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 {
270 // Notify Universe about new heap usage. This has implications for
271 // global soft refs policy, and we better report it every time heap
272 // usage goes down.
273 ShenandoahHeapLocker locker(heap->lock());
274 heap->update_capacity_and_used_at_gc();
275 }
276
277 // Signal that we have completed a visit to all live objects.
278 heap->record_whole_heap_examined_timestamp();
279
280 // Disable forced counters update, and update counters one more time
281 // to capture the state at the end of GC session.
282 heap->handle_force_counters_update();
283 heap->set_forced_counters_update(false);
284
285 // Retract forceful part of soft refs policy
286 heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
287
288 // Clear metaspace oom flag, if current cycle unloaded classes
289 if (heap->unload_classes()) {
290 global_heuristics->clear_metaspace_oom();
291 }
292
293 process_phase_timings(heap);
294
295 // Print Metaspace change following GC (if logging is enabled).
296 MetaspaceUtils::print_metaspace_change(meta_sizes);
297
298 // GC is over, we are at idle now
299 if (ShenandoahPacing) {
300 heap->pacer()->setup_for_idle();
301 }
302 } else {
303 // Report to pacer that we have seen this many words allocated
304 if (ShenandoahPacing && (allocs_seen > 0)) {
305 heap->pacer()->report_alloc(allocs_seen);
306 }
307 }
308
309 const double current = os::elapsedTime();
310
311 if (ShenandoahUncommit && (is_gc_requested || soft_max_changed || (current - last_shrink_time > shrink_period))) {
312 // Explicit GC tries to uncommit everything down to min capacity.
313 // Soft max change tries to uncommit everything down to target capacity.
314 // Periodic uncommit tries to uncommit suitable regions down to min capacity.
315
316 double shrink_before = (is_gc_requested || soft_max_changed) ?
317 current :
318 current - (ShenandoahUncommitDelay / 1000.0);
319
320 size_t shrink_until = soft_max_changed ?
321 heap->soft_max_capacity() :
322 heap->min_capacity();
323
324 heap->maybe_uncommit(shrink_before, shrink_until);
325 heap->phase_timings()->flush_cycle_to_global();
326 last_shrink_time = current;
327 }
328
329 // Wait for ShenandoahControlIntervalMax unless there was an allocation failure or another request was made mid-cycle.
330 if (!is_alloc_failure_gc() && _requested_gc_cause == GCCause::_no_gc) {
331 // The timed wait is necessary because this thread has a responsibility to send
332 // 'alloc_words' to the pacer when it does not perform a GC.
333 MonitorLocker lock(&_control_lock, Mutex::_no_safepoint_check_flag);
334 lock.wait(ShenandoahControlIntervalMax);
335 }
336 }
337
338 // Wait for the actual stop(), can't leave run_service() earlier.
339 while (!should_terminate()) {
340 os::naked_short_sleep(ShenandoahControlIntervalMin);
341 }
342 }
343
344 void ShenandoahGenerationalControlThread::process_phase_timings(const ShenandoahGenerationalHeap* heap) {
345 // Commit worker statistics to cycle data
346 heap->phase_timings()->flush_par_workers_to_cycle();
347 if (ShenandoahPacing) {
348 heap->pacer()->flush_stats_to_cycle();
349 }
350
351 ShenandoahEvacuationTracker* evac_tracker = heap->evac_tracker();
352 ShenandoahCycleStats evac_stats = evac_tracker->flush_cycle_to_global();
353
354 // Print GC stats for current cycle
355 {
356 LogTarget(Info, gc, stats) lt;
357 if (lt.is_enabled()) {
358 ResourceMark rm;
359 LogStream ls(lt);
360 heap->phase_timings()->print_cycle_on(&ls);
361 evac_tracker->print_evacuations_on(&ls, &evac_stats.workers,
362 &evac_stats.mutators);
363 if (ShenandoahPacing) {
364 heap->pacer()->print_cycle_on(&ls);
365 }
366 }
367 }
368
369 // Commit statistics to globals
370 heap->phase_timings()->flush_cycle_to_global();
371 }
372
373 // Young and old concurrent cycles are initiated by the regulator. Implicit
374 // and explicit GC requests are handled by the controller thread and always
375 // run a global cycle (which is concurrent by default, but may be overridden
376 // by command line options). Old cycles always degenerate to a global cycle.
