1 /* 2 * Copyright (c) 2001, 2016, 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 "classfile/classLoaderData.hpp" 27 #include "gc/g1/concurrentMarkThread.inline.hpp" 28 #include "gc/g1/g1Analytics.hpp" 29 #include "gc/g1/g1CollectedHeap.inline.hpp" 30 #include "gc/g1/g1ConcurrentMark.inline.hpp" 31 #include "gc/g1/g1MMUTracker.hpp" 32 #include "gc/g1/g1Policy.hpp" 33 #include "gc/g1/suspendibleThreadSet.hpp" 34 #include "gc/g1/vm_operations_g1.hpp" 35 #include "gc/shared/gcId.hpp" 36 #include "gc/shared/gcTrace.hpp" 37 #include "gc/shared/gcTraceTime.inline.hpp" 38 #include "logging/log.hpp" 39 #include "memory/resourceArea.hpp" 40 #include "runtime/vmThread.hpp" 41 42 // ======= Concurrent Mark Thread ======== 43 44 // The CM thread is created when the G1 garbage collector is used 45 46 ConcurrentMarkThread::ConcurrentMarkThread(G1ConcurrentMark* 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 G1ConcurrentMark* _cm; 60 public: 61 62 CMCheckpointRootsFinalClosure(G1ConcurrentMark* 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 G1ConcurrentMark* _cm; 72 public: 73 74 CMCleanUp(G1ConcurrentMark* 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(G1Policy* g1_policy, bool remark) { 84 const G1Analytics* analytics = g1_policy->analytics(); 85 if (g1_policy->adaptive_young_list_length()) { 86 double now = os::elapsedTime(); 87 double prediction_ms = remark ? analytics->predict_remark_time_ms() 88 : analytics->predict_cleanup_time_ms(); 89 G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker(); 90 jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms); 91 os::sleep(this, sleep_time_ms, false); 92 } 93 } 94 95 class G1ConcPhaseTimer : public GCTraceConcTimeImpl<LogLevel::Info, LOG_TAGS(gc, marking)> { 96 G1ConcurrentMark* _cm; 97 98 public: 99 G1ConcPhaseTimer(G1ConcurrentMark* cm, const char* title) : 100 GCTraceConcTimeImpl<LogLevel::Info, LogTag::_gc, LogTag::_marking>(title), 101 _cm(cm) { 102 _cm->gc_timer_cm()->register_gc_concurrent_start(title); 103 } 104 105 ~G1ConcPhaseTimer() { 106 _cm->gc_timer_cm()->register_gc_concurrent_end(); 107 } 108 }; 109 110 void ConcurrentMarkThread::run_service() { 111 _vtime_start = os::elapsedVTime(); 112 113 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 114 G1Policy* g1_policy = g1h->g1_policy(); 115 116 while (!should_terminate()) { 117 // wait until started is set. 118 sleepBeforeNextCycle(); 119 if (should_terminate()) { 120 break; 121 } 122 123 GCIdMark gc_id_mark; 124 125 cm()->concurrent_cycle_start(); 126 127 assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC."); 128 129 GCTraceConcTime(Info, gc) tt("Concurrent Cycle"); 130 { 131 ResourceMark rm; 132 HandleMark hm; 133 double cycle_start = os::elapsedVTime(); 134 135 { 136 G1ConcPhaseTimer t(_cm, "Concurrent Clear Claimed Marks"); 137 ClassLoaderDataGraph::clear_claimed_marks(); 138 } 139 140 // We have to ensure that we finish scanning the root regions 141 // before the next GC takes place. To ensure this we have to 142 // make sure that we do not join the STS until the root regions 143 // have been scanned. If we did then it's possible that a 144 // subsequent GC could block us from joining the STS and proceed 145 // without the root regions have been scanned which would be a 146 // correctness issue. 147 148 { 149 G1ConcPhaseTimer t(_cm, "Concurrent Scan Root Regions"); 150 _cm->scan_root_regions(); 151 } 152 153 // It would be nice to use the GCTraceConcTime class here but 154 // the "end" logging is inside the loop and not at the end of 155 // a scope. Mimicking the same log output as GCTraceConcTime instead. 156 jlong mark_start = os::elapsed_counter(); 157 log_info(gc, marking)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start)); 158 159 int iter = 0; 160 do { 161 iter++; 162 if (!cm()->has_aborted()) { 163 G1ConcPhaseTimer t(_cm, "Concurrent Mark From Roots"); 164 _cm->mark_from_roots(); 165 } 166 167 double mark_end_time = os::elapsedVTime(); 168 jlong mark_end = os::elapsed_counter(); 169 _vtime_mark_accum += (mark_end_time - cycle_start); 170 if (!cm()->has_aborted()) { 171 delay_to_keep_mmu(g1_policy, true /* remark */); 172 log_info(gc, marking)("Concurrent Mark (%.3fs, %.3fs) %.3fms", 173 TimeHelper::counter_to_seconds(mark_start), 174 TimeHelper::counter_to_seconds(mark_end), 175 TimeHelper::counter_to_millis(mark_end - mark_start)); 176 177 CMCheckpointRootsFinalClosure final_cl(_cm); 178 VM_CGC_Operation op(&final_cl, "Pause Remark"); 179 VMThread::execute(&op); 180 } 181 if (cm()->restart_for_overflow()) { 182 log_debug(gc, marking)("Restarting Concurrent Marking because of Mark Stack Overflow in Remark (Iteration #%d).", iter); 183 log_info(gc, marking)("Concurrent Mark Restart due to overflow"); 184 } 185 } while (cm()->restart_for_overflow()); 186 187 if (!cm()->has_aborted()) { 188 G1ConcPhaseTimer t(_cm, "Concurrent Create Live Data"); 189 cm()->create_live_data(); 190 } 191 192 double end_time = os::elapsedVTime(); 193 // Update the total virtual time before doing this, since it will try 194 // to measure it to get the vtime for this marking. We purposely 195 // neglect the presumably-short "completeCleanup" phase here. 196 _vtime_accum = (end_time - _vtime_start); 197 198 if (!cm()->has_aborted()) { 199 delay_to_keep_mmu(g1_policy, false /* cleanup */); 200 201 CMCleanUp cl_cl(_cm); 202 VM_CGC_Operation op(&cl_cl, "Pause Cleanup"); 203 VMThread::execute(&op); 204 } else { 205 // We don't want to update the marking status if a GC pause 206 // is already underway. 