1 /* 2 * Copyright (c) 2001, 2016, 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 "classfile/classLoaderData.hpp" 27 #include "gc/g1/concurrentMarkThread.inline.hpp" 28 #include "gc/g1/g1Analytics.hpp" 29 #include "gc/g1/g1CollectedHeap.inline.hpp" 30 #include "gc/g1/g1CollectorPolicy.hpp" 31 #include "gc/g1/g1MMUTracker.hpp" 32 #include "gc/g1/suspendibleThreadSet.hpp" 33 #include "gc/g1/vm_operations_g1.hpp" 34 #include "gc/shared/gcId.hpp" 35 #include "gc/shared/gcTrace.hpp" 36 #include "gc/shared/gcTraceTime.inline.hpp" 37 #include "logging/log.hpp" 38 #include "memory/resourceArea.hpp" 39 #include "runtime/vmThread.hpp" 40 41 // ======= Concurrent Mark Thread ======== 42 43 // The CM thread is created when the G1 garbage collector is used 44 45 SurrogateLockerThread* 46 ConcurrentMarkThread::_slt = NULL; 47 48 ConcurrentMarkThread::ConcurrentMarkThread(G1ConcurrentMark* cm) : 49 ConcurrentGCThread(), 50 _cm(cm), 51 _state(Idle), 52 _vtime_accum(0.0), 53 _vtime_mark_accum(0.0) { 54 55 set_name("G1 Main Marker"); 56 create_and_start(); 57 } 58 59 class CMCheckpointRootsFinalClosure: public VoidClosure { 60 61 G1ConcurrentMark* _cm; 62 public: 63 64 CMCheckpointRootsFinalClosure(G1ConcurrentMark* cm) : 65 _cm(cm) {} 66 67 void do_void(){ 68 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs 69 } 70 }; 71 72 class CMCleanUp: public VoidClosure { 73 G1ConcurrentMark* _cm; 74 public: 75 76 CMCleanUp(G1ConcurrentMark* cm) : 77 _cm(cm) {} 78 79 void do_void(){ 80 _cm->cleanup(); 81 } 82 }; 83 84 // Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU. 85 void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) { 86 const G1Analytics* analytics = g1_policy->analytics(); 87 if (g1_policy->adaptive_young_list_length()) { 88 double now = os::elapsedTime(); 89 double prediction_ms = remark ? analytics->predict_remark_time_ms() 90 : analytics->predict_cleanup_time_ms(); 91 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker(); 92 jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms); 93 os::sleep(this, sleep_time_ms, false); 94 } 95 } 96 97 class GCConcPhaseTimer : StackObj { 98 G1ConcurrentMark* _cm; 99 100 public: 101 GCConcPhaseTimer(G1ConcurrentMark* cm, const char* title) : _cm(cm) { 102 _cm->register_concurrent_phase_start(title); 103 } 104 105 ~GCConcPhaseTimer() { 106 _cm->register_concurrent_phase_end(); 107 } 108 }; 109 110 void ConcurrentMarkThread::run() { 111 initialize_in_thread(); 112 wait_for_universe_init(); 113 114 run_service(); 115 116 terminate(); 117 } 118 119 void ConcurrentMarkThread::run_service() { 120 _vtime_start = os::elapsedVTime(); 121 122 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 123 G1CollectorPolicy* g1_policy = g1h->g1_policy(); 124 125 while (!_should_terminate) { 126 // wait until started is set. 127 sleepBeforeNextCycle(); 128 if (_should_terminate) { 129 _cm->root_regions()->cancel_scan(); 130 break; 131 } 132 133 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC."); 134 { 135 ResourceMark rm; 136 HandleMark hm; 137 double cycle_start = os::elapsedVTime(); 138 139 { 140 GCConcPhaseTimer(_cm, "Concurrent Clearing of Claimed Marks"); 141 ClassLoaderDataGraph::clear_claimed_marks(); 142 } 143 144 // We have to ensure that we finish scanning the root regions 145 // before the next GC takes place. To ensure this we have to 146 // make sure that we do not join the STS until the root regions 147 // have been scanned. If we did then it's possible that a 148 // subsequent GC could block us from joining the STS and proceed 149 // without the root regions have been scanned which would be a 150 // correctness issue. 151 152 { 153 GCConcPhaseTimer(_cm, "Concurrent Root Region Scanning"); 154 _cm->scanRootRegions(); 155 } 156 157 // It would be nice to use the GCTraceConcTime class here but 158 // the "end" logging is inside the loop and not at the end of 159 // a scope. Mimicking the same log output as GCTraceConcTime instead. 160 jlong mark_start = os::elapsed_counter(); 161 log_info(gc)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start)); 162 163 int iter = 0; 164 do { 165 iter++; 166 if (!cm()->has_aborted()) { 167 GCConcPhaseTimer(_cm, "Concurrent Mark"); 168 _cm->markFromRoots(); 169 } 170 171 double mark_end_time = os::elapsedVTime(); 172 jlong mark_end = os::elapsed_counter(); 173 _vtime_mark_accum += (mark_end_time - cycle_start); 174 if (!cm()->has_aborted()) { 175 delay_to_keep_mmu(g1_policy, true /* remark */); 176 log_info(gc)("Concurrent Mark (%.3fs, %.3fs) %.3fms", 177 TimeHelper::counter_to_seconds(mark_start), 178 TimeHelper::counter_to_seconds(mark_end), 179 TimeHelper::counter_to_millis(mark_end - mark_start)); 180 181 CMCheckpointRootsFinalClosure final_cl(_cm); 182 VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */); 183 VMThread::execute(&op); 184 } 185 if (cm()->restart_for_overflow()) { 