1 /*
2 * Copyright (c) 2013, 2021, Red Hat, Inc. All rights reserved.
3 * Copyright (C) 2022, Tencent. 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 "gc/shenandoah/heuristics/shenandoahHeuristics.hpp"
27 #include "gc/shenandoah/mode/shenandoahMode.hpp"
28 #include "gc/shenandoah/shenandoahCollectorPolicy.hpp"
29 #include "gc/shenandoah/shenandoahConcurrentGC.hpp"
30 #include "gc/shenandoah/shenandoahControlThread.hpp"
31 #include "gc/shenandoah/shenandoahDegeneratedGC.hpp"
32 #include "gc/shenandoah/shenandoahFreeSet.hpp"
33 #include "gc/shenandoah/shenandoahFullGC.hpp"
34 #include "gc/shenandoah/shenandoahGeneration.hpp"
35 #include "gc/shenandoah/shenandoahHeap.inline.hpp"
36 #include "gc/shenandoah/shenandoahMonitoringSupport.hpp"
37 #include "gc/shenandoah/shenandoahPacer.inline.hpp"
38 #include "gc/shenandoah/shenandoahUtils.hpp"
39 #include "logging/log.hpp"
40 #include "memory/metaspaceStats.hpp"
41 #include "memory/metaspaceUtils.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 const GCMode default_mode = concurrent_normal;
54 const GCCause::Cause default_cause = GCCause::_shenandoah_concurrent_gc;
55 int sleep = ShenandoahControlIntervalMin;
56
57 double last_sleep_adjust_time = os::elapsedTime();
58
59 ShenandoahCollectorPolicy* const policy = heap->shenandoah_policy();
60 ShenandoahHeuristics* const heuristics = heap->heuristics();
61 while (!should_terminate()) {
62 const GCCause::Cause cancelled_cause = heap->cancelled_cause();
63 if (cancelled_cause == GCCause::_shenandoah_stop_vm) {
64 break;
65 }
66
67 // Figure out if we have pending requests.
68 const bool alloc_failure_pending = ShenandoahCollectorPolicy::is_allocation_failure(cancelled_cause);
69 const bool is_gc_requested = _gc_requested.is_set();
70 const GCCause::Cause requested_gc_cause = _requested_gc_cause;
71
72 // This control loop iteration has seen this much allocation.
73 const size_t allocs_seen = reset_allocs_seen();
74
75 // Choose which GC mode to run in. The block below should select a single mode.
76 GCMode mode = none;
77 GCCause::Cause cause = GCCause::_last_gc_cause;
78 ShenandoahGC::ShenandoahDegenPoint degen_point = ShenandoahGC::_degenerated_unset;
79
80 if (alloc_failure_pending) {
81 // Allocation failure takes precedence: we have to deal with it first thing
82 heuristics->log_trigger("Handle Allocation Failure");
83
84 cause = GCCause::_allocation_failure;
85
86 // Consume the degen point, and seed it with default value
87 degen_point = _degen_point;
88 _degen_point = ShenandoahGC::_degenerated_outside_cycle;
89
90 if (ShenandoahDegeneratedGC && heuristics->should_degenerate_cycle()) {
91 heuristics->record_allocation_failure_gc();
92 policy->record_alloc_failure_to_degenerated(degen_point);
93 mode = stw_degenerated;
94 } else {
95 heuristics->record_allocation_failure_gc();
96 policy->record_alloc_failure_to_full();
97 mode = stw_full;
98 }
99 } else if (is_gc_requested) {
100 cause = requested_gc_cause;
101 heuristics->log_trigger("GC request (%s)", GCCause::to_string(cause));
102 heuristics->record_requested_gc();
103
104 if (ShenandoahCollectorPolicy::should_run_full_gc(cause)) {
105 mode = stw_full;
106 } else {
107 mode = default_mode;
108 // Unload and clean up everything
109 heap->set_unload_classes(heuristics->can_unload_classes());
110 }
111 } else {
112 // Potential normal cycle: ask heuristics if it wants to act
113 if (heuristics->should_start_gc()) {
114 mode = default_mode;
115 cause = default_cause;
116 }
117
118 // Ask policy if this cycle wants to process references or unload classes
119 heap->set_unload_classes(heuristics->should_unload_classes());
120 }
121
122 // Blow all soft references on this cycle, if handling allocation failure,
123 // either implicit or explicit GC request, or we are requested to do so unconditionally.