377 // Young cycles are degenerated to complete the young cycle. Young
378 // and old degen may upgrade to Full GC. Full GC may also be
379 // triggered directly by a System.gc() invocation.
380 //
381 //
382 // +-----+ Idle +-----+-----------+---------------------+
383 // | + | | |
384 // | | | | |
385 // | | v | |
386 // | | Bootstrap Old +-- | ------------+ |
387 // | | + | | |
388 // | | | | | |
389 // | v v v v |
390 // | Resume Old <----------+ Young +--> Young Degen |
391 // | + + ^ + + |
392 // v | | | | | |
393 // Global <-+ | +----------------------------+ | |
394 // + | | |
395 // | v v |
396 // +---> Global Degen +--------------------> Full <----+
397 //
398 void ShenandoahGenerationalControlThread::service_concurrent_normal_cycle(ShenandoahGenerationalHeap* heap,
399 const ShenandoahGenerationType generation,
400 GCCause::Cause cause) {
401 GCIdMark gc_id_mark;
402 switch (generation) {
403 case YOUNG: {
404 // Run a young cycle. This might or might not, have interrupted an ongoing
405 // concurrent mark in the old generation. We need to think about promotions
406 // in this case. Promoted objects should be above the TAMS in the old regions
407 // they end up in, but we have to be sure we don't promote into any regions
408 // that are in the cset.
409 log_info(gc, ergo)("Start GC cycle (Young)");
410 service_concurrent_cycle(heap->young_generation(), cause, false);
411 break;
412 }
413 case OLD: {
414 log_info(gc, ergo)("Start GC cycle (Old)");
415 service_concurrent_old_cycle(heap, cause);
416 break;
417 }
418 case GLOBAL: {
419 log_info(gc, ergo)("Start GC cycle (Global)");
420 service_concurrent_cycle(heap->global_generation(), cause, false);
421 break;
422 }
423 default:
424 ShouldNotReachHere();
425 }
426 }
427
428 void ShenandoahGenerationalControlThread::service_concurrent_old_cycle(ShenandoahGenerationalHeap* heap, GCCause::Cause &cause) {
429 ShenandoahOldGeneration* old_generation = heap->old_generation();
430 ShenandoahYoungGeneration* young_generation = heap->young_generation();
431 ShenandoahOldGeneration::State original_state = old_generation->state();
432
433 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
434
435 switch (original_state) {
436 case ShenandoahOldGeneration::FILLING: {
437 ShenandoahGCSession session(cause, old_generation);
438 _allow_old_preemption.set();
439 old_generation->entry_coalesce_and_fill();
440 _allow_old_preemption.unset();
441
442 // Before bootstrapping begins, we must acknowledge any cancellation request.
443 // If the gc has not been cancelled, this does nothing. If it has been cancelled,
444 // this will clear the cancellation request and exit before starting the bootstrap
445 // phase. This will allow the young GC cycle to proceed normally. If we do not
446 // acknowledge the cancellation request, the subsequent young cycle will observe
447 // the request and essentially cancel itself.
448 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) {
449 log_info(gc)("Preparation for old generation cycle was cancelled");
450 return;
451 }
452
453 // Coalescing threads completed and nothing was cancelled. it is safe to transition from this state.
454 old_generation->transition_to(ShenandoahOldGeneration::WAITING_FOR_BOOTSTRAP);
455 return;
456 }
457 case ShenandoahOldGeneration::WAITING_FOR_BOOTSTRAP:
458 old_generation->transition_to(ShenandoahOldGeneration::BOOTSTRAPPING);
459 case ShenandoahOldGeneration::BOOTSTRAPPING: {
460 // Configure the young generation's concurrent mark to put objects in
461 // old regions into the concurrent mark queues associated with the old
462 // generation. The young cycle will run as normal except that rather than
463 // ignore old references it will mark and enqueue them in the old concurrent
464 // task queues but it will not traverse them.
