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/shenandoahGeneration.hpp"
34 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
35 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
36 #include "gc/shenandoah/shenandoahPacer.inline.hpp"
37 #include "gc/shenandoah/shenandoahUtils.hpp"
38 #include "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
39 #include "gc/shenandoah/mode/shenandoahMode.hpp"
40 #include "logging/log.hpp"
41 #include "memory/metaspaceUtils.hpp"
42 #include "memory/metaspaceStats.hpp"
43
44 ShenandoahControlThread::ShenandoahControlThread() :
45 ShenandoahController(),
46 _requested_gc_cause(GCCause::_no_cause_specified),
47 _degen_point(ShenandoahGC::_degenerated_outside_cycle) {
48 set_name("Shenandoah Control Thread");
49 create_and_start();
50 }
51
52 void ShenandoahControlThread::run_service() {
53 ShenandoahHeap* const heap = ShenandoahHeap::heap();
54
55 const GCMode default_mode = concurrent_normal;
56 const GCCause::Cause default_cause = GCCause::_shenandoah_concurrent_gc;
57 int sleep = ShenandoahControlIntervalMin;
58
59 double last_shrink_time = os::elapsedTime();
60 double last_sleep_adjust_time = os::elapsedTime();
61
62 // Shrink period avoids constantly polling regions for shrinking.
63 // Having a period 10x lower than the delay would mean we hit the
64 // shrinking with lag of less than 1/10-th of true delay.
65 // ShenandoahUncommitDelay is in msecs, but shrink_period is in seconds.
66 const double shrink_period = (double)ShenandoahUncommitDelay / 1000 / 10;
67
68 ShenandoahCollectorPolicy* const policy = heap->shenandoah_policy();
69 ShenandoahHeuristics* const heuristics = heap->heuristics();
70 while (!in_graceful_shutdown() && !should_terminate()) {
71 // Figure out if we have pending requests.
72 const bool alloc_failure_pending = _alloc_failure_gc.is_set();
73 const bool is_gc_requested = _gc_requested.is_set();
74 const GCCause::Cause requested_gc_cause = _requested_gc_cause;
75
76 // This control loop iteration has seen this much allocation.
77 const size_t allocs_seen = reset_allocs_seen();
78
79 // Check if we have seen a new target for soft max heap size.
80 const bool soft_max_changed = heap->check_soft_max_changed();
81
82 // Choose which GC mode to run in. The block below should select a single mode.
83 GCMode mode = none;
84 GCCause::Cause cause = GCCause::_last_gc_cause;
85 ShenandoahGC::ShenandoahDegenPoint degen_point = ShenandoahGC::_degenerated_unset;
86
87 if (alloc_failure_pending) {
88 // Allocation failure takes precedence: we have to deal with it first thing
89 log_info(gc)("Trigger: Handle Allocation Failure");
90
91 cause = GCCause::_allocation_failure;
92
93 // Consume the degen point, and seed it with default value
94 degen_point = _degen_point;
95 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
96
97 if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle()) {
98 heuristics->record_allocation_failure_gc();
99 policy->record_alloc_failure_to_degenerated(degen_point);
100 mode = stw_degenerated;
101 } else {
102 heuristics->record_allocation_failure_gc();
103 policy->record_alloc_failure_to_full();
104 mode = stw_full;
105 }
106 } else if (is_gc_requested) {
107 cause = requested_gc_cause;
108 log_info(gc)("Trigger: GC request (%s)", GCCause::to_string(cause));
109 heuristics->record_requested_gc();
110
111 if (ShenandoahCollectorPolicy::should_run_full_gc(cause)) {
112 mode = stw_full;
113 } else {
114 mode = default_mode;
115 // Unload and clean up everything
116 heap->set_unload_classes(heuristics->can_unload_classes());
117 }
118 } else {
119 // Potential normal cycle: ask heuristics if it wants to act
120 if (heuristics->should_start_gc()) {
121 mode = default_mode;
122 cause = default_cause;
123 }
124
125 // Ask policy if this cycle wants to process references or unload classes
126 heap->set_unload_classes(heuristics->should_unload_classes());
127 }
128
129 // Blow all soft references on this cycle, if handling allocation failure,
130 // either implicit or explicit GC request, or we are requested to do so unconditionally.
131 if (alloc_failure_pending || is_gc_requested || ShenandoahAlwaysClearSoftRefs) {
132 heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
133 }
134
135 const bool gc_requested = (mode != none);
136 assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
137
138 if (gc_requested) {
139 // GC is starting, bump the internal ID
140 update_gc_id();
141
142 heap->reset_bytes_allocated_since_gc_start();
143
144 MetaspaceCombinedStats meta_sizes = MetaspaceUtils::get_combined_statistics();
145
146 // If GC was requested, we are sampling the counters even without actual triggers
147 // from allocation machinery. This captures GC phases more accurately.
