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/gcTrace.hpp" 34 #include "memory/resourceArea.hpp" 35 #include "runtime/vmThread.hpp" 36 37 // ======= Concurrent Mark Thread ======== 38 39 // The CM thread is created when the G1 garbage collector is used 40 41 SurrogateLockerThread* 42 ConcurrentMarkThread::_slt = NULL; 43 44 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* cm) : 45 ConcurrentGCThread(), 46 _cm(cm), 47 _state(Idle), 48 _vtime_accum(0.0), 49 _vtime_mark_accum(0.0) { 50 51 set_name("G1 Main Marker"); 52 create_and_start(); 53 } 54 55 class CMCheckpointRootsFinalClosure: public VoidClosure { 56 57 ConcurrentMark* _cm; 58 public: 59 60 CMCheckpointRootsFinalClosure(ConcurrentMark* cm) : 61 _cm(cm) {} 62 63 void do_void(){ 64 _cm->checkpointRootsFinal(false); // !clear_all_soft_refs 65 } 66 }; 67 68 class CMCleanUp: public VoidClosure { 69 ConcurrentMark* _cm; 70 public: 71 72 CMCleanUp(ConcurrentMark* cm) : 73 _cm(cm) {} 74 75 void do_void(){ 76 _cm->cleanup(); 77 } 78 }; 79 80 // We want to avoid that the logging from the concurrent thread is mixed 81 // with the logging from a STW GC. So, if necessary join the STS to ensure 82 // that the logging is done either before or after the STW logging. 83 void ConcurrentMarkThread::cm_log(bool doit, bool join_sts, const char* fmt, ...) { 84 if (doit) { 85 SuspendibleThreadSetJoiner sts_joiner(join_sts); 86 va_list args; 87 va_start(args, fmt); 88 gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id()); 89 gclog_or_tty->vprint_cr(fmt, args); 90 va_end(args); 91 } 92 } 93 94 void ConcurrentMarkThread::run() { 95 initialize_in_thread(); 96 _vtime_start = os::elapsedVTime(); 97 wait_for_universe_init(); 98 99 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 100 G1CollectorPolicy* g1_policy = g1h->g1_policy(); 101 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker(); 102 Thread *current_thread = Thread::current(); 103 104 while (!_should_terminate) { 105 // wait until started is set. 106 sleepBeforeNextCycle(); 107 if (_should_terminate) { 108 break; 109 } 110 111 { 112 ResourceMark rm; 113 HandleMark hm; 114 double cycle_start = os::elapsedVTime(); 115 116 // We have to ensure that we finish scanning the root regions 117 // before the next GC takes place. To ensure this we have to 118 // make sure that we do not join the STS until the root regions 119 // have been scanned. If we did then it's possible that a 120 // subsequent GC could block us from joining the STS and proceed 121 // without the root regions have been scanned which would be a 122 // correctness issue. 123 124 if (!cm()->has_aborted()) { 125 _cm->scanRootRegions(); 126 } 127 128 double mark_start_sec = os::elapsedTime(); 129 cm_log(G1Log::fine(), true, "[GC concurrent-mark-start]"); 130 131 int iter = 0; 132 do { 133 iter++; 134 if (!cm()->has_aborted()) { 135 _cm->markFromRoots(); 136 } 137 138 double mark_end_time = os::elapsedVTime(); 139 double mark_end_sec = os::elapsedTime(); 140 _vtime_mark_accum += (mark_end_time - cycle_start); 141 if (!cm()->has_aborted()) { 142 if (g1_policy->adaptive_young_list_length()) { 143 double now = os::elapsedTime(); 144 double remark_prediction_ms = g1_policy->predict_remark_time_ms(); 145 jlong sleep_time_ms = mmu_tracker->when_ms(now, remark_prediction_ms); 146 os::sleep(current_thread, sleep_time_ms, false); 147 } 148 149 cm_log(G1Log::fine(), true, "[GC concurrent-mark-end, %1.7lf secs]", mark_end_sec - mark_start_sec); 150 151 CMCheckpointRootsFinalClosure final_cl(_cm); 152 VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */); 153 VMThread::execute(&op); 154 } 155 if (cm()->restart_for_overflow()) { 156 cm_log(G1TraceMarkStackOverflow, true, "Restarting conc marking because of MS overflow in remark (restart #%d).", iter); 157 cm_log(G1Log::fine(), true, "[GC concurrent-mark-restart-for-overflow]"); 158 } 159 } while (cm()->restart_for_overflow()); 160 161 double end_time = os::elapsedVTime(); 162 // Update the total virtual time before doing this, since it will try 163 // to measure it to get the vtime for this marking. We purposely 164 // neglect the presumably-short "completeCleanup" phase here. 165 _vtime_accum = (end_time - _vtime_start); 166 167 if (!cm()->has_aborted()) { 168 if (g1_policy->adaptive_young_list_length()) { 169 double now = os::elapsedTime(); 170 double cleanup_prediction_ms = g1_policy->predict_cleanup_time_ms(); 171 jlong sleep_time_ms = mmu_tracker->when_ms(now, cleanup_prediction_ms); 172 os::sleep(current_thread, sleep_time_ms, false); 173 } 174 175 CMCleanUp cl_cl(_cm); 176 VM_CGC_Operation op(&cl_cl, "GC 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 double cleanup_start_sec = os::elapsedTime(); 197 cm_log(G1Log::fine(), true, "[GC concurrent-cleanup-start]"); 198 199 // Now do the concurrent cleanup operation. 