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 /*

  * Copyright (c) 2001, 2012, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

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  */

 #include "precompiled.hpp"

 #include "gc_implementation/g1/concurrentMarkThread.inline.hpp"

 #include "gc_implementation/g1/g1CollectedHeap.inline.hpp"

 #include "gc_implementation/g1/g1CollectorPolicy.hpp"

 #include "gc_implementation/g1/g1MMUTracker.hpp"

 #include "gc_implementation/g1/vm_operations_g1.hpp"

 #include "memory/resourceArea.hpp"

 #include "runtime/vmThread.hpp"

 // ======= Concurrent Mark Thread ========

 // The CM thread is created when the G1 garbage collector is used

 SurrogateLockerThread*

      ConcurrentMarkThread::_slt = NULL;

 ConcurrentMarkThread::ConcurrentMarkThread(ConcurrentMark* cm) :

   ConcurrentGCThread(),

   _cm(cm),

   _started(false),

   _in_progress(false),

   _vtime_accum(0.0),

   _vtime_mark_accum(0.0) {

   create_and_start();

 }

 class CMCheckpointRootsFinalClosure: public VoidClosure {

   ConcurrentMark* _cm;

 public:

   CMCheckpointRootsFinalClosure(ConcurrentMark* cm) :

     _cm(cm) {}

   void do_void(){

     _cm->checkpointRootsFinal(false); // !clear_all_soft_refs

   }

 };

 class CMCleanUp: public VoidClosure {

   ConcurrentMark* _cm;

 public:

   CMCleanUp(ConcurrentMark* cm) :

     _cm(cm) {}

   void do_void(){

     _cm->cleanup();

   }

 };

 void ConcurrentMarkThread::run() {

   initialize_in_thread();

   _vtime_start = os::elapsedVTime();

   wait_for_universe_init();

   G1CollectedHeap* g1h = G1CollectedHeap::heap();

   G1CollectorPolicy* g1_policy = g1h->g1_policy();

   G1MMUTracker *mmu_tracker = g1_policy->mmu_tracker();

   Thread *current_thread = Thread::current();

   while (!_should_terminate) {

     // wait until started is set.

     sleepBeforeNextCycle();

     {

       ResourceMark rm;

       HandleMark   hm;

       double cycle_start = os::elapsedVTime();

       char verbose_str[128];

       // We have to ensure that we finish scanning the root regions

       // before the next GC takes place. To ensure this we have to

       // make sure that we do not join the STS until the root regions

       // have been scanned. If we did then it's possible that a

       // subsequent GC could block us from joining the STS and proceed

       // without the root regions have been scanned which would be a

       // correctness issue.

       double scan_start = os::elapsedTime();

       if (!cm()->has_aborted()) {

         if (PrintGC) {

           gclog_or_tty->date_stamp(PrintGCDateStamps);

           gclog_or_tty->stamp(PrintGCTimeStamps);

           gclog_or_tty->print_cr("[GC concurrent-root-region-scan-start]");

         }

         _cm->scanRootRegions();

         double scan_end = os::elapsedTime();

         if (PrintGC) {

           gclog_or_tty->date_stamp(PrintGCDateStamps);

           gclog_or_tty->stamp(PrintGCTimeStamps);

           gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf]",

                                  scan_end - scan_start);

         }

       }

       double mark_start_sec = os::elapsedTime();

       if (PrintGC) {

         gclog_or_tty->date_stamp(PrintGCDateStamps);

         gclog_or_tty->stamp(PrintGCTimeStamps);

         gclog_or_tty->print_cr("[GC concurrent-mark-start]");

       }

       int iter = 0;

       do {

         iter++;

         if (!cm()->has_aborted()) {

           _cm->markFromRoots();

         }

         double mark_end_time = os::elapsedVTime();

         double mark_end_sec = os::elapsedTime();

         _vtime_mark_accum += (mark_end_time - cycle_start);

         if (!cm()->has_aborted()) {

           if (g1_policy->adaptive_young_list_length()) {

             double now = os::elapsedTime();

             double remark_prediction_ms = g1_policy->predict_remark_time_ms();

             jlong sleep_time_ms = mmu_tracker->when_ms(now, remark_prediction_ms);

             os::sleep(current_thread, sleep_time_ms, false);

