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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 "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   _started(false),
  48   _in_progress(false),
  49   _vtime_accum(0.0),
  50   _vtime_mark_accum(0.0) {
  51 
  52   set_name("G1 Main Marker");
  53   create_and_start();
  54 }
  55 
  56 class CMCheckpointRootsFinalClosure: public VoidClosure {
  57 
  58   ConcurrentMark* _cm;
  59 public:
  60 
  61   CMCheckpointRootsFinalClosure(ConcurrentMark* cm) :
  62     _cm(cm) {}
  63 
  64   void do_void(){
  65     _cm->checkpointRootsFinal(false); // !clear_all_soft_refs
  66   }
  67 };
  68 
  69 class CMCleanUp: public VoidClosure {
  70   ConcurrentMark* _cm;
  71 public:
  72 
  73   CMCleanUp(ConcurrentMark* cm) :
  74     _cm(cm) {}
  75 
  76   void do_void(){
  77     _cm->cleanup();
  78   }
  79 };
  80 
  81 // We want to avoid that the logging from the concurrent thread is mixed
  82 // with the logging from a STW GC. So, if necessary join the STS to ensure
  83 // that the logging is done either before or after the STW logging.
  84 void ConcurrentMarkThread::cm_log(bool doit, bool join_sts, const char* fmt, ...) {
  85   if (doit) {
  86     SuspendibleThreadSetJoiner sts_joiner(join_sts);
  87     va_list args;
  88     va_start(args, fmt);
  89     gclog_or_tty->gclog_stamp(cm()->concurrent_gc_id());
  90     gclog_or_tty->vprint_cr(fmt, args);
  91     va_end(args);
  92   }
  93 }
  94 
  95 void ConcurrentMarkThread::run() {
  96   initialize_in_thread();
  97   _vtime_start = os::elapsedVTime();
  98   wait_for_universe_init();
  99 
 100   G1CollectedHeap* g1h = G1CollectedHeap::heap();
 101   G1CollectorPolicy* g1_policy = g1h->g1_policy();
 102   G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();
 103   Thread *current_thread = Thread::current();
 104 
 105   while (!_should_terminate) {
 106     // wait until started is set.
 107     sleepBeforeNextCycle();
 108     if (_should_terminate) {
 109       break;
 110     }
 111 
 112     {
 113       ResourceMark rm;
 114       HandleMark   hm;
 115       double cycle_start = os::elapsedVTime();
 116 
 117       // We have to ensure that we finish scanning the root regions
 118       // before the next GC takes place. To ensure this we have to
 119       // make sure that we do not join the STS until the root regions
 120       // have been scanned. If we did then it's possible that a
 121       // subsequent GC could block us from joining the STS and proceed
 122       // without the root regions have been scanned which would be a
 123       // correctness issue.
 124 
 125       if (!cm()->has_aborted()) {
 126         _cm->scanRootRegions();
 127       }
 128 
 129       double mark_start_sec = os::elapsedTime();
 130       cm_log(G1Log::fine(), true, "[GC concurrent-mark-start]");
 131 
 132       int iter = 0;
 133       do {
 134         iter++;
 135         if (!cm()->has_aborted()) {
 136           _cm->markFromRoots();
 137         }
 138 
 139         double mark_end_time = os::elapsedVTime();
 140         double mark_end_sec = os::elapsedTime();
 141         _vtime_mark_accum += (mark_end_time - cycle_start);
 142         if (!cm()->has_aborted()) {
 143           if (g1_policy->adaptive_young_list_length()) {
 144             double now = os::elapsedTime();
 145             double remark_prediction_ms = g1_policy->predict_remark_time_ms();
 146             jlong sleep_time_ms = mmu_tracker->when_ms(now, remark_prediction_ms);
 147             os::sleep(current_thread, sleep_time_ms, false);
 148           }
 149 
 150           cm_log(G1Log::fine(), true, "[GC concurrent-mark-end, %1.7lf secs]", mark_end_sec - mark_start_sec);
 151 
 152           CMCheckpointRootsFinalClosure final_cl(_cm);
 153           VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
 154           VMThread::execute(&op);
 155         }
 156         if (cm()->restart_for_overflow()) {
 157           cm_log(G1TraceMarkStackOverflow, true, "Restarting conc marking because of MS overflow in remark (restart #%d).", iter);
 158           cm_log(G1Log::fine(), true, "[GC concurrent-mark-restart-for-overflow]");
 159         }
 160       } while (cm()->restart_for_overflow());
 161 
 162       double end_time = os::elapsedVTime();
 163       // Update the total virtual time before doing this, since it will try
 164       // to measure it to get the vtime for this marking.  We purposely
 165       // neglect the presumably-short "completeCleanup" phase here.
