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 "logging/log.hpp"
35 #include "memory/resourceArea.hpp"
36 #include "runtime/vmThread.hpp"
37
38 // ======= Concurrent Mark Thread ========
39
40 // The CM thread is created when the G1 garbage collector is used
41
42 SurrogateLockerThread*
43 ConcurrentMarkThread::_slt = NULL;
44
45 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* cm) :
46 ConcurrentGCThread(),
47 _cm(cm),
48 _state(Idle),
49 _vtime_accum(0.0),
50 _vtime_mark_accum(0.0) {
51
52 set_name("G1 Main Marker");
53 create_and_start();
54 }
55
56 class CMCheckpointRootsFinalClosure: public VoidClosure {
57
58 ConcurrentMark* _cm;
59 public:
60
61 CMCheckpointRootsFinalClosure(ConcurrentMark* cm) :
62 _cm(cm) {}
63
64 void do_void(){
65 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
66 }
67 };
68
69 class CMCleanUp: public VoidClosure {
70 ConcurrentMark* _cm;
71 public:
72
73 CMCleanUp(ConcurrentMark* cm) :
74 _cm(cm) {}
75
76 void do_void(){
77 _cm->cleanup();
78 }
79 };
80
81 // Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU.
82 void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) {
83 if (g1_policy->adaptive_young_list_length()) {
84 double now = os::elapsedTime();
85 double prediction_ms = remark ? g1_policy->predict_remark_time_ms()
86 : g1_policy->predict_cleanup_time_ms();
87 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
88 jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms);
89 os::sleep(this, sleep_time_ms, false);
90 }
91 }
92 void ConcurrentMarkThread::run() {
93 initialize_in_thread();
94 wait_for_universe_init();
95
96 run_service();
97
98 terminate();
99 }
100
101 void ConcurrentMarkThread::run_service() {
102 _vtime_start = os::elapsedVTime();
103
104 G1CollectedHeap* g1h = G1CollectedHeap::heap();
105 G1CollectorPolicy* g1_policy = g1h->g1_policy();
106
107 while (!_should_terminate) {
108 // wait until started is set.
109 sleepBeforeNextCycle();
110 if (_should_terminate) {
111 break;
112 }
113
114 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC.");
115 {
116 ResourceMark rm;
117 HandleMark hm;
118 double cycle_start = os::elapsedVTime();
119
120 // We have to ensure that we finish scanning the root regions
121 // before the next GC takes place. To ensure this we have to
122 // make sure that we do not join the STS until the root regions
123 // have been scanned. If we did then it's possible that a
124 // subsequent GC could block us from joining the STS and proceed
125 // without the root regions have been scanned which would be a
126 // correctness issue.
127
128 if (!cm()->has_aborted()) {
129 _cm->scanRootRegions();
130 }
131
132 double mark_start_sec = os::elapsedTime();
133 log_info(gc)("GC concurrent-mark-start");
134
135 int iter = 0;
136 do {
137 iter++;
138 if (!cm()->has_aborted()) {
139 _cm->markFromRoots();
140 }
141
142 double mark_end_time = os::elapsedVTime();
143 double mark_end_sec = os::elapsedTime();
144 _vtime_mark_accum += (mark_end_time - cycle_start);
145 if (!cm()->has_aborted()) {
146 delay_to_keep_mmu(g1_policy, true /* remark */);
147
148 log_info(gc)("GC concurrent-mark-end, %1.7lf secs", mark_end_sec - mark_start_sec);
149
150 CMCheckpointRootsFinalClosure final_cl(_cm);
151 VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
152 VMThread::execute(&op);
153 }
154 if (cm()->restart_for_overflow()) {
155 log_debug(gc)("Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
156 log_info(gc)("GC concurrent-mark-restart-for-overflow");
157 }
158 } while (cm()->restart_for_overflow());
159
160 double end_time = os::elapsedVTime();
161 // Update the total virtual time before doing this, since it will try
162 // to measure it to get the vtime for this marking. We purposely
163 // neglect the presumably-short "completeCleanup" phase here.
164 _vtime_accum = (end_time - _vtime_start);
165
166 if (!cm()->has_aborted()) {
167 delay_to_keep_mmu(g1_policy, false /* cleanup */);
168
169 CMCleanUp cl_cl(_cm);
170 VM_CGC_Operation op(&cl_cl, "GC cleanup", false /* needs_pll */);
171 VMThread::execute(&op);
172 } else {
173 // We don't want to update the marking status if a GC pause
174 // is already underway.
175 SuspendibleThreadSetJoiner sts_join;
176 g1h->collector_state()->set_mark_in_progress(false);
177 }
178
179 // Check if cleanup set the free_regions_coming flag. If it
180 // hasn't, we can just skip the next step.
