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  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).
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  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/g1CollectorPolicy.hpp"
  31 #include "gc/g1/g1MMUTracker.hpp"
  32 #include "gc/g1/suspendibleThreadSet.hpp"
  33 #include "gc/g1/vm_operations_g1.hpp"
  34 #include "gc/shared/gcId.hpp"
  35 #include "gc/shared/gcTrace.hpp"
  36 #include "gc/shared/gcTraceTime.inline.hpp"
  37 #include "logging/log.hpp"
  38 #include "memory/resourceArea.hpp"
  39 #include "runtime/vmThread.hpp"
  40 
  41 // ======= Concurrent Mark Thread ========
  42 
  43 // The CM thread is created when the G1 garbage collector is used
  44 
  45 SurrogateLockerThread*
  46      ConcurrentMarkThread::_slt = NULL;
  47 
  48 ConcurrentMarkThread::ConcurrentMarkThread(G1ConcurrentMark* cm) :
  49   ConcurrentGCThread(),
  50   _cm(cm),
  51   _state(Idle),
  52   _vtime_accum(0.0),
  53   _vtime_mark_accum(0.0) {
  54 
  55   set_name("G1 Main Marker");
  56   create_and_start();
  57 }
  58 
  59 class CMCheckpointRootsFinalClosure: public VoidClosure {
  60 
  61   G1ConcurrentMark* _cm;
  62 public:
  63 
  64   CMCheckpointRootsFinalClosure(G1ConcurrentMark* cm) :
  65     _cm(cm) {}
  66 
  67   void do_void(){
  68     _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
  69   }
  70 };
  71 
  72 class CMCleanUp: public VoidClosure {
  73   G1ConcurrentMark* _cm;
  74 public:
  75 
  76   CMCleanUp(G1ConcurrentMark* cm) :
  77     _cm(cm) {}
  78 
  79   void do_void(){
  80     _cm->cleanup();
  81   }
  82 };
  83 
  84 // Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU.
  85 void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) {
  86   const G1Analytics* analytics = g1_policy->analytics();
  87   if (g1_policy->adaptive_young_list_length()) {
  88     double now = os::elapsedTime();
  89     double prediction_ms = remark ? analytics->predict_remark_time_ms()
  90                                   : analytics->predict_cleanup_time_ms();
  91     G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
  92     jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms);
  93     os::sleep(this, sleep_time_ms, false);
  94   }
  95 }
  96 
  97 class GCConcPhaseTimer : StackObj {
  98   G1ConcurrentMark* _cm;
  99 
 100  public:
 101   GCConcPhaseTimer(G1ConcurrentMark* cm, const char* title) : _cm(cm) {
 102     _cm->register_concurrent_phase_start(title);
 103   }
 104 
 105   ~GCConcPhaseTimer() {
 106     _cm->register_concurrent_phase_end();
 107   }
 108 };
 109 
 110 void ConcurrentMarkThread::run() {
 111   initialize_in_thread();
 112   wait_for_universe_init();
 113 
 114   run_service();
 115 
 116   terminate();
 117 }
 118 
 119 void ConcurrentMarkThread::run_service() {
 120   _vtime_start = os::elapsedVTime();
 121 
 122   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 123   G1CollectorPolicy* g1_policy = g1h->g1_policy();
 124 
 125   while (!_should_terminate) {
 126     // wait until started is set.
 127     sleepBeforeNextCycle();
 128     if (_should_terminate) {
 129       _cm->root_regions()->cancel_scan();
 130       break;
 131     }
 132 
 133     assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC.");
 134     {
 135       ResourceMark rm;
 136       HandleMark   hm;
 137       double cycle_start = os::elapsedVTime();
 138 
 139       {
 140         GCConcPhaseTimer(_cm, "Concurrent Clearing of Claimed Marks");
 141         ClassLoaderDataGraph::clear_claimed_marks();
 142       }
 143 
 144       // We have to ensure that we finish scanning the root regions
 145       // before the next GC takes place. To ensure this we have to
 146       // make sure that we do not join the STS until the root regions
 147       // have been scanned. If we did then it's possible that a
 148       // subsequent GC could block us from joining the STS and proceed
 149       // without the root regions have been scanned which would be a
 150       // correctness issue.
