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