1 /*
2 * Copyright (c) 2001, 2016, 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(G1ConcurrentMark* 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 G1ConcurrentMark* _cm;
60 public:
61
62 CMCheckpointRootsFinalClosure(G1ConcurrentMark* 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 G1ConcurrentMark* _cm;
72 public:
73
74 CMCleanUp(G1ConcurrentMark* 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 G1ConcurrentMark* _cm;
96
97 public:
98 GCConcPhaseTimer(G1ConcurrentMark* 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 _cm->root_regions()->cancel_scan();
127 break;
128 }
129
130 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC.");
131 {
132 ResourceMark rm;
133 HandleMark hm;
134 double cycle_start = os::elapsedVTime();
135
136 // We have to ensure that we finish scanning the root regions
137 // before the next GC takes place. To ensure this we have to
138 // make sure that we do not join the STS until the root regions
139 // have been scanned. If we did then it's possible that a
140 // subsequent GC could block us from joining the STS and proceed
141 // without the root regions have been scanned which would be a
142 // correctness issue.
143
144 if (_cm->root_regions()->scan_in_progress()) {
145 assert(!cm()->has_aborted(), "Aborting before root region scanning is finished not supported.");
146 GCConcPhaseTimer(_cm, "Concurrent Root Region Scanning");
147 _cm->scanRootRegions();
148 }
149
150 // It would be nice to use the GCTraceConcTime class here but
151 // the "end" logging is inside the loop and not at the end of
152 // a scope. Mimicking the same log output as GCTraceConcTime instead.
153 jlong mark_start = os::elapsed_counter();
154 log_info(gc)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start));
155
156 int iter = 0;
157 do {
158 iter++;
159 if (!cm()->has_aborted()) {
160 GCConcPhaseTimer(_cm, "Concurrent Mark");
161 _cm->markFromRoots();
162 }
163
164 double mark_end_time = os::elapsedVTime();
165 jlong mark_end = os::elapsed_counter();
166 _vtime_mark_accum += (mark_end_time - cycle_start);
167 if (!cm()->has_aborted()) {
168 delay_to_keep_mmu(g1_policy, true /* remark */);
169 log_info(gc)("Concurrent Mark (%.3fs, %.3fs) %.3fms",
170 TimeHelper::counter_to_seconds(mark_start),
171 TimeHelper::counter_to_seconds(mark_end),
172 TimeHelper::counter_to_millis(mark_end - mark_start));
173
174 CMCheckpointRootsFinalClosure final_cl(_cm);
175 VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */);
176 VMThread::execute(&op);
177 }
178 if (cm()->restart_for_overflow()) {
179 log_debug(gc)("Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
180 log_info(gc)("Concurrent Mark restart for overflow");
181 }
182 } while (cm()->restart_for_overflow());
183
184 double end_time = os::elapsedVTime();
185 // Update the total virtual time before doing this, since it will try
186 // to measure it to get the vtime for this marking. We purposely
187 // neglect the presumably-short "completeCleanup" phase here.
188 _vtime_accum = (end_time - _vtime_start);
189
190 if (!cm()->has_aborted()) {
191 delay_to_keep_mmu(g1_policy, false /* cleanup */);
192
193 CMCleanUp cl_cl(_cm);
194 VM_CGC_Operation op(&cl_cl, "Pause Cleanup", false /* needs_pll */);
195 VMThread::execute(&op);
196 } else {
197 // We don't want to update the marking status if a GC pause
198 // is already underway.
199 SuspendibleThreadSetJoiner sts_join;
200 g1h->collector_state()->set_mark_in_progress(false);
201 }
202
203 // Check if cleanup set the free_regions_coming flag. If it
204 // hasn't, we can just skip the next step.
205 if (g1h->free_regions_coming()) {
206 // The following will finish freeing up any regions that we
207 // found to be empty during cleanup. We'll do this part
208 // without joining the suspendible set. If an evacuation pause
209 // takes place, then we would carry on freeing regions in
210 // case they are needed by the pause. If a Full GC takes
211 // place, it would wait for us to process the regions
212 // reclaimed by cleanup.
213
214 GCTraceConcTime(Info, gc) tt("Concurrent Cleanup");
215 GCConcPhaseTimer(_cm, "Concurrent Cleanup");
216
217 // Now do the concurrent cleanup operation.