148 heap->set_forced_counters_update(true);
149
150 // If GC was requested, we better dump freeset data for performance debugging
151 heap->free_set()->log_status_under_lock();
152
153 switch (mode) {
154 case concurrent_normal:
155 service_concurrent_normal_cycle(cause);
156 break;
157 case stw_degenerated:
158 service_stw_degenerated_cycle(cause, degen_point);
159 break;
160 case stw_full:
161 service_stw_full_cycle(cause);
162 break;
163 default:
164 ShouldNotReachHere();
165 }
166
167 // If this was the requested GC cycle, notify waiters about it
168 if (is_gc_requested) {
169 notify_gc_waiters();
170 }
171
172 // If this was the allocation failure GC cycle, notify waiters about it
173 if (alloc_failure_pending) {
174 notify_alloc_failure_waiters();
175 }
176
177 // Report current free set state at the end of cycle, whether
178 // it is a normal completion, or the abort.
179 heap->free_set()->log_status_under_lock();
180
181 // Notify Universe about new heap usage. This has implications for
182 // global soft refs policy, and we better report it every time heap
183 // usage goes down.
184 heap->update_capacity_and_used_at_gc();
185
186 // Signal that we have completed a visit to all live objects.
187 heap->record_whole_heap_examined_timestamp();
188
189 // Disable forced counters update, and update counters one more time
190 // to capture the state at the end of GC session.
191 heap->handle_force_counters_update();
192 heap->set_forced_counters_update(false);
193
194 // Retract forceful part of soft refs policy
195 heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
196
197 // Clear metaspace oom flag, if current cycle unloaded classes
198 if (heap->unload_classes()) {
199 heuristics->clear_metaspace_oom();
200 }
201
202 // Commit worker statistics to cycle data
203 heap->phase_timings()->flush_par_workers_to_cycle();
204 if (ShenandoahPacing) {
205 heap->pacer()->flush_stats_to_cycle();
206 }
207
208 // Print GC stats for current cycle
209 {
210 LogTarget(Info, gc, stats) lt;
211 if (lt.is_enabled()) {
212 ResourceMark rm;
213 LogStream ls(lt);
214 heap->phase_timings()->print_cycle_on(&ls);
215 if (ShenandoahPacing) {
216 heap->pacer()->print_cycle_on(&ls);
217 }
218 }
219 }
220
221 // Commit statistics to globals
222 heap->phase_timings()->flush_cycle_to_global();
223
224 // Print Metaspace change following GC (if logging is enabled).
225 MetaspaceUtils::print_metaspace_change(meta_sizes);
226
227 // GC is over, we are at idle now
228 if (ShenandoahPacing) {
229 heap->pacer()->setup_for_idle();
230 }
231 } else {
232 // Report to pacer that we have seen this many words allocated
233 if (ShenandoahPacing && (allocs_seen > 0)) {
234 heap->pacer()->report_alloc(allocs_seen);
235 }
236 }
237
238 const double current = os::elapsedTime();
239
240 if (ShenandoahUncommit && (is_gc_requested || soft_max_changed || (current - last_shrink_time > shrink_period))) {
241 // Explicit GC tries to uncommit everything down to min capacity.
242 // Soft max change tries to uncommit everything down to target capacity.
243 // Periodic uncommit tries to uncommit suitable regions down to min capacity.
244
245 double shrink_before = (is_gc_requested || soft_max_changed) ?
246 current :
247 current - (ShenandoahUncommitDelay / 1000.0);
248
249 size_t shrink_until = soft_max_changed ?
250 heap->soft_max_capacity() :
251 heap->min_capacity();
252
253 heap->maybe_uncommit(shrink_before, shrink_until);
254 heap->phase_timings()->flush_cycle_to_global();
255 last_shrink_time = current;
256 }
257
258 // Wait before performing the next action. If allocation happened during this wait,
259 // we exit sooner, to let heuristics re-evaluate new conditions. If we are at idle,
260 // back off exponentially.
261 if (heap->has_changed()) {
262 sleep = ShenandoahControlIntervalMin;
263 } else if ((current - last_sleep_adjust_time) * 1000 > ShenandoahControlIntervalAdjustPeriod){
264 sleep = MIN2<int>(ShenandoahControlIntervalMax, MAX2(1, sleep * 2));
265 last_sleep_adjust_time = current;
266 }
267 os::naked_short_sleep(sleep);
268 }
269
270 // Wait for the actual stop(), can't leave run_service() earlier.
271 while (!should_terminate()) {
272 os::naked_short_sleep(ShenandoahControlIntervalMin);
273 }
274 }
275
276 void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cause) {
277 // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
278 // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
279 // If second allocation failure happens during Degenerated GC cycle (for example, when GC
280 // tries to evac something and no memory is available), cycle degrades to Full GC.