465 set_gc_mode(bootstrapping_old);
466 young_generation->set_old_gen_task_queues(old_generation->task_queues());
467 ShenandoahGCSession session(cause, young_generation);
468 service_concurrent_cycle(heap, young_generation, cause, true);
469 process_phase_timings(heap);
470 if (heap->cancelled_gc()) {
471 // Young generation bootstrap cycle has failed. Concurrent mark for old generation
472 // is going to resume after degenerated bootstrap cycle completes.
473 log_info(gc)("Bootstrap cycle for old generation was cancelled");
474 return;
475 }
476
477 // Reset the degenerated point. Normally this would happen at the top
478 // of the control loop, but here we have just completed a young cycle
479 // which has bootstrapped the old concurrent marking.
480 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
481
482 // From here we will 'resume' the old concurrent mark. This will skip reset
483 // and init mark for the concurrent mark. All of that work will have been
484 // done by the bootstrapping young cycle.
485 set_gc_mode(servicing_old);
486 old_generation->transition_to(ShenandoahOldGeneration::MARKING);
487 }
488 case ShenandoahOldGeneration::MARKING: {
489 ShenandoahGCSession session(cause, old_generation);
490 bool marking_complete = resume_concurrent_old_cycle(old_generation, cause);
491 if (marking_complete) {
492 assert(old_generation->state() != ShenandoahOldGeneration::MARKING, "Should not still be marking");
493 if (original_state == ShenandoahOldGeneration::MARKING) {
494 heap->mmu_tracker()->record_old_marking_increment(true);
495 heap->log_heap_status("At end of Concurrent Old Marking finishing increment");
496 }
497 } else if (original_state == ShenandoahOldGeneration::MARKING) {
498 heap->mmu_tracker()->record_old_marking_increment(false);
499 heap->log_heap_status("At end of Concurrent Old Marking increment");
500 }
501 break;
502 }
503 default:
504 fatal("Unexpected state for old GC: %s", ShenandoahOldGeneration::state_name(old_generation->state()));
505 }
506 }
507
508 bool ShenandoahGenerationalControlThread::resume_concurrent_old_cycle(ShenandoahOldGeneration* generation, GCCause::Cause cause) {
509 assert(ShenandoahHeap::heap()->is_concurrent_old_mark_in_progress(), "Old mark should be in progress");
510 log_debug(gc)("Resuming old generation with " UINT32_FORMAT " marking tasks queued", generation->task_queues()->tasks());
511
512 ShenandoahHeap* heap = ShenandoahHeap::heap();
513
514 // We can only tolerate being cancelled during concurrent marking or during preparation for mixed
515 // evacuation. This flag here (passed by reference) is used to control precisely where the regulator
516 // is allowed to cancel a GC.
517 ShenandoahOldGC gc(generation, _allow_old_preemption);
518 if (gc.collect(cause)) {
519 heap->notify_gc_progress();
520 generation->record_success_concurrent(false);
521 }
522
523 if (heap->cancelled_gc()) {
524 // It's possible the gc cycle was cancelled after the last time
525 // the collection checked for cancellation. In which case, the
526 // old gc cycle is still completed, and we have to deal with this
527 // cancellation. We set the degeneration point to be outside
528 // the cycle because if this is an allocation failure, that is
529 // what must be done (there is no degenerated old cycle). If the
530 // cancellation was due to a heuristic wanting to start a young
531 // cycle, then we are not actually going to a degenerated cycle,
532 // so the degenerated point doesn't matter here.
533 check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle);
534 if (_requested_gc_cause == GCCause::_shenandoah_concurrent_gc) {
535 heap->shenandoah_policy()->record_interrupted_old();
536 }
537 return false;
538 }
539 return true;
540 }
541
542 void ShenandoahGenerationalControlThread::service_concurrent_cycle(ShenandoahGeneration* generation, GCCause::Cause cause, bool do_old_gc_bootstrap) {
543 // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
544 // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
545 // If second allocation failure happens during Degenerated GC cycle (for example, when GC
546 // tries to evac something and no memory is available), cycle degrades to Full GC.
