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   6  * under the terms of the GNU General Public License version 2 only, as
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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/g1CollectedHeap.inline.hpp"
  29 #include "gc/g1/g1CollectorPolicy.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 "gc/shared/gcTraceTime.inline.hpp"
  36 #include "logging/log.hpp"
  37 #include "memory/resourceArea.hpp"
  38 #include "runtime/vmThread.hpp"
  39 
  40 // ======= Concurrent Mark Thread ========
  41 
  42 // The CM thread is created when the G1 garbage collector is used
  43 
  44 SurrogateLockerThread*
  45      ConcurrentMarkThread::_slt = NULL;
  46 
  47 ConcurrentMarkThread::ConcurrentMarkThread(G1ConcurrentMark* cm) :
  48   ConcurrentGCThread(),
  49   _cm(cm),
  50   _state(Idle),
  51   _vtime_accum(0.0),
  52   _vtime_mark_accum(0.0) {
  53 
  54   set_name("G1 Main Marker");
  55   create_and_start();
  56 }
  57 
  58 class CMCheckpointRootsFinalClosure: public VoidClosure {
  59 
  60   G1ConcurrentMark* _cm;
  61 public:
  62 
  63   CMCheckpointRootsFinalClosure(G1ConcurrentMark* cm) :
  64     _cm(cm) {}
  65 
  66   void do_void(){
  67     _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
  68   }
  69 };
  70 
  71 class CMCleanUp: public VoidClosure {
  72   G1ConcurrentMark* _cm;
  73 public:
  74 
  75   CMCleanUp(G1ConcurrentMark* cm) :
  76     _cm(cm) {}
  77 
  78   void do_void(){
  79     _cm->cleanup();
  80   }
  81 };
  82 
  83 // Marking pauses can be scheduled flexibly, so we might delay marking to meet MMU.
  84 void ConcurrentMarkThread::delay_to_keep_mmu(G1CollectorPolicy* g1_policy, bool remark) {
  85   if (g1_policy->adaptive_young_list_length()) {
  86     double now = os::elapsedTime();
  87     double prediction_ms = remark ? g1_policy->predict_remark_time_ms()
  88                                   : g1_policy->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, LogTag::_gc, LogTag::_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->register_concurrent_phase_start(title);
 103   }
 104 
 105   ~G1ConcPhaseTimer() {
 106     _cm->register_concurrent_phase_end();
 107   }
 108 };
 109 
 110 void ConcurrentMarkThread::run_service() {
 111   _vtime_start = os::elapsedVTime();
 112 
 113   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 114   G1CollectorPolicy* g1_policy = g1h->g1_policy();
 115 
 116   while (!should_terminate()) {
 117     // wait until started is set.
 118     sleepBeforeNextCycle();
 119     if (should_terminate()) {
 120       _cm->root_regions()->cancel_scan();
 121       break;
 122     }
 123 
 124     assert(GCId::current() != GCId::undefined(), "GC id should have been set up by the initial mark GC.");
 125     {
 126       ResourceMark rm;
 127       HandleMark   hm;
 128       double cycle_start = os::elapsedVTime();
 129 
 130       {
 131         G1ConcPhaseTimer t(_cm, "Concurrent Clear Claimed Marks");
 132         ClassLoaderDataGraph::clear_claimed_marks();
 133       }
 134 
 135       // We have to ensure that we finish scanning the root regions
 136       // before the next GC takes place. To ensure this we have to
 137       // make sure that we do not join the STS until the root regions
 138       // have been scanned. If we did then it's possible that a
 139       // subsequent GC could block us from joining the STS and proceed
 140       // without the root regions have been scanned which would be a
 141       // correctness issue.
 142 
 143       {
 144         G1ConcPhaseTimer t(_cm, "Concurrent Scan Root Regions");
 145         _cm->scan_root_regions();
 146       }
 147 
 148       // It would be nice to use the GCTraceConcTime class here but
 149       // the "end" logging is inside the loop and not at the end of
 150       // a scope. Mimicking the same log output as GCTraceConcTime instead.
