1 /*
2 * Copyright (c) 2001, 2013, 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_implementation/g1/concurrentMarkThread.inline.hpp"
27 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"
28 #include "gc_implementation/g1/g1CollectorPolicy.hpp"
29 #include "gc_implementation/g1/g1Log.hpp"
30 #include "gc_implementation/g1/g1MMUTracker.hpp"
31 #include "gc_implementation/g1/vm_operations_g1.hpp"
32 #include "gc_implementation/shared/gcTrace.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "runtime/vmThread.hpp"
35
36 // ======= Concurrent Mark Thread ========
37
38 // The CM thread is created when the G1 garbage collector is used
39
40 SurrogateLockerThread*
41 ConcurrentMarkThread::_slt = NULL;
42
ConcurrentMarkThread(ConcurrentMark * cm)43 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* cm) :
44 ConcurrentGCThread(),
45 _cm(cm),
46 _state(Idle),
47 _vtime_accum(0.0),
48 _vtime_mark_accum(0.0) {
49 create_and_start();
50 }
51
52 class CMCheckpointRootsFinalClosure: public VoidClosure {
53
54 ConcurrentMark* _cm;
55 public:
56
CMCheckpointRootsFinalClosure(ConcurrentMark * cm)57 CMCheckpointRootsFinalClosure(ConcurrentMark* cm) :
58 _cm(cm) {}
59
do_void()60 void do_void(){
61 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
62 }
63 };
64
65 class CMCleanUp: public VoidClosure {
66 ConcurrentMark* _cm;
67 public:
68
CMCleanUp(ConcurrentMark * cm)69 CMCleanUp(ConcurrentMark* cm) :
70 _cm(cm) {}
71
do_void()72 void do_void(){
73 _cm->cleanup();
74 }
75 };
76
77
78
run()79 void ConcurrentMarkThread::run() {
80 initialize_in_thread();
81 _vtime_start = os::elapsedVTime();
82 wait_for_universe_init();
83
84 G1CollectedHeap* g1h = G1CollectedHeap::heap();
85 G1CollectorPolicy* g1_policy = g1h->g1_policy();
86 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
87 Thread *current_thread = Thread::current();
88
89 while (!_should_terminate) {
90 // wait until started is set.
91 sleepBeforeNextCycle();
92 if (_should_terminate) {
93 break;
94 }
95
96 {
97 ResourceMark rm;
98 HandleMark hm;
99 double cycle_start = os::elapsedVTime();
100
101 // We have to ensure that we finish scanning the root regions
102 // before the next GC takes place. To ensure this we have to
103 // make sure that we do not join the STS until the root regions
104 // have been scanned. If we did then it's possible that a
105 // subsequent GC could block us from joining the STS and proceed
106 // without the root regions have been scanned which would be a
107 // correctness issue.
108
109 double scan_start = os::elapsedTime();
110 if (!cm()->has_aborted()) {
111 if (G1Log::fine()) {
112 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
113 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-start]");
114 }
115
116 _cm->scanRootRegions();
117
118 double scan_end = os::elapsedTime();
119 if (G1Log::fine()) {
120 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
121 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf secs]",
122 scan_end - scan_start);
123 }
124 }
125
126 double mark_start_sec = os::elapsedTime();
127 if (G1Log::fine()) {
128 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
129 gclog_or_tty->print_cr("[GC concurrent-mark-start]");
130 }
131
132 int iter = 0;
133 do {
134 iter++;
135 if (!cm()->has_aborted()) {
136 _cm->markFromRoots();
137 }
138
139 double mark_end_time = os::elapsedVTime();
140 double mark_end_sec = os::elapsedTime();
141 _vtime_mark_accum += (mark_end_time - cycle_start);
142 if (!cm()->has_aborted()) {
143 if (g1_policy->adaptive_young_list_length()) {
144 double now = os::elapsedTime();
145 double remark_prediction_ms = g1_policy->predict_remark_time_ms();
146 jlong sleep_time_ms = mmu_tracker->when_ms(now, remark_prediction_ms);
147 os::sleep(current_thread, sleep_time_ms, false);
148 }
149
150 if (G1Log::fine()) {
151 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
152 gclog_or_tty->print_cr("[GC concurrent-mark-end, %1.7lf secs]",
153 mark_end_sec - mark_start_sec);
154 }
155
156 CMCheckpointRootsFinalClosure final_cl(_cm);
157 VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
158 VMThread::execute(&op);
159 }
160 if (cm()->restart_for_overflow()) {
161 if (G1TraceMarkStackOverflow) {
162 gclog_or_tty->print_cr("Restarting conc marking because of MS overflow "
163 "in remark (restart #%d).", iter);
164 }
165 if (G1Log::fine()) {
166 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
167 gclog_or_tty->print_cr("[GC concurrent-mark-restart-for-overflow]");
168 }
169 }
170 } while (cm()->restart_for_overflow());
171
172 double end_time = os::elapsedVTime();
173 // Update the total virtual time before doing this, since it will try
174 // to measure it to get the vtime for this marking. We purposely
175 // neglect the presumably-short "completeCleanup" phase here.
176 _vtime_accum = (end_time - _vtime_start);
177
178 if (!cm()->has_aborted()) {
179 if (g1_policy->adaptive_young_list_length()) {
180 double now = os::elapsedTime();
181 double cleanup_prediction_ms = g1_policy->predict_cleanup_time_ms();
182 jlong sleep_time_ms = mmu_tracker->when_ms(now, cleanup_prediction_ms);
183 os::sleep(current_thread, sleep_time_ms, false);
184 }
185
186 CMCleanUp cl_cl(_cm);
187 VM_CGC_Operation op(&cl_cl, "GC cleanup", false /* needs_pll */);
188 VMThread::execute(&op);
189 } else {
190 // We don't want to update the marking status if a GC pause
191 // is already underway.
