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 "classfile/classLoaderData.hpp"
27 #include "gc/g1/concurrentMarkThread.inline.hpp"
28 #include "gc/g1/g1Analytics.hpp"
29 #include "gc/g1/g1CollectedHeap.inline.hpp"
30 #include "gc/g1/g1ConcurrentMark.inline.hpp"
31 #include "gc/g1/g1MMUTracker.hpp"
32 #include "gc/g1/g1Policy.hpp"
33 #include "gc/g1/suspendibleThreadSet.hpp"
34 #include "gc/g1/vm_operations_g1.hpp"
35 #include "gc/shared/gcId.hpp"
36 #include "gc/shared/gcTrace.hpp"
37 #include "gc/shared/gcTraceTime.inline.hpp"
38 #include "logging/log.hpp"
39 #include "memory/resourceArea.hpp"
40 #include "runtime/vmThread.hpp"
41
42 // ======= Concurrent Mark Thread ========
43
44 // The CM thread is created when the G1 garbage collector is used
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(G1Policy* g1_policy, bool remark) {
84 const G1Analytics* analytics = g1_policy->analytics();
85 if (g1_policy->adaptive_young_list_length()) {
86 double now = os::elapsedTime();
87 double prediction_ms = remark ? analytics->predict_remark_time_ms()
88 : analytics->predict_cleanup_time_ms();
89 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
90 jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms);
91 os::sleep(this, sleep_time_ms, false);
92 }
93 }
94
95 class G1ConcPhaseTimer : public GCTraceConcTimeImpl<LogLevel::Info, LOG_TAGS(gc, marking)> {
96 G1ConcurrentMark* _cm;
97
98 public:
99 G1ConcPhaseTimer(G1ConcurrentMark* cm, const char* title) :
100 GCTraceConcTimeImpl<LogLevel::Info, LogTag::_gc, LogTag::_marking>(title),
101 _cm(cm) {
102 _cm->gc_timer_cm()->register_gc_concurrent_start(title);
103 }
104
105 ~G1ConcPhaseTimer() {
106 _cm->gc_timer_cm()->register_gc_concurrent_end();
107 }
108 };
109
110 void ConcurrentMarkThread::run_service() {
111 _vtime_start = os::elapsedVTime();
112
113 G1CollectedHeap* g1h = G1CollectedHeap::heap();
114 G1Policy* g1_policy = g1h->g1_policy();
115
116 while (!should_terminate()) {
117 // wait until started is set.
118 sleepBeforeNextCycle();
119 if (should_terminate()) {
120 break;
121 }
122
123 GCIdMark gc_id_mark;
124
125 cm()->concurrent_cycle_start();
126
127 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC.");
128
129 GCTraceConcTime(Info, gc) tt("Concurrent Cycle");
130 {
131 ResourceMark rm;
132 HandleMark hm;
133 double cycle_start = os::elapsedVTime();
134
135 {
136 G1ConcPhaseTimer t(_cm, "Concurrent Clear Claimed Marks");
137 ClassLoaderDataGraph::clear_claimed_marks();
138 }
139
140 // We have to ensure that we finish scanning the root regions
141 // before the next GC takes place. To ensure this we have to
142 // make sure that we do not join the STS until the root regions
143 // have been scanned. If we did then it's possible that a
144 // subsequent GC could block us from joining the STS and proceed
145 // without the root regions have been scanned which would be a
146 // correctness issue.
147
148 {
149 G1ConcPhaseTimer t(_cm, "Concurrent Scan Root Regions");
150 _cm->scan_root_regions();
151 }
152
153 // It would be nice to use the GCTraceConcTime class here but
154 // the "end" logging is inside the loop and not at the end of
155 // a scope. Mimicking the same log output as GCTraceConcTime instead.
156 jlong mark_start = os::elapsed_counter();
157 log_info(gc, marking)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start));
158
159 for (uint iter = 1; true; ++iter) {
160 if (!cm()->has_aborted()) {
161 G1ConcPhaseTimer t(_cm, "Concurrent Mark From Roots");
162 _cm->mark_from_roots();
163 }
164
165 double mark_end_time = os::elapsedVTime();
166 jlong mark_end = os::elapsed_counter();
167 _vtime_mark_accum += (mark_end_time - cycle_start);
168 if (!cm()->has_aborted()) {
169 delay_to_keep_mmu(g1_policy, true /* remark */);
170 log_info(gc, marking)("Concurrent Mark (%.3fs, %.3fs) %.3fms",
171 TimeHelper::counter_to_seconds(mark_start),
172 TimeHelper::counter_to_seconds(mark_end),
173 TimeHelper::counter_to_millis(mark_end - mark_start));
174
175 CMCheckpointRootsFinalClosure final_cl(_cm);
176 VM_CGC_Operation op(&final_cl, "Pause Remark");
177 VMThread::execute(&op);
178 }
179
180 if (!cm()->restart_for_overflow() || cm()->has_aborted()) {
181 break;
182 }
183
184 log_info(gc, marking)("Concurrent Mark Restart due to overflow"
185 " (iteration #%u", iter);
186 }
187
188 if (!cm()->has_aborted()) {
189 G1ConcPhaseTimer t(_cm, "Concurrent Create Live Data");
190 cm()->create_live_data();
191 }
192
193 double end_time = os::elapsedVTime();
194 // Update the total virtual time before doing this, since it will try
195 // to measure it to get the vtime for this marking. We purposely
196 // neglect the presumably-short "completeCleanup" phase here.
