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