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/g1CollectedHeap.inline.hpp" 29 #include "gc/g1/g1CollectorPolicy.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 "gc/shared/gcTraceTime.inline.hpp" 36 #include "logging/log.hpp" 37 #include "memory/resourceArea.hpp" 38 #include "runtime/vmThread.hpp" 39 40 // ======= Concurrent Mark Thread ======== 41 42 // The CM thread is created when the G1 garbage collector is used 43 44 SurrogateLockerThread* 45 ConcurrentMarkThread::_slt = NULL; 46 47 ConcurrentMarkThread::ConcurrentMarkThread(G1ConcurrentMark* cm) : 48 ConcurrentGCThread(), 49 _cm(cm), 50 _state(Idle), 51 _vtime_accum(0.0), 52 _vtime_mark_accum(0.0) { 53 54 set_name("G1 Main Marker"); 55 create_and_start(); 56 } 57 58 class CMCheckpointRootsFinalClosure: public VoidClosure { 59 60 G1ConcurrentMark* _cm; 61 public: 62 63 CMCheckpointRootsFinalClosure(G1ConcurrentMark* cm) : 64 _cm(cm) {} 65 66 void do_void(){ 67 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs 68 } 69 }; 70 71 class CMCleanUp: public VoidClosure { 72 G1ConcurrentMark* _cm; 73 public: 74 75 CMCleanUp(G1ConcurrentMark* cm) : 76 _cm(cm) {} 77 78 void do_void(){ 79 _cm->cleanup(); 80 } 81 }; 82 83 // Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU. 84 void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) { 85 if (g1_policy->adaptive_young_list_length()) { 86 double now = os::elapsedTime(); 87 double prediction_ms = remark ? g1_policy->predict_remark_time_ms() 88 : g1_policy->predict_cleanup_time_ms(); 89 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker(); 90 jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms); 91 os::sleep(this, sleep_time_ms, false); 92 } 93 } 94 95 class GCConcPhaseTimer : StackObj { 96 G1ConcurrentMark* _cm; 97 98 public: 99 GCConcPhaseTimer(G1ConcurrentMark* cm, const char* title) : _cm(cm) { 100 _cm->register_concurrent_phase_start(title); 101 } 102 103 ~GCConcPhaseTimer() { 104 _cm->register_concurrent_phase_end(); 105 } 106 }; 107 108 void ConcurrentMarkThread::run() { 109 initialize_in_thread(); 110 wait_for_universe_init(); 111 112 run_service(); 113 114 terminate(); 115 } 116 117 void ConcurrentMarkThread::run_service() { 118 _vtime_start = os::elapsedVTime(); 119 120 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 121 G1CollectorPolicy* g1_policy = g1h->g1_policy(); 122 123 while (!_should_terminate) { 124 // wait until started is set. 125 sleepBeforeNextCycle(); 126 if (_should_terminate) { 127 _cm->root_regions()->cancel_scan(); 128 break; 129 } 130 131 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC."); 132 { 133 ResourceMark rm; 134 HandleMark hm; 135 double cycle_start = os::elapsedVTime(); 136 137 { 138 GCConcPhaseTimer(_cm, "Concurrent Clearing of Claimed Marks"); 139 ClassLoaderDataGraph::clear_claimed_marks(); 140 } 141 142 // We have to ensure that we finish scanning the root regions 143 // before the next GC takes place. To ensure this we have to 144 // make sure that we do not join the STS until the root regions 145 // have been scanned. If we did then it's possible that a 146 // subsequent GC could block us from joining the STS and proceed 147 // without the root regions have been scanned which would be a 148 // correctness issue. 149 150 { 151 GCConcPhaseTimer(_cm, "Concurrent Root Region Scanning"); 152 _cm->scanRootRegions(); 153 } 154 155 // It would be nice to use the GCTraceConcTime class here but 156 // the "end" logging is inside the loop and not at the end of 157 // a scope. Mimicking the same log output as GCTraceConcTime instead. 158 jlong mark_start = os::elapsed_counter(); 159 log_info(gc)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start)); 160 161 int iter = 0; 162 do { 163 iter++; 164 if (!cm()->has_aborted()) { 165 GCConcPhaseTimer(_cm, "Concurrent Mark"); 166 _cm->markFromRoots(); 167 } 168 169 double mark_end_time = os::elapsedVTime(); 170 jlong mark_end = os::elapsed_counter(); 171 _vtime_mark_accum += (mark_end_time - cycle_start); 172 if (!cm()->has_aborted()) { 173 delay_to_keep_mmu(g1_policy, true /* remark */); 174 log_info(gc)("Concurrent Mark (%.3fs, %.3fs) %.3fms", 175 TimeHelper::counter_to_seconds(mark_start), 176 TimeHelper::counter_to_seconds(mark_end), 177 TimeHelper::counter_to_millis(mark_end - mark_start)); 178 179 CMCheckpointRootsFinalClosure final_cl(_cm); 180 VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */); 181 VMThread::execute(&op); 182 } 183 if (cm()->restart_for_overflow()) { 184 log_debug(gc)("Restarting conc marking because of MS overflow in remark (restart #%d).", iter); 185 log_info(gc)("Concurrent Mark restart for overflow"); 186 } 187 } while (cm()->restart_for_overflow()); 188 189 double end_time = os::elapsedVTime(); 190 // Update the total virtual time before doing this, since it will try 191 // to measure it to get the vtime for this marking. We purposely 192 // neglect the presumably-short "completeCleanup" phase here. 193 _vtime_accum = (end_time - _vtime_start); 194 195 if (!cm()->has_aborted()) { 196 delay_to_keep_mmu(g1_policy, false /* cleanup */); 197 198 CMCleanUp cl_cl(_cm); 199 VM_CGC_Operation op(&cl_cl, "Pause Cleanup", false /* needs_pll */); 200 VMThread::execute(&op); 201 } else { 202 // We don't want to update the marking status if a GC pause 203 // is already underway. 