Tue, 05 Jun 2012 22:30:24 +0200
7172388: G1: _total_full_collections should not be incremented for concurrent cycles
Reviewed-by: azeemj, jmasa
1 /*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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23 */
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 "memory/resourceArea.hpp"
33 #include "runtime/vmThread.hpp"
35 // ======= Concurrent Mark Thread ========
37 // The CM thread is created when the G1 garbage collector is used
39 SurrogateLockerThread*
40 ConcurrentMarkThread::_slt = NULL;
42 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* cm) :
43 ConcurrentGCThread(),
44 _cm(cm),
45 _started(false),
46 _in_progress(false),
47 _vtime_accum(0.0),
48 _vtime_mark_accum(0.0) {
49 create_and_start();
50 }
52 class CMCheckpointRootsFinalClosure: public VoidClosure {
54 ConcurrentMark* _cm;
55 public:
57 CMCheckpointRootsFinalClosure(ConcurrentMark* cm) :
58 _cm(cm) {}
60 void do_void(){
61 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
62 }
63 };
65 class CMCleanUp: public VoidClosure {
66 ConcurrentMark* _cm;
67 public:
69 CMCleanUp(ConcurrentMark* cm) :
70 _cm(cm) {}
72 void do_void(){
73 _cm->cleanup();
74 }
75 };
79 void ConcurrentMarkThread::run() {
80 initialize_in_thread();
81 _vtime_start = os::elapsedVTime();
82 wait_for_universe_init();
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();
89 while (!_should_terminate) {
90 // wait until started is set.
91 sleepBeforeNextCycle();
92 {
93 ResourceMark rm;
94 HandleMark hm;
95 double cycle_start = os::elapsedVTime();
96 char verbose_str[128];
98 // We have to ensure that we finish scanning the root regions
99 // before the next GC takes place. To ensure this we have to
100 // make sure that we do not join the STS until the root regions
101 // have been scanned. If we did then it's possible that a
102 // subsequent GC could block us from joining the STS and proceed
103 // without the root regions have been scanned which would be a
104 // correctness issue.
106 double scan_start = os::elapsedTime();
107 if (!cm()->has_aborted()) {
108 if (G1Log::fine()) {
109 gclog_or_tty->date_stamp(PrintGCDateStamps);
110 gclog_or_tty->stamp(PrintGCTimeStamps);
111 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-start]");
112 }
114 _cm->scanRootRegions();
116 double scan_end = os::elapsedTime();
117 if (G1Log::fine()) {
118 gclog_or_tty->date_stamp(PrintGCDateStamps);
119 gclog_or_tty->stamp(PrintGCTimeStamps);
120 gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf]",
121 scan_end - scan_start);
122 }
123 }
125 double mark_start_sec = os::elapsedTime();
126 if (G1Log::fine()) {
127 gclog_or_tty->date_stamp(PrintGCDateStamps);
128 gclog_or_tty->stamp(PrintGCTimeStamps);
129 gclog_or_tty->print_cr("[GC concurrent-mark-start]");
130 }
132 int iter = 0;
133 do {
134 iter++;
135 if (!cm()->has_aborted()) {
136 _cm->markFromRoots();
137 }
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 }
150 if (G1Log::fine()) {
151 gclog_or_tty->date_stamp(PrintGCDateStamps);
152 gclog_or_tty->stamp(PrintGCTimeStamps);
153 gclog_or_tty->print_cr("[GC concurrent-mark-end, %1.7lf sec]",
154 mark_end_sec - mark_start_sec);
155 }
157 CMCheckpointRootsFinalClosure final_cl(_cm);
158 sprintf(verbose_str, "GC remark");
159 VM_CGC_Operation op(&final_cl, verbose_str, true /* needs_pll */);
160 VMThread::execute(&op);
161 }
162 if (cm()->restart_for_overflow() &&
163 G1TraceMarkStackOverflow) {
164 gclog_or_tty->print_cr("Restarting conc marking because of MS overflow "
165 "in remark (restart #%d).", iter);
166 }
168 if (cm()->restart_for_overflow()) {
169 if (G1Log::fine()) {
170 gclog_or_tty->date_stamp(PrintGCDateStamps);
171 gclog_or_tty->stamp(PrintGCTimeStamps);
172 gclog_or_tty->print_cr("[GC concurrent-mark-restart-for-overflow]");
173 }
174 }
175 } while (cm()->restart_for_overflow());
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);
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 }
191 CMCleanUp cl_cl(_cm);
192 sprintf(verbose_str, "GC cleanup");
193 VM_CGC_Operation op(&cl_cl, verbose_str, false /* needs_pll */);
194 VMThread::execute(&op);
195 } else {
196 // We don't want to update the marking status if a GC pause
197 // is already underway.
198 _sts.join();
199 g1h->set_marking_complete();
200 _sts.leave();
201 }
203 // Check if cleanup set the free_regions_coming flag. If it
204 // hasn't, we can just skip the next step.
205 if (g1h->free_regions_coming()) {
206 // The following will finish freeing up any regions that we
207 // found to be empty during cleanup. We'll do this part
208 // without joining the suspendible set. If an evacuation pause
209 // takes place, then we would carry on freeing regions in
210 // case they are needed by the pause. If a Full GC takes
211 // place, it would wait for us to process the regions
212 // reclaimed by cleanup.