 151       jlong mark_start = os::elapsed_counter();
 152       log_info(gc, marking)("Concurrent Mark (%.3fs)", TimeHelper::counter_to_seconds(mark_start));
 153 
 154       int iter = 0;
 155       do {
 156         iter++;
 157         if (!cm()->has_aborted()) {
 158           G1ConcPhaseTimer t(_cm, "Concurrent Mark From Roots");
 159           _cm->mark_from_roots();
 160         }
 161 
 162         double mark_end_time = os::elapsedVTime();
 163         jlong mark_end = os::elapsed_counter();
 164         _vtime_mark_accum += (mark_end_time - cycle_start);
 165         if (!cm()->has_aborted()) {
 166           delay_to_keep_mmu(g1_policy, true /* remark */);
 167           log_info(gc, marking)("Concurrent Mark (%.3fs, %.3fs) %.3fms",
 168                                 TimeHelper::counter_to_seconds(mark_start),
 169                                 TimeHelper::counter_to_seconds(mark_end),
 170                                 TimeHelper::counter_to_millis(mark_end - mark_start));
 171 
 172           CMCheckpointRootsFinalClosure final_cl(_cm);
 173           VM_CGC_Operation op(&final_cl, "Pause Remark", true /* needs_pll */);
 174           VMThread::execute(&op);
 175         }
 176         if (cm()->restart_for_overflow()) {
 177           log_debug(gc, marking)("Restarting Concurrent Marking because of Mark Stack Overflow in Remark (Iteration #%d).", iter);
 178           log_info(gc, marking)("Concurrent Mark Restart due to overflow");
 179         }
 180       } while (cm()->restart_for_overflow());
 181 
 182       double end_time = os::elapsedVTime();
 183       // Update the total virtual time before doing this, since it will try
 184       // to measure it to get the vtime for this marking.  We purposely
 185       // neglect the presumably-short "completeCleanup" phase here.
 186       _vtime_accum = (end_time - _vtime_start);
 187 
 188       if (!cm()->has_aborted()) {
 189         delay_to_keep_mmu(g1_policy, false /* cleanup */);
 190 
 191         CMCleanUp cl_cl(_cm);
 192         VM_CGC_Operation op(&cl_cl, "Pause Cleanup", false /* needs_pll */);
 193         VMThread::execute(&op);
 194       } else {
 195         // We don't want to update the marking status if a GC pause
 196         // is already underway.
 197         SuspendibleThreadSetJoiner sts_join;
 198         g1h->collector_state()->set_mark_in_progress(false);
 199       }
 200 
 201       // Check if cleanup set the free_regions_coming flag. If it
 202       // hasn't, we can just skip the next step.
 203       if (g1h->free_regions_coming()) {
 204         // The following will finish freeing up any regions that we
 205         // found to be empty during cleanup. We'll do this part
 206         // without joining the suspendible set. If an evacuation pause
 207         // takes place, then we would carry on freeing regions in
 208         // case they are needed by the pause. If a Full GC takes
 209         // place, it would wait for us to process the regions
 210         // reclaimed by cleanup.
 211 
 212         G1ConcPhaseTimer t(_cm, "Concurrent Complete Cleanup");
 213 
 214         // Now do the concurrent cleanup operation.
 215         _cm->complete_cleanup();
 216 
 217         // Notify anyone who's waiting that there are no more free
 218         // regions coming. We have to do this before we join the STS
 219         // (in fact, we should not attempt to join the STS in the
 220         // interval between finishing the cleanup pause and clearing
 221         // the free_regions_coming flag) otherwise we might deadlock:
 222         // a GC worker could be blocked waiting for the notification
 223         // whereas this thread will be blocked for the pause to finish
 224         // while it's trying to join the STS, which is conditional on
 225         // the GC workers finishing.