           }

           if (PrintGC) {

             gclog_or_tty->date_stamp(PrintGCDateStamps);

             gclog_or_tty->stamp(PrintGCTimeStamps);

             gclog_or_tty->print_cr("[GC concurrent-mark-end, %1.7lf sec]",

                                       mark_end_sec - mark_start_sec);

           }

           CMCheckpointRootsFinalClosure final_cl(_cm);

           sprintf(verbose_str, "GC remark");

           VM_CGC_Operation op(&final_cl, verbose_str, true /* needs_pll */);

           VMThread::execute(&op);

         }

         if (cm()->restart_for_overflow() &&

             G1TraceMarkStackOverflow) {

           gclog_or_tty->print_cr("Restarting conc marking because of MS overflow "

                                  "in remark (restart #%d).", iter);

         }

         if (cm()->restart_for_overflow()) {

           if (PrintGC) {

             gclog_or_tty->date_stamp(PrintGCDateStamps);

             gclog_or_tty->stamp(PrintGCTimeStamps);

             gclog_or_tty->print_cr("[GC concurrent-mark-restart-for-overflow]");

           }

         }

       } while (cm()->restart_for_overflow());

       double end_time = os::elapsedVTime();

       // Update the total virtual time before doing this, since it will try

       // to measure it to get the vtime for this marking.  We purposely

       // neglect the presumably-short "completeCleanup" phase here.

       _vtime_accum = (end_time - _vtime_start);

       if (!cm()->has_aborted()) {

         if (g1_policy->adaptive_young_list_length()) {

           double now = os::elapsedTime();

           double cleanup_prediction_ms = g1_policy->predict_cleanup_time_ms();

           jlong sleep_time_ms = mmu_tracker->when_ms(now, cleanup_prediction_ms);

           os::sleep(current_thread, sleep_time_ms, false);

         }

         CMCleanUp cl_cl(_cm);

         sprintf(verbose_str, "GC cleanup");

         VM_CGC_Operation op(&cl_cl, verbose_str, false /* needs_pll */);

         VMThread::execute(&op);

       } else {

         // We don't want to update the marking status if a GC pause

         // is already underway.

         _sts.join();

         g1h->set_marking_complete();

         _sts.leave();

       }

       // Check if cleanup set the free_regions_coming flag. If it

       // hasn't, we can just skip the next step.

       if (g1h->free_regions_coming()) {

         // The following will finish freeing up any regions that we

         // found to be empty during cleanup. We'll do this part

         // without joining the suspendible set. If an evacuation pause

         // takes place, then we would carry on freeing regions in

         // case they are needed by the pause. If a Full GC takes

         // place, it would wait for us to process the regions

         // reclaimed by cleanup.

         double cleanup_start_sec = os::elapsedTime();

         if (PrintGC) {

           gclog_or_tty->date_stamp(PrintGCDateStamps);

           gclog_or_tty->stamp(PrintGCTimeStamps);

           gclog_or_tty->print_cr("[GC concurrent-cleanup-start]");

         }

         // Now do the concurrent cleanup operation.

         _cm->completeCleanup();

         // Notify anyone who's waiting that there are no more free

         // regions coming. We have to do this before we join the STS

         // (in fact, we should not attempt to join the STS in the

         // interval between finishing the cleanup pause and clearing

         // the free_regions_coming flag) otherwise we might deadlock:

         // a GC worker could be blocked waiting for the notification

         // whereas this thread will be blocked for the pause to finish

         // while it's trying to join the STS, which is conditional on

         // the GC workers finishing.

         g1h->reset_free_regions_coming();

         double cleanup_end_sec = os::elapsedTime();

         if (PrintGC) {

           gclog_or_tty->date_stamp(PrintGCDateStamps);

           gclog_or_tty->stamp(PrintGCTimeStamps);

           gclog_or_tty->print_cr("[GC concurrent-cleanup-end, %1.7lf]",

                                  cleanup_end_sec - cleanup_start_sec);

