1  /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
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  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).
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  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/g1MMUTracker.hpp"
  30 #include "gc/g1/suspendibleThreadSet.hpp"
  31 #include "gc/g1/vm_operations_g1.hpp"
  32 #include "gc/shared/gcId.hpp"
  33 #include "gc/shared/gcTrace.hpp"
  34 #include "gc/shared/gcTraceTime.hpp"
  35 #include "logging/log.hpp"
  36 #include "memory/resourceArea.hpp"
  37 #include "runtime/vmThread.hpp"
  38 
  39 // ======= Concurrent Mark Thread ========
  40 
  41 // The CM thread is created when the G1 garbage collector is used
  42 
  43 SurrogateLockerThread*
  44      ConcurrentMarkThread::_slt = NULL;
  45 
  46 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* 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   ConcurrentMark* _cm;
  60 public:
  61 
  62   CMCheckpointRootsFinalClosure(ConcurrentMark* 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   ConcurrentMark* _cm;
  72 public:
  73 
  74   CMCleanUp(ConcurrentMark* 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(G1CollectorPolicy* g1_policy, bool remark) {
  84   if (g1_policy->adaptive_young_list_length()) {
  85     double now = os::elapsedTime();
  86     double prediction_ms = remark ? g1_policy->predict_remark_time_ms()
  87                                   : g1_policy->predict_cleanup_time_ms();
  88     G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
  89     jlong sleep_time_ms = mmu_tracker->when_ms(now, prediction_ms);
  90     os::sleep(this, sleep_time_ms, false);
  91   }
  92 }
  93 void ConcurrentMarkThread::run() {
  94   initialize_in_thread();
  95   wait_for_universe_init();
  96 
  97   run_service();
  98 
  99   terminate();
 100 }
 101 
 102 void ConcurrentMarkThread::run_service() {
 103   _vtime_start = os::elapsedVTime();
 104 
 105   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 106   G1CollectorPolicy* g1_policy = g1h->g1_policy();
 107 
 108   while (!_should_terminate) {
 109     // wait until started is set.
 110     sleepBeforeNextCycle();
 111     if (_should_terminate) {
 112       break;
 113     }
 114 
 115     assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC.");
 116     {
 117       ResourceMark rm;
 118       HandleMark   hm;
 119       double cycle_start = os::elapsedVTime();
 120 
 121       // We have to ensure that we finish scanning the root regions
 122       // before the next GC takes place. To ensure this we have to
 123       // make sure that we do not join the STS until the root regions
 124       // have been scanned. If we did then it's possible that a
 125       // subsequent GC could block us from joining the STS and proceed
 126       // without the root regions have been scanned which would be a
 127       // correctness issue.
 128 
 129       if (!cm()->has_aborted()) {
 130         _cm->scanRootRegions();
 131       }
 132 
 133       // It would be nice to use the GCTraceConcTime class here but
 134       // the "end" logging is inside the loop and not at the end of
 135       // a scope. Mimicking the same log output as GCTraceConcTime instead.
 136       jlong mark_start = os::elapsed_counter();
 137       log_info(gc)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start));
 138 
 139       int iter = 0;
 140       do {
 141         iter++;
 142         if (!cm()->has_aborted()) {
 143           _cm->markFromRoots();
 144         }
 145 
 146         double mark_end_time = os::elapsedVTime();
 147         jlong mark_end = os::elapsed_counter();
 148         _vtime_mark_accum += (mark_end_time - cycle_start);
 149         if (!cm()->has_aborted()) {
 150           delay_to_keep_mmu(g1_policy, true /* remark */);
 151           log_info(gc)("Concurrent Mark (%.3fs, %.3fs) %.3fms",
 152                        TimeHelper::counter_to_seconds(mark_start),
 153                        TimeHelper::counter_to_seconds(mark_end),
 154                        TimeHelper::counter_to_millis(mark_end - mark_start));
 155 
 156           CMCheckpointRootsFinalClosure final_cl(_cm);
 157           VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */);
 158           VMThread::execute(&op);
 159         }
 160         if (cm()->restart_for_overflow()) {
 161           log_debug(gc)("Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
 162           log_info(gc)("Concurrent Mark restart for overflow");
 163         }
 164       } while (cm()->restart_for_overflow());
 165 
 166       double end_time = os::elapsedVTime();
 167       // Update the total virtual time before doing this, since it will try
 168       // to measure it to get the vtime for this marking.  We purposely
 169       // neglect the presumably-short "completeCleanup" phase here.
 170       _vtime_accum = (end_time - _vtime_start);
 171 
 172       if (!cm()->has_aborted()) {
 173         delay_to_keep_mmu(g1_policy, false /* cleanup */);
 174 
 175         CMCleanUp cl_cl(_cm);
 176         VM_CGC_Operation op(&cl_cl, "Pause 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         GCTraceConcTime(Info, gc) tt("Concurrent Cleanup");

 197 
 198         // Now do the concurrent cleanup operation.
