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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
5 *
6 * This code is free software; you can redistribute it and/or modify it
7 * under the terms of the GNU General Public License version 2 only, as
8 * published by the Free Software Foundation.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 *
24 */
25
26 #include "precompiled.hpp"
27 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
28 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
29 #include "gc/shenandoah/shenandoahControlThread.hpp"
30 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
31 #include "gc/shenandoah/shenandoahFreeSet.hpp"
32 #include "gc/shenandoah/shenandoahFullGC.hpp"
33 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
34 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
35 #include "gc/shenandoah/shenandoahPacer.inline.hpp"
36 #include "gc/shenandoah/shenandoahUtils.hpp"
37 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
38 #include "memory/metaspaceUtils.hpp"
39 #include "memory/metaspaceStats.hpp"
40 #include "memory/resourceArea.hpp"
41 #include "runtime/atomic.hpp"
42
43 ShenandoahControlThread::ShenandoahControlThread() :
44 ConcurrentGCThread(),
45 _alloc_failure_waiters_lock(Mutex::safepoint-2, "ShenandoahAllocFailureGC_lock", true),
46 _gc_waiters_lock(Mutex::safepoint-2, "ShenandoahRequestedGC_lock", true),
47 _requested_gc_cause(GCCause::_no_cause_specified),
48 _degen_point(ShenandoahGC::_degenerated_outside_cycle),
49 _allocs_seen(0) {
50 set_name("Shenandoah Control Thread");
51 reset_gc_id();
52 create_and_start();
53 }
54
55 void ShenandoahControlThread::run_service() {
56 ShenandoahHeap* heap = ShenandoahHeap::heap();
57
58 const GCMode default_mode = concurrent_normal;
59 const GCCause::Cause default_cause = GCCause::_shenandoah_concurrent_gc;
60 int sleep = ShenandoahControlIntervalMin;
61
62 double last_shrink_time = os::elapsedTime();
63 double last_sleep_adjust_time = os::elapsedTime();
64
65 // Shrink period avoids constantly polling regions for shrinking.
66 // Having a period 10x lower than the delay would mean we hit the
67 // shrinking with lag of less than 1/10-th of true delay.
68 // ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
69 const double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
70
71 ShenandoahCollectorPolicy* const policy = heap->shenandoah_policy();
72 ShenandoahHeuristics* const heuristics = heap->heuristics();
73 while (!in_graceful_shutdown() && !should_terminate()) {
74 // Figure out if we have pending requests.
75 const bool alloc_failure_pending = _alloc_failure_gc.is_set();
76 const bool is_gc_requested = _gc_requested.is_set();
77 const GCCause::Cause requested_gc_cause = _requested_gc_cause;
78
79 // This control loop iteration has seen this much allocation.
80 const size_t allocs_seen = Atomic::xchg(&_allocs_seen, (size_t)0, memory_order_relaxed);
81
82 // Check if we have seen a new target for soft max heap size.
83 const bool soft_max_changed = heap->check_soft_max_changed();
84
85 // Choose which GC mode to run in. The block below should select a single mode.
86 GCMode mode = none;
87 GCCause::Cause cause = GCCause::_last_gc_cause;
88 ShenandoahGC::ShenandoahDegenPoint degen_point = ShenandoahGC::_degenerated_unset;
89
90 if (alloc_failure_pending) {
91 // Allocation failure takes precedence: we have to deal with it first thing
92 log_info(gc)("Trigger: Handle Allocation Failure");
93
94 cause = GCCause::_allocation_failure;
95
96 // Consume the degen point, and seed it with default value
97 degen_point = _degen_point;
98 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
99
100 if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle()) {
101 heuristics->record_allocation_failure_gc();
102 policy->record_alloc_failure_to_degenerated(degen_point);
103 mode = stw_degenerated;
104 } else {
105 heuristics->record_allocation_failure_gc();
106 policy->record_alloc_failure_to_full();
107 mode = stw_full;
108 }
109
110 } else if (is_gc_requested) {
111 cause = requested_gc_cause;
112 log_info(gc)("Trigger: GC request (%s)", GCCause::to_string(cause));
113 heuristics->record_requested_gc();
114
115 if (ShenandoahCollectorPolicy::should_run_full_gc(cause)) {
116 mode = stw_full;
117 } else {
118 mode = default_mode;
119 // Unload and clean up everything
120 heap->set_unload_classes(heuristics->can_unload_classes());
121 }
122 } else {
123 // Potential normal cycle: ask heuristics if it wants to act
124 if (heuristics->should_start_gc()) {
125 mode = default_mode;
126 cause = default_cause;
127 }
128
129 // Ask policy if this cycle wants to process references or unload classes
130 heap->set_unload_classes(heuristics->should_unload_classes());
131 }
132
133 // Blow all soft references on this cycle, if handling allocation failure,
134 // either implicit or explicit GC request, or we are requested to do so unconditionally.
