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 _started(false),
48 _in_progress(false),
49 _vtime_accum(0.0),
50 _vtime_mark_accum(0.0) {
51
52 set_name("G1 Main Marker");
53 create_and_start();
54 }
55
56 class CMCheckpointRootsFinalClosure: public VoidClosure {
57
58 ConcurrentMark* _cm;
59 public:
60
61 CMCheckpointRootsFinalClosure(ConcurrentMark* cm) :
62 _cm(cm) {}
63
64 void do_void(){
65 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
66 }
67 };
68
69 class CMCleanUp: public VoidClosure {
70 ConcurrentMark* _cm;
71 public:
72
73 CMCleanUp(ConcurrentMark* cm) :
74 _cm(cm) {}
75
76 void do_void(){
77 _cm->cleanup();
78 }
79 };
80
81 // We want to avoid that the logging from the concurrent thread is mixed
82 // with the logging from a STW GC. So, if necessary join the STS to ensure
83 // that the logging is done either before or after the STW logging.
84 void ConcurrentMarkThread::cm_log(bool doit, bool join_sts, const char* fmt, ...) {
85 if (doit) {
86 SuspendibleThreadSetJoiner sts_joiner(join_sts);
87 va_list args;
88 va_start(args, fmt);
89 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
90 gclog_or_tty->vprint_cr(fmt, args);
91 va_end(args);
92 }
93 }
94
95 void ConcurrentMarkThread::run() {
96 initialize_in_thread();
97 _vtime_start = os::elapsedVTime();
98 wait_for_universe_init();
99
100 G1CollectedHeap* g1h = G1CollectedHeap::heap();
101 G1CollectorPolicy* g1_policy = g1h->g1_policy();
102 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
103 Thread *current_thread = Thread::current();
104
105 while (!_should_terminate) {
106 // wait until started is set.
107 sleepBeforeNextCycle();
108 if (_should_terminate) {
109 break;
110 }
111
112 {
113 ResourceMark rm;
114 HandleMark hm;
115 double cycle_start = os::elapsedVTime();
116
117 // We have to ensure that we finish scanning the root regions
118 // before the next GC takes place. To ensure this we have to
119 // make sure that we do not join the STS until the root regions
120 // have been scanned. If we did then it's possible that a
121 // subsequent GC could block us from joining the STS and proceed
122 // without the root regions have been scanned which would be a
123 // correctness issue.
124
125 double scan_start = os::elapsedTime();
126 if (!cm()->has_aborted()) {
127 cm_log(G1Log::fine(), false, "[GC concurrent-root-region-scan-start]");
128
129 _cm->scanRootRegions();
130
131 cm_log(G1Log::fine(), false, "[GC concurrent-root-region-scan-end, %1.7lf secs]", os::elapsedTime() - scan_start);
132 }
133
134 double mark_start_sec = os::elapsedTime();
135 cm_log(G1Log::fine(), true, "[GC concurrent-mark-start]");
136
137 int iter = 0;
138 do {
139 iter++;
140 if (!cm()->has_aborted()) {
141 _cm->markFromRoots();
142 }
143
144 double mark_end_time = os::elapsedVTime();
145 double mark_end_sec = os::elapsedTime();
146 _vtime_mark_accum += (mark_end_time - cycle_start);
147 if (!cm()->has_aborted()) {
148 if (g1_policy->adaptive_young_list_length()) {
149 double now = os::elapsedTime();
150 double remark_prediction_ms = g1_policy->predict_remark_time_ms();
151 jlong sleep_time_ms = mmu_tracker->when_ms(now, remark_prediction_ms);
152 os::sleep(current_thread, sleep_time_ms, false);
153 }
154
155 cm_log(G1Log::fine(), true, "[GC concurrent-mark-end, %1.7lf secs]", mark_end_sec - mark_start_sec);
156
157 CMCheckpointRootsFinalClosure final_cl(_cm);
158 VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
159 VMThread::execute(&op);
160 }
161 if (cm()->restart_for_overflow()) {
162 cm_log(G1TraceMarkStackOverflow, true, "Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
163 cm_log(G1Log::fine(), true, "[GC concurrent-mark-restart-for-overflow]");
164 }
165 } while (cm()->restart_for_overflow());
166
167 double end_time = os::elapsedVTime();
168 // Update the total virtual time before doing this, since it will try
169 // to measure it to get the vtime for this marking. We purposely
170 // neglect the presumably-short "completeCleanup" phase here.
171 _vtime_accum = (end_time - _vtime_start);
172
173 if (!cm()->has_aborted()) {
174 if (g1_policy->adaptive_young_list_length()) {
175 double now = os::elapsedTime();
176 double cleanup_prediction_ms = g1_policy->predict_cleanup_time_ms();
177 jlong sleep_time_ms = mmu_tracker->when_ms(now, cleanup_prediction_ms);
178 os::sleep(current_thread, sleep_time_ms, false);
179 }
180
181 CMCleanUp cl_cl(_cm);
182 VM_CGC_Operation op(&cl_cl, "GC cleanup", false /* needs_pll */);
183 VMThread::execute(&op);
184 } else {
185 // We don't want to update the marking status if a GC pause
186 // is already underway.