281 //
282 // There are also a shortcut through the normal cycle: immediate garbage shortcut, when
283 // heuristics says there are no regions to compact, and all the collection comes from immediately
284 // reclaimable regions.
285 //
286 // ................................................................................................
287 //
288 // (immediate garbage shortcut) Concurrent GC
289 // /-------------------------------------------\
290 // | |
291 // | |
292 // | |
293 // | v
294 // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
295 // | | | ^
296 // | (af) | (af) | (af) |
297 // ..................|....................|.................|..............|.......................
298 // | | | |
299 // | | | | Degenerated GC
300 // v v v |
301 // STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
302 // | | | ^
303 // | (af) | (af) | (af) |
304 // ..................|....................|.................|..............|.......................
305 // | | | |
306 // | v | | Full GC
307 // \------------------->o<----------------/ |
308 // | |
309 // v |
310 // Full GC --------------------------/
311 //
312 ShenandoahHeap* heap = ShenandoahHeap::heap();
313 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) return;
314
315 GCIdMark gc_id_mark;
316 ShenandoahGCSession session(cause, heap->global_generation());
317
318 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
319
320 ShenandoahConcurrentGC gc(heap->global_generation(), false);
321 if (gc.collect(cause)) {
322 // Cycle is complete. There were no failed allocation requests and no degeneration, so count this as good progress.
323 heap->notify_gc_progress();
324 heap->global_generation()->heuristics()->record_success_concurrent();
325 heap->shenandoah_policy()->record_success_concurrent(false, gc.abbreviated());
326 heap->log_heap_status("At end of GC");
327 } else {
328 assert(heap->cancelled_gc(), "Must have been cancelled");
329 check_cancellation_or_degen(gc.degen_point());
330 heap->log_heap_status("At end of cancelled GC");
331 }
332 }
333
334 bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
335 ShenandoahHeap* heap = ShenandoahHeap::heap();
336 if (heap->cancelled_gc()) {
337 assert (is_alloc_failure_gc() || in_graceful_shutdown(), "Cancel GC either for alloc failure GC, or gracefully exiting");
338 if (!in_graceful_shutdown()) {
339 assert (_degen_point == ShenandoahGC::_degenerated_outside_cycle,
340 "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
341 _degen_point = point;
342 }
343 return true;
344 }
345 return false;
346 }
347
348 void ShenandoahControlThread::stop_service() {
349 // Nothing to do here.
350 }
351
352 void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
353 ShenandoahHeap* const heap = ShenandoahHeap::heap();
354 GCIdMark gc_id_mark;
355 ShenandoahGCSession session(cause, heap->global_generation());
356
357 ShenandoahFullGC gc;
358 gc.collect(cause);
359 }
360
361 void ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point) {
362 assert (point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
363 ShenandoahHeap* const heap = ShenandoahHeap::heap();
364 GCIdMark gc_id_mark;
365 ShenandoahGCSession session(cause, heap->global_generation());
366
367 ShenandoahDegenGC gc(point, heap->global_generation());
368 gc.collect(cause);
369 }
370
371 void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
372 if (ShenandoahCollectorPolicy::should_handle_requested_gc(cause)) {
373 handle_requested_gc(cause);
374 }
375 }
376
377 void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
378 // For normal requested GCs (System.gc) we want to block the caller. However,
379 // for whitebox requested GC, we want to initiate the GC and return immediately.
380 // The whitebox caller thread will arrange for itself to wait until the GC notifies
381 // it that has reached the requested breakpoint (phase in the GC).
382 if (cause == GCCause::_wb_breakpoint) {
383 _requested_gc_cause = cause;
384 _gc_requested.set();
385 return;
386 }
387
388 // Make sure we have at least one complete GC cycle before unblocking
389 // from the explicit GC request.
390 //
391 // This is especially important for weak references cleanup and/or native
392 // resources (e.g. DirectByteBuffers) machinery: when explicit GC request
393 // comes very late in the already running cycle, it would miss lots of new
394 // opportunities for cleanup that were made available before the caller
395 // requested the GC.
396
397 MonitorLocker ml(&_gc_waiters_lock);
398 size_t current_gc_id = get_gc_id();
399 size_t required_gc_id = current_gc_id + 1;
400 while (current_gc_id < required_gc_id) {
401 // Although setting gc request is under _gc_waiters_lock, but read side (run_service())
402 // does not take the lock. We need to enforce following order, so that read side sees
403 // latest requested gc cause when the flag is set.
404 _requested_gc_cause = cause;
405 _gc_requested.set();
406
407 ml.wait();
408 current_gc_id = get_gc_id();
409 }
410 }
411
412 void ShenandoahControlThread::notify_gc_waiters() {
413 _gc_requested.unset();
414 MonitorLocker ml(&_gc_waiters_lock);
415 ml.notify_all();
416 }