135 if (alloc_failure_pending || is_gc_requested || ShenandoahAlwaysClearSoftRefs) {
136 heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
137 }
138
139 const bool gc_requested = (mode != none);
140 assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
141
142 if (gc_requested) {
143 // GC is starting, bump the internal ID
144 update_gc_id();
145
146 heap->reset_bytes_allocated_since_gc_start();
147
148 MetaspaceCombinedStats meta_sizes = MetaspaceUtils::get_combined_statistics();
149
150 // If GC was requested, we are sampling the counters even without actual triggers
151 // from allocation machinery. This captures GC phases more accurately.
152 heap->set_forced_counters_update(true);
153
154 // If GC was requested, we better dump freeset data for performance debugging
155 {
156 ShenandoahHeapLocker locker(heap->lock());
157 heap->free_set()->log_status();
158 }
159
160 switch (mode) {
161 case concurrent_normal:
162 service_concurrent_normal_cycle(cause);
163 break;
164 case stw_degenerated:
165 service_stw_degenerated_cycle(cause, degen_point);
166 break;
167 case stw_full:
168 service_stw_full_cycle(cause);
169 break;
170 default:
171 ShouldNotReachHere();
172 }
173
174 // If this was the requested GC cycle, notify waiters about it
175 if (is_gc_requested) {
176 notify_gc_waiters();
177 }
178
179 // If this was the allocation failure GC cycle, notify waiters about it
180 if (alloc_failure_pending) {
181 notify_alloc_failure_waiters();
182 }
183
184 // Report current free set state at the end of cycle, whether
185 // it is a normal completion, or the abort.
186 {
187 ShenandoahHeapLocker locker(heap->lock());
188 heap->free_set()->log_status();
189
190 // Notify Universe about new heap usage. This has implications for
191 // global soft refs policy, and we better report it every time heap
192 // usage goes down.
193 heap->update_capacity_and_used_at_gc();
194
195 // Signal that we have completed a visit to all live objects.
196 heap->record_whole_heap_examined_timestamp();
197 }
198
199 // Disable forced counters update, and update counters one more time
200 // to capture the state at the end of GC session.
201 heap->handle_force_counters_update();
202 heap->set_forced_counters_update(false);
203
204 // Retract forceful part of soft refs policy
205 heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
206
207 // Clear metaspace oom flag, if current cycle unloaded classes
208 if (heap->unload_classes()) {
209 heuristics->clear_metaspace_oom();
210 }
211
212 // Commit worker statistics to cycle data
213 heap->phase_timings()->flush_par_workers_to_cycle();
214 if (ShenandoahPacing) {
215 heap->pacer()->flush_stats_to_cycle();
216 }
217
218 // Print GC stats for current cycle
219 {
220 LogTarget(Info, gc, stats) lt;
221 if (lt.is_enabled()) {
222 ResourceMark rm;
223 LogStream ls(lt);
224 heap->phase_timings()->print_cycle_on(&ls);
225 if (ShenandoahPacing) {
226 heap->pacer()->print_cycle_on(&ls);
227 }
228 }
229 }
230
231 // Commit statistics to globals
232 heap->phase_timings()->flush_cycle_to_global();
233
234 // Print Metaspace change following GC (if logging is enabled).
235 MetaspaceUtils::print_metaspace_change(meta_sizes);
236
237 // GC is over, we are at idle now
238 if (ShenandoahPacing) {
239 heap->pacer()->setup_for_idle();
240 }
241 } else {
242 // Allow allocators to know we have seen this much regions
243 if (ShenandoahPacing && (allocs_seen > 0)) {
244 heap->pacer()->report_alloc(allocs_seen);
245 }
246 }
247
248 const double current = os::elapsedTime();
249
250 if (ShenandoahUncommit && (is_gc_requested || soft_max_changed || (current - last_shrink_time > shrink_period))) {
251 // Explicit GC tries to uncommit everything down to min capacity.