200 _cm->completeCleanup(); 201 202 // Notify anyone who's waiting that there are no more free 203 // regions coming. We have to do this before we join the STS 204 // (in fact, we should not attempt to join the STS in the 205 // interval between finishing the cleanup pause and clearing 206 // the free_regions_coming flag) otherwise we might deadlock: 207 // a GC worker could be blocked waiting for the notification 208 // whereas this thread will be blocked for the pause to finish 209 // while it's trying to join the STS, which is conditional on 210 // the GC workers finishing. 211 g1h->reset_free_regions_coming(); 212 213 double cleanup_end_sec = os::elapsedTime(); 214 cm_log(G1Log::fine(), true, "[GC concurrent-cleanup-end, %1.7lf secs]", cleanup_end_sec - cleanup_start_sec); 215 } 216 guarantee(cm()->cleanup_list_is_empty(), 217 "at this point there should be no regions on the cleanup list"); 218 219 // There is a tricky race before recording that the concurrent 220 // cleanup has completed and a potential Full GC starting around 221 // the same time. We want to make sure that the Full GC calls 222 // abort() on concurrent mark after 223 // record_concurrent_mark_cleanup_completed(), since abort() is 224 // the method that will reset the concurrent mark state. If we 225 // end up calling record_concurrent_mark_cleanup_completed() 226 // after abort() then we might incorrectly undo some of the work 227 // abort() did. Checking the has_aborted() flag after joining 228 // the STS allows the correct ordering of the two methods. There 229 // are two scenarios: 230 // 231 // a) If we reach here before the Full GC, the fact that we have 232 // joined the STS means that the Full GC cannot start until we 233 // leave the STS, so record_concurrent_mark_cleanup_completed() 234 // will complete before abort() is called. 235 // 236 // b) If we reach here during the Full GC, we'll be held up from 237 // joining the STS until the Full GC is done, which means that 238 // abort() will have completed and has_aborted() will return 239 // true to prevent us from calling 240 // record_concurrent_mark_cleanup_completed() (and, in fact, it's 241 // not needed any more as the concurrent mark state has been 242 // already reset). 243 { 244 SuspendibleThreadSetJoiner sts_join; 245 if (!cm()->has_aborted()) { 246 g1_policy->record_concurrent_mark_cleanup_completed(); 247 } else { 248 cm_log(G1Log::fine(), false, "[GC concurrent-mark-abort]"); 249 } 250 } 251 252 // We now want to allow clearing of the marking bitmap to be 253 // suspended by a collection pause. 254 // We may have aborted just before the remark. Do not bother clearing the 255 // bitmap then, as it has been done during mark abort. 256 if (!cm()->has_aborted()) { 257 _cm->clearNextBitmap(); 258 } else { 259 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear"); 260 } 261 } 262 263 // Update the number of full collections that have been 264 // completed. This will also notify the FullGCCount_lock in case a 265 // Java thread is waiting for a full GC to happen (e.g., it 266 // called System.gc() with +ExplicitGCInvokesConcurrent). 267 { 268 SuspendibleThreadSetJoiner sts_join; 269 g1h->increment_old_marking_cycles_completed(true /* concurrent */); 270 g1h->register_concurrent_cycle_end(); 271 } 272 } 273 assert(_should_terminate, "just checking"); 274 275 terminate(); 276 } 277 278 void ConcurrentMarkThread::stop() { 279 { 280 MutexLockerEx ml(Terminator_lock); 281 _should_terminate = true; 282 } 283 284 { 285 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag); 286 CGC_lock->notify_all(); 287 } 288 289 { 290 MutexLockerEx ml(Terminator_lock); 291 while (!_has_terminated) { 292 Terminator_lock->wait(); 293 } 294 } 295 } 296 297 void ConcurrentMarkThread::sleepBeforeNextCycle() { 298 // We join here because we don't want to do the "shouldConcurrentMark()" 299 // below while the world is otherwise stopped. 300 assert(!in_progress(), "should have been cleared"); 301 302 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 303 while (!started() && !_should_terminate) { 304 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 305 } 306 307 if (started()) { 308 set_in_progress(); 309 } 310 } 311 312 // Note: As is the case with CMS - this method, although exported 313 // by the ConcurrentMarkThread, which is a non-JavaThread, can only 314 // be called by a JavaThread. Currently this is done at vm creation 315 // time (post-vm-init) by the main/Primordial (Java)Thread. 316 // XXX Consider changing this in the future to allow the CM thread 317 // itself to create this thread? 318 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) { 319 assert(UseG1GC, "SLT thread needed only for concurrent GC"); 320 assert(THREAD->is_Java_thread(), "must be a Java thread"); 321 assert(_slt == NULL, "SLT already created"); 322 _slt = SurrogateLockerThread::make(THREAD); 323 }