         }

       }

       guarantee(cm()->cleanup_list_is_empty(),

                 "at this point there should be no regions on the cleanup list");

       // There is a tricky race before recording that the concurrent

       // cleanup has completed and a potential Full GC starting around

       // the same time. We want to make sure that the Full GC calls

       // abort() on concurrent mark after

       // record_concurrent_mark_cleanup_completed(), since abort() is

       // the method that will reset the concurrent mark state. If we

       // end up calling record_concurrent_mark_cleanup_completed()

       // after abort() then we might incorrectly undo some of the work

       // abort() did. Checking the has_aborted() flag after joining

       // the STS allows the correct ordering of the two methods. There

       // are two scenarios:

       //

       // a) If we reach here before the Full GC, the fact that we have

       // joined the STS means that the Full GC cannot start until we

       // leave the STS, so record_concurrent_mark_cleanup_completed()

       // will complete before abort() is called.

       //

       // b) If we reach here during the Full GC, we'll be held up from

       // joining the STS until the Full GC is done, which means that

       // abort() will have completed and has_aborted() will return

       // true to prevent us from calling

       // record_concurrent_mark_cleanup_completed() (and, in fact, it's

       // not needed any more as the concurrent mark state has been

       // already reset).

       _sts.join();

       if (!cm()->has_aborted()) {

         g1_policy->record_concurrent_mark_cleanup_completed();

       }

       _sts.leave();

       if (cm()->has_aborted()) {

         if (PrintGC) {

           gclog_or_tty->date_stamp(PrintGCDateStamps);

           gclog_or_tty->stamp(PrintGCTimeStamps);

           gclog_or_tty->print_cr("[GC concurrent-mark-abort]");

         }

       }

       // We now want to allow clearing of the marking bitmap to be

       // suspended by a collection pause.

       _sts.join();

       _cm->clearNextBitmap();

       _sts.leave();

     }

     // Update the number of full collections that have been

     // completed. This will also notify the FullGCCount_lock in case a

     // Java thread is waiting for a full GC to happen (e.g., it

     // called System.gc() with +ExplicitGCInvokesConcurrent).

     _sts.join();

     g1h->increment_full_collections_completed(true /* concurrent */);

     _sts.leave();

   }

   assert(_should_terminate, "just checking");

   terminate();

 }

 void ConcurrentMarkThread::yield() {

   _sts.yield("Concurrent Mark");

 }

 void ConcurrentMarkThread::stop() {

   // it is ok to take late safepoints here, if needed

   MutexLockerEx mu(Terminator_lock);

   _should_terminate = true;

   while (!_has_terminated) {

     Terminator_lock->wait();

   }

 }

 void ConcurrentMarkThread::print() const {

   print_on(tty);

 }

 void ConcurrentMarkThread::print_on(outputStream* st) const {

   st->print("\"G1 Main Concurrent Mark GC Thread\" ");

   Thread::print_on(st);

   st->cr();

 }

 void ConcurrentMarkThread::sleepBeforeNextCycle() {

   // We join here because we don't want to do the "shouldConcurrentMark()"

   // below while the world is otherwise stopped.

   assert(!in_progress(), "should have been cleared");

   MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag);

   while (!started()) {

     CGC_lock->wait(Mutex::_no_safepoint_check_flag);

   }

   set_in_progress();

   clear_started();

 }

 // Note: As is the case with CMS - this method, although exported

 // by the ConcurrentMarkThread, which is a non-JavaThread, can only

 // be called by a JavaThread. Currently this is done at vm creation

 // time (post-vm-init) by the main/Primordial (Java)Thread.

 // XXX Consider changing this in the future to allow the CM thread

 // itself to create this thread?

 void ConcurrentMarkThread::makeSurrogateLockerThread(TRAPS) {

   assert(UseG1GC, "SLT thread needed only for concurrent GC");

   assert(THREAD->is_Java_thread(), "must be a Java thread");

   assert(_slt == NULL, "SLT already created");

   _slt = SurrogateLockerThread::make(THREAD);

 }