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/gcId.hpp" 34 #include "gc/shared/gcTrace.hpp" 35 #include "memory/resourceArea.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 _state(Idle), 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. So, if necessary join the STS to ensure 83 // that the logging is done either before or after the STW logging. 84 void ConcurrentMarkThread::cm_log(bool doit, bool join_sts, const char* fmt, ...) { 85 if (doit) { 86 SuspendibleThreadSetJoiner sts_joiner(join_sts); 87 va_list args; 88 va_start(args, fmt); 89 gclog_or_tty->gclog_stamp(); 90 gclog_or_tty->vprint_cr(fmt, args); 91 va_end(args); 92 } 93 } 94 95 // Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU. 96 void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) { 97 if (g1_policy->adaptive_young_list_length()) { 98 double now = os::elapsedTime(); 99 double prediction_ms = remark ? g1_policy->predict_remark_time_ms() 100 : g1_policy->predict_cleanup_time_ms(); 101 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker(); 102 jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms); 103 os::sleep(this, sleep_time_ms, false); 104 } 105 } 106 void ConcurrentMarkThread::run() { 107 initialize_in_thread(); 108 wait_for_universe_init(); 109 110 run_service(); 111 112 terminate(); 113 } 114 115 void ConcurrentMarkThread::run_service() { 116 _vtime_start = os::elapsedVTime(); 117 118 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 119 G1CollectorPolicy* g1_policy = g1h->g1_policy(); 120 121 while (!_should_terminate) { 122 // wait until started is set. 123 sleepBeforeNextCycle(); 124 if (_should_terminate) { 125 break; 126 } 127 128 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC."); 129 { 130 ResourceMark rm; 131 HandleMark hm; 132 double cycle_start = os::elapsedVTime(); 133 134 // We have to ensure that we finish scanning the root regions 135 // before the next GC takes place. To ensure this we have to 136 // make sure that we do not join the STS until the root regions 137 // have been scanned. If we did then it's possible that a 138 // subsequent GC could block us from joining the STS and proceed 139 // without the root regions have been scanned which would be a 140 // correctness issue. 141 142 if (!cm()->has_aborted()) { 143 _cm->scanRootRegions(); 144 } 145 146 double mark_start_sec = os::elapsedTime(); 147 cm_log(G1Log::fine(), true, "[GC concurrent-mark-start]"); 148 149 int iter = 0; 150 do { 151 iter++; 152 if (!cm()->has_aborted()) { 153 _cm->markFromRoots(); 154 } 155 156 double mark_end_time = os::elapsedVTime(); 157 double mark_end_sec = os::elapsedTime(); 158 _vtime_mark_accum += (mark_end_time - cycle_start); 159 if (!cm()->has_aborted()) { 160 delay_to_keep_mmu(g1_policy, true /* remark */); 161 162 cm_log(G1Log::fine(), true, "[GC concurrent-mark-end, %1.7lf secs]", mark_end_sec - mark_start_sec); 163 164 CMCheckpointRootsFinalClosure final_cl(_cm); 165 VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */); 166 VMThread::execute(&op); 167 } 168 if (cm()->restart_for_overflow()) { 169 cm_log(G1TraceMarkStackOverflow, true, "Restarting conc marking because of MS overflow in remark (restart #%d).", iter); 170 cm_log(G1Log::fine(), true, "[GC concurrent-mark-restart-for-overflow]"); 171 } 172 } while (cm()->restart_for_overflow()); 173 174 double end_time = os::elapsedVTime(); 175 // Update the total virtual time before doing this, since it will try 176 // to measure it to get the vtime for this marking. We purposely 177 // neglect the presumably-short "completeCleanup" phase here. 178 _vtime_accum = (end_time - _vtime_start); 179 180 if (!cm()->has_aborted()) { 181 delay_to_keep_mmu(g1_policy, false /* cleanup */); 182 183 CMCleanUp cl_cl(_cm); 184 VM_CGC_Operation op(&cl_cl, "GC cleanup", false /* needs_pll */); 185 VMThread::execute(&op); 186 } else { 187 // We don't want to update the marking status if a GC pause 188 // is already underway. 189 SuspendibleThreadSetJoiner sts_join; 190 g1h->collector_state()->set_mark_in_progress(false); 191 } 192 193 // Check if cleanup set the free_regions_coming flag. If it 194 // hasn't, we can just skip the next step. 195 if (g1h->free_regions_coming()) { 196 // The following will finish freeing up any regions that we 197 // found to be empty during cleanup. We'll do this part 198 // without joining the suspendible set. If an evacuation pause 199 // takes place, then we would carry on freeing regions in 200 // case they are needed by the pause. If a Full GC takes 201 // place, it would wait for us to process the regions 202 // reclaimed by cleanup. 203 204 double cleanup_start_sec = os::elapsedTime(); 205 cm_log(G1Log::fine(), false, "[GC concurrent-cleanup-start]"); 206 207 // Now do the concurrent cleanup operation. 