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/g1CollectedHeap.inline.hpp"
29 #include "gc/g1/g1CollectorPolicy.hpp"
30 #include "gc/g1/g1MMUTracker.hpp"
31 #include "gc/g1/suspendibleThreadSet.hpp"
32 #include "gc/g1/vm_operations_g1.hpp"
33 #include "gc/shared/gcId.hpp"
34 #include "gc/shared/gcTrace.hpp"
35 #include "gc/shared/gcTraceTime.inline.hpp"
36 #include "logging/log.hpp"
37 #include "memory/resourceArea.hpp"
38 #include "runtime/vmThread.hpp"
39
40 // ======= Concurrent Mark Thread ========
41
42 // The CM thread is created when the G1 garbage collector is used
43
44 ConcurrentMarkThread::ConcurrentMarkThread(G1ConcurrentMark* cm) :
45 ConcurrentGCThread(),
46 _cm(cm),
47 _state(Idle),
48 _vtime_accum(0.0),
49 _vtime_mark_accum(0.0) {
50
51 set_name("G1 Main Marker");
52 create_and_start();
53 }
54
55 class CMCheckpointRootsFinalClosure: public VoidClosure {
56
57 G1ConcurrentMark* _cm;
58 public:
59
60 CMCheckpointRootsFinalClosure(G1ConcurrentMark* cm) :
61 _cm(cm) {}
62
63 void do_void(){
64 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
65 }
66 };
67
68 class CMCleanUp: public VoidClosure {
69 G1ConcurrentMark* _cm;
70 public:
71
72 CMCleanUp(G1ConcurrentMark* cm) :
73 _cm(cm) {}
74
75 void do_void(){
76 _cm->cleanup();
77 }
78 };
79
80 // Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU.
81 void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) {
82 if (g1_policy->adaptive_young_list_length()) {
83 double now = os::elapsedTime();
84 double prediction_ms = remark ? g1_policy->predict_remark_time_ms()
85 : g1_policy->predict_cleanup_time_ms();
86 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
87 jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms);
88 os::sleep(this, sleep_time_ms, false);
89 }
90 }
91
92 class GCConcPhaseTimer : StackObj {
93 G1ConcurrentMark* _cm;
94
95 public:
96 GCConcPhaseTimer(G1ConcurrentMark* cm, const char* title) : _cm(cm) {
97 _cm->register_concurrent_phase_start(title);
98 }
99
100 ~GCConcPhaseTimer() {
101 _cm->register_concurrent_phase_end();
102 }
103 };
104
105 void ConcurrentMarkThread::run_service() {
106 _vtime_start = os::elapsedVTime();
107
108 G1CollectedHeap* g1h = G1CollectedHeap::heap();
109 G1CollectorPolicy* g1_policy = g1h->g1_policy();
110
111 while (!should_terminate()) {
112 // wait until started is set.
113 sleepBeforeNextCycle();
114 if (should_terminate()) {
115 _cm->root_regions()->cancel_scan();
116 break;
117 }
118
119 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC.");
120 {
121 ResourceMark rm;
122 HandleMark hm;
123 double cycle_start = os::elapsedVTime();
124
125 {
126 GCConcPhaseTimer(_cm, "Concurrent Clearing of Claimed Marks");
127 ClassLoaderDataGraph::clear_claimed_marks();
128 }
129
130 // We have to ensure that we finish scanning the root regions
131 // before the next GC takes place. To ensure this we have to
132 // make sure that we do not join the STS until the root regions
133 // have been scanned. If we did then it's possible that a
134 // subsequent GC could block us from joining the STS and proceed
135 // without the root regions have been scanned which would be a
136 // correctness issue.
137
138 {
139 GCConcPhaseTimer(_cm, "Concurrent Root Region Scanning");
140 _cm->scanRootRegions();
141 }
142
143 // It would be nice to use the GCTraceConcTime class here but
144 // the "end" logging is inside the loop and not at the end of
145 // a scope. Mimicking the same log output as GCTraceConcTime instead.
146 jlong mark_start = os::elapsed_counter();
147 log_info(gc)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start));
148
149 int iter = 0;
150 do {
151 iter++;
152 if (!cm()->has_aborted()) {
153 GCConcPhaseTimer(_cm, "Concurrent Mark");
154 _cm->markFromRoots();
155 }
156
157 double mark_end_time = os::elapsedVTime();
158 jlong mark_end = os::elapsed_counter();
159 _vtime_mark_accum += (mark_end_time - cycle_start);
160 if (!cm()->has_aborted()) {
161 delay_to_keep_mmu(g1_policy, true /* remark */);
162 log_info(gc)("Concurrent Mark (%.3fs, %.3fs) %.3fms",
163 TimeHelper::counter_to_seconds(mark_start),
164 TimeHelper::counter_to_seconds(mark_end),
165 TimeHelper::counter_to_millis(mark_end - mark_start));
166
167 CMCheckpointRootsFinalClosure final_cl(_cm);
168 VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */);
169 VMThread::execute(&op);
170 }
171 if (cm()->restart_for_overflow()) {
172 log_debug(gc)("Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
173 log_info(gc)("Concurrent Mark restart for overflow");
174 }
175 } while (cm()->restart_for_overflow());
176
177 double end_time = os::elapsedVTime();
178 // Update the total virtual time before doing this, since it will try
179 // to measure it to get the vtime for this marking. We purposely
180 // neglect the presumably-short "completeCleanup" phase here.