 151 
 152       {
 153         GCConcPhaseTimer(_cm, "Concurrent Root Region Scanning");
 154         _cm->scanRootRegions();
 155       }
 156 
 157       // It would be nice to use the GCTraceConcTime class here but
 158       // the "end" logging is inside the loop and not at the end of
 159       // a scope. Mimicking the same log output as GCTraceConcTime instead.
 160       jlong mark_start = os::elapsed_counter();
 161       log_info(gc)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start));
 162 
 163       int iter = 0;
 164       do {
 165         iter++;
 166         if (!cm()->has_aborted()) {
 167           GCConcPhaseTimer(_cm, "Concurrent Mark");
 168           _cm->markFromRoots();
 169         }
 170 
 171         double mark_end_time = os::elapsedVTime();
 172         jlong mark_end = os::elapsed_counter();
 173         _vtime_mark_accum += (mark_end_time - cycle_start);
 174         if (!cm()->has_aborted()) {
 175           delay_to_keep_mmu(g1_policy, true /* remark */);
 176           log_info(gc)("Concurrent Mark (%.3fs, %.3fs) %.3fms",
 177                        TimeHelper::counter_to_seconds(mark_start),
 178                        TimeHelper::counter_to_seconds(mark_end),
 179                        TimeHelper::counter_to_millis(mark_end - mark_start));
 180 
 181           CMCheckpointRootsFinalClosure final_cl(_cm);
 182           VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */);
 183           VMThread::execute(&op);
 184         }
 185         if (cm()->restart_for_overflow()) {
 186           log_debug(gc)("Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
 187           log_info(gc)("Concurrent Mark restart for overflow");
 188         }
 189       } while (cm()->restart_for_overflow());
 190 
 191       double end_time = os::elapsedVTime();
 192       // Update the total virtual time before doing this, since it will try
 193       // to measure it to get the vtime for this marking.  We purposely
 194       // neglect the presumably-short "completeCleanup" phase here.
 195       _vtime_accum = (end_time - _vtime_start);
 196 
 197       if (!cm()->has_aborted()) {
 198         delay_to_keep_mmu(g1_policy, false /* cleanup */);
 199 
 200         CMCleanUp cl_cl(_cm);
 201         VM_CGC_Operation op(&cl_cl, "Pause Cleanup", false /* needs_pll */);
 202         VMThread::execute(&op);
 203       } else {
 204         // We don't want to update the marking status if a GC pause
 205         // is already underway.
 206         SuspendibleThreadSetJoiner sts_join;
 207         g1h->collector_state()->set_mark_in_progress(false);
 208       }
 209 
 210       // Check if cleanup set the free_regions_coming flag. If it
 211       // hasn't, we can just skip the next step.
 212       if (g1h->free_regions_coming()) {
 213         // The following will finish freeing up any regions that we
 214         // found to be empty during cleanup. We'll do this part
 215         // without joining the suspendible set. If an evacuation pause
 216         // takes place, then we would carry on freeing regions in
 217         // case they are needed by the pause. If a Full GC takes
 218         // place, it would wait for us to process the regions
 219         // reclaimed by cleanup.
 220 
 221         GCTraceConcTime(Info, gc) tt("Concurrent Cleanup");
 222         GCConcPhaseTimer(_cm, "Concurrent Cleanup");
 223 
 224         // Now do the concurrent cleanup operation.
 225         _cm->completeCleanup();
 226 
 227         // Notify anyone who's waiting that there are no more free
 228         // regions coming. We have to do this before we join the STS
 229         // (in fact, we should not attempt to join the STS in the
 230         // interval between finishing the cleanup pause and clearing
 231         // the free_regions_coming flag) otherwise we might deadlock:
 232         // a GC worker could be blocked waiting for the notification
 233         // whereas this thread will be blocked for the pause to finish
 234         // while it's trying to join the STS, which is conditional on
 235         // the GC workers finishing.
