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