207 SuspendibleThreadSetJoiner sts_join; 208 g1h->collector_state()->set_mark_in_progress(false); 209 } 210 211 // Check if cleanup set the free_regions_coming flag. If it 212 // hasn't, we can just skip the next step. 213 if (g1h->free_regions_coming()) { 214 // The following will finish freeing up any regions that we 215 // found to be empty during cleanup. We'll do this part 216 // without joining the suspendible set. If an evacuation pause 217 // takes place, then we would carry on freeing regions in 218 // case they are needed by the pause. If a Full GC takes 219 // place, it would wait for us to process the regions 220 // reclaimed by cleanup. 221 222 G1ConcPhaseTimer t(_cm, "Concurrent Complete Cleanup"); 223 // Now do the concurrent cleanup operation. 224 _cm->complete_cleanup(); 225 226 // Notify anyone who's waiting that there are no more free 227 // regions coming. We have to do this before we join the STS 228 // (in fact, we should not attempt to join the STS in the 229 // interval between finishing the cleanup pause and clearing 230 // the free_regions_coming flag) otherwise we might deadlock: 231 // a GC worker could be blocked waiting for the notification 232 // whereas this thread will be blocked for the pause to finish 233 // while it's trying to join the STS, which is conditional on 234 // the GC workers finishing. 235 g1h->reset_free_regions_coming(); 236 } 237 guarantee(cm()->cleanup_list_is_empty(), 238 "at this point there should be no regions on the cleanup list"); 239 240 // There is a tricky race before recording that the concurrent 241 // cleanup has completed and a potential Full GC starting around 242 // the same time. We want to make sure that the Full GC calls 243 // abort() on concurrent mark after 244 // record_concurrent_mark_cleanup_completed(), since abort() is 245 // the method that will reset the concurrent mark state. If we 246 // end up calling record_concurrent_mark_cleanup_completed() 247 // after abort() then we might incorrectly undo some of the work 248 // abort() did. Checking the has_aborted() flag after joining 249 // the STS allows the correct ordering of the two methods. There 250 // are two scenarios: 251 // 252 // a) If we reach here before the Full GC, the fact that we have 253 // joined the STS means that the Full GC cannot start until we 254 // leave the STS, so record_concurrent_mark_cleanup_completed() 255 // will complete before abort() is called. 256 // 257 // b) If we reach here during the Full GC, we'll be held up from 258 // joining the STS until the Full GC is done, which means that 259 // abort() will have completed and has_aborted() will return 260 // true to prevent us from calling 261 // record_concurrent_mark_cleanup_completed() (and, in fact, it's 262 // not needed any more as the concurrent mark state has been 263 // already reset). 264 { 265 SuspendibleThreadSetJoiner sts_join; 266 if (!cm()->has_aborted()) { 267 g1_policy->record_concurrent_mark_cleanup_completed(); 268 } else { 269 log_info(gc, marking)("Concurrent Mark Abort"); 270 } 271 } 272 273 // We now want to allow clearing of the marking bitmap to be 274 // suspended by a collection pause. 275 // We may have aborted just before the remark. Do not bother clearing the 276 // bitmap then, as it has been done during mark abort. 277 if (!cm()->has_aborted()) { 278 G1ConcPhaseTimer t(_cm, "Concurrent Cleanup for Next Mark"); 279 _cm->cleanup_for_next_mark(); 280 } else { 281 assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear"); 282 } 283 } 284 285 // Update the number of full collections that have been 286 // completed. This will also notify the FullGCCount_lock in case a 287 // Java thread is waiting for a full GC to happen (e.g., it 288 // called System.gc() with +ExplicitGCInvokesConcurrent). 289 { 290 SuspendibleThreadSetJoiner sts_join; 291 g1h->increment_old_marking_cycles_completed(true /* concurrent */); 292 293 cm()->concurrent_cycle_end(); 294 } 295 } 296 _cm->root_regions()->cancel_scan(); 297 } 298 299 void ConcurrentMarkThread::stop_service() { 300 MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag); 301 CGC_lock->notify_all(); 302 } 303 304 void ConcurrentMarkThread::sleepBeforeNextCycle() { 305 // We join here because we don't want to do the "shouldConcurrentMark()" 306 // below while the world is otherwise stopped. 307 assert(!in_progress(), "should have been cleared"); 308 309 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); 310 while (!started() && !should_terminate()) { 311 CGC_lock->wait(Mutex::_no_safepoint_check_flag); 312 } 313 314 if (started()) { 315 set_in_progress(); 316 } 317 }