1 /*
2 * Copyright (c) 2001, 2015, 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/g1Log.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/gcTrace.hpp"
34 #include "memory/resourceArea.hpp"
35 #include "runtime/vmThread.hpp"
36
37 // ======= Concurrent Mark Thread ========
38
39 // The CM thread is created when the G1 garbage collector is used
40
41 SurrogateLockerThread*
42 ConcurrentMarkThread::_slt = NULL;
43
44 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* 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 ConcurrentMark* _cm;
58 public:
59
60 CMCheckpointRootsFinalClosure(ConcurrentMark* 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 ConcurrentMark* _cm;
70 public:
71
72 CMCleanUp(ConcurrentMark* cm) :
73 _cm(cm) {}
74
75 void do_void(){
76 _cm->cleanup();
77 }
78 };
79
80 // We want to avoid that the logging from the concurrent thread is mixed
81 // with the logging from a STW GC. So, if necessary join the STS to ensure
82 // that the logging is done either before or after the STW logging.
83 void ConcurrentMarkThread::cm_log(bool doit, bool join_sts, const char* fmt, ...) {
84 if (doit) {
85 SuspendibleThreadSetJoiner sts_joiner(join_sts);
86 va_list args;
87 va_start(args, fmt);
88 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
89 gclog_or_tty->vprint_cr(fmt, args);
90 va_end(args);
91 }
92 }
93
94 void ConcurrentMarkThread::run() {
95 initialize_in_thread();
96 _vtime_start = os::elapsedVTime();
97 wait_for_universe_init();
98
99 G1CollectedHeap* g1h = G1CollectedHeap::heap();
100 G1CollectorPolicy* g1_policy = g1h->g1_policy();
101 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
102 Thread *current_thread = Thread::current();
103
104 while (!_should_terminate) {
105 // wait until started is set.
106 sleepBeforeNextCycle();
107 if (_should_terminate) {
108 break;
109 }
110
111 {
112 ResourceMark rm;
113 HandleMark hm;
114 double cycle_start = os::elapsedVTime();
115
116 // We have to ensure that we finish scanning the root regions
117 // before the next GC takes place. To ensure this we have to
118 // make sure that we do not join the STS until the root regions
119 // have been scanned. If we did then it's possible that a
120 // subsequent GC could block us from joining the STS and proceed
121 // without the root regions have been scanned which would be a
122 // correctness issue.
123
124 if (!cm()->has_aborted()) {
125 _cm->scanRootRegions();
126 }
127
128 double mark_start_sec = os::elapsedTime();
129 cm_log(G1Log::fine(), true, "[GC concurrent-mark-start]");
130
131 int iter = 0;
132 do {
133 iter++;
134 if (!cm()->has_aborted()) {
135 _cm->markFromRoots();
136 }
137
138 double mark_end_time = os::elapsedVTime();
139 double mark_end_sec = os::elapsedTime();
140 _vtime_mark_accum += (mark_end_time - cycle_start);
141 if (!cm()->has_aborted()) {
142 if (g1_policy->adaptive_young_list_length()) {
143 double now = os::elapsedTime();
144 double remark_prediction_ms = g1_policy->predict_remark_time_ms();
145 jlong sleep_time_ms = mmu_tracker->when_ms(now, remark_prediction_ms);
146 os::sleep(current_thread, sleep_time_ms, false);
147 }
148
149 cm_log(G1Log::fine(), true, "[GC concurrent-mark-end, %1.7lf secs]", mark_end_sec - mark_start_sec);
150
151 CMCheckpointRootsFinalClosure final_cl(_cm);
152 VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
153 VMThread::execute(&op);
154 }
155 if (cm()->restart_for_overflow()) {
156 cm_log(G1TraceMarkStackOverflow, true, "Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
157 cm_log(G1Log::fine(), true, "[GC concurrent-mark-restart-for-overflow]");
158 }
159 } while (cm()->restart_for_overflow());
160
161 double end_time = os::elapsedVTime();
162 // Update the total virtual time before doing this, since it will try
163 // to measure it to get the vtime for this marking. We purposely
164 // neglect the presumably-short "completeCleanup" phase here.
165 _vtime_accum = (end_time - _vtime_start);
166
167 if (!cm()->has_aborted()) {
168 if (g1_policy->adaptive_young_list_length()) {
169 double now = os::elapsedTime();
170 double cleanup_prediction_ms = g1_policy->predict_cleanup_time_ms();
171 jlong sleep_time_ms = mmu_tracker->when_ms(now, cleanup_prediction_ms);
172 os::sleep(current_thread, sleep_time_ms, false);
173 }
174
175 CMCleanUp cl_cl(_cm);
176 VM_CGC_Operation op(&cl_cl, "GC cleanup", false /* needs_pll */);
177 VMThread::execute(&op);
178 } else {
179 // We don't want to update the marking status if a GC pause
180 // is already underway.
181 SuspendibleThreadSetJoiner sts_join;
182 g1h->collector_state()->set_mark_in_progress(false);
183 }
184
185 // Check if cleanup set the free_regions_coming flag. If it
186 // hasn't, we can just skip the next step.