192 SuspendibleThreadSetJoiner sts;
193 g1h->set_marking_complete();
194 }
195
196 // Check if cleanup set the free_regions_coming flag. If it
197 // hasn't, we can just skip the next step.
198 if (g1h->free_regions_coming()) {
199 // The following will finish freeing up any regions that we
200 // found to be empty during cleanup. We'll do this part
201 // without joining the suspendible set. If an evacuation pause
202 // takes place, then we would carry on freeing regions in
203 // case they are needed by the pause. If a Full GC takes
204 // place, it would wait for us to process the regions
205 // reclaimed by cleanup.
206
207 double cleanup_start_sec = os::elapsedTime();
208 if (G1Log::fine()) {
209 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
210 gclog_or_tty->print_cr("[GC concurrent-cleanup-start]");
211 }
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 double cleanup_end_sec = os::elapsedTime();
228 if (G1Log::fine()) {
229 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
230 gclog_or_tty->print_cr("[GC concurrent-cleanup-end, %1.7lf secs]",
231 cleanup_end_sec - cleanup_start_sec);
232 }
233 }
234 guarantee(cm()->cleanup_list_is_empty(),
235 "at this point there should be no regions on the cleanup list");
236
237 // There is a tricky race before recording that the concurrent
238 // cleanup has completed and a potential Full GC starting around
239 // the same time. We want to make sure that the Full GC calls
240 // abort() on concurrent mark after
241 // record_concurrent_mark_cleanup_completed(), since abort() is
242 // the method that will reset the concurrent mark state. If we
243 // end up calling record_concurrent_mark_cleanup_completed()
244 // after abort() then we might incorrectly undo some of the work
245 // abort() did. Checking the has_aborted() flag after joining
246 // the STS allows the correct ordering of the two methods. There
247 // are two scenarios:
248 //
249 // a) If we reach here before the Full GC, the fact that we have
250 // joined the STS means that the Full GC cannot start until we
251 // leave the STS, so record_concurrent_mark_cleanup_completed()
252 // will complete before abort() is called.
253 //
254 // b) If we reach here during the Full GC, we'll be held up from
255 // joining the STS until the Full GC is done, which means that
256 // abort() will have completed and has_aborted() will return
257 // true to prevent us from calling
258 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
259 // not needed any more as the concurrent mark state has been
260 // already reset).
261 {
262 SuspendibleThreadSetJoiner sts;
263 if (!cm()->has_aborted()) {
264 g1_policy->record_concurrent_mark_cleanup_completed();
265 }
266 }
267
268 if (cm()->has_aborted()) {
269 if (G1Log::fine()) {
270 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
271 gclog_or_tty->print_cr("[GC concurrent-mark-abort]");
272 }
273 }
274
275 // We now want to allow clearing of the marking bitmap to be
276 // suspended by a collection pause.
277 // We may have aborted just before the remark. Do not bother clearing the
278 // bitmap then, as it has been done during mark abort.
279 if (!cm()->has_aborted()) {
280 SuspendibleThreadSetJoiner sts;
281 _cm->clearNextBitmap();
282 } else {
283 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
284 }
285 }
286
287 // Update the number of full collections that have been
288 // completed. This will also notify the FullGCCount_lock in case a
289 // Java thread is waiting for a full GC to happen (e.g., it
290 // called System.gc() with +ExplicitGCInvokesConcurrent).
291 {
292 SuspendibleThreadSetJoiner sts;
293 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
294 g1h->register_concurrent_cycle_end();
295 }
296 }
297 assert(_should_terminate, "just checking");
298
299 terminate();
300 }
301
stop()302 void ConcurrentMarkThread::stop() {
303 {
304 MutexLockerEx ml(Terminator_lock);
305 _should_terminate = true;
306 }
307
308 {
309 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
310 CGC_lock->notify_all();
311 }
312
313 {
314 MutexLockerEx ml(Terminator_lock);
315 while (!_has_terminated) {
316 Terminator_lock->wait();
317 }
318 }
319 }
320
print() const321 void ConcurrentMarkThread::print() const {
322 print_on(tty);
323 }
324
print_on(outputStream * st) const325 void ConcurrentMarkThread::print_on(outputStream* st) const {
326 st->print("\"G1 Main Concurrent Mark GC Thread\" ");
327 Thread::print_on(st);
328 st->cr();
329 }
330
sleepBeforeNextCycle()331 void ConcurrentMarkThread::sleepBeforeNextCycle() {
332 // We join here because we don't want to do the "shouldConcurrentMark()"
333 // below while the world is otherwise stopped.
334 assert(!in_progress(), "should have been cleared");
335
336 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
337 while (!started() && !_should_terminate) {
338 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
339 }
340
341 if (started()) {
342 set_in_progress();
343 }
344 }
345
346 // Note: As is the case with CMS - this method, although exported
347 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
348 // be called by a JavaThread. Currently this is done at vm creation
349 // time (post-vm-init) by the main/Primordial (Java)Thread.
350 // XXX Consider changing this in the future to allow the CM thread
351 // itself to create this thread?
makeSurrogateLockerThread(TRAPS)352 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
353 assert(UseG1GC, "SLT thread needed only for concurrent GC");
354 assert(THREAD->is_Java_thread(), "must be a Java thread");
355 assert(_slt == NULL, "SLT already created");
356 _slt = SurrogateLockerThread::make(THREAD);
357 }
358