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