 166       _vtime_accum = (end_time - _vtime_start);
 167 
 168       if (!cm()->has_aborted()) {
 169         if (g1_policy->adaptive_young_list_length()) {
 170           double now = os::elapsedTime();
 171           double cleanup_prediction_ms = g1_policy->predict_cleanup_time_ms();
 172           jlong sleep_time_ms = mmu_tracker->when_ms(now, cleanup_prediction_ms);
 173           os::sleep(current_thread, sleep_time_ms, false);
 174         }
 175 
 176         CMCleanUp cl_cl(_cm);
 177         VM_CGC_Operation op(&cl_cl, "GC cleanup", false /* needs_pll */);
 178         VMThread::execute(&op);
 179       } else {
 180         // We don't want to update the marking status if a GC pause
 181         // is already underway.
 182         SuspendibleThreadSetJoiner sts_join;
 183         g1h->collector_state()->set_mark_in_progress(false);
 184       }
 185 
 186       // Check if cleanup set the free_regions_coming flag. If it
 187       // hasn't, we can just skip the next step.
 188       if (g1h->free_regions_coming()) {
 189         // The following will finish freeing up any regions that we
 190         // found to be empty during cleanup. We'll do this part
 191         // without joining the suspendible set. If an evacuation pause
 192         // takes place, then we would carry on freeing regions in
 193         // case they are needed by the pause. If a Full GC takes
 194         // place, it would wait for us to process the regions
 195         // reclaimed by cleanup.
 196 
 197         double cleanup_start_sec = os::elapsedTime();
 198         cm_log(G1Log::fine(), true, "[GC concurrent-cleanup-start]");
 199 
 200         // Now do the concurrent cleanup operation.
 201         _cm->completeCleanup();
 202 
 203         // Notify anyone who's waiting that there are no more free
 204         // regions coming. We have to do this before we join the STS
 205         // (in fact, we should not attempt to join the STS in the
 206         // interval between finishing the cleanup pause and clearing
 207         // the free_regions_coming flag) otherwise we might deadlock:
 208         // a GC worker could be blocked waiting for the notification
 209         // whereas this thread will be blocked for the pause to finish
 210         // while it's trying to join the STS, which is conditional on
 211         // the GC workers finishing.
 212         g1h->reset_free_regions_coming();
 213 
 214         double cleanup_end_sec = os::elapsedTime();
 215         cm_log(G1Log::fine(), true, "[GC concurrent-cleanup-end, %1.7lf secs]", cleanup_end_sec - cleanup_start_sec);
 216       }
 217       guarantee(cm()->cleanup_list_is_empty(),
 218                 "at this point there should be no regions on the cleanup list");
 219 
 220       // There is a tricky race before recording that the concurrent
 221       // cleanup has completed and a potential Full GC starting around
 222       // the same time. We want to make sure that the Full GC calls
 223       // abort() on concurrent mark after
 224       // record_concurrent_mark_cleanup_completed(), since abort() is
 225       // the method that will reset the concurrent mark state. If we
 226       // end up calling record_concurrent_mark_cleanup_completed()
 227       // after abort() then we might incorrectly undo some of the work
 228       // abort() did. Checking the has_aborted() flag after joining
 229       // the STS allows the correct ordering of the two methods. There
 230       // are two scenarios:
 231       //
 232       // a) If we reach here before the Full GC, the fact that we have
 233       // joined the STS means that the Full GC cannot start until we
 234       // leave the STS, so record_concurrent_mark_cleanup_completed()
 235       // will complete before abort() is called.
