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. Join the STS to ensure that the logging
83 // is done either before or after the STW logging.
84 void ConcurrentMarkThread::cm_log(bool doit, const char* fmt, ...) {
85 if (doit) {
86 SuspendibleThreadSetJoiner sts_joiner;
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 // This means that we can not use the cm_log() method for the logging
125 // regarding the root region scanning below.
126
127 double scan_start = os::elapsedTime();
128 if (!cm()->has_aborted()) {
129 if (G1Log::fine()) {
130 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
131 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-start]");
132 }
133
134 _cm->scanRootRegions();
135
136 double scan_end = os::elapsedTime();
137 if (G1Log::fine()) {
138 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
139 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf secs]",
140 scan_end - scan_start);
141 }
142 }
143
144 double mark_start_sec = os::elapsedTime();
145 cm_log(G1Log::fine(), "[GC concurrent-mark-start]");
146
147 int iter = 0;
148 do {
149 iter++;
150 if (!cm()->has_aborted()) {
151 _cm->markFromRoots();
152 }
153
154 double mark_end_time = os::elapsedVTime();
155 double mark_end_sec = os::elapsedTime();
156 _vtime_mark_accum += (mark_end_time - cycle_start);
157 if (!cm()->has_aborted()) {
158 if (g1_policy->adaptive_young_list_length()) {
159 double now = os::elapsedTime();
160 double remark_prediction_ms = g1_policy->predict_remark_time_ms();
161 jlong sleep_time_ms = mmu_tracker->when_ms(now, remark_prediction_ms);
162 os::sleep(current_thread, sleep_time_ms, false);
163 }
164
165 cm_log(G1Log::fine(), "[GC concurrent-mark-end, %1.7lf secs]", mark_end_sec - mark_start_sec);
166
167 CMCheckpointRootsFinalClosure final_cl(_cm);
168 VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
169 VMThread::execute(&op);
170 }
171 if (cm()->restart_for_overflow()) {
172 cm_log(G1TraceMarkStackOverflow, "Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
173 cm_log(G1Log::fine(), "[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 if (g1_policy->adaptive_young_list_length()) {
185 double now = os::elapsedTime();
186 double cleanup_prediction_ms = g1_policy->predict_cleanup_time_ms();
187 jlong sleep_time_ms = mmu_tracker->when_ms(now, cleanup_prediction_ms);
188 os::sleep(current_thread, sleep_time_ms, false);
189 }
190
191 CMCleanUp cl_cl(_cm);
192 VM_CGC_Operation op(&cl_cl, "GC cleanup", false /* needs_pll */);
193 VMThread::execute(&op);
194 } else {
195 // We don't want to update the marking status if a GC pause
196 // is already underway.
197 SuspendibleThreadSetJoiner sts_join;
198 g1h->collector_state()->set_mark_in_progress(false);
199 }
200
201 // Check if cleanup set the free_regions_coming flag. If it
202 // hasn't, we can just skip the next step.
203 if (g1h->free_regions_coming()) {
204 // The following will finish freeing up any regions that we
205 // found to be empty during cleanup. We'll do this part
206 // without joining the suspendible set. If an evacuation pause
207 // takes place, then we would carry on freeing regions in
208 // case they are needed by the pause. If a Full GC takes
209 // place, it would wait for us to process the regions
210 // reclaimed by cleanup.
211
212 double cleanup_start_sec = os::elapsedTime();
213 cm_log(G1Log::fine(), "[GC concurrent-cleanup-start]");
214
215 // Now do the concurrent cleanup operation.
216 _cm->completeCleanup();
217
218 // Notify anyone who's waiting that there are no more free
219 // regions coming. We have to do this before we join the STS
220 // (in fact, we should not attempt to join the STS in the
221 // interval between finishing the cleanup pause and clearing
222 // the free_regions_coming flag) otherwise we might deadlock:
223 // a GC worker could be blocked waiting for the notification
224 // whereas this thread will be blocked for the pause to finish
225 // while it's trying to join the STS, which is conditional on
226 // the GC workers finishing.
227 g1h->reset_free_regions_coming();
228
229 double cleanup_end_sec = os::elapsedTime();
230 cm_log(G1Log::fine(), "[GC concurrent-cleanup-end, %1.7lf secs]", cleanup_end_sec - cleanup_start_sec);
231 }
232 guarantee(cm()->cleanup_list_is_empty(),
233 "at this point there should be no regions on the cleanup list");
234
235 // There is a tricky race before recording that the concurrent
236 // cleanup has completed and a potential Full GC starting around
237 // the same time. We want to make sure that the Full GC calls
238 // abort() on concurrent mark after
239 // record_concurrent_mark_cleanup_completed(), since abort() is
240 // the method that will reset the concurrent mark state. If we
241 // end up calling record_concurrent_mark_cleanup_completed()
242 // after abort() then we might incorrectly undo some of the work
243 // abort() did. Checking the has_aborted() flag after joining
244 // the STS allows the correct ordering of the two methods. There
245 // are two scenarios:
246 //
247 // a) If we reach here before the Full GC, the fact that we have
248 // joined the STS means that the Full GC cannot start until we
249 // leave the STS, so record_concurrent_mark_cleanup_completed()
250 // will complete before abort() is called.
251 //
252 // b) If we reach here during the Full GC, we'll be held up from
253 // joining the STS until the Full GC is done, which means that
254 // abort() will have completed and has_aborted() will return
255 // true to prevent us from calling
256 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
257 // not needed any more as the concurrent mark state has been
258 // already reset).
259 {
260 SuspendibleThreadSetJoiner sts_join;
261 if (!cm()->has_aborted()) {
262 g1_policy->record_concurrent_mark_cleanup_completed();
263 } else {
264 if (G1Log::fine()) {
265 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
266 gclog_or_tty->print_cr("[GC concurrent-mark-abort]");
267 }
268 }
269 }
270
271 // We now want to allow clearing of the marking bitmap to be
272 // suspended by a collection pause.
273 // We may have aborted just before the remark. Do not bother clearing the
274 // bitmap then, as it has been done during mark abort.
275 if (!cm()->has_aborted()) {
276 _cm->clearNextBitmap();
277 } else {
278 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
279 }
280 }
281
282 // Update the number of full collections that have been
283 // completed. This will also notify the FullGCCount_lock in case a
284 // Java thread is waiting for a full GC to happen (e.g., it
285 // called System.gc() with +ExplicitGCInvokesConcurrent).
286 {
287 SuspendibleThreadSetJoiner sts_join;
288 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
289 g1h->register_concurrent_cycle_end();
290 }
291 }
292 assert(_should_terminate, "just checking");
293
294 terminate();
295 }
296
297 void ConcurrentMarkThread::stop() {
298 {
299 MutexLockerEx ml(Terminator_lock);
300 _should_terminate = true;
301 }
302
303 {
304 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
305 CGC_lock->notify_all();
306 }
307
308 {
309 MutexLockerEx ml(Terminator_lock);
310 while (!_has_terminated) {
311 Terminator_lock->wait();
312 }
313 }
314 }
315
316 void ConcurrentMarkThread::sleepBeforeNextCycle() {
317 // We join here because we don't want to do the "shouldConcurrentMark()"
318 // below while the world is otherwise stopped.
319 assert(!in_progress(), "should have been cleared");
320
321 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
322 while (!started() && !_should_terminate) {
323 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
324 }
325
326 if (started()) {
327 set_in_progress();
328 clear_started();
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 }