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 SurrogateLockerThread*
45 ConcurrentMarkThread::_slt = NULL;
46
47 ConcurrentMarkThread::ConcurrentMarkThread(G1ConcurrentMark* cm) :
48 ConcurrentGCThread(),
49 _cm(cm),
50 _state(Idle),
51 _vtime_accum(0.0),
52 _vtime_mark_accum(0.0) {
53
54 set_name("G1 Main Marker");
55 create_and_start();
56 }
57
58 class CMCheckpointRootsFinalClosure: public VoidClosure {
59
60 G1ConcurrentMark* _cm;
61 public:
62
63 CMCheckpointRootsFinalClosure(G1ConcurrentMark* cm) :
64 _cm(cm) {}
65
66 void do_void(){
67 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
68 }
69 };
70
71 class CMCleanUp: public VoidClosure {
72 G1ConcurrentMark* _cm;
73 public:
74
75 CMCleanUp(G1ConcurrentMark* cm) :
76 _cm(cm) {}
77
78 void do_void(){
79 _cm->cleanup();
80 }
81 };
82
83 // Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU.
84 void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) {
85 if (g1_policy->adaptive_young_list_length()) {
86 double now = os::elapsedTime();
87 double prediction_ms = remark ? g1_policy->predict_remark_time_ms()
88 : g1_policy->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 GCConcPhaseTimer : StackObj {
96 G1ConcurrentMark* _cm;
97
98 public:
99 GCConcPhaseTimer(G1ConcurrentMark* cm, const char* title) : _cm(cm) {
100 _cm->register_concurrent_phase_start(title);
101 }
102
103 ~GCConcPhaseTimer() {
104 _cm->register_concurrent_phase_end();
105 }
106 };
107
108 void ConcurrentMarkThread::run() {
109 initialize_in_thread();
110 wait_for_universe_init();
111
112 run_service();
113
114 terminate();
115 }
116
117 void ConcurrentMarkThread::run_service() {
118 _vtime_start = os::elapsedVTime();
119
120 G1CollectedHeap* g1h = G1CollectedHeap::heap();
121 G1CollectorPolicy* g1_policy = g1h->g1_policy();
122
123 while (!_should_terminate) {
124 // wait until started is set.
125 sleepBeforeNextCycle();
126 if (_should_terminate) {
127 _cm->root_regions()->cancel_scan();
128 break;
129 }
130
131 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC.");
132 {
133 ResourceMark rm;
134 HandleMark hm;
135 double cycle_start = os::elapsedVTime();
136
137 {
138 GCConcPhaseTimer(_cm, "Concurrent Clearing of Claimed Marks");
139 ClassLoaderDataGraph::clear_claimed_marks();
140 }
141
142 // We have to ensure that we finish scanning the root regions
143 // before the next GC takes place. To ensure this we have to
144 // make sure that we do not join the STS until the root regions
145 // have been scanned. If we did then it's possible that a
146 // subsequent GC could block us from joining the STS and proceed
147 // without the root regions have been scanned which would be a
148 // correctness issue.
149
150 {
151 GCConcPhaseTimer(_cm, "Concurrent Root Region Scanning");
152 _cm->scanRootRegions();
153 }
154
155 // It would be nice to use the GCTraceConcTime class here but
156 // the "end" logging is inside the loop and not at the end of
157 // a scope. Mimicking the same log output as GCTraceConcTime instead.
158 jlong mark_start = os::elapsed_counter();
159 log_info(gc)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start));
160
161 int iter = 0;
162 do {
163 iter++;
164 if (!cm()->has_aborted()) {
165 GCConcPhaseTimer(_cm, "Concurrent Mark");
166 _cm->markFromRoots();
167 }
168
169 double mark_end_time = os::elapsedVTime();
170 jlong mark_end = os::elapsed_counter();
171 _vtime_mark_accum += (mark_end_time - cycle_start);
172 if (!cm()->has_aborted()) {
173 delay_to_keep_mmu(g1_policy, true /* remark */);
174 log_info(gc)("Concurrent Mark (%.3fs, %.3fs) %.3fms",
175 TimeHelper::counter_to_seconds(mark_start),
176 TimeHelper::counter_to_seconds(mark_end),
177 TimeHelper::counter_to_millis(mark_end - mark_start));
178
179 CMCheckpointRootsFinalClosure final_cl(_cm);
180 VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */);
181 VMThread::execute(&op);
182 }
183 if (cm()->restart_for_overflow()) {
184 log_debug(gc)("Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
185 log_info(gc)("Concurrent Mark restart for overflow");
186 }
187 } while (cm()->restart_for_overflow());
188
189 double end_time = os::elapsedVTime();
190 // Update the total virtual time before doing this, since it will try
191 // to measure it to get the vtime for this marking. We purposely
192 // neglect the presumably-short "completeCleanup" phase here.
193 _vtime_accum = (end_time - _vtime_start);
194
195 if (!cm()->has_aborted()) {
196 delay_to_keep_mmu(g1_policy, false /* cleanup */);
197
198 CMCleanUp cl_cl(_cm);
199 VM_CGC_Operation op(&cl_cl, "Pause Cleanup", false /* needs_pll */);
200 VMThread::execute(&op);
201 } else {
202 // We don't want to update the marking status if a GC pause
203 // is already underway.