204 SuspendibleThreadSetJoiner sts_join; 205 g1h->collector_state()->set_mark_in_progress(false); 206 } 207 208 // Check if cleanup set the free_regions_coming flag. If it 209 // hasn't, we can just skip the next step. 210 if (g1h->free_regions_coming()) { 211 // The following will finish freeing up any regions that we 212 // found to be empty during cleanup. We'll do this part 213 // without joining the suspendible set. If an evacuation pause 214 // takes place, then we would carry on freeing regions in 215 // case they are needed by the pause. If a Full GC takes 216 // place, it would wait for us to process the regions 217 // reclaimed by cleanup. 218 219 GCTraceConcTime(Info, gc) tt("Concurrent Cleanup"); 220 GCConcPhaseTimer(_cm, "Concurrent Cleanup"); 221 222 // Now do the concurrent cleanup operation. 223 _cm->completeCleanup(); 224 225 // Notify anyone who's waiting that there are no more free 226 // regions coming. We have to do this before we join the STS 227 // (in fact, we should not attempt to join the STS in the 228 // interval between finishing the cleanup pause and clearing 229 // the free_regions_coming flag) otherwise we might deadlock: 230 // a GC worker could be blocked waiting for the notification 231 // whereas this thread will be blocked for the pause to finish 232 // while it's trying to join the STS, which is conditional on 233 // the GC workers finishing. 234 g1h->reset_free_regions_coming(); 235 } 236 guarantee(cm()->cleanup_list_is_empty(), 237 "at this point there should be no regions on the cleanup list"); 238 239 // There is a tricky race before recording that the concurrent 240 // cleanup has completed and a potential Full GC starting around 241 // the same time. We want to make sure that the Full GC calls 242 // abort() on concurrent mark after 243 // record_concurrent_mark_cleanup_completed(), since abort() is 244 // the method that will reset the concurrent mark state. If we 245 // end up calling record_concurrent_mark_cleanup_completed() 246 // after abort() then we might incorrectly undo some of the work 247 // abort() did. Checking the has_aborted() flag after joining 248 // the STS allows the correct ordering of the two methods. There 249 // are two scenarios: 250 // 251 // a) If we reach here before the Full GC, the fact that we have 252 // joined the STS means that the Full GC cannot start until we 253 // leave the STS, so record_concurrent_mark_cleanup_completed() 254 // will complete before abort() is called. 255 // 256 // b) If we reach here during the Full GC, we'll be held up from 257 // joining the STS until the Full GC is done, which means that 258 // abort() will have completed and has_aborted() will return 259 // true to prevent us from calling 260 // record_concurrent_mark_cleanup_completed() (and, in fact, it's 261 // not needed any more as the concurrent mark state has been 262 // already reset). 263 { 264 SuspendibleThreadSetJoiner sts_join; 265 if (!cm()->has_aborted()) { 266 g1_policy->record_concurrent_mark_cleanup_completed(); 267 } else { 268 log_info(gc)("Concurrent Mark abort"); 269 } 270 } 271 272 // We now want to allow clearing of the marking bitmap to be 273 // suspended by a collection pause. 274 // We may have aborted just before the remark. Do not bother clearing the 275 // bitmap then, as it has been done during mark abort. 276 if (!cm()->has_aborted()) { 277 GCConcPhaseTimer(_cm, "Concurrent Bitmap Clearing"); 278 _cm->clearNextBitmap(); 279 } else { 280 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear"); 281 } 282 } 283 284 // Update the number of full collections that have been 285 // completed. This will also notify the FullGCCount_lock in case a 286 // Java thread is waiting for a full GC to happen (e.g., it 287 // called System.gc() with +ExplicitGCInvokesConcurrent). 288 { 289 SuspendibleThreadSetJoiner sts_join; 290 g1h->increment_old_marking_cycles_completed(true /* concurrent */); 291 g1h->register_concurrent_cycle_end(); 292 } 293 } 294 } 295 296 void ConcurrentMarkThread::stop() { 297 { 298 MutexLockerEx ml(Terminator_lock); 299 _should_terminate = true; 300 } 301 302 stop_service(); 303 304 { 305 MutexLockerEx ml(Terminator_lock); 306 while (!_has_terminated) { 307 Terminator_lock->wait(); 308 } 309 } 310 } 311 312 void ConcurrentMarkThread::stop_service() { 313 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag); 314 CGC_lock->notify_all(); 315 } 316 317 void ConcurrentMarkThread::sleepBeforeNextCycle() { 318 // We join here because we don't want to do the "shouldConcurrentMark()" 319 // below while the world is otherwise stopped. 320 assert(!in_progress(), "should have been cleared"); 321 322 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 323 while (!started() && !_should_terminate) { 324 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 325 } 326 327 if (started()) { 328 set_in_progress(); 329 } 330 } 331 332 // Note: As is the case with CMS - this method, although exported 333 // by the ConcurrentMarkThread, which is a non-JavaThread, can only 334 // be called by a JavaThread. Currently this is done at vm creation 335 // time (post-vm-init) by the main/Primordial (Java)Thread. 336 // XXX Consider changing this in the future to allow the CM thread 337 // itself to create this thread? 338 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) { 339 assert(UseG1GC, "SLT thread needed only for concurrent GC"); 340 assert(THREAD->is_Java_thread(), "must be a Java thread"); 341 assert(_slt == NULL, "SLT already created"); 342 _slt = SurrogateLockerThread::make(THREAD); 343 }