252 // Soft max change tries to uncommit everything down to target capacity.
253 // Periodic uncommit tries to uncommit suitable regions down to min capacity.
254
255 double shrink_before = (is_gc_requested || soft_max_changed) ?
256 current :
257 current - (ShenandoahUncommitDelay / 1000.0);
258
259 size_t shrink_until = soft_max_changed ?
260 heap->soft_max_capacity() :
261 heap->min_capacity();
262
263 heap->maybe_uncommit(shrink_before, shrink_until);
264 heap->phase_timings()->flush_cycle_to_global();
265 last_shrink_time = current;
266 }
267
268 // Wait before performing the next action. If allocation happened during this wait,
269 // we exit sooner, to let heuristics re-evaluate new conditions. If we are at idle,
270 // back off exponentially.
271 if (heap->has_changed()) {
272 sleep = ShenandoahControlIntervalMin;
273 } else if ((current - last_sleep_adjust_time) * 1000 > ShenandoahControlIntervalAdjustPeriod){
274 sleep = MIN2<int>(ShenandoahControlIntervalMax, MAX2(1, sleep * 2));
275 last_sleep_adjust_time = current;
276 }
277 os::naked_short_sleep(sleep);
278 }
279
280 // Wait for the actual stop(), can't leave run_service() earlier.
281 while (!should_terminate()) {
282 os::naked_short_sleep(ShenandoahControlIntervalMin);
283 }
284 }
285
286 void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cause) {
287 // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
288 // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
289 // If second allocation failure happens during Degenerated GC cycle (for example, when GC
290 // tries to evac something and no memory is available), cycle degrades to Full GC.
291 //
292 // There are also a shortcut through the normal cycle: immediate garbage shortcut, when
293 // heuristics says there are no regions to compact, and all the collection comes from immediately
294 // reclaimable regions.
295 //
296 // ................................................................................................
297 //
298 // (immediate garbage shortcut) Concurrent GC
299 // /-------------------------------------------\
300 // | |
301 // | |
302 // | |
303 // | v
304 // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
305 // | | | ^
306 // | (af) | (af) | (af) |
307 // ..................|....................|.................|..............|.......................
308 // | | | |
309 // | | | | Degenerated GC
310 // v v v |
311 // STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
312 // | | | ^
313 // | (af) | (af) | (af) |
314 // ..................|....................|.................|..............|.......................
315 // | | | |
316 // | v | | Full GC
317 // \------------------->o<----------------/ |
318 // | |
319 // v |
320 // Full GC --------------------------/
321 //
322 ShenandoahHeap* heap = ShenandoahHeap::heap();
323 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) return;
324
325 GCIdMark gc_id_mark;
326 ShenandoahGCSession session(cause);
327
328 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
329
330 ShenandoahConcurrentGC gc;
331 if (gc.collect(cause)) {
332 // Cycle is complete
333 heap->heuristics()->record_success_concurrent();
334 heap->shenandoah_policy()->record_success_concurrent(gc.abbreviated());
335 } else {
336 assert(heap->cancelled_gc(), "Must have been cancelled");
337 check_cancellation_or_degen(gc.degen_point());
338 }
339 }
340
341 bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
342 ShenandoahHeap* heap = ShenandoahHeap::heap();
343 if (heap->cancelled_gc()) {
344 assert (is_alloc_failure_gc() || in_graceful_shutdown(), "Cancel GC either for alloc failure GC, or gracefully exiting");
345 if (!in_graceful_shutdown()) {
346 assert (_degen_point == ShenandoahGC::_degenerated_outside_cycle,
347 "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
348 _degen_point = point;
349 }
350 return true;
351 }
352 return false;
353 }
354
355 void ShenandoahControlThread::stop_service() {
356 // Nothing to do here.
357 }
358
359 void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
360 GCIdMark gc_id_mark;
361 ShenandoahGCSession session(cause);
362
363 ShenandoahFullGC gc;
364 gc.collect(cause);
365 }
366
367 void ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point) {
368 assert (point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
369
370 GCIdMark gc_id_mark;
371 ShenandoahGCSession session(cause);
372
373 ShenandoahDegenGC gc(point);
374 gc.collect(cause);
375 }
376
377 void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
378 if (ShenandoahCollectorPolicy::should_handle_requested_gc(cause)) {
379 handle_requested_gc(cause);
380 }
381 }
382
383 void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
384 // Make sure we have at least one complete GC cycle before unblocking
385 // from the explicit GC request.