 236         g1h->reset_free_regions_coming();
 237       }
 238       guarantee(cm()->cleanup_list_is_empty(),
 239                 "at this point there should be no regions on the cleanup list");
 240 
 241       // There is a tricky race before recording that the concurrent
 242       // cleanup has completed and a potential Full GC starting around
 243       // the same time. We want to make sure that the Full GC calls
 244       // abort() on concurrent mark after
 245       // record_concurrent_mark_cleanup_completed(), since abort() is
 246       // the method that will reset the concurrent mark state. If we
 247       // end up calling record_concurrent_mark_cleanup_completed()
 248       // after abort() then we might incorrectly undo some of the work
 249       // abort() did. Checking the has_aborted() flag after joining
 250       // the STS allows the correct ordering of the two methods. There
 251       // are two scenarios:
 252       //
 253       // a) If we reach here before the Full GC, the fact that we have
 254       // joined the STS means that the Full GC cannot start until we
 255       // leave the STS, so record_concurrent_mark_cleanup_completed()
 256       // will complete before abort() is called.
 257       //
 258       // b) If we reach here during the Full GC, we'll be held up from
 259       // joining the STS until the Full GC is done, which means that
 260       // abort() will have completed and has_aborted() will return
 261       // true to prevent us from calling
 262       // record_concurrent_mark_cleanup_completed() (and, in fact, it's
 263       // not needed any more as the concurrent mark state has been
 264       // already reset).
 265       {
 266         SuspendibleThreadSetJoiner sts_join;
 267         if (!cm()->has_aborted()) {
 268           g1_policy->record_concurrent_mark_cleanup_completed();
 269         } else {
 270           log_info(gc)("Concurrent Mark abort");
 271         }
 272       }
 273 
 274       // We now want to allow clearing of the marking bitmap to be
 275       // suspended by a collection pause.
 276       // We may have aborted just before the remark. Do not bother clearing the
 277       // bitmap then, as it has been done during mark abort.
 278       if (!cm()->has_aborted()) {
 279         GCConcPhaseTimer(_cm, "Concurrent Bitmap Clearing");
 280         _cm->clearNextBitmap();
 281       } else {
 282         assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
 283       }
 284     }
 285 
 286     // Update the number of full collections that have been
 287     // completed. This will also notify the FullGCCount_lock in case a
 288     // Java thread is waiting for a full GC to happen (e.g., it
 289     // called System.gc() with +ExplicitGCInvokesConcurrent).
 290     {
 291       SuspendibleThreadSetJoiner sts_join;
 292       g1h->increment_old_marking_cycles_completed(true /* concurrent */);
 293       g1h->register_concurrent_cycle_end();
 294     }
 295   }
 296 }
 297 
 298 void ConcurrentMarkThread::stop() {
 299   {
 300     MutexLockerEx ml(Terminator_lock);
 301     _should_terminate = true;
 302   }
 303 
 304   stop_service();
 305 
 306   {
 307     MutexLockerEx ml(Terminator_lock);
 308     while (!_has_terminated) {
 309       Terminator_lock->wait();
 310     }
 311   }
 312 }
 313 
 314 void ConcurrentMarkThread::stop_service() {
 315   MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
 316   CGC_lock->notify_all();
 317 }
 318 
 319 void ConcurrentMarkThread::sleepBeforeNextCycle() {
 320   // We join here because we don't want to do the "shouldConcurrentMark()"
 321   // below while the world is otherwise stopped.
 322   assert(!in_progress(), "should have been cleared");
 323 
 324   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 325   while (!started() && !_should_terminate) {
 326     CGC_lock->wait(Mutex::_no_safepoint_check_flag);
 327   }
 328 
 329   if (started()) {
 330     set_in_progress();
 331   }
 332 }
 333 
 334 // Note: As is the case with CMS - this method, although exported
 335 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
 336 // be called by a JavaThread. Currently this is done at vm creation
 337 // time (post-vm-init) by the main/Primordial (Java)Thread.
 338 // XXX Consider changing this in the future to allow the CM thread
 339 // itself to create this thread?
 340 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
 341   assert(UseG1GC, "SLT thread needed only for concurrent GC");
 342   assert(THREAD->is_Java_thread(), "must be a Java thread");
 343   assert(_slt == NULL, "SLT already created");
 344   _slt = SurrogateLockerThread::make(THREAD);
 345 }