218 _cm->completeCleanup();
219
220 // Notify anyone who's waiting that there are no more free
221 // regions coming. We have to do this before we join the STS
222 // (in fact, we should not attempt to join the STS in the
223 // interval between finishing the cleanup pause and clearing
224 // the free_regions_coming flag) otherwise we might deadlock:
225 // a GC worker could be blocked waiting for the notification
226 // whereas this thread will be blocked for the pause to finish
227 // while it's trying to join the STS, which is conditional on
228 // the GC workers finishing.
229 g1h->reset_free_regions_coming();
230 }
231 guarantee(cm()->cleanup_list_is_empty(),
232 "at this point there should be no regions on the cleanup list");
233
234 // There is a tricky race before recording that the concurrent
235 // cleanup has completed and a potential Full GC starting around
236 // the same time. We want to make sure that the Full GC calls
237 // abort() on concurrent mark after
238 // record_concurrent_mark_cleanup_completed(), since abort() is
239 // the method that will reset the concurrent mark state. If we
240 // end up calling record_concurrent_mark_cleanup_completed()
241 // after abort() then we might incorrectly undo some of the work
242 // abort() did. Checking the has_aborted() flag after joining
243 // the STS allows the correct ordering of the two methods. There
244 // are two scenarios:
245 //
246 // a) If we reach here before the Full GC, the fact that we have
247 // joined the STS means that the Full GC cannot start until we
248 // leave the STS, so record_concurrent_mark_cleanup_completed()
249 // will complete before abort() is called.
250 //
251 // b) If we reach here during the Full GC, we'll be held up from
252 // joining the STS until the Full GC is done, which means that
253 // abort() will have completed and has_aborted() will return
254 // true to prevent us from calling
255 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
256 // not needed any more as the concurrent mark state has been
257 // already reset).
258 {
259 SuspendibleThreadSetJoiner sts_join;
260 if (!cm()->has_aborted()) {
261 g1_policy->record_concurrent_mark_cleanup_completed();
262 } else {
263 log_info(gc)("Concurrent Mark abort");
264 }
265 }
266
267 // We now want to allow clearing of the marking bitmap to be
268 // suspended by a collection pause.
269 // We may have aborted just before the remark. Do not bother clearing the
270 // bitmap then, as it has been done during mark abort.
271 if (!cm()->has_aborted()) {
272 GCConcPhaseTimer(_cm, "Concurrent Bitmap Clearing");
273 _cm->clearNextBitmap();
274 } else {
275 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
276 }
277 }
278
279 // Update the number of full collections that have been
280 // completed. This will also notify the FullGCCount_lock in case a
281 // Java thread is waiting for a full GC to happen (e.g., it
282 // called System.gc() with +ExplicitGCInvokesConcurrent).
283 {
284 SuspendibleThreadSetJoiner sts_join;
285 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
286 g1h->register_concurrent_cycle_end();
287 }
288 }
289 }
290
291 void ConcurrentMarkThread::stop() {
292 {
293 MutexLockerEx ml(Terminator_lock);
294 _should_terminate = true;
295 }
296
297 stop_service();
298
299 {
300 MutexLockerEx ml(Terminator_lock);
301 while (!_has_terminated) {
302 Terminator_lock->wait();
303 }
304 }
305 }
306
307 void ConcurrentMarkThread::stop_service() {
308 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
309 CGC_lock->notify_all();
310 }
311
312 void ConcurrentMarkThread::sleepBeforeNextCycle() {
313 // We join here because we don't want to do the "shouldConcurrentMark()"
314 // below while the world is otherwise stopped.
315 assert(!in_progress(), "should have been cleared");
316
317 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
318 while (!started() && !_should_terminate) {
319 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
320 }
321
322 if (started()) {
323 set_in_progress();
324 }
325 }
326
327 // Note: As is the case with CMS - this method, although exported
328 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
329 // be called by a JavaThread. Currently this is done at vm creation
330 // time (post-vm-init) by the main/Primordial (Java)Thread.
331 // XXX Consider changing this in the future to allow the CM thread
332 // itself to create this thread?
333 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
334 assert(UseG1GC, "SLT thread needed only for concurrent GC");
335 assert(THREAD->is_Java_thread(), "must be a Java thread");
336 assert(_slt == NULL, "SLT already created");
337 _slt = SurrogateLockerThread::make(THREAD);
338 }