1 /*
2 * Copyright (c) 2001, 2015, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "gc/g1/concurrentMarkThread.inline.hpp"
27 #include "gc/g1/g1CollectedHeap.inline.hpp"
28 #include "gc/g1/g1CollectorPolicy.hpp"
29 #include "gc/g1/g1MMUTracker.hpp"
30 #include "gc/g1/suspendibleThreadSet.hpp"
31 #include "gc/g1/vm_operations_g1.hpp"
32 #include "gc/shared/gcId.hpp"
33 #include "gc/shared/gcTrace.hpp"
34 #include "gc/shared/gcTraceTime.inline.hpp"
35 #include "logging/log.hpp"
36 #include "memory/resourceArea.hpp"
37 #include "runtime/vmThread.hpp"
38
39 // ======= Concurrent Mark Thread ========
40
41 // The CM thread is created when the G1 garbage collector is used
42
43 SurrogateLockerThread*
44 ConcurrentMarkThread::_slt = NULL;
45
46 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* cm) :
47 ConcurrentGCThread(),
48 _cm(cm),
49 _state(Idle),
50 _vtime_accum(0.0),
51 _vtime_mark_accum(0.0) {
52
53 set_name("G1 Main Marker");
54 create_and_start();
55 }
56
57 class CMCheckpointRootsFinalClosure: public VoidClosure {
58
59 ConcurrentMark* _cm;
60 public:
61
62 CMCheckpointRootsFinalClosure(ConcurrentMark* cm) :
63 _cm(cm) {}
64
65 void do_void(){
66 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
67 }
68 };
69
70 class CMCleanUp: public VoidClosure {
71 ConcurrentMark* _cm;
72 public:
73
74 CMCleanUp(ConcurrentMark* cm) :
75 _cm(cm) {}
76
77 void do_void(){
78 _cm->cleanup();
79 }
80 };
81
82 // Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU.
83 void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) {
84 if (g1_policy->adaptive_young_list_length()) {
85 double now = os::elapsedTime();
86 double prediction_ms = remark ? g1_policy->predict_remark_time_ms()
87 : g1_policy->predict_cleanup_time_ms();
88 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
89 jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms);
90 os::sleep(this, sleep_time_ms, false);
91 }
92 }
93
94 class GCConcPhaseTimer : StackObj {
95 ConcurrentMark* _cm;
96
97 public:
98 GCConcPhaseTimer(ConcurrentMark* cm, const char* title) : _cm(cm) {
99 _cm->register_concurrent_phase_start(title);
100 }
101
102 ~GCConcPhaseTimer() {
103 _cm->register_concurrent_phase_end();
104 }
105 };
106
107 void ConcurrentMarkThread::run() {
108 initialize_in_thread();
109 wait_for_universe_init();
110
111 run_service();
112
113 terminate();
114 }
115
116 void ConcurrentMarkThread::run_service() {
117 _vtime_start = os::elapsedVTime();
118
119 G1CollectedHeap* g1h = G1CollectedHeap::heap();
120 G1CollectorPolicy* g1_policy = g1h->g1_policy();
121
122 while (!_should_terminate) {
123 // wait until started is set.
124 sleepBeforeNextCycle();
125 if (_should_terminate) {
126 break;
127 }
128
129 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC.");
130 {
131 ResourceMark rm;
132 HandleMark hm;
133 double cycle_start = os::elapsedVTime();
134
135 // We have to ensure that we finish scanning the root regions
136 // before the next GC takes place. To ensure this we have to
137 // make sure that we do not join the STS until the root regions
138 // have been scanned. If we did then it's possible that a
139 // subsequent GC could block us from joining the STS and proceed
140 // without the root regions have been scanned which would be a
141 // correctness issue.
142
143 if (!cm()->has_aborted()) {
144 GCConcPhaseTimer(_cm, "Concurrent Root Region Scanning");
145 _cm->scanRootRegions();
146 }
147
148 // It would be nice to use the GCTraceConcTime class here but
149 // the "end" logging is inside the loop and not at the end of
150 // a scope. Mimicking the same log output as GCTraceConcTime instead.
151 jlong mark_start = os::elapsed_counter();
152 log_info(gc)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start));
153
154 int iter = 0;
155 do {
156 iter++;
157 if (!cm()->has_aborted()) {
158 GCConcPhaseTimer(_cm, "Concurrent Mark");
159 _cm->markFromRoots();
160 }
161
162 double mark_end_time = os::elapsedVTime();
163 jlong mark_end = os::elapsed_counter();
164 _vtime_mark_accum += (mark_end_time - cycle_start);
165 if (!cm()->has_aborted()) {
166 delay_to_keep_mmu(g1_policy, true /* remark */);
167 log_info(gc)("Concurrent Mark (%.3fs, %.3fs) %.3fms",
168 TimeHelper::counter_to_seconds(mark_start),
169 TimeHelper::counter_to_seconds(mark_end),
170 TimeHelper::counter_to_millis(mark_end - mark_start));
171
172 CMCheckpointRootsFinalClosure final_cl(_cm);
173 VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */);
174 VMThread::execute(&op);
175 }
176 if (cm()->restart_for_overflow()) {
177 log_debug(gc)("Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
178 log_info(gc)("Concurrent Mark restart for overflow");
179 }
180 } while (cm()->restart_for_overflow());
181
182 double end_time = os::elapsedVTime();
183 // Update the total virtual time before doing this, since it will try
184 // to measure it to get the vtime for this marking. We purposely
185 // neglect the presumably-short "completeCleanup" phase here.