 236       //
 237       // b) If we reach here during the Full GC, we'll be held up from
 238       // joining the STS until the Full GC is done, which means that
 239       // abort() will have completed and has_aborted() will return
 240       // true to prevent us from calling
 241       // record_concurrent_mark_cleanup_completed() (and, in fact, it's
 242       // not needed any more as the concurrent mark state has been
 243       // already reset).
 244       {
 245         SuspendibleThreadSetJoiner sts_join;
 246         if (!cm()->has_aborted()) {
 247           g1_policy->record_concurrent_mark_cleanup_completed();
 248         } else {
 249           cm_log(G1Log::fine(), false, "[GC concurrent-mark-abort]");
 250         }
 251       }
 252 
 253       // We now want to allow clearing of the marking bitmap to be
 254       // suspended by a collection pause.
 255       // We may have aborted just before the remark. Do not bother clearing the
 256       // bitmap then, as it has been done during mark abort.
 257       if (!cm()->has_aborted()) {
 258         _cm->clearNextBitmap();
 259       } else {
 260         assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
 261       }
 262     }
 263 
 264     // Update the number of full collections that have been
 265     // completed. This will also notify the FullGCCount_lock in case a
 266     // Java thread is waiting for a full GC to happen (e.g., it
 267     // called System.gc() with +ExplicitGCInvokesConcurrent).
 268     {
 269       SuspendibleThreadSetJoiner sts_join;
 270       g1h->increment_old_marking_cycles_completed(true /* concurrent */);
 271       g1h->register_concurrent_cycle_end();
 272     }
 273   }
 274   assert(_should_terminate, "just checking");
 275 
 276   terminate();
 277 }
 278 
 279 void ConcurrentMarkThread::stop() {
 280   {
 281     MutexLockerEx ml(Terminator_lock);
 282     _should_terminate = true;
 283   }
 284 
 285   {
 286     MutexLockerEx ml(CGC_lock, Mutex::_no_safepoint_check_flag);
 287     CGC_lock->notify_all();
 288   }
 289 
 290   {
 291     MutexLockerEx ml(Terminator_lock);
 292     while (!_has_terminated) {
 293       Terminator_lock->wait();
 294     }
 295   }
 296 }
 297 
 298 void ConcurrentMarkThread::sleepBeforeNextCycle() {
 299   // We join here because we don't want to do the "shouldConcurrentMark()"
 300   // below while the world is otherwise stopped.
 301   assert(!in_progress(), "should have been cleared");
 302 
 303   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);
 304   while (!started() && !_should_terminate) {
 305     CGC_lock->wait(Mutex::_no_safepoint_check_flag);
 306   }
 307 
 308   if (started()) {
 309     set_in_progress();
 310     clear_started();
 311   }
 312 }
 313 
 314 // Note: As is the case with CMS - this method, although exported
 315 // by the ConcurrentMarkThread, which is a non-JavaThread, can only
 316 // be called by a JavaThread. Currently this is done at vm creation
 317 // time (post-vm-init) by the main/Primordial (Java)Thread.
 318 // XXX Consider changing this in the future to allow the CM thread
 319 // itself to create this thread?
 320 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {
 321   assert(UseG1GC, "SLT thread needed only for concurrent GC");
 322   assert(THREAD->is_Java_thread(), "must be a Java thread");
 323   assert(_slt == NULL, "SLT already created");
 324   _slt = SurrogateLockerThread::make(THREAD);
 325 }