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/orderAccess.hpp"
36 #include "runtime/vmThread.hpp"
37
38 // ======= Concurrent Mark Thread ========
39
40 // The CM thread is created when the G1 garbage collector is used
41
42 SurrogateLockerThread*
43 ConcurrentMarkThread::_slt = NULL;
44
45 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* cm) :
46 ConcurrentGCThread(),
47 _cm(cm),
48 _started(false),
49 _in_progress(false),
50 _vtime_accum(0.0),
51 _vtime_mark_accum(0.0) {
52
53 set_name("G1 Main Marker");
54 create_and_start();
55 }
56
57 class CMCheckpointRootsFinalClosure: public VoidClosure {
58
59 ConcurrentMark* _cm;
60 public:
61
62 CMCheckpointRootsFinalClosure(ConcurrentMark* cm) :
63 _cm(cm) {}
64
65 void do_void(){
66 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
67 }
68 };
69
70 class CMCleanUp: public VoidClosure {
71 ConcurrentMark* _cm;
72 public:
73
74 CMCleanUp(ConcurrentMark* cm) :
75 _cm(cm) {}
76
77 void do_void(){
78 _cm->cleanup();
79 }
80 };
81
82
83
84 void ConcurrentMarkThread::run() {
85 initialize_in_thread();
86 _vtime_start = os::elapsedVTime();
87 wait_for_universe_init();
88
89 G1CollectedHeap* g1h = G1CollectedHeap::heap();
90 G1CollectorPolicy* g1_policy = g1h->g1_policy();
91 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
92 Thread *current_thread = Thread::current();
93
94 while (!_should_terminate) {
95 // wait until started is set.
96 sleepBeforeNextCycle();
97 if (_should_terminate) {
98 break;
99 }
100
101 {
102 ResourceMark rm;
103 HandleMark hm;
104 double cycle_start = os::elapsedVTime();
105
106 // We have to ensure that we finish scanning the root regions
107 // before the next GC takes place. To ensure this we have to
108 // make sure that we do not join the STS until the root regions
109 // have been scanned. If we did then it's possible that a
110 // subsequent GC could block us from joining the STS and proceed
111 // without the root regions have been scanned which would be a
112 // correctness issue.
113
114 double scan_start = os::elapsedTime();
115 if (!cm()->has_aborted()) {
116 if (G1Log::fine()) {
117 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
118 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-start]");
119 }
120
121 _cm->scanRootRegions();
122
123 double scan_end = os::elapsedTime();
124 if (G1Log::fine()) {
125 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
126 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf secs]",
127 scan_end - scan_start);
128 }
129 }
130
131 double mark_start_sec = os::elapsedTime();
132 if (G1Log::fine()) {
133 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
134 gclog_or_tty->print_cr("[GC concurrent-mark-start]");
135 }
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 if (G1Log::fine()) {
156 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
157 gclog_or_tty->print_cr("[GC concurrent-mark-end, %1.7lf secs]",
158 mark_end_sec - mark_start_sec);
159 }
160
161 CMCheckpointRootsFinalClosure final_cl(_cm);
162 VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
163 VMThread::execute(&op);
164 }
165 if (cm()->restart_for_overflow()) {
166 if (G1TraceMarkStackOverflow) {
167 gclog_or_tty->print_cr("Restarting conc marking because of MS overflow "
168 "in remark (restart #%d).", iter);
169 }
170 if (G1Log::fine()) {
171 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
172 gclog_or_tty->print_cr("[GC concurrent-mark-restart-for-overflow]");
173 }
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 if (G1Log::fine()) {
214 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
215 gclog_or_tty->print_cr("[GC concurrent-cleanup-start]");
216 }
217
218 // Now do the concurrent cleanup operation.
219 _cm->completeCleanup();
220
221 // Notify anyone who's waiting that there are no more free
222 // regions coming. We have to do this before we join the STS
223 // (in fact, we should not attempt to join the STS in the
224 // interval between finishing the cleanup pause and clearing
225 // the free_regions_coming flag) otherwise we might deadlock:
226 // a GC worker could be blocked waiting for the notification
227 // whereas this thread will be blocked for the pause to finish
228 // while it's trying to join the STS, which is conditional on
229 // the GC workers finishing.