197 _vtime_accum = (end_time - _vtime_start);
198
199 if (!cm()->has_aborted()) {
200 delay_to_keep_mmu(g1_policy, false /* cleanup */);
201
202 CMCleanUp cl_cl(_cm);
203 VM_CGC_Operation op(&cl_cl, "Pause Cleanup");
204 VMThread::execute(&op);
205 } else {
206 // We don't want to update the marking status if a GC pause
207 // is already underway.
208 SuspendibleThreadSetJoiner sts_join;
209 g1h->collector_state()->set_mark_in_progress(false);
210 }
211
212 // Check if cleanup set the free_regions_coming flag. If it
213 // hasn't, we can just skip the next step.
214 if (g1h->free_regions_coming()) {
215 // The following will finish freeing up any regions that we
216 // found to be empty during cleanup. We'll do this part
217 // without joining the suspendible set. If an evacuation pause
218 // takes place, then we would carry on freeing regions in
219 // case they are needed by the pause. If a Full GC takes
220 // place, it would wait for us to process the regions
221 // reclaimed by cleanup.
222
223 G1ConcPhaseTimer t(_cm, "Concurrent Complete Cleanup");
224 // Now do the concurrent cleanup operation.
225 _cm->complete_cleanup();
226
227 // Notify anyone who's waiting that there are no more free
228 // regions coming. We have to do this before we join the STS
229 // (in fact, we should not attempt to join the STS in the
230 // interval between finishing the cleanup pause and clearing
231 // the free_regions_coming flag) otherwise we might deadlock:
232 // a GC worker could be blocked waiting for the notification
233 // whereas this thread will be blocked for the pause to finish
234 // while it's trying to join the STS, which is conditional on
235 // the GC workers finishing.
236 g1h->reset_free_regions_coming();
237 }
238 guarantee(cm()->cleanup_list_is_empty(),
239 "at this point there should be no regions on the cleanup list");
240
241 // There is a tricky race before recording that the concurrent
242 // cleanup has completed and a potential Full GC starting around
243 // the same time. We want to make sure that the Full GC calls
244 // abort() on concurrent mark after
245 // record_concurrent_mark_cleanup_completed(), since abort() is
246 // the method that will reset the concurrent mark state. If we
247 // end up calling record_concurrent_mark_cleanup_completed()
248 // after abort() then we might incorrectly undo some of the work
249 // abort() did. Checking the has_aborted() flag after joining
250 // the STS allows the correct ordering of the two methods. There
251 // are two scenarios:
252 //
253 // a) If we reach here before the Full GC, the fact that we have
254 // joined the STS means that the Full GC cannot start until we
255 // leave the STS, so record_concurrent_mark_cleanup_completed()
256 // will complete before abort() is called.
257 //
258 // b) If we reach here during the Full GC, we'll be held up from
259 // joining the STS until the Full GC is done, which means that
260 // abort() will have completed and has_aborted() will return
261 // true to prevent us from calling
262 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
263 // not needed any more as the concurrent mark state has been
264 // already reset).
265 {
266 SuspendibleThreadSetJoiner sts_join;
267 if (!cm()->has_aborted()) {
268 g1_policy->record_concurrent_mark_cleanup_completed();
269 } else {
270 log_info(gc, marking)("Concurrent Mark Abort");
271 }
272 }
273
274 // We now want to allow clearing of the marking bitmap to be
275 // suspended by a collection pause.
276 // We may have aborted just before the remark. Do not bother clearing the
277 // bitmap then, as it has been done during mark abort.
278 if (!cm()->has_aborted()) {
279 G1ConcPhaseTimer t(_cm, "Concurrent Cleanup for Next Mark");
280 _cm->cleanup_for_next_mark();
281 } else {
282 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
283 }
284 }
285
286 // Update the number of full collections that have been
287 // completed. This will also notify the FullGCCount_lock in case a
288 // Java thread is waiting for a full GC to happen (e.g., it
289 // called System.gc() with +ExplicitGCInvokesConcurrent).
290 {
291 SuspendibleThreadSetJoiner sts_join;
292 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
293
294 cm()->concurrent_cycle_end();
295 }
296 }
297 _cm->root_regions()->cancel_scan();
298 }
299
300 void ConcurrentMarkThread::stop_service() {
301 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
302 CGC_lock->notify_all();
303 }
304
305 void ConcurrentMarkThread::sleepBeforeNextCycle() {
306 // We join here because we don't want to do the "shouldConcurrentMark()"
307 // below while the world is otherwise stopped.
308 assert(!in_progress(), "should have been cleared");
309
310 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
311 while (!started() && !should_terminate()) {
312 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
313 }
314
315 if (started()) {
316 set_in_progress();
317 }
318 }