread::stop_service() {
673 // Nothing to do here.
674 }
675
676 void ShenandoahGenerationalControlThread::service_stw_full_cycle(GCCause::Cause cause) {
677 ShenandoahHeap* const heap = ShenandoahHeap::heap();
678
679 GCIdMark gc_id_mark;
680 ShenandoahGCSession session(cause, heap->global_generation());
681
682 ShenandoahFullGC gc;
683 gc.collect(cause);
684 }
685
686 void ShenandoahGenerationalControlThread::service_stw_degenerated_cycle(GCCause::Cause cause,
687 ShenandoahGC::ShenandoahDegenPoint point) {
688 assert(point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
689 ShenandoahHeap* const heap = ShenandoahHeap::heap();
690
691 GCIdMark gc_id_mark;
692 ShenandoahGCSession session(cause, _degen_generation);
693
694 ShenandoahDegenGC gc(point, _degen_generation);
695 gc.collect(cause);
696
697 assert(heap->young_generation()->task_queues()->is_empty(), "Unexpected young generation marking tasks");
698 if (_degen_generation->is_global()) {
699 assert(heap->old_generation()->task_queues()->is_empty(), "Unexpected old generation marking tasks");
700 assert(heap->global_generation()->task_queues()->is_empty(), "Unexpected global generation marking tasks");
701 } else {
702 assert(_degen_generation->is_young(), "Expected degenerated young cycle, if not global.");
703 ShenandoahOldGeneration* old = heap->old_generation();
704 if (old->is_bootstrapping()) {
705 old->transition_to(ShenandoahOldGeneration::MARKING);
706 }
707 }
708 }
709
710 void ShenandoahGenerationalControlThread::request_gc(GCCause::Cause cause) {
711 if (ShenandoahCollectorPolicy::should_handle_requested_gc(cause)) {
712 handle_requested_gc(cause);
713 }
714 }
715
716 bool ShenandoahGenerationalControlThread::request_concurrent_gc(ShenandoahGenerationType generation) {
717 if (_preemption_requested.is_set() || _requested_gc_cause != GCCause::_no_gc || ShenandoahHeap::heap()->cancelled_gc()) {
718 // Ignore subsequent requests from the heuristics
719 log_debug(gc, thread)("Reject request for concurrent gc: preemption_requested: %s, gc_requested: %s, gc_cancelled: %s",
720 BOOL_TO_STR(_preemption_requested.is_set()),
721 GCCause::to_string(_requested_gc_cause),
722 BOOL_TO_STR(ShenandoahHeap::heap()->cancelled_gc()));
723 return false;
724 }
725
726 if (gc_mode() == none) {
727 GCCause::Cause existing = Atomic::cmpxchg(&_requested_gc_cause, GCCause::_no_gc, GCCause::_shenandoah_concurrent_gc);
728 if (existing != GCCause::_no_gc) {
729 log_debug(gc, thread)("Reject request for concurrent gc because another gc is pending: %s", GCCause::to_string(existing));
730 return false;
731 }
732
733 _requested_generation = generation;
734 notify_control_thread();
735
736 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
737 while (gc_mode() == none) {
738 ml.wait();
739 }
740 return true;
741 }
742
743 if (preempt_old_marking(generation)) {
744 assert(gc_mode() == servicing_old, "Expected to be servicing old, but was: %s.", gc_mode_name(gc_mode()));
745 GCCause::Cause existing = Atomic::cmpxchg(&_requested_gc_cause, GCCause::_no_gc, GCCause::_shenandoah_concurrent_gc);
746 if (existing != GCCause::_no_gc) {
747 log_debug(gc, thread)("Reject request to interrupt old gc because another gc is pending: %s", GCCause::to_string(existing));
748 return false;
749 }
750
751 log_info(gc)("Preempting old generation mark to allow %s GC", shenandoah_generation_name(generation));
752 _requested_generation = generation;
753 _preemption_requested.set();
754 ShenandoahHeap::heap()->cancel_gc(GCCause::_shenandoah_concurrent_gc);
755 notify_control_thread();
756
757 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
758 while (gc_mode() == servicing_old) {
759 ml.wait();
760 }
761 return true;
762 }
763
764 log_debug(gc, thread)("Reject request for concurrent gc: mode: %s, allow_old_preemption: %s",
765 gc_mode_name(gc_mode()),
766 BOOL_TO_STR(_allow_old_preemption.is_set()));
767 return false;
768 }
769
770 void ShenandoahGenerationalControlThread::notify_control_thread() {
771 MonitorLocker locker(&_control_lock, Mutex::_no_safepoint_check_flag);
772 _control_lock.notify();
773 }
774
775 bool ShenandoahGenerationalControlThread::preempt_old_marking(ShenandoahGenerationType generation) {
776 return (generation == YOUNG) && _allow_old_preemption.try_unset();
777 }
778
779 void ShenandoahGenerationalControlThread::handle_requested_gc(GCCause::Cause cause) {
780 // For normal requested GCs (System.gc) we want to block the caller. However,
781 // for whitebox requested GC, we want to initiate the GC and return immediately.
782 // The whitebox caller thread will arrange for itself to wait until the GC notifies
783 // it that has reached the requested breakpoint (phase in the GC).
784 if (cause == GCCause::_wb_breakpoint) {
785 Atomic::xchg(&_requested_gc_cause, cause);
786 notify_control_thread();
787 return;
788 }
789
790 // Make sure we have at least one complete GC cycle before unblocking
791 // from the explicit GC request.
792 //
793 // This is especially important for weak references cleanup and/or native
794 // resources (e.g. DirectByteBuffers) machinery: when explicit GC request
795 // comes very late in the already running cycle, it would miss lots of new
796 // opportunities for cleanup that were made available before the caller
797 // requested the GC.
798
799 MonitorLocker ml(&_gc_waiters_lock);
800 size_t current_gc_id = get_gc_id();
801 size_t required_gc_id = current_gc_id + 1;
802 while (current_gc_id < required_gc_id) {
803 // This races with the regulator thread to start a concurrent gc and the
804 // control thread to clear it at the start of a cycle. Threads here are
805 // allowed to escalate a heuristic's request for concurrent gc.
806 GCCause::Cause existing = Atomic::xchg(&_requested_gc_cause, cause);
807 if (existing != GCCause::_no_gc) {
808 log_debug(gc, thread)("GC request supersedes existing request: %s", GCCause::to_string(existing));
809 }
810
811 notify_control_thread();
812 ml.wait();
813 current_gc_id = get_gc_id();
814 }
815 }
816
817 void ShenandoahGenerationalControlThread::notify_gc_waiters() {
818 MonitorLocker ml(&_gc_waiters_lock);
819 ml.notify_all();
820 }
821
822 const char* ShenandoahGenerationalControlThread::gc_mode_name(ShenandoahGenerationalControlThread::GCMode mode) {
823 switch (mode) {
824 case none: return "idle";
825 case concurrent_normal: return "normal";
826 case stw_degenerated: return "degenerated";
827 case stw_full: return "full";
828 case servicing_old: return "old";
829 case bootstrapping_old: return "bootstrap";
830 default: return "unknown";
831 }
832 }
833
834 void ShenandoahGenerationalControlThread::set_gc_mode(ShenandoahGenerationalControlThread::GCMode new_mode) {
835 if (_mode != new_mode) {
836 log_debug(gc)("Transition from: %s to: %s", gc_mode_name(_mode), gc_mode_name(new_mode));
837 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
838 _mode = new_mode;
839 ml.notify_all();
840 }
841 }