124 if (alloc_failure_pending || is_gc_requested || ShenandoahAlwaysClearSoftRefs) {
125 heap->soft_ref_policy()->set_should_clear_all_soft_refs(true);
126 }
127
128 const bool gc_requested = (mode != none);
129 assert (!gc_requested || cause != GCCause::_last_gc_cause, "GC cause should be set");
130
131 if (gc_requested) {
132 // Cannot uncommit bitmap slices during concurrent reset
133 ShenandoahNoUncommitMark forbid_region_uncommit(heap);
134
135 // GC is starting, bump the internal ID
136 update_gc_id();
137
138 GCIdMark gc_id_mark;
139
140 heuristics->cancel_trigger_request();
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 cycle completed without being cancelled, notify waiters about it
173 if (!heap->cancelled_gc()) {
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 {
182 // Notify Universe about new heap usage. This has implications for
183 // global soft refs policy, and we better report it every time heap
184 // usage goes down.
185 ShenandoahHeapLocker locker(heap->lock());
186 heap->update_capacity_and_used_at_gc();
187 }
188
189 // Signal that we have completed a visit to all live objects.
190 heap->record_whole_heap_examined_timestamp();
191
192 // Disable forced counters update, and update counters one more time
193 // to capture the state at the end of GC session.
194 heap->handle_force_counters_update();
195 heap->set_forced_counters_update(false);
196
197 // Retract forceful part of soft refs policy
198 heap->soft_ref_policy()->set_should_clear_all_soft_refs(false);
199
200 // Clear metaspace oom flag, if current cycle unloaded classes
201 if (heap->unload_classes()) {
202 heuristics->clear_metaspace_oom();
203 }
204
205 // Commit worker statistics to cycle data
206 heap->phase_timings()->flush_par_workers_to_cycle();
207 if (ShenandoahPacing) {
208 heap->pacer()->flush_stats_to_cycle();
209 }
210
211 // Print GC stats for current cycle
212 {
213 LogTarget(Info, gc, stats) lt;
214 if (lt.is_enabled()) {
215 ResourceMark rm;
216 LogStream ls(lt);
217 heap->phase_timings()->print_cycle_on(&ls);
218 if (ShenandoahPacing) {
219 heap->pacer()->print_cycle_on(&ls);
220 }
221 }
222 }
223
224 // Commit statistics to globals
225 heap->phase_timings()->flush_cycle_to_global();
226
227 // Print Metaspace change following GC (if logging is enabled).
228 MetaspaceUtils::print_metaspace_change(meta_sizes);
229
230 // GC is over, we are at idle now
231 if (ShenandoahPacing) {
232 heap->pacer()->setup_for_idle();
233 }
234 } else {
235 // Report to pacer that we have seen this many words allocated
236 if (ShenandoahPacing && (allocs_seen > 0)) {
237 heap->pacer()->report_alloc(allocs_seen);
238 }
239 }
240
241 // Check if we have seen a new target for soft max heap size or if a gc was requested.
242 // Either of these conditions will attempt to uncommit regions.
243 if (ShenandoahUncommit) {
244 if (heap->check_soft_max_changed()) {
245 heap->notify_soft_max_changed();
246 } else if (is_gc_requested) {
247 heap->notify_explicit_gc_requested();
248 }
249 }
250
251 // Wait before performing the next action. If allocation happened during this wait,
252 // we exit sooner, to let heuristics re-evaluate new conditions. If we are at idle,
253 // back off exponentially.
254 const double current = os::elapsedTime();
255 if (heap->has_changed()) {
256 sleep = ShenandoahControlIntervalMin;
257 } else if ((current - last_sleep_adjust_time) * 1000 > ShenandoahControlIntervalAdjustPeriod){
258 sleep = MIN2<int>(ShenandoahControlIntervalMax, MAX2(1, sleep * 2));
259 last_sleep_adjust_time = current;
260 }
261 os::naked_short_sleep(sleep);
262 }
263 }
264
265 void ShenandoahControlThread::service_concurrent_normal_cycle(GCCause::Cause cause) {
266 // Normal cycle goes via all concurrent phases. If allocation failure (af) happens during
267 // any of the concurrent phases, it first degrades to Degenerated GC and completes GC there.
268 // If second allocation failure happens during Degenerated GC cycle (for example, when GC
269 // tries to evac something and no memory is available), cycle degrades to Full GC.
270 //
271 // There are also a shortcut through the normal cycle: immediate garbage shortcut, when
272 // heuristics says there are no regions to compact, and all the collection comes from immediately
273 // reclaimable regions.