181 if (g1h->free_regions_coming()) {
182 // The following will finish freeing up any regions that we
183 // found to be empty during cleanup. We'll do this part
184 // without joining the suspendible set. If an evacuation pause
185 // takes place, then we would carry on freeing regions in
186 // case they are needed by the pause. If a Full GC takes
187 // place, it would wait for us to process the regions
188 // reclaimed by cleanup.
189
190 double cleanup_start_sec = os::elapsedTime();
191 log_info(gc)("GC concurrent-cleanup-start");
192
193 // Now do the concurrent cleanup operation.
194 _cm->completeCleanup();
195
196 // Notify anyone who's waiting that there are no more free
197 // regions coming. We have to do this before we join the STS
198 // (in fact, we should not attempt to join the STS in the
199 // interval between finishing the cleanup pause and clearing
200 // the free_regions_coming flag) otherwise we might deadlock:
201 // a GC worker could be blocked waiting for the notification
202 // whereas this thread will be blocked for the pause to finish
203 // while it's trying to join the STS, which is conditional on
204 // the GC workers finishing.
205 g1h->reset_free_regions_coming();
206
207 double cleanup_end_sec = os::elapsedTime();
208 log_info(gc)("GC concurrent-cleanup-end, %1.7lf secs", cleanup_end_sec - cleanup_start_sec);
209 }
210 guarantee(cm()->cleanup_list_is_empty(),
211 "at this point there should be no regions on the cleanup list");
212
213 // There is a tricky race before recording that the concurrent
214 // cleanup has completed and a potential Full GC starting around
215 // the same time. We want to make sure that the Full GC calls
216 // abort() on concurrent mark after
217 // record_concurrent_mark_cleanup_completed(), since abort() is
218 // the method that will reset the concurrent mark state. If we
219 // end up calling record_concurrent_mark_cleanup_completed()
220 // after abort() then we might incorrectly undo some of the work
221 // abort() did. Checking the has_aborted() flag after joining
222 // the STS allows the correct ordering of the two methods. There
223 // are two scenarios:
224 //
225 // a) If we reach here before the Full GC, the fact that we have
226 // joined the STS means that the Full GC cannot start until we
227 // leave the STS, so record_concurrent_mark_cleanup_completed()
228 // will complete before abort() is called.
229 //
230 // b) If we reach here during the Full GC, we'll be held up from
231 // joining the STS until the Full GC is done, which means that
232 // abort() will have completed and has_aborted() will return
233 // true to prevent us from calling
234 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
235 // not needed any more as the concurrent mark state has been
236 // already reset).
237 {
238 SuspendibleThreadSetJoiner sts_join;
239 if (!cm()->has_aborted()) {
240 g1_policy->record_concurrent_mark_cleanup_completed();
241 } else {
242 log_info(gc)("GC concurrent-mark-abort");
243 }
244 }
245
246 // We now want to allow clearing of the marking bitmap to be
247 // suspended by a collection pause.
248 // We may have aborted just before the remark. Do not bother clearing the
249 // bitmap then, as it has been done during mark abort.
250 if (!cm()->has_aborted()) {
251 _cm->clearNextBitmap();
252 } else {
253 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
254 }
255 }
256
257 // Update the number of full collections that have been
258 // completed. This will also notify the FullGCCount_lock in case a
259 // Java thread is waiting for a full GC to happen (e.g., it
260 // called System.gc() with +ExplicitGCInvokesConcurrent).
261 {
262 SuspendibleThreadSetJoiner sts_join;
263 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
264 g1h->register_concurrent_cycle_end();
265 }
266 }
267 }
268
269 void ConcurrentMarkThread::stop() {
270 {
271 MutexLockerEx ml(Terminator_lock);
272 _should_terminate = true;
273 }
274
275 stop_service();
276
277 {
278 MutexLockerEx ml(Terminator_lock);
279 while (!_has_terminated) {
280 Terminator_lock->wait();
281 }
282 }
283 }
284
285 void ConcurrentMarkThread::stop_service() {
286 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
287 CGC_lock->notify_all();
288 }
289
290 void ConcurrentMarkThread::sleepBeforeNextCycle() {
291 // We join here because we don't want to do the "shouldConcurrentMark()"
292 // below while the world is otherwise stopped.
293 assert(!in_progress(), "should have been cleared");
294
295 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
296 while (!started() && !_should_terminate) {
297 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
298 }
299
300 if (started()) {
301 set_in_progress();
302 }
303 }
304
305 // Note: As is the case with CMS - this method, although exported
306 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
307 // be called by a JavaThread. Currently this is done at vm creation
308 // time (post-vm-init) by the main/Primordial (Java)Thread.
309 // XXX Consider changing this in the future to allow the CM thread
310 // itself to create this thread?
311 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
312 assert(UseG1GC, "SLT thread needed only for concurrent GC");
313 assert(THREAD->is_Java_thread(), "must be a Java thread");
314 assert(_slt == NULL, "SLT already created");
315 _slt = SurrogateLockerThread::make(THREAD);
316 }