386 //
387 // This is especially important for weak references cleanup and/or native
388 // resources (e.g. DirectByteBuffers) machinery: when explicit GC request
389 // comes very late in the already running cycle, it would miss lots of new
390 // opportunities for cleanup that were made available before the caller
391 // requested the GC.
392
393 MonitorLocker ml(&_gc_waiters_lock);
394 size_t current_gc_id = get_gc_id();
395 size_t required_gc_id = current_gc_id + 1;
396 while (current_gc_id < required_gc_id) {
397 // Although setting gc request is under _gc_waiters_lock, but read side (run_service())
398 // does not take the lock. We need to enforce following order, so that read side sees
399 // latest requested gc cause when the flag is set.
400 _requested_gc_cause = cause;
401 _gc_requested.set();
402
403 if (cause != GCCause::_wb_breakpoint) {
404 ml.wait();
405 }
406 current_gc_id = get_gc_id();
407 }
408 }
409
410 void ShenandoahControlThread::handle_alloc_failure(ShenandoahAllocRequest& req, bool block) {
411 ShenandoahHeap* heap = ShenandoahHeap::heap();
412
413 assert(current()->is_Java_thread(), "expect Java thread here");
414
415 if (try_set_alloc_failure_gc()) {
416 // Only report the first allocation failure
417 log_info(gc)("Failed to allocate %s, " SIZE_FORMAT "%s",
418 req.type_string(),
419 byte_size_in_proper_unit(req.size() * HeapWordSize), proper_unit_for_byte_size(req.size() * HeapWordSize));
420
421 // Now that alloc failure GC is scheduled, we can abort everything else
422 heap->cancel_gc(GCCause::_allocation_failure);
423 }
424
425
426 if (block) {
427 MonitorLocker ml(&_alloc_failure_waiters_lock);
428 while (is_alloc_failure_gc()) {
429 ml.wait();
430 }
431 }
432 }
433
434 void ShenandoahControlThread::handle_alloc_failure_evac(size_t words) {
435 ShenandoahHeap* heap = ShenandoahHeap::heap();
436
437 if (try_set_alloc_failure_gc()) {
438 // Only report the first allocation failure
439 log_info(gc)("Failed to allocate " SIZE_FORMAT "%s for evacuation",
440 byte_size_in_proper_unit(words * HeapWordSize), proper_unit_for_byte_size(words * HeapWordSize));
441 }
442
443 // Forcefully report allocation failure
444 heap->cancel_gc(GCCause::_shenandoah_allocation_failure_evac);
445 }
446
447 void ShenandoahControlThread::notify_alloc_failure_waiters() {
448 _alloc_failure_gc.unset();
449 MonitorLocker ml(&_alloc_failure_waiters_lock);
450 ml.notify_all();
451 }
452
453 bool ShenandoahControlThread::try_set_alloc_failure_gc() {
454 return _alloc_failure_gc.try_set();
455 }
456
457 bool ShenandoahControlThread::is_alloc_failure_gc() {
458 return _alloc_failure_gc.is_set();
459 }
460
461 void ShenandoahControlThread::notify_gc_waiters() {
462 _gc_requested.unset();
463 MonitorLocker ml(&_gc_waiters_lock);
464 ml.notify_all();
465 }
466
467 void ShenandoahControlThread::pacing_notify_alloc(size_t words) {
468 assert(ShenandoahPacing, "should only call when pacing is enabled");
469 Atomic::add(&_allocs_seen, words, memory_order_relaxed);
470 }
471
472 void ShenandoahControlThread::reset_gc_id() {
473 Atomic::store(&_gc_id, (size_t)0);
474 }
475
476 void ShenandoahControlThread::update_gc_id() {
477 Atomic::inc(&_gc_id);
478 }
479
480 size_t ShenandoahControlThread::get_gc_id() {
481 return Atomic::load(&_gc_id);
482 }
483
484 void ShenandoahControlThread::start() {
485 create_and_start();
486 }
487
488 void ShenandoahControlThread::prepare_for_graceful_shutdown() {
489 _graceful_shutdown.set();
490 }
491
492 bool ShenandoahControlThread::in_graceful_shutdown() {
493 return _graceful_shutdown.is_set();
494 }