547 //
548 // There are also a shortcut through the normal cycle: immediate garbage shortcut, when
549 // heuristics says there are no regions to compact, and all the collection comes from immediately
550 // reclaimable regions.
551 //
552 // ................................................................................................
553 //
554 // (immediate garbage shortcut) Concurrent GC
555 // /-------------------------------------------\
556 // | |
557 // | |
558 // | |
559 // | v
560 // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
561 // | | | ^
562 // | (af) | (af) | (af) |
563 // ..................|....................|.................|..............|.......................
564 // | | | |
565 // | | | | Degenerated GC
566 // v v v |
567 // STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
568 // | | | ^
569 // | (af) | (af) | (af) |
570 // ..................|....................|.................|..............|.......................
571 // | | | |
572 // | v | | Full GC
573 // \------------------->o<----------------/ |
574 // | |
575 // v |
576 // Full GC --------------------------/
577 //
578 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) return;
579
580 ShenandoahHeap* heap = ShenandoahHeap::heap();
581 ShenandoahGCSession session(cause, generation);
582 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
583
584 service_concurrent_cycle(heap, generation, cause, do_old_gc_bootstrap);
585 }
586
587 void ShenandoahGenerationalControlThread::service_concurrent_cycle(ShenandoahHeap* heap,
588 ShenandoahGeneration* generation,
589 GCCause::Cause& cause,
590 bool do_old_gc_bootstrap) {
591 assert(!generation->is_old(), "Old GC takes a different control path");
592
593 ShenandoahConcurrentGC gc(generation, do_old_gc_bootstrap);
594 if (gc.collect(cause)) {
595 // Cycle is complete
596 heap->notify_gc_progress();
597 generation->record_success_concurrent(gc.abbreviated());
598 } else {
599 assert(heap->cancelled_gc(), "Must have been cancelled");
600 check_cancellation_or_degen(gc.degen_point());
601
602 // Concurrent young-gen collection degenerates to young
603 // collection. Same for global collections.
604 _degen_generation = generation;
605 }
606 const char* msg;
607 ShenandoahMmuTracker* mmu_tracker = heap->mmu_tracker();
608 if (generation->is_young()) {
609 if (heap->cancelled_gc()) {
610 msg = (do_old_gc_bootstrap) ? "At end of Interrupted Concurrent Bootstrap GC" :
611 "At end of Interrupted Concurrent Young GC";
612 } else {
613 // We only record GC results if GC was successful
614 msg = (do_old_gc_bootstrap) ? "At end of Concurrent Bootstrap GC" :
615 "At end of Concurrent Young GC";
616 if (heap->collection_set()->has_old_regions()) {
617 mmu_tracker->record_mixed(get_gc_id());
618 } else if (do_old_gc_bootstrap) {
619 mmu_tracker->record_bootstrap(get_gc_id());
620 } else {
621 mmu_tracker->record_young(get_gc_id());
622 }
623 }
624 } else {
625 assert(generation->is_global(), "If not young, must be GLOBAL");
626 assert(!do_old_gc_bootstrap, "Do not bootstrap with GLOBAL GC");
627 if (heap->cancelled_gc()) {
628 msg = "At end of Interrupted Concurrent GLOBAL GC";
629 } else {
630 // We only record GC results if GC was successful
631 msg = "At end of Concurrent Global GC";
632 mmu_tracker->record_global(get_gc_id());
633 }
634 }
635 heap->log_heap_status(msg);
636 }
637
638 bool ShenandoahGenerationalControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
639 ShenandoahHeap* heap = ShenandoahHeap::heap();
640 if (!heap->cancelled_gc()) {
641 return false;
642 }
643
644 if (in_graceful_shutdown()) {
645 return true;
646 }
647
648 assert(_degen_point == ShenandoahGC::_degenerated_outside_cycle,
649 "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
650
651 if (is_alloc_failure_gc()) {
652 _degen_point = point;
653 _preemption_requested.unset();
654 return true;
655 }
656
657 if (_preemption_requested.is_set()) {
658 assert(_requested_generation == YOUNG, "Only young GCs may preempt old.");
659 _preemption_requested.unset();
660
661 // Old generation marking is only cancellable during concurrent marking.