274 //
275 // ................................................................................................
276 //
277 // (immediate garbage shortcut) Concurrent GC
278 // /-------------------------------------------\
279 // | |
280 // | |
281 // | |
282 // | v
283 // [START] ----> Conc Mark ----o----> Conc Evac --o--> Conc Update-Refs ---o----> [END]
284 // | | | ^
285 // | (af) | (af) | (af) |
286 // ..................|....................|.................|..............|.......................
287 // | | | |
288 // | | | | Degenerated GC
289 // v v v |
290 // STW Mark ----------> STW Evac ----> STW Update-Refs ----->o
291 // | | | ^
292 // | (af) | (af) | (af) |
293 // ..................|....................|.................|..............|.......................
294 // | | | |
295 // | v | | Full GC
296 // \------------------->o<----------------/ |
297 // | |
298 // v |
299 // Full GC --------------------------/
300 //
301 ShenandoahHeap* heap = ShenandoahHeap::heap();
302 if (check_cancellation_or_degen(ShenandoahGC::_degenerated_outside_cycle)) {
303 log_info(gc)("Cancelled");
304 return;
305 }
306
307 ShenandoahGCSession session(cause, heap->global_generation());
308
309 TraceCollectorStats tcs(heap->monitoring_support()->concurrent_collection_counters());
310
311 ShenandoahConcurrentGC gc(heap->global_generation(), false);
312 if (gc.collect(cause)) {
313 // Cycle is complete. There were no failed allocation requests and no degeneration, so count this as good progress.
314 heap->notify_gc_progress();
315 heap->global_generation()->heuristics()->record_success_concurrent();
316 heap->shenandoah_policy()->record_success_concurrent(false, gc.abbreviated());
317 heap->log_heap_status("At end of GC");
318 } else {
319 assert(heap->cancelled_gc(), "Must have been cancelled");
320 check_cancellation_or_degen(gc.degen_point());
321 heap->log_heap_status("At end of cancelled GC");
322 }
323 }
324
325 bool ShenandoahControlThread::check_cancellation_or_degen(ShenandoahGC::ShenandoahDegenPoint point) {
326 ShenandoahHeap* heap = ShenandoahHeap::heap();
327 if (heap->cancelled_gc()) {
328 if (heap->cancelled_cause() == GCCause::_shenandoah_stop_vm) {
329 return true;
330 }
331
332 if (ShenandoahCollectorPolicy::is_allocation_failure(heap->cancelled_cause())) {
333 assert (_degen_point == ShenandoahGC::_degenerated_outside_cycle,
334 "Should not be set yet: %s", ShenandoahGC::degen_point_to_string(_degen_point));
335 _degen_point = point;
336 return true;
337 }
338
339 fatal("Unexpected reason for cancellation: %s", GCCause::to_string(heap->cancelled_cause()));
340 }
341 return false;
342 }
343
344 void ShenandoahControlThread::stop_service() {
345 ShenandoahHeap::heap()->cancel_gc(GCCause::_shenandoah_stop_vm);
346 }
347
348 void ShenandoahControlThread::service_stw_full_cycle(GCCause::Cause cause) {
349 ShenandoahHeap* const heap = ShenandoahHeap::heap();
350 ShenandoahGCSession session(cause, heap->global_generation());
351
352 ShenandoahFullGC gc;
353 gc.collect(cause);
354 }
355
356 void ShenandoahControlThread::service_stw_degenerated_cycle(GCCause::Cause cause, ShenandoahGC::ShenandoahDegenPoint point) {
357 assert (point != ShenandoahGC::_degenerated_unset, "Degenerated point should be set");
358 ShenandoahHeap* const heap = ShenandoahHeap::heap();
359 ShenandoahGCSession session(cause, heap->global_generation());
360
361 ShenandoahDegenGC gc(point, heap->global_generation());
362 gc.collect(cause);
363 }
364
365 void ShenandoahControlThread::request_gc(GCCause::Cause cause) {
366 if (ShenandoahCollectorPolicy::should_handle_requested_gc(cause)) {
367 handle_requested_gc(cause);
368 }
369 }
370
371 void ShenandoahControlThread::handle_requested_gc(GCCause::Cause cause) {
372 if (should_terminate()) {
373 log_info(gc)("Control thread is terminating, no more GCs");
374 return;
375 }
376
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 && !should_terminate()) {
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 }