181 _vtime_accum = (end_time - _vtime_start);
182
183 if (!cm()->has_aborted()) {
184 delay_to_keep_mmu(g1_policy, false /* cleanup */);
185
186 CMCleanUp cl_cl(_cm);
187 VM_CGC_Operation op(&cl_cl, "Pause Cleanup", false /* needs_pll */);
188 VMThread::execute(&op);
189 } else {
190 // We don't want to update the marking status if a GC pause
191 // is already underway.
192 SuspendibleThreadSetJoiner sts_join;
193 g1h->collector_state()->set_mark_in_progress(false);
194 }
195
196 // Check if cleanup set the free_regions_coming flag. If it
197 // hasn't, we can just skip the next step.
198 if (g1h->free_regions_coming()) {
199 // The following will finish freeing up any regions that we
200 // found to be empty during cleanup. We'll do this part
201 // without joining the suspendible set. If an evacuation pause
202 // takes place, then we would carry on freeing regions in
203 // case they are needed by the pause. If a Full GC takes
204 // place, it would wait for us to process the regions
205 // reclaimed by cleanup.
206
207 GCTraceConcTime(Info, gc) tt("Concurrent Cleanup");
208 GCConcPhaseTimer(_cm, "Concurrent Cleanup");
209
210 // Now do the concurrent cleanup operation.
211 _cm->completeCleanup();
212
213 // Notify anyone who's waiting that there are no more free
214 // regions coming. We have to do this before we join the STS
215 // (in fact, we should not attempt to join the STS in the
216 // interval between finishing the cleanup pause and clearing
217 // the free_regions_coming flag) otherwise we might deadlock:
218 // a GC worker could be blocked waiting for the notification
219 // whereas this thread will be blocked for the pause to finish
220 // while it's trying to join the STS, which is conditional on
221 // the GC workers finishing.
222 g1h->reset_free_regions_coming();
223 }
224 guarantee(cm()->cleanup_list_is_empty(),
225 "at this point there should be no regions on the cleanup list");
226
227 // There is a tricky race before recording that the concurrent
228 // cleanup has completed and a potential Full GC starting around
229 // the same time. We want to make sure that the Full GC calls
230 // abort() on concurrent mark after
231 // record_concurrent_mark_cleanup_completed(), since abort() is
232 // the method that will reset the concurrent mark state. If we
233 // end up calling record_concurrent_mark_cleanup_completed()
234 // after abort() then we might incorrectly undo some of the work
235 // abort() did. Checking the has_aborted() flag after joining
236 // the STS allows the correct ordering of the two methods. There
237 // are two scenarios:
238 //
239 // a) If we reach here before the Full GC, the fact that we have
240 // joined the STS means that the Full GC cannot start until we
241 // leave the STS, so record_concurrent_mark_cleanup_completed()
242 // will complete before abort() is called.
243 //
244 // b) If we reach here during the Full GC, we'll be held up from
245 // joining the STS until the Full GC is done, which means that
246 // abort() will have completed and has_aborted() will return
247 // true to prevent us from calling
248 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
249 // not needed any more as the concurrent mark state has been
250 // already reset).
251 {
252 SuspendibleThreadSetJoiner sts_join;
253 if (!cm()->has_aborted()) {
254 g1_policy->record_concurrent_mark_cleanup_completed();
255 } else {
256 log_info(gc)("Concurrent Mark abort");
257 }
258 }
259
260 // We now want to allow clearing of the marking bitmap to be
261 // suspended by a collection pause.
262 // We may have aborted just before the remark. Do not bother clearing the
263 // bitmap then, as it has been done during mark abort.
264 if (!cm()->has_aborted()) {
265 GCConcPhaseTimer(_cm, "Concurrent Bitmap Clearing");
266 _cm->clearNextBitmap();
267 } else {
268 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
269 }
270 }
271
272 // Update the number of full collections that have been
273 // completed. This will also notify the FullGCCount_lock in case a
274 // Java thread is waiting for a full GC to happen (e.g., it
275 // called System.gc() with +ExplicitGCInvokesConcurrent).
276 {
277 SuspendibleThreadSetJoiner sts_join;
278 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
279 g1h->register_concurrent_cycle_end();
280 }
281 }
282 }
283
284 void ConcurrentMarkThread::stop_service() {
285 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
286 CGC_lock->notify_all();
287 }
288
289 void ConcurrentMarkThread::sleepBeforeNextCycle() {
290 // We join here because we don't want to do the "shouldConcurrentMark()"
291 // below while the world is otherwise stopped.
292 assert(!in_progress(), "should have been cleared");
293
294 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
295 while (!started() && !should_terminate()) {
296 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
297 }
298
299 if (started()) {
300 set_in_progress();
301 }
302 }