662 // Once final mark is complete, the code does not check again for cancellation.
663 // If old generation was cancelled for an allocation failure, we wouldn't
664 // make it to this case. The calling code is responsible for forcing a
665 // cancellation due to allocation failure into a degenerated cycle.
666 _degen_point = point;
667 heap->clear_cancelled_gc(false /* clear oom handler */);
668 return true;
669 }
670
671 fatal("Cancel GC either for alloc failure GC, or gracefully exiting, or to pause old generation marking");
672 return false;
673 }
674
675 void ShenandoahGenerationalControlThread::stop_service() {
676 // Nothing to do here.
677 }
678
679 void ShenandoahGenerationalControlThread::service_stw_full_cycle(GCCause::Cause cause) {
680 ShenandoahHeap* const heap = ShenandoahHeap::heap();
681
682 GCIdMark gc_id_mark;
683 ShenandoahGCSession session(cause, heap->global_generation());
684
685 ShenandoahFullGC gc;
686 gc.collect(cause);
687 }
688
689 void ShenandoahGenerationalControlThread::service_stw_degenerated_cycle(GCCause::Cause cause,
690 ShenandoahGC::ShenandoahDegenPoint point) {
691 assert(point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
692 ShenandoahHeap* const heap = ShenandoahHeap::heap();
693
694 GCIdMark gc_id_mark;
695 ShenandoahGCSession session(cause, _degen_generation);
696
697 ShenandoahDegenGC gc(point, _degen_generation);
698 gc.collect(cause);
699
700 assert(heap->young_generation()->task_queues()->is_empty(), "Unexpected young generation marking tasks");
701 if (_degen_generation->is_global()) {
702 assert(heap->old_generation()->task_queues()->is_empty(), "Unexpected old generation marking tasks");
703 assert(heap->global_generation()->task_queues()->is_empty(), "Unexpected global generation marking tasks");
704 } else {
705 assert(_degen_generation->is_young(), "Expected degenerated young cycle, if not global.");
706 ShenandoahOldGeneration* old = heap->old_generation();
707 if (old->is_bootstrapping()) {
708 old->transition_to(ShenandoahOldGeneration::MARKING);
709 }
710 }
711 }
712
713 void ShenandoahGenerationalControlThread::request_gc(GCCause::Cause cause) {
714 if (ShenandoahCollectorPolicy::should_handle_requested_gc(cause)) {
715 handle_requested_gc(cause);
716 }
717 }
718
719 bool ShenandoahGenerationalControlThread::request_concurrent_gc(ShenandoahGenerationType generation) {
720 if (_preemption_requested.is_set() || _requested_gc_cause != GCCause::_no_gc || ShenandoahHeap::heap()->cancelled_gc()) {
721 // Ignore subsequent requests from the heuristics
722 log_debug(gc, thread)("Reject request for concurrent gc: preemption_requested: %s, gc_requested: %s, gc_cancelled: %s",
723 BOOL_TO_STR(_preemption_requested.is_set()),
724 GCCause::to_string(_requested_gc_cause),
725 BOOL_TO_STR(ShenandoahHeap::heap()->cancelled_gc()));
726 return false;
727 }
728
729 if (gc_mode() == none) {
730 GCCause::Cause existing = Atomic::cmpxchg(&_requested_gc_cause, GCCause::_no_gc, GCCause::_shenandoah_concurrent_gc);
731 if (existing != GCCause::_no_gc) {
732 log_debug(gc, thread)("Reject request for concurrent gc because another gc is pending: %s", GCCause::to_string(existing));
733 return false;
734 }
735
736 _requested_generation = generation;
737 notify_control_thread();
738
739 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
740 while (gc_mode() == none) {
741 ml.wait();
742 }
743 return true;
744 }
745
746 if (preempt_old_marking(generation)) {
747 assert(gc_mode() == servicing_old, "Expected to be servicing old, but was: %s.", gc_mode_name(gc_mode()));
748 GCCause::Cause existing = Atomic::cmpxchg(&_requested_gc_cause, GCCause::_no_gc, GCCause::_shenandoah_concurrent_gc);
749 if (existing != GCCause::_no_gc) {