208 _cm->completeCleanup(); 209 210 // Notify anyone who's waiting that there are no more free 211 // regions coming. We have to do this before we join the STS 212 // (in fact, we should not attempt to join the STS in the 213 // interval between finishing the cleanup pause and clearing 214 // the free_regions_coming flag) otherwise we might deadlock: 215 // a GC worker could be blocked waiting for the notification 216 // whereas this thread will be blocked for the pause to finish 217 // while it's trying to join the STS, which is conditional on 218 // the GC workers finishing. 219 g1h->reset_free_regions_coming(); 220 221 double cleanup_end_sec = os::elapsedTime(); 222 cm_log(G1Log::fine(), true, "[GC concurrent-cleanup-end, %1.7lf secs]", cleanup_end_sec - cleanup_start_sec); 223 } 224 guarantee(cm()->cleanup_list_is_empty(), 225 "at this point there should be no regions on the cleanup list"); 226 227 // There is a tricky race before recording that the concurrent 228 // cleanup has completed and a potential Full GC starting around 229 // the same time. We want to make sure that the Full GC calls 230 // abort() on concurrent mark after 231 // record_concurrent_mark_cleanup_completed(), since abort() is 232 // the method that will reset the concurrent mark state. If we 233 // end up calling record_concurrent_mark_cleanup_completed() 234 // after abort() then we might incorrectly undo some of the work 235 // abort() did. Checking the has_aborted() flag after joining 236 // the STS allows the correct ordering of the two methods. There 237 // are two scenarios: 238 // 239 // a) If we reach here before the Full GC, the fact that we have 240 // joined the STS means that the Full GC cannot start until we 241 // leave the STS, so record_concurrent_mark_cleanup_completed() 242 // will complete before abort() is called. 243 // 244 // b) If we reach here during the Full GC, we'll be held up from 245 // joining the STS until the Full GC is done, which means that 246 // abort() will have completed and has_aborted() will return 247 // true to prevent us from calling 248 // record_concurrent_mark_cleanup_completed() (and, in fact, it's 249 // not needed any more as the concurrent mark state has been 250 // already reset). 251 { 252 SuspendibleThreadSetJoiner sts_join; 253 if (!cm()->has_aborted()) { 254 g1_policy->record_concurrent_mark_cleanup_completed(); 255 } else { 256 cm_log(G1Log::fine(), false, "[GC concurrent-mark-abort]"); 257 } 258 } 259 260 // We now want to allow clearing of the marking bitmap to be 261 // suspended by a collection pause. 262 // We may have aborted just before the remark. Do not bother clearing the 263 // bitmap then, as it has been done during mark abort. 264 if (!cm()->has_aborted()) { 265 _cm->clearNextBitmap(); 266 } else { 267 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear"); 268 } 269 } 270 271 // Update the number of full collections that have been 272 // completed. This will also notify the FullGCCount_lock in case a 273 // Java thread is waiting for a full GC to happen (e.g., it 274 // called System.gc() with +ExplicitGCInvokesConcurrent). 275 { 276 SuspendibleThreadSetJoiner sts_join; 277 g1h->increment_old_marking_cycles_completed(true /* concurrent */); 278 g1h->register_concurrent_cycle_end(); 279 } 280 } 281 } 282 283 void ConcurrentMarkThread::stop() { 284 { 285 MutexLockerEx ml(Terminator_lock); 286 _should_terminate = true; 287 } 288 289 stop_service(); 290 291 { 292 MutexLockerEx ml(Terminator_lock); 293 while (!_has_terminated) { 294 Terminator_lock->wait(); 295 } 296 } 297 } 298 299 void ConcurrentMarkThread::stop_service() { 300 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag); 301 CGC_lock->notify_all(); 302 } 303 304 void ConcurrentMarkThread::sleepBeforeNextCycle() { 305 // We join here because we don't want to do the "shouldConcurrentMark()" 306 // below while the world is otherwise stopped. 307 assert(!in_progress(), "should have been cleared"); 308 309 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 310 while (!started() && !_should_terminate) { 311 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 312 } 313 314 if (started()) { 315 set_in_progress(); 316 } 317 } 318 319 // Note: As is the case with CMS - this method, although exported 320 // by the ConcurrentMarkThread, which is a non-JavaThread, can only 321 // be called by a JavaThread. Currently this is done at vm creation 322 // time (post-vm-init) by the main/Primordial (Java)Thread. 323 // XXX Consider changing this in the future to allow the CM thread 324 // itself to create this thread? 325 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) { 326 assert(UseG1GC, "SLT thread needed only for concurrent GC"); 327 assert(THREAD->is_Java_thread(), "must be a Java thread"); 328 assert(_slt == NULL, "SLT already created"); 329 _slt = SurrogateLockerThread::make(THREAD); 330 }