 199         _cm->completeCleanup();
 200 
 201         // Notify anyone who's waiting that there are no more free
 202         // regions coming. We have to do this before we join the STS
 203         // (in fact, we should not attempt to join the STS in the
 204         // interval between finishing the cleanup pause and clearing
 205         // the free_regions_coming flag) otherwise we might deadlock:
 206         // a GC worker could be blocked waiting for the notification
 207         // whereas this thread will be blocked for the pause to finish
 208         // while it's trying to join the STS, which is conditional on
 209         // the GC workers finishing.
 210         g1h->reset_free_regions_coming();



 211       }
 212       guarantee(cm()->cleanup_list_is_empty(),
 213                 "at this point there should be no regions on the cleanup list");
 214 
 215       // There is a tricky race before recording that the concurrent
 216       // cleanup has completed and a potential Full GC starting around
 217       // the same time. We want to make sure that the Full GC calls
 218       // abort() on concurrent mark after
 219       // record_concurrent_mark_cleanup_completed(), since abort() is
 220       // the method that will reset the concurrent mark state. If we
 221       // end up calling record_concurrent_mark_cleanup_completed()
 222       // after abort() then we might incorrectly undo some of the work
 223       // abort() did. Checking the has_aborted() flag after joining
 224       // the STS allows the correct ordering of the two methods. There
 225       // are two scenarios:
 226       //
 227       // a) If we reach here before the Full GC, the fact that we have
 228       // joined the STS means that the Full GC cannot start until we
 229       // leave the STS, so record_concurrent_mark_cleanup_completed()
 230       // will complete before abort() is called.
 231       //
 232       // b) If we reach here during the Full GC, we'll be held up from
 233       // joining the STS until the Full GC is done, which means that
 234       // abort() will have completed and has_aborted() will return
 235       // true to prevent us from calling
 236       // record_concurrent_mark_cleanup_completed() (and, in fact, it's
 237       // not needed any more as the concurrent mark state has been
 238       // already reset).
 239       {
 240         SuspendibleThreadSetJoiner sts_join;
 241         if (!cm()->has_aborted()) {
 242           g1_policy->record_concurrent_mark_cleanup_completed();
 243         } else {
 244           log_info(gc)("Concurrent Mark abort");
 245         }
 246       }
 247 
 248       // We now want to allow clearing of the marking bitmap to be
 249       // suspended by a collection pause.
 250       // We may have aborted just before the remark. Do not bother clearing the
 251       // bitmap then, as it has been done during mark abort.
 252       if (!cm()->has_aborted()) {
 253         _cm->clearNextBitmap();
 254       } else {
 255         assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
 256       }
 257     }
 258 
 259     // Update the number of full collections that have been
 260     // completed. This will also notify the FullGCCount_lock in case a
 261     // Java thread is waiting for a full GC to happen (e.g., it
 262     // called System.gc() with +ExplicitGCInvokesConcurrent).
 263     {
 264       SuspendibleThreadSetJoiner sts_join;
 265       g1h->increment_old_marking_cycles_completed(true /* concurrent */);
 266       g1h->register_concurrent_cycle_end();
 267     }
 268   }
 269 }
 270 
 271 void ConcurrentMarkThread::stop() {
 272   {
 273     MutexLockerEx ml(Terminator_lock);
 274     _should_terminate = true;
 275   }
 276 
 277   stop_service();
 278 
 279   {
 280     MutexLockerEx ml(Terminator_lock);
 281     while (!_has_terminated) {
 282       Terminator_lock->wait();
 283     }
 284   }
 285 }
 286 
 287 void ConcurrentMarkThread::stop_service() {
 288   MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
 289   CGC_lock->notify_all();
 290 }
 291 
 292 void ConcurrentMarkThread::sleepBeforeNextCycle() {
 293   // We join here because we don't want to do the "shouldConcurrentMark()"
 294   // below while the world is otherwise stopped.
 295   assert(!in_progress(), "should have been cleared");
 296 
 297   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 298   while (!started() && !_should_terminate) {
 299     CGC_lock->wait(Mutex::_no_safepoint_check_flag);
 300   }
 301 
 302   if (started()) {
 303     set_in_progress();
 304   }
 305 }
 306 
 307 // Note: As is the case with CMS - this method, although exported
 308 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
 309 // be called by a JavaThread. Currently this is done at vm creation
 310 // time (post-vm-init) by the main/Primordial (Java)Thread.
 311 // XXX Consider changing this in the future to allow the CM thread
 312 // itself to create this thread?
 313 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
 314   assert(UseG1GC, "SLT thread needed only for concurrent GC");
 315   assert(THREAD->is_Java_thread(), "must be a Java thread");
 316   assert(_slt == NULL, "SLT already created");
 317   _slt = SurrogateLockerThread::make(THREAD);
 318 }
--- EOF ---