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/g1MMUTracker.hpp" 30 #include "gc/g1/suspendibleThreadSet.hpp" 31 #include "gc/g1/vm_operations_g1.hpp" 32 #include "gc/shared/gcId.hpp" 33 #include "gc/shared/gcTrace.hpp" 34 #include "gc/shared/gcTraceTime.hpp" 35 #include "logging/log.hpp" 36 #include "memory/resourceArea.hpp" 37 #include "runtime/vmThread.hpp" 38 39 // ======= Concurrent Mark Thread ======== 40 41 // The CM thread is created when the G1 garbage collector is used 42 43 SurrogateLockerThread* 44 ConcurrentMarkThread::_slt = NULL; 45 46 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* cm) : 47 ConcurrentGCThread(), 48 _cm(cm), 49 _state(Idle), 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 // Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU. 83 void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) { 84 if (g1_policy->adaptive_young_list_length()) { 85 double now = os::elapsedTime(); 86 double prediction_ms = remark ? g1_policy->predict_remark_time_ms() 87 : g1_policy->predict_cleanup_time_ms(); 88 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker(); 89 jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms); 90 os::sleep(this, sleep_time_ms, false); 91 } 92 } 93 void ConcurrentMarkThread::run() { 94 initialize_in_thread(); 95 wait_for_universe_init(); 96 97 run_service(); 98 99 terminate(); 100 } 101 102 void ConcurrentMarkThread::run_service() { 103 _vtime_start = os::elapsedVTime(); 104 105 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 106 G1CollectorPolicy* g1_policy = g1h->g1_policy(); 107 108 while (!_should_terminate) { 109 // wait until started is set. 110 sleepBeforeNextCycle(); 111 if (_should_terminate) { 112 break; 113 } 114 115 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC."); 116 { 117 ResourceMark rm; 118 HandleMark hm; 119 double cycle_start = os::elapsedVTime(); 120 121 // We have to ensure that we finish scanning the root regions 122 // before the next GC takes place. To ensure this we have to 123 // make sure that we do not join the STS until the root regions 124 // have been scanned. If we did then it's possible that a 125 // subsequent GC could block us from joining the STS and proceed 126 // without the root regions have been scanned which would be a 127 // correctness issue. 128 129 if (!cm()->has_aborted()) { 130 _cm->scanRootRegions(); 131 } 132 133 // It would be nice to use the GCTraceConcTime class here but 134 // the "end" logging is inside the loop and not at the end of 135 // a scope. Mimicking the same log output as GCTraceConcTime instead. 136 jlong mark_start = os::elapsed_counter(); 137 log_info(gc)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start)); 138 139 int iter = 0; 140 do { 141 iter++; 142 if (!cm()->has_aborted()) { 143 _cm->markFromRoots(); 144 } 145 146 double mark_end_time = os::elapsedVTime(); 147 jlong mark_end = os::elapsed_counter(); 148 _vtime_mark_accum += (mark_end_time - cycle_start); 149 if (!cm()->has_aborted()) { 150 delay_to_keep_mmu(g1_policy, true /* remark */); 151 log_info(gc)("Concurrent Mark (%.3fs, %.3fs) %.3fms", 152 TimeHelper::counter_to_seconds(mark_start), 153 TimeHelper::counter_to_seconds(mark_end), 154 TimeHelper::counter_to_millis(mark_end - mark_start)); 155 156 CMCheckpointRootsFinalClosure final_cl(_cm); 157 VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */); 158 VMThread::execute(&op); 159 } 160 if (cm()->restart_for_overflow()) { 161 log_debug(gc)("Restarting conc marking because of MS overflow in remark (restart #%d).", iter); 162 log_info(gc)("Concurrent Mark restart for overflow"); 163 } 164 } while (cm()->restart_for_overflow()); 165 166 double end_time = os::elapsedVTime(); 167 // Update the total virtual time before doing this, since it will try 168 // to measure it to get the vtime for this marking. We purposely 169 // neglect the presumably-short "completeCleanup" phase here. 170 _vtime_accum = (end_time - _vtime_start); 171 172 if (!cm()->has_aborted()) { 173 delay_to_keep_mmu(g1_policy, false /* cleanup */); 174 175 CMCleanUp cl_cl(_cm); 176 VM_CGC_Operation op(&cl_cl, "Pause Cleanup", false /* needs_pll */); 177 VMThread::execute(&op); 178 } else { 179 // We don't want to update the marking status if a GC pause 180 // is already underway. 181 SuspendibleThreadSetJoiner sts_join; 182 g1h->collector_state()->set_mark_in_progress(false); 183 } 184 185 // Check if cleanup set the free_regions_coming flag. If it 186 // hasn't, we can just skip the next step. 187 if (g1h->free_regions_coming()) { 188 // The following will finish freeing up any regions that we 189 // found to be empty during cleanup. We'll do this part 190 // without joining the suspendible set. If an evacuation pause 191 // takes place, then we would carry on freeing regions in 192 // case they are needed by the pause. If a Full GC takes 193 // place, it would wait for us to process the regions 194 // reclaimed by cleanup. 