187 if (g1h->free_regions_coming()) {
188 // The following will finish freeing up any regions that we
189 // found to be empty during cleanup. We'll do this part
190 // without joining the suspendible set. If an evacuation pause
191 // takes place, then we would carry on freeing regions in
192 // case they are needed by the pause. If a Full GC takes
193 // place, it would wait for us to process the regions
194 // reclaimed by cleanup.
195
196 double cleanup_start_sec = os::elapsedTime();
197 cm_log(G1Log::fine(), true, "[GC concurrent-cleanup-start]");
198
199 // Now do the concurrent cleanup operation.
200 _cm->completeCleanup();
201
202 // Notify anyone who's waiting that there are no more free
203 // regions coming. We have to do this before we join the STS
204 // (in fact, we should not attempt to join the STS in the
205 // interval between finishing the cleanup pause and clearing
206 // the free_regions_coming flag) otherwise we might deadlock:
207 // a GC worker could be blocked waiting for the notification
208 // whereas this thread will be blocked for the pause to finish
209 // while it's trying to join the STS, which is conditional on
210 // the GC workers finishing.
211 g1h->reset_free_regions_coming();
212
213 double cleanup_end_sec = os::elapsedTime();
214 cm_log(G1Log::fine(), true, "[GC concurrent-cleanup-end, %1.7lf secs]", cleanup_end_sec - cleanup_start_sec);
215 }
216 guarantee(cm()->cleanup_list_is_empty(),
217 "at this point there should be no regions on the cleanup list");
218
219 // There is a tricky race before recording that the concurrent
220 // cleanup has completed and a potential Full GC starting around
221 // the same time. We want to make sure that the Full GC calls
222 // abort() on concurrent mark after
223 // record_concurrent_mark_cleanup_completed(), since abort() is
224 // the method that will reset the concurrent mark state. If we
225 // end up calling record_concurrent_mark_cleanup_completed()
226 // after abort() then we might incorrectly undo some of the work
227 // abort() did. Checking the has_aborted() flag after joining
228 // the STS allows the correct ordering of the two methods. There
229 // are two scenarios:
230 //
231 // a) If we reach here before the Full GC, the fact that we have
232 // joined the STS means that the Full GC cannot start until we
233 // leave the STS, so record_concurrent_mark_cleanup_completed()
234 // will complete before abort() is called.
235 //
236 // b) If we reach here during the Full GC, we'll be held up from
237 // joining the STS until the Full GC is done, which means that
238 // abort() will have completed and has_aborted() will return
239 // true to prevent us from calling
240 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
241 // not needed any more as the concurrent mark state has been
242 // already reset).
243 {
244 SuspendibleThreadSetJoiner sts_join;
245 if (!cm()->has_aborted()) {
246 g1_policy->record_concurrent_mark_cleanup_completed();
247 } else {
248 cm_log(G1Log::fine(), false, "[GC concurrent-mark-abort]");
249 }
250 }
251
252 // We now want to allow clearing of the marking bitmap to be
253 // suspended by a collection pause.
254 // We may have aborted just before the remark. Do not bother clearing the
255 // bitmap then, as it has been done during mark abort.
256 if (!cm()->has_aborted()) {
257 _cm->clearNextBitmap();
258 } else {
259 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
260 }
261 }
262
263 // Update the number of full collections that have been
264 // completed. This will also notify the FullGCCount_lock in case a
265 // Java thread is waiting for a full GC to happen (e.g., it
266 // called System.gc() with +ExplicitGCInvokesConcurrent).
267 {
268 SuspendibleThreadSetJoiner sts_join;
269 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
270 g1h->register_concurrent_cycle_end();
271 }
272 }
273 assert(_should_terminate, "just checking");
274
275 terminate();
276 }
277
278 void ConcurrentMarkThread::stop() {
279 {
280 MutexLockerEx ml(Terminator_lock);
281 _should_terminate = true;
282 }
283
284 {
285 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
286 CGC_lock->notify_all();
287 }
288
289 {
290 MutexLockerEx ml(Terminator_lock);
291 while (!_has_terminated) {
292 Terminator_lock->wait();
293 }
294 }
295 }
296
297 void ConcurrentMarkThread::sleepBeforeNextCycle() {
298 // We join here because we don't want to do the "shouldConcurrentMark()"
299 // below while the world is otherwise stopped.
300 assert(!in_progress(), "should have been cleared");
301
302 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
303 while (!started() && !_should_terminate) {
304 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
305 }
306
307 if (started()) {
308 set_in_progress();
309 }
310 }
311
312 // Note: As is the case with CMS - this method, although exported
313 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
314 // be called by a JavaThread. Currently this is done at vm creation
315 // time (post-vm-init) by the main/Primordial (Java)Thread.
316 // XXX Consider changing this in the future to allow the CM thread
317 // itself to create this thread?
318 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
319 assert(UseG1GC, "SLT thread needed only for concurrent GC");
320 assert(THREAD->is_Java_thread(), "must be a Java thread");
321 assert(_slt == NULL, "SLT already created");
322 _slt = SurrogateLockerThread::make(THREAD);
323 }