186 _vtime_accum = (end_time - _vtime_start);
187
188 if (!cm()->has_aborted()) {
189 delay_to_keep_mmu(g1_policy, false /* cleanup */);
190
191 CMCleanUp cl_cl(_cm);
192 VM_CGC_Operation op(&cl_cl, "Pause Cleanup", false /* needs_pll */);
193 VMThread::execute(&op);
194 } else {
195 // We don't want to update the marking status if a GC pause
196 // is already underway.
197 SuspendibleThreadSetJoiner sts_join;
198 g1h->collector_state()->set_mark_in_progress(false);
199 }
200
201 // Check if cleanup set the free_regions_coming flag. If it
202 // hasn't, we can just skip the next step.
203 if (g1h->free_regions_coming()) {
204 // The following will finish freeing up any regions that we
205 // found to be empty during cleanup. We'll do this part
206 // without joining the suspendible set. If an evacuation pause
207 // takes place, then we would carry on freeing regions in
208 // case they are needed by the pause. If a Full GC takes
209 // place, it would wait for us to process the regions
210 // reclaimed by cleanup.
211
212 GCTraceConcTime(Info, gc) tt("Concurrent Cleanup");
213 GCConcPhaseTimer(_cm, "Concurrent Cleanup");
214
215 // Now do the concurrent cleanup operation.
216 _cm->completeCleanup();
217
218 // Notify anyone who's waiting that there are no more free
219 // regions coming. We have to do this before we join the STS
220 // (in fact, we should not attempt to join the STS in the
221 // interval between finishing the cleanup pause and clearing
222 // the free_regions_coming flag) otherwise we might deadlock:
223 // a GC worker could be blocked waiting for the notification
224 // whereas this thread will be blocked for the pause to finish
225 // while it's trying to join the STS, which is conditional on
226 // the GC workers finishing.
227 g1h->reset_free_regions_coming();
228 }
229 guarantee(cm()->cleanup_list_is_empty(),
230 "at this point there should be no regions on the cleanup list");
231
232 // There is a tricky race before recording that the concurrent
233 // cleanup has completed and a potential Full GC starting around
234 // the same time. We want to make sure that the Full GC calls
235 // abort() on concurrent mark after
236 // record_concurrent_mark_cleanup_completed(), since abort() is
237 // the method that will reset the concurrent mark state. If we
238 // end up calling record_concurrent_mark_cleanup_completed()
239 // after abort() then we might incorrectly undo some of the work
240 // abort() did. Checking the has_aborted() flag after joining
241 // the STS allows the correct ordering of the two methods. There
242 // are two scenarios:
243 //
244 // a) If we reach here before the Full GC, the fact that we have
245 // joined the STS means that the Full GC cannot start until we
246 // leave the STS, so record_concurrent_mark_cleanup_completed()
247 // will complete before abort() is called.
248 //
249 // b) If we reach here during the Full GC, we'll be held up from
250 // joining the STS until the Full GC is done, which means that
251 // abort() will have completed and has_aborted() will return
252 // true to prevent us from calling
253 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
254 // not needed any more as the concurrent mark state has been
255 // already reset).
256 {
257 SuspendibleThreadSetJoiner sts_join;
258 if (!cm()->has_aborted()) {
259 g1_policy->record_concurrent_mark_cleanup_completed();
260 } else {
261 log_info(gc)("Concurrent Mark abort");
262 }
263 }
264
265 // We now want to allow clearing of the marking bitmap to be
266 // suspended by a collection pause.
267 // We may have aborted just before the remark. Do not bother clearing the
268 // bitmap then, as it has been done during mark abort.
269 if (!cm()->has_aborted()) {
270 GCConcPhaseTimer(_cm, "Concurrent Bitmap Clearing");
271 _cm->clearNextBitmap();
272 } else {
273 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
274 }
275 }
276
277 // Update the number of full collections that have been
278 // completed. This will also notify the FullGCCount_lock in case a
279 // Java thread is waiting for a full GC to happen (e.g., it
280 // called System.gc() with +ExplicitGCInvokesConcurrent).
281 {
282 SuspendibleThreadSetJoiner sts_join;
283 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
284 g1h->register_concurrent_cycle_end();
285 }
286 }
287 }
288
289 void ConcurrentMarkThread::stop() {
290 {
291 MutexLockerEx ml(Terminator_lock);
292 _should_terminate = true;
293 }
294
295 stop_service();
296
297 {
298 MutexLockerEx ml(Terminator_lock);
299 while (!_has_terminated) {
300 Terminator_lock->wait();
301 }
302 }
303 }
304
305 void ConcurrentMarkThread::stop_service() {
306 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
307 CGC_lock->notify_all();
308 }
309
310 void ConcurrentMarkThread::sleepBeforeNextCycle() {
311 // We join here because we don't want to do the "shouldConcurrentMark()"
312 // below while the world is otherwise stopped.
313 assert(!in_progress(), "should have been cleared");
314
315 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
316 while (!started() && !_should_terminate) {
317 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
318 }
319
320 if (started()) {
321 set_in_progress();
322 }
323 }
324
325 // Note: As is the case with CMS - this method, although exported
326 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
327 // be called by a JavaThread. Currently this is done at vm creation
328 // time (post-vm-init) by the main/Primordial (Java)Thread.
329 // XXX Consider changing this in the future to allow the CM thread
330 // itself to create this thread?
331 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
332 assert(UseG1GC, "SLT thread needed only for concurrent GC");
333 assert(THREAD->is_Java_thread(), "must be a Java thread");
334 assert(_slt == NULL, "SLT already created");
335 _slt = SurrogateLockerThread::make(THREAD);
336 }