214 double cleanup_start_sec = os::elapsedTime();
215 if (G1Log::fine()) {
216 gclog_or_tty->date_stamp(PrintGCDateStamps);
217 gclog_or_tty->stamp(PrintGCTimeStamps);
218 gclog_or_tty->print_cr("[GC concurrent-cleanup-start]");
219 }
221 // Now do the concurrent cleanup operation.
222 _cm->completeCleanup();
224 // Notify anyone who's waiting that there are no more free
225 // regions coming. We have to do this before we join the STS
226 // (in fact, we should not attempt to join the STS in the
227 // interval between finishing the cleanup pause and clearing
228 // the free_regions_coming flag) otherwise we might deadlock:
229 // a GC worker could be blocked waiting for the notification
230 // whereas this thread will be blocked for the pause to finish
231 // while it's trying to join the STS, which is conditional on
232 // the GC workers finishing.
233 g1h->reset_free_regions_coming();
235 double cleanup_end_sec = os::elapsedTime();
236 if (G1Log::fine()) {
237 gclog_or_tty->date_stamp(PrintGCDateStamps);
238 gclog_or_tty->stamp(PrintGCTimeStamps);
239 gclog_or_tty->print_cr("[GC concurrent-cleanup-end, %1.7lf]",
240 cleanup_end_sec - cleanup_start_sec);
241 }
242 }
243 guarantee(cm()->cleanup_list_is_empty(),
244 "at this point there should be no regions on the cleanup list");
246 // There is a tricky race before recording that the concurrent
247 // cleanup has completed and a potential Full GC starting around
248 // the same time. We want to make sure that the Full GC calls
249 // abort() on concurrent mark after
250 // record_concurrent_mark_cleanup_completed(), since abort() is
251 // the method that will reset the concurrent mark state. If we
252 // end up calling record_concurrent_mark_cleanup_completed()
253 // after abort() then we might incorrectly undo some of the work
254 // abort() did. Checking the has_aborted() flag after joining
255 // the STS allows the correct ordering of the two methods. There
256 // are two scenarios:
257 //
258 // a) If we reach here before the Full GC, the fact that we have
259 // joined the STS means that the Full GC cannot start until we
260 // leave the STS, so record_concurrent_mark_cleanup_completed()
261 // will complete before abort() is called.
262 //
263 // b) If we reach here during the Full GC, we'll be held up from
264 // joining the STS until the Full GC is done, which means that
265 // abort() will have completed and has_aborted() will return
266 // true to prevent us from calling
267 // record_concurrent_mark_cleanup_completed() (and, in fact, it's
268 // not needed any more as the concurrent mark state has been
269 // already reset).
270 _sts.join();
271 if (!cm()->has_aborted()) {
272 g1_policy->record_concurrent_mark_cleanup_completed();
273 }
274 _sts.leave();
276 if (cm()->has_aborted()) {
277 if (G1Log::fine()) {
278 gclog_or_tty->date_stamp(PrintGCDateStamps);
279 gclog_or_tty->stamp(PrintGCTimeStamps);
280 gclog_or_tty->print_cr("[GC concurrent-mark-abort]");
281 }
282 }
284 // We now want to allow clearing of the marking bitmap to be
285 // suspended by a collection pause.
286 _sts.join();
287 _cm->clearNextBitmap();
288 _sts.leave();
289 }
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 _sts.join();
296 g1h->increment_old_marking_cycles_completed(true /* concurrent */);
297 _sts.leave();
298 }
299 assert(_should_terminate, "just checking");
301 terminate();
302 }
305 void ConcurrentMarkThread::yield() {
306 _sts.yield("Concurrent Mark");
307 }
309 void ConcurrentMarkThread::stop() {
310 // it is ok to take late safepoints here, if needed
311 MutexLockerEx mu(Terminator_lock);
312 _should_terminate = true;
313 while (!_has_terminated) {
314 Terminator_lock->wait();
315 }
316 }
318 void ConcurrentMarkThread::print() const {
319 print_on(tty);
320 }
322 void ConcurrentMarkThread::print_on(outputStream* st) const {
323 st->print("\"G1 Main Concurrent Mark GC Thread\" ");
324 Thread::print_on(st);
325 st->cr();
326 }
328 void ConcurrentMarkThread::sleepBeforeNextCycle() {
329 // We join here because we don't want to do the "shouldConcurrentMark()"
330 // below while the world is otherwise stopped.
331 assert(!in_progress(), "should have been cleared");
333 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
334 while (!started()) {
335 CGC_lock->wait(Mutex::_no_safepoint_check_flag);
336 }
337 set_in_progress();
338 clear_started();
339 }
341 // Note: As is the case with CMS - this method, although exported
342 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
343 // be called by a JavaThread. Currently this is done at vm creation
344 // time (post-vm-init) by the main/Primordial (Java)Thread.
345 // XXX Consider changing this in the future to allow the CM thread
346 // itself to create this thread?
347 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
348 assert(UseG1GC, "SLT thread needed only for concurrent GC");
349 assert(THREAD->is_Java_thread(), "must be a Java thread");
350 assert(_slt == NULL, "SLT already created");
351 _slt = SurrogateLockerThread::make(THREAD);
352 }