 226         g1h->reset_free_regions_coming();
 227       }
 228       guarantee(cm()->cleanup_list_is_empty(),
 229                 "at this point there should be no regions on the cleanup list");
 230 
 231       // There is a tricky race before recording that the concurrent
 232       // cleanup has completed and a potential Full GC starting around
 233       // the same time. We want to make sure that the Full GC calls
 234       // abort() on concurrent mark after
 235       // record_concurrent_mark_cleanup_completed(), since abort() is
 236       // the method that will reset the concurrent mark state. If we
 237       // end up calling record_concurrent_mark_cleanup_completed()
 238       // after abort() then we might incorrectly undo some of the work
 239       // abort() did. Checking the has_aborted() flag after joining
 240       // the STS allows the correct ordering of the two methods. There
 241       // are two scenarios:
 242       //
 243       // a) If we reach here before the Full GC, the fact that we have
 244       // joined the STS means that the Full GC cannot start until we
 245       // leave the STS, so record_concurrent_mark_cleanup_completed()
 246       // will complete before abort() is called.
 247       //
 248       // b) If we reach here during the Full GC, we'll be held up from
 249       // joining the STS until the Full GC is done, which means that
 250       // abort() will have completed and has_aborted() will return
 251       // true to prevent us from calling
 252       // record_concurrent_mark_cleanup_completed() (and, in fact, it's
 253       // not needed any more as the concurrent mark state has been
 254       // already reset).
 255       {
 256         SuspendibleThreadSetJoiner sts_join;
 257         if (!cm()->has_aborted()) {
 258           g1_policy->record_concurrent_mark_cleanup_completed();
 259         } else {
 260           log_info(gc, marking)("Concurrent Mark Abort");
 261         }
 262       }
 263 
 264       // We now want to allow clearing of the marking bitmap to be
 265       // suspended by a collection pause.
 266       // We may have aborted just before the remark. Do not bother clearing the
 267       // bitmap then, as it has been done during mark abort.
 268       if (!cm()->has_aborted()) {
 269         G1ConcPhaseTimer t(_cm, "Concurrent Cleanup for Next Mark");
 270         _cm->cleanup_for_next_mark();
 271       } else {
 272         assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
 273       }
 274     }
 275 
 276     // Update the number of full collections that have been
 277     // completed. This will also notify the FullGCCount_lock in case a
 278     // Java thread is waiting for a full GC to happen (e.g., it
 279     // called System.gc() with +ExplicitGCInvokesConcurrent).
 280     {
 281       SuspendibleThreadSetJoiner sts_join;
 282       g1h->increment_old_marking_cycles_completed(true /* concurrent */);
 283       g1h->register_concurrent_cycle_end();
 284     }
 285   }
 286 }
 287 
 288 void ConcurrentMarkThread::stop_service() {
 289   MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
 290   CGC_lock->notify_all();
 291 }
 292 
 293 void ConcurrentMarkThread::sleepBeforeNextCycle() {
 294   // We join here because we don't want to do the "shouldConcurrentMark()"
 295   // below while the world is otherwise stopped.
 296   assert(!in_progress(), "should have been cleared");
 297 
 298   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 299   while (!started() && !should_terminate()) {
 300     CGC_lock->wait(Mutex::_no_safepoint_check_flag);
 301   }
 302 
 303   if (started()) {
 304     set_in_progress();
 305   }
 306 }
 307 
 308 // Note: As is the case with CMS - this method, although exported
 309 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
 310 // be called by a JavaThread. Currently this is done at vm creation
 311 // time (post-vm-init) by the main/Primordial (Java)Thread.
 312 // XXX Consider changing this in the future to allow the CM thread
 313 // itself to create this thread?
 314 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
 315   assert(UseG1GC, "SLT thread needed only for concurrent GC");
 316   assert(THREAD->is_Java_thread(), "must be a Java thread");
 317   assert(_slt == NULL, "SLT already created");
 318   _slt = SurrogateLockerThread::make(THREAD);
 319 }