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