204 SuspendibleThreadSetJoiner sts_join;
205 g1h->collector_state()->set_mark_in_progress(false);
206 }
207
208 // Check if cleanup set the free_regions_coming flag. If it
209 // hasn't, we can just skip the next step.
210 if (g1h->free_regions_coming()) {
211 // The following will finish freeing up any regions that we
212 // found to be empty during cleanup. We'll do this part
213 // without joining the suspendible set. If an evacuation pause
214 // takes place, then we would carry on freeing regions in
215 // case they are needed by the pause. If a Full GC takes
216 // place, it would wait for us to process the regions
217 // reclaimed by cleanup.
218
219 GCTraceConcTime(Info, gc) tt("Concurrent Cleanup");
220 GCConcPhaseTimer(_cm, "Concurrent Cleanup");
221
222 // Now do the concurrent cleanup operation.
223 _cm->completeCleanup();
224
225 // Notify anyone who's waiting that there are no more free
226 // regions coming. We have to do this before we join the STS
227 // (in fact, we should not attempt to join the STS in the
228 // interval between finishing the cleanup pause and clearing
229 // the free_regions_coming flag) otherwise we might deadlock:
230 // a GC worker could be blocked waiting for the notification
231 // whereas this thread will be blocked for the pause to finish
232 // while it's trying to join the STS, which is conditional on
233 // the GC workers finishing.
234 g1h->reset_free_regions_coming();
235 }
236 guarantee(cm()->cleanup_list_is_empty(),
237 "at this point there should be no regions on the cleanup list");
238
239 // There is a tricky race before recording that the concurrent
240 // cleanup has completed and a potential Full GC starting around
241 // the same time. We want to make sure that the Full GC calls
242 // abort() on concurrent mark after
243 // record_concurrent_mark_cleanup_completed(), since abort() is
244 // the method that will reset the concurrent mark state. If we
245 // end up calling record_concurrent_mark_cleanup_completed()
246 // after abort() then we might incorrectly undo some of the work
247 // abort() did. Checking the has_aborted() flag after joining
248 // the STS allows the correct ordering of the two methods. There
249 // are two scenarios:
250 //
251 // a) If we reach here before the Full GC, the fact that we have
252 // joined the STS means that the Full GC cannot start until we
253 // leave the STS, so record_concurrent_mark_cleanup_completed()
254 // will complete before abort() is called.
255 //
256 // b) If we reach here during the Full GC, we'll be held up from
257 // joining the STS until the Full GC is done, which means that
258 // abort() will have completed and has_aborted() will return
259 // true to prevent us from calling
260 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
261 // not needed any more as the concurrent mark state has been
262 // already reset).
263 {
264 SuspendibleThreadSetJoiner sts_join;
265 if (!cm()->has_aborted()) {
266 g1_policy->record_concurrent_mark_cleanup_completed();
267 } else {
268 log_info(gc)("Concurrent Mark abort");
269 }
270 }
271
272 // We now want to allow clearing of the marking bitmap to be
273 // suspended by a collection pause.
274 // We may have aborted just before the remark. Do not bother clearing the
275 // bitmap then, as it has been done during mark abort.
276 if (!cm()->has_aborted()) {
277 GCConcPhaseTimer(_cm, "Concurrent Bitmap Clearing");
278 _cm->cleanup_for_next_mark();
279 } else {
280 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
281 }
282 }
283
284 // Update the number of full collections that have been
285 // completed. This will also notify the FullGCCount_lock in case a
286 // Java thread is waiting for a full GC to happen (e.g., it
287 // called System.gc() with +ExplicitGCInvokesConcurrent).
288 {
289 SuspendibleThreadSetJoiner sts_join;
290 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
291 g1h->register_concurrent_cycle_end();
292 }
293 }
294 }
295
296 void ConcurrentMarkThread::stop() {
297 {
298 MutexLockerEx ml(Terminator_lock);
299 _should_terminate = true;
300 }
301
302 stop_service();
303
304 {
305 MutexLockerEx ml(Terminator_lock);
306 while (!_has_terminated) {
307 Terminator_lock->wait();
308 }
309 }
310 }
311
312 void ConcurrentMarkThread::stop_service() {
313 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
314 CGC_lock->notify_all();
315 }
316
317 void ConcurrentMarkThread::sleepBeforeNextCycle() {
318 // We join here because we don't want to do the "shouldConcurrentMark()"
319 // below while the world is otherwise stopped.
320 assert(!in_progress(), "should have been cleared");
321
322 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
323 while (!started() && !_should_terminate) {
324 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
325 }
326
327 if (started()) {
328 set_in_progress();
329 }
330 }
331
332 // Note: As is the case with CMS - this method, although exported
333 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
334 // be called by a JavaThread. Currently this is done at vm creation
335 // time (post-vm-init) by the main/Primordial (Java)Thread.
336 // XXX Consider changing this in the future to allow the CM thread
337 // itself to create this thread?
338 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
339 assert(UseG1GC, "SLT thread needed only for concurrent GC");
340 assert(THREAD->is_Java_thread(), "must be a Java thread");
341 assert(_slt == NULL, "SLT already created");
342 _slt = SurrogateLockerThread::make(THREAD);
343 }