195 196 GCTraceConcTime(Info, gc) tt("Concurrent Cleanup"); 197 198 // Now do the concurrent cleanup operation. 199 _cm->completeCleanup(); 200 201 // Notify anyone who's waiting that there are no more free 202 // regions coming. We have to do this before we join the STS 203 // (in fact, we should not attempt to join the STS in the 204 // interval between finishing the cleanup pause and clearing 205 // the free_regions_coming flag) otherwise we might deadlock: 206 // a GC worker could be blocked waiting for the notification 207 // whereas this thread will be blocked for the pause to finish 208 // while it's trying to join the STS, which is conditional on 209 // the GC workers finishing. 210 g1h->reset_free_regions_coming(); 211 } 212 guarantee(cm()->cleanup_list_is_empty(), 213 "at this point there should be no regions on the cleanup list"); 214 215 // There is a tricky race before recording that the concurrent 216 // cleanup has completed and a potential Full GC starting around 217 // the same time. We want to make sure that the Full GC calls 218 // abort() on concurrent mark after 219 // record_concurrent_mark_cleanup_completed(), since abort() is 220 // the method that will reset the concurrent mark state. If we 221 // end up calling record_concurrent_mark_cleanup_completed() 222 // after abort() then we might incorrectly undo some of the work 223 // abort() did. Checking the has_aborted() flag after joining 224 // the STS allows the correct ordering of the two methods. There 225 // are two scenarios: 226 // 227 // a) If we reach here before the Full GC, the fact that we have 228 // joined the STS means that the Full GC cannot start until we 229 // leave the STS, so record_concurrent_mark_cleanup_completed() 230 // will complete before abort() is called. 231 // 232 // b) If we reach here during the Full GC, we'll be held up from 233 // joining the STS until the Full GC is done, which means that 234 // abort() will have completed and has_aborted() will return 235 // true to prevent us from calling 236 // record_concurrent_mark_cleanup_completed() (and, in fact, it's 237 // not needed any more as the concurrent mark state has been 238 // already reset). 239 { 240 SuspendibleThreadSetJoiner sts_join; 241 if (!cm()->has_aborted()) { 242 g1_policy->record_concurrent_mark_cleanup_completed(); 243 } else { 244 log_info(gc)("Concurrent Mark abort"); 245 } 246 } 247 248 // We now want to allow clearing of the marking bitmap to be 249 // suspended by a collection pause. 250 // We may have aborted just before the remark. Do not bother clearing the 251 // bitmap then, as it has been done during mark abort. 252 if (!cm()->has_aborted()) { 253 _cm->clearNextBitmap(); 254 } else { 255 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear"); 256 } 257 } 258 259 // Update the number of full collections that have been 260 // completed. This will also notify the FullGCCount_lock in case a 261 // Java thread is waiting for a full GC to happen (e.g., it 262 // called System.gc() with +ExplicitGCInvokesConcurrent). 263 { 264 SuspendibleThreadSetJoiner sts_join; 265 g1h->increment_old_marking_cycles_completed(true /* concurrent */); 266 g1h->register_concurrent_cycle_end(); 267 } 268 } 269 } 270 271 void ConcurrentMarkThread::stop() { 272 { 273 MutexLockerEx ml(Terminator_lock); 274 _should_terminate = true; 275 } 276 277 stop_service(); 278 279 { 280 MutexLockerEx ml(Terminator_lock); 281 while (!_has_terminated) { 282 Terminator_lock->wait(); 283 } 284 } 285 } 286 287 void ConcurrentMarkThread::stop_service() { 288 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag); 289 CGC_lock->notify_all(); 290 } 291 292 void ConcurrentMarkThread::sleepBeforeNextCycle() { 293 // We join here because we don't want to do the "shouldConcurrentMark()" 294 // below while the world is otherwise stopped. 295 assert(!in_progress(), "should have been cleared"); 296 297 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 298 while (!started() && !_should_terminate) { 299 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 300 } 301 302 if (started()) { 303 set_in_progress(); 304 } 305 } 306 307 // Note: As is the case with CMS - this method, although exported 308 // by the ConcurrentMarkThread, which is a non-JavaThread, can only 309 // be called by a JavaThread. Currently this is done at vm creation 310 // time (post-vm-init) by the main/Primordial (Java)Thread. 311 // XXX Consider changing this in the future to allow the CM thread 312 // itself to create this thread? 313 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) { 314 assert(UseG1GC, "SLT thread needed only for concurrent GC"); 315 assert(THREAD->is_Java_thread(), "must be a Java thread"); 316 assert(_slt == NULL, "SLT already created"); 317 _slt = SurrogateLockerThread::make(THREAD); 318 }