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
82
83 void ConcurrentMarkThread::run() {
84 initialize_in_thread();
85 _vtime_start = os::elapsedVTime();
86 wait_for_universe_init();
87
88 G1CollectedHeap* g1h = G1CollectedHeap::heap();
89 G1CollectorPolicy* g1_policy = g1h->g1_policy();
90 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
91 Thread *current_thread = Thread::current();
92
93 while (!_should_terminate) {
94 // wait until started is set.
95 sleepBeforeNextCycle();
96 if (_should_terminate) {
97 break;
98 }
99
100 {
101 ResourceMark rm;
102 HandleMark hm;
103 double cycle_start = os::elapsedVTime();
104
105 // We have to ensure that we finish scanning the root regions
106 // before the next GC takes place. To ensure this we have to
107 // make sure that we do not join the STS until the root regions
108 // have been scanned. If we did then it's possible that a
109 // subsequent GC could block us from joining the STS and proceed
110 // without the root regions have been scanned which would be a
111 // correctness issue.
112
113 double scan_start = os::elapsedTime();
114 if (!cm()->has_aborted()) {
115 if (G1Log::fine()) {
116 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
117 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-start]");
118 }
119
120 _cm->scanRootRegions();
121
122 double scan_end = os::elapsedTime();
123 if (G1Log::fine()) {
124 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
125 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf secs]",
126 scan_end - scan_start);
127 }
128 }
129
130 double mark_start_sec = os::elapsedTime();
131 if (G1Log::fine()) {
132 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
133 gclog_or_tty->print_cr("[GC concurrent-mark-start]");
134 }
135
136 int iter = 0;
137 do {
138 iter++;
139 if (!cm()->has_aborted()) {
140 _cm->markFromRoots();
141 }
142
143 double mark_end_time = os::elapsedVTime();
144 double mark_end_sec = os::elapsedTime();
145 _vtime_mark_accum += (mark_end_time - cycle_start);
146 if (!cm()->has_aborted()) {
147 if (g1_policy->adaptive_young_list_length()) {
148 double now = os::elapsedTime();
149 double remark_prediction_ms = g1_policy->predict_remark_time_ms();
150 jlong sleep_time_ms = mmu_tracker->when_ms(now, remark_prediction_ms);
151 os::sleep(current_thread, sleep_time_ms, false);
152 }
153
154 if (G1Log::fine()) {
155 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
156 gclog_or_tty->print_cr("[GC concurrent-mark-end, %1.7lf secs]",
157 mark_end_sec - mark_start_sec);
158 }
159
160 CMCheckpointRootsFinalClosure final_cl(_cm);
161 VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
162 VMThread::execute(&op);
163 }
164 if (cm()->restart_for_overflow()) {
165 if (G1TraceMarkStackOverflow) {
166 gclog_or_tty->print_cr("Restarting conc marking because of MS overflow "
167 "in remark (restart #%d).", iter);
168 }
169 if (G1Log::fine()) {
170 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
171 gclog_or_tty->print_cr("[GC concurrent-mark-restart-for-overflow]");
172 }
173 }
174 } while (cm()->restart_for_overflow());
175
176 double end_time = os::elapsedVTime();
177 // Update the total virtual time before doing this, since it will try
178 // to measure it to get the vtime for this marking. We purposely
179 // neglect the presumably-short "completeCleanup" phase here.
180 _vtime_accum = (end_time - _vtime_start);
181
182 if (!cm()->has_aborted()) {
183 if (g1_policy->adaptive_young_list_length()) {
184 double now = os::elapsedTime();
185 double cleanup_prediction_ms = g1_policy->predict_cleanup_time_ms();
186 jlong sleep_time_ms = mmu_tracker->when_ms(now, cleanup_prediction_ms);
187 os::sleep(current_thread, sleep_time_ms, false);
188 }
189
190 CMCleanUp cl_cl(_cm);
191 VM_CGC_Operation op(&cl_cl, "GC cleanup", false /* needs_pll */);
192 VMThread::execute(&op);
193 } else {
194 // We don't want to update the marking status if a GC pause
195 // is already underway.
196 SuspendibleThreadSetJoiner sts_join;
197 g1h->set_marking_complete();
198 }
199
200 // Check if cleanup set the free_regions_coming flag. If it
201 // hasn't, we can just skip the next step.
202 if (g1h->free_regions_coming()) {
203 // The following will finish freeing up any regions that we
204 // found to be empty during cleanup. We'll do this part
205 // without joining the suspendible set. If an evacuation pause
206 // takes place, then we would carry on freeing regions in
207 // case they are needed by the pause. If a Full GC takes
208 // place, it would wait for us to process the regions
209 // reclaimed by cleanup.