186 log_debug(gc)("Restarting conc marking because of MS overflow in remark (restart #%d).", iter); 187 log_info(gc)("Concurrent Mark restart for overflow"); 188 } 189 } while (cm()->restart_for_overflow()); 190 191 double end_time = os::elapsedVTime(); 192 // Update the total virtual time before doing this, since it will try 193 // to measure it to get the vtime for this marking. We purposely 194 // neglect the presumably-short "completeCleanup" phase here. 195 _vtime_accum = (end_time - _vtime_start); 196 197 if (!cm()->has_aborted()) { 198 delay_to_keep_mmu(g1_policy, false /* cleanup */); 199 200 CMCleanUp cl_cl(_cm); 201 VM_CGC_Operation op(&cl_cl, "Pause Cleanup", false /* needs_pll */); 202 VMThread::execute(&op); 203 } else { 204 // We don't want to update the marking status if a GC pause 205 // is already underway. 206 SuspendibleThreadSetJoiner sts_join; 207 g1h->collector_state()->set_mark_in_progress(false); 208 } 209 210 // Check if cleanup set the free_regions_coming flag. If it 211 // hasn't, we can just skip the next step. 212 if (g1h->free_regions_coming()) { 213 // The following will finish freeing up any regions that we 214 // found to be empty during cleanup. We'll do this part 215 // without joining the suspendible set. If an evacuation pause 216 // takes place, then we would carry on freeing regions in 217 // case they are needed by the pause. If a Full GC takes 218 // place, it would wait for us to process the regions 219 // reclaimed by cleanup. 220 221 GCTraceConcTime(Info, gc) tt("Concurrent Cleanup"); 222 GCConcPhaseTimer(_cm, "Concurrent Cleanup"); 223 224 // Now do the concurrent cleanup operation. 225 _cm->completeCleanup(); 226 227 // Notify anyone who's waiting that there are no more free 228 // regions coming. We have to do this before we join the STS 229 // (in fact, we should not attempt to join the STS in the 230 // interval between finishing the cleanup pause and clearing 231 // the free_regions_coming flag) otherwise we might deadlock: 232 // a GC worker could be blocked waiting for the notification 233 // whereas this thread will be blocked for the pause to finish 234 // while it's trying to join the STS, which is conditional on 235 // the GC workers finishing. 236 g1h->reset_free_regions_coming(); 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 } else { 270 log_info(gc)("Concurrent Mark abort"); 271 } 272 } 273 274 // We now want to allow clearing of the marking bitmap to be 275 // suspended by a collection pause. 276 // We may have aborted just before the remark. Do not bother clearing the 277 // bitmap then, as it has been done during mark abort. 278 if (!cm()->has_aborted()) { 279 GCConcPhaseTimer(_cm, "Concurrent Bitmap Clearing"); 280 _cm->clearNextBitmap(); 281 } else { 282 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear"); 283 } 284 } 285 286 // Update the number of full collections that have been 287 // completed. This will also notify the FullGCCount_lock in case a 288 // Java thread is waiting for a full GC to happen (e.g., it 289 // called System.gc() with +ExplicitGCInvokesConcurrent). 290 { 291 SuspendibleThreadSetJoiner sts_join; 292 g1h->increment_old_marking_cycles_completed(true /* concurrent */); 293 g1h->register_concurrent_cycle_end(); 294 } 295 } 296 } 297 298 void ConcurrentMarkThread::stop() { 299 { 300 MutexLockerEx ml(Terminator_lock); 301 _should_terminate = true; 302 } 303 304 stop_service(); 305 306 { 307 MutexLockerEx ml(Terminator_lock); 308 while (!_has_terminated) { 309 Terminator_lock->wait(); 310 } 311 } 312 } 313 314 void ConcurrentMarkThread::stop_service() { 315 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag); 316 CGC_lock->notify_all(); 317 } 318 319 void ConcurrentMarkThread::sleepBeforeNextCycle() { 320 // We join here because we don't want to do the "shouldConcurrentMark()" 321 // below while the world is otherwise stopped. 322 assert(!in_progress(), "should have been cleared"); 323 324 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 325 while (!started() && !_should_terminate) { 326 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 327 } 328 329 if (started()) { 330 set_in_progress(); 331 } 332 } 333 334 // Note: As is the case with CMS - this method, although exported 335 // by the ConcurrentMarkThread, which is a non-JavaThread, can only 336 // be called by a JavaThread. Currently this is done at vm creation 337 // time (post-vm-init) by the main/Primordial (Java)Thread. 338 // XXX Consider changing this in the future to allow the CM thread 339 // itself to create this thread? 340 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) { 341 assert(UseG1GC, "SLT thread needed only for concurrent GC"); 342 assert(THREAD->is_Java_thread(), "must be a Java thread"); 343 assert(_slt == NULL, "SLT already created"); 344 _slt = SurrogateLockerThread::make(THREAD); 345 }