187 SuspendibleThreadSetJoiner sts_join;
188 g1h->collector_state()->set_mark_in_progress(false);
189 }
190
191 // Check if cleanup set the free_regions_coming flag. If it
192 // hasn't, we can just skip the next step.
193 if (g1h->free_regions_coming()) {
194 // The following will finish freeing up any regions that we
195 // found to be empty during cleanup. We'll do this part
196 // without joining the suspendible set. If an evacuation pause
197 // takes place, then we would carry on freeing regions in
198 // case they are needed by the pause. If a Full GC takes
199 // place, it would wait for us to process the regions
200 // reclaimed by cleanup.
201
202 double cleanup_start_sec = os::elapsedTime();
203 cm_log(G1Log::fine(), true, "[GC concurrent-cleanup-start]");
204
205 // Now do the concurrent cleanup operation.
206 _cm->completeCleanup();
207
208 // Notify anyone who's waiting that there are no more free
209 // regions coming. We have to do this before we join the STS
210 // (in fact, we should not attempt to join the STS in the
211 // interval between finishing the cleanup pause and clearing
212 // the free_regions_coming flag) otherwise we might deadlock:
213 // a GC worker could be blocked waiting for the notification
214 // whereas this thread will be blocked for the pause to finish
215 // while it's trying to join the STS, which is conditional on
216 // the GC workers finishing.
217 g1h->reset_free_regions_coming();
218
219 double cleanup_end_sec = os::elapsedTime();
220 cm_log(G1Log::fine(), true, "[GC concurrent-cleanup-end, %1.7lf secs]", cleanup_end_sec - cleanup_start_sec);
221 }
222 guarantee(cm()->cleanup_list_is_empty(),
223 "at this point there should be no regions on the cleanup list");
224
225 // There is a tricky race before recording that the concurrent
226 // cleanup has completed and a potential Full GC starting around
227 // the same time. We want to make sure that the Full GC calls
228 // abort() on concurrent mark after
229 // record_concurrent_mark_cleanup_completed(), since abort() is
230 // the method that will reset the concurrent mark state. If we
231 // end up calling record_concurrent_mark_cleanup_completed()
232 // after abort() then we might incorrectly undo some of the work
233 // abort() did. Checking the has_aborted() flag after joining
234 // the STS allows the correct ordering of the two methods. There
235 // are two scenarios:
236 //
237 // a) If we reach here before the Full GC, the fact that we have
238 // joined the STS means that the Full GC cannot start until we
239 // leave the STS, so record_concurrent_mark_cleanup_completed()
240 // will complete before abort() is called.
241 //
242 // b) If we reach here during the Full GC, we'll be held up from
243 // joining the STS until the Full GC is done, which means that
244 // abort() will have completed and has_aborted() will return
245 // true to prevent us from calling
246 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
247 // not needed any more as the concurrent mark state has been
248 // already reset).
249 {
250 SuspendibleThreadSetJoiner sts_join;
251 if (!cm()->has_aborted()) {
252 g1_policy->record_concurrent_mark_cleanup_completed();
253 } else {
254 cm_log(G1Log::fine(), false, "[GC concurrent-mark-abort]");
255 }
256 }
257
258 // We now want to allow clearing of the marking bitmap to be
259 // suspended by a collection pause.
260 // We may have aborted just before the remark. Do not bother clearing the
261 // bitmap then, as it has been done during mark abort.
262 if (!cm()->has_aborted()) {
263 _cm->clearNextBitmap();
264 } else {
265 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
266 }
267 }
268
269 // Update the number of full collections that have been
270 // completed. This will also notify the FullGCCount_lock in case a
271 // Java thread is waiting for a full GC to happen (e.g., it
272 // called System.gc() with +ExplicitGCInvokesConcurrent).
273 {
274 SuspendibleThreadSetJoiner sts_join;
275 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
276 g1h->register_concurrent_cycle_end();
277 }
278 }
279 assert(_should_terminate, "just checking");
280
281 terminate();
282 }
283
284 void ConcurrentMarkThread::stop() {
285 {
286 MutexLockerEx ml(Terminator_lock);
287 _should_terminate = true;
288 }
289
290 {
291 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
292 CGC_lock->notify_all();
293 }
294
295 {
296 MutexLockerEx ml(Terminator_lock);
297 while (!_has_terminated) {
298 Terminator_lock->wait();
299 }
300 }
301 }
302
303 void ConcurrentMarkThread::sleepBeforeNextCycle() {
304 // We join here because we don't want to do the "shouldConcurrentMark()"
305 // below while the world is otherwise stopped.
306 assert(!in_progress(), "should have been cleared");
307
308 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
309 while (!started() && !_should_terminate) {
310 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
311 }
312
313 if (started()) {
314 set_in_progress();
315 clear_started();
316 }
317 }
318
319 // Note: As is the case with CMS - this method, although exported
320 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
321 // be called by a JavaThread. Currently this is done at vm creation
322 // time (post-vm-init) by the main/Primordial (Java)Thread.
323 // XXX Consider changing this in the future to allow the CM thread
324 // itself to create this thread?
325 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
326 assert(UseG1GC, "SLT thread needed only for concurrent GC");
327 assert(THREAD->is_Java_thread(), "must be a Java thread");
328 assert(_slt == NULL, "SLT already created");
329 _slt = SurrogateLockerThread::make(THREAD);
330 }