750 log_debug(gc, thread)("Reject request to interrupt old gc because another gc is pending: %s", GCCause::to_string(existing));
751 return false;
752 }
753
754 log_info(gc)("Preempting old generation mark to allow %s GC", shenandoah_generation_name(generation));
755 _requested_generation = generation;
756 _preemption_requested.set();
757 ShenandoahHeap::heap()->cancel_gc(GCCause::_shenandoah_concurrent_gc);
758 notify_control_thread();
759
760 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
761 while (gc_mode() == servicing_old) {
762 ml.wait();
763 }
764 return true;
765 }
766
767 log_debug(gc, thread)("Reject request for concurrent gc: mode: %s, allow_old_preemption: %s",
768 gc_mode_name(gc_mode()),
769 BOOL_TO_STR(_allow_old_preemption.is_set()));
770 return false;
771 }
772
773 void ShenandoahGenerationalControlThread::notify_control_thread() {
774 MonitorLocker locker(&_control_lock, Mutex::_no_safepoint_check_flag);
775 _control_lock.notify();
776 }
777
778 bool ShenandoahGenerationalControlThread::preempt_old_marking(ShenandoahGenerationType generation) {
779 return (generation == YOUNG) && _allow_old_preemption.try_unset();
780 }
781
782 void ShenandoahGenerationalControlThread::handle_requested_gc(GCCause::Cause cause) {
783 // For normal requested GCs (System.gc) we want to block the caller. However,
784 // for whitebox requested GC, we want to initiate the GC and return immediately.
785 // The whitebox caller thread will arrange for itself to wait until the GC notifies
786 // it that has reached the requested breakpoint (phase in the GC).
787 if (cause == GCCause::_wb_breakpoint) {
788 Atomic::xchg(&_requested_gc_cause, cause);
789 notify_control_thread();
790 return;
791 }
792
793 // Make sure we have at least one complete GC cycle before unblocking
794 // from the explicit GC request.
795 //
796 // This is especially important for weak references cleanup and/or native
797 // resources (e.g. DirectByteBuffers) machinery: when explicit GC request
798 // comes very late in the already running cycle, it would miss lots of new
799 // opportunities for cleanup that were made available before the caller
800 // requested the GC.
801
802 MonitorLocker ml(&_gc_waiters_lock);
803 size_t current_gc_id = get_gc_id();
804 size_t required_gc_id = current_gc_id + 1;
805 while (current_gc_id < required_gc_id) {
806 // This races with the regulator thread to start a concurrent gc and the
807 // control thread to clear it at the start of a cycle. Threads here are
808 // allowed to escalate a heuristic's request for concurrent gc.
809 GCCause::Cause existing = Atomic::xchg(&_requested_gc_cause, cause);
810 if (existing != GCCause::_no_gc) {
811 log_debug(gc, thread)("GC request supersedes existing request: %s", GCCause::to_string(existing));
812 }
813
814 notify_control_thread();
815 ml.wait();
816 current_gc_id = get_gc_id();
817 }
818 }
819
820 void ShenandoahGenerationalControlThread::notify_gc_waiters() {
821 MonitorLocker ml(&_gc_waiters_lock);
822 ml.notify_all();
823 }
824
825 const char* ShenandoahGenerationalControlThread::gc_mode_name(ShenandoahGenerationalControlThread::GCMode mode) {
826 switch (mode) {
827 case none: return "idle";
828 case concurrent_normal: return "normal";
829 case stw_degenerated: return "degenerated";
830 case stw_full: return "full";
831 case servicing_old: return "old";
832 case bootstrapping_old: return "bootstrap";
833 default: return "unknown";
834 }
835 }
836
837 void ShenandoahGenerationalControlThread::set_gc_mode(ShenandoahGenerationalControlThread::GCMode new_mode) {
838 if (_mode != new_mode) {
839 log_debug(gc)("Transition from: %s to: %s", gc_mode_name(_mode), gc_mode_name(new_mode));
840 MonitorLocker ml(&_regulator_lock, Mutex::_no_safepoint_check_flag);
841 _mode = new_mode;
842 ml.notify_all();
843 }
844 }