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