210
211 double cleanup_start_sec = os::elapsedTime();
212 if (G1Log::fine()) {
213 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
214 gclog_or_tty->print_cr("[GC concurrent-cleanup-start]");
215 }
216
217 // Now do the concurrent cleanup operation.
218 _cm->completeCleanup();
219
220 // Notify anyone who's waiting that there are no more free
221 // regions coming. We have to do this before we join the STS
222 // (in fact, we should not attempt to join the STS in the
223 // interval between finishing the cleanup pause and clearing
224 // the free_regions_coming flag) otherwise we might deadlock:
225 // a GC worker could be blocked waiting for the notification
226 // whereas this thread will be blocked for the pause to finish
227 // while it's trying to join the STS, which is conditional on
228 // the GC workers finishing.
229 g1h->reset_free_regions_coming();
230
231 double cleanup_end_sec = os::elapsedTime();
232 if (G1Log::fine()) {
233 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
234 gclog_or_tty->print_cr("[GC concurrent-cleanup-end, %1.7lf secs]",
235 cleanup_end_sec - cleanup_start_sec);
236 }
237 }
238 guarantee(cm()->cleanup_list_is_empty(),
239 "at this point there should be no regions on the cleanup list");
240
241 // There is a tricky race before recording that the concurrent
242 // cleanup has completed and a potential Full GC starting around
243 // the same time. We want to make sure that the Full GC calls
244 // abort() on concurrent mark after
245 // record_concurrent_mark_cleanup_completed(), since abort() is
246 // the method that will reset the concurrent mark state. If we
247 // end up calling record_concurrent_mark_cleanup_completed()
248 // after abort() then we might incorrectly undo some of the work
249 // abort() did. Checking the has_aborted() flag after joining
250 // the STS allows the correct ordering of the two methods. There
251 // are two scenarios:
252 //
253 // a) If we reach here before the Full GC, the fact that we have
254 // joined the STS means that the Full GC cannot start until we
255 // leave the STS, so record_concurrent_mark_cleanup_completed()
256 // will complete before abort() is called.
257 //
258 // b) If we reach here during the Full GC, we'll be held up from
259 // joining the STS until the Full GC is done, which means that
260 // abort() will have completed and has_aborted() will return
261 // true to prevent us from calling
262 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
263 // not needed any more as the concurrent mark state has been
264 // already reset).
265 {
266 SuspendibleThreadSetJoiner sts_join;
267 if (!cm()->has_aborted()) {
268 g1_policy->record_concurrent_mark_cleanup_completed();
269 }
270 }
271
272 if (cm()->has_aborted()) {
273 if (G1Log::fine()) {
274 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
275 gclog_or_tty->print_cr("[GC concurrent-mark-abort]");
276 }
277 }
278
279 // We now want to allow clearing of the marking bitmap to be
280 // suspended by a collection pause.
281 // We may have aborted just before the remark. Do not bother clearing the
282 // bitmap then, as it has been done during mark abort.
283 if (!cm()->has_aborted()) {
284 _cm->clearNextBitmap();
285 } else {
286 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
287 }
288 }
289
290 // Update the number of full collections that have been
291 // completed. This will also notify the FullGCCount_lock in case a
292 // Java thread is waiting for a full GC to happen (e.g., it
293 // called System.gc() with +ExplicitGCInvokesConcurrent).
294 {
295 SuspendibleThreadSetJoiner sts_join;
296 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
297 g1h->register_concurrent_cycle_end();
298 }
299 }
300 assert(_should_terminate, "just checking");
301
302 terminate();
303 }
304
305 void ConcurrentMarkThread::stop() {
306 {
307 MutexLockerEx ml(Terminator_lock);
308 _should_terminate = true;
309 }
310
311 {
312 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
313 CGC_lock->notify_all();
314 }
315
316 {
317 MutexLockerEx ml(Terminator_lock);
318 while (!_has_terminated) {
319 Terminator_lock->wait();
320 }
321 }
322 }
323
324 void ConcurrentMarkThread::sleepBeforeNextCycle() {
325 // We join here because we don't want to do the "shouldConcurrentMark()"
326 // below while the world is otherwise stopped.
327 assert(!in_progress(), "should have been cleared");
328
329 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
330 while (!started() && !_should_terminate) {
331 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
332 }
333
334 if (started()) {
335 set_in_progress();
336 clear_started();
337 }
338 }
339
340 // Note: As is the case with CMS - this method, although exported
341 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
342 // be called by a JavaThread. Currently this is done at vm creation
343 // time (post-vm-init) by the main/Primordial (Java)Thread.
344 // XXX Consider changing this in the future to allow the CM thread
345 // itself to create this thread?
346 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
347 assert(UseG1GC, "SLT thread needed only for concurrent GC");
348 assert(THREAD->is_Java_thread(), "must be a Java thread");
349 assert(_slt == NULL, "SLT already created");
350 _slt = SurrogateLockerThread::make(THREAD);
351 }