230 g1h->reset_free_regions_coming();
231
232 double cleanup_end_sec = os::elapsedTime();
233 if (G1Log::fine()) {
234 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
235 gclog_or_tty->print_cr("[GC concurrent-cleanup-end, %1.7lf secs]",
236 cleanup_end_sec - cleanup_start_sec);
237 }
238 }
239 guarantee(cm()->cleanup_list_is_empty(),
240 "at this point there should be no regions on the cleanup list");
241
242 // There is a tricky race before recording that the concurrent
243 // cleanup has completed and a potential Full GC starting around
244 // the same time. We want to make sure that the Full GC calls
245 // abort() on concurrent mark after
246 // record_concurrent_mark_cleanup_completed(), since abort() is
247 // the method that will reset the concurrent mark state. If we
248 // end up calling record_concurrent_mark_cleanup_completed()
249 // after abort() then we might incorrectly undo some of the work
250 // abort() did. Checking the has_aborted() flag after joining
251 // the STS allows the correct ordering of the two methods. There
252 // are two scenarios:
253 //
254 // a) If we reach here before the Full GC, the fact that we have
255 // joined the STS means that the Full GC cannot start until we
256 // leave the STS, so record_concurrent_mark_cleanup_completed()
257 // will complete before abort() is called.
258 //
259 // b) If we reach here during the Full GC, we'll be held up from
260 // joining the STS until the Full GC is done, which means that
261 // abort() will have completed and has_aborted() will return
262 // true to prevent us from calling
263 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
264 // not needed any more as the concurrent mark state has been
265 // already reset).
266 {
267 SuspendibleThreadSetJoiner sts_join;
268 if (!cm()->has_aborted()) {
269 g1_policy->record_concurrent_mark_cleanup_completed();
270 }
271 }
272
273 if (cm()->has_aborted()) {
274 if (G1Log::fine()) {
275 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
276 gclog_or_tty->print_cr("[GC concurrent-mark-abort]");
277 }
278 }
279
280 // We now want to allow clearing of the marking bitmap to be
281 // suspended by a collection pause.
282 // We may have aborted just before the remark. Do not bother clearing the
283 // bitmap then, as it has been done during mark abort.
284 if (!cm()->has_aborted()) {
285 _cm->clearNextBitmap();
286 } else {
287 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
288 }
289 }
290
291 // Update the number of full collections that have been
292 // completed. This will also notify the FullGCCount_lock in case a
293 // Java thread is waiting for a full GC to happen (e.g., it
294 // called System.gc() with +ExplicitGCInvokesConcurrent).
295 {
296 SuspendibleThreadSetJoiner sts_join;
297 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
298 g1h->register_concurrent_cycle_end();
299 }
300 }
301 assert(_should_terminate, "just checking");
302
303 terminate();
304 }
305
306 void ConcurrentMarkThread::stop() {
307 {
308 MutexLockerEx ml(Terminator_lock);
309 _should_terminate = true;
310 }
311
312 {
313 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
314 CGC_lock->notify_all();
315 }
316
317 {
318 MutexLockerEx ml(Terminator_lock);
319 while (!_has_terminated) {
320 Terminator_lock->wait();
321 }
322 }
323 }
324
325 void ConcurrentMarkThread::sleepBeforeNextCycle() {
326 // We join here because we don't want to do the "shouldConcurrentMark()"
327 // below while the world is otherwise stopped.
328 assert(!in_progress(), "should have been cleared");
329
330 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
331 while (!started() && !_should_terminate) {
332 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
333 }
334
335 if (started()) {
336 set_in_progress();
337 OrderAccess::storestore();
338 clear_started();
339 }
340 }
341
342 // Note: As is the case with CMS - this method, although exported
343 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
344 // be called by a JavaThread. Currently this is done at vm creation
345 // time (post-vm-init) by the main/Primordial (Java)Thread.
346 // XXX Consider changing this in the future to allow the CM thread
347 // itself to create this thread?
348 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
349 assert(UseG1GC, "SLT thread needed only for concurrent GC");
350 assert(THREAD->is_Java_thread(), "must be a Java thread");
351 assert(_slt == NULL, "SLT already created");
352 _slt = SurrogateLockerThread::make(THREAD);
353 }