Java example source code file (concurrentMarkThread.cpp)

This example Java source code file (concurrentMarkThread.cpp) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

cmcheckpointrootsfinalclosure, cmcleanup, concurrentmark, concurrentmarkthread\:\:concurrentmarkthread, g1log::fine, mutexlockerex, null, slt, thread, vm_cgc_operation, vmthread\:\:execute, voidclosure

The concurrentMarkThread.cpp Java example source code

/*
 * Copyright (c) 2001, 2013, 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.
 *
 */

#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/g1Log.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();

      // 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 (G1Log::fine()) {
          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 (G1Log::fine()) {
          gclog_or_tty->date_stamp(PrintGCDateStamps);
          gclog_or_tty->stamp(PrintGCTimeStamps);
          gclog_or_tty->print_cr("[GC concurrent-root-region-scan-end, %1.7lf secs]",
                                 scan_end - scan_start);
        }
      }

      double mark_start_sec = os::elapsedTime();
      if (G1Log::fine()) {
        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 (G1Log::fine()) {
            gclog_or_tty->date_stamp(PrintGCDateStamps);
            gclog_or_tty->stamp(PrintGCTimeStamps);
            gclog_or_tty->print_cr("[GC concurrent-mark-end, %1.7lf secs]",
                                      mark_end_sec - mark_start_sec);
          }

          CMCheckpointRootsFinalClosure final_cl(_cm);
          VM_CGC_Operation op(&final_cl, "GC remark", true /* needs_pll */);
          VMThread::execute(&op);
        }
        if (cm()->restart_for_overflow()) {
          if (G1TraceMarkStackOverflow) {
            gclog_or_tty->print_cr("Restarting conc marking because of MS overflow "
                                   "in remark (restart #%d).", iter);
          }
          if (G1Log::fine()) {
            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);
        VM_CGC_Operation op(&cl_cl, "GC cleanup", 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 (G1Log::fine()) {
          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 (G1Log::fine()) {
          gclog_or_tty->date_stamp(PrintGCDateStamps);
          gclog_or_tty->stamp(PrintGCTimeStamps);
          gclog_or_tty->print_cr("[GC concurrent-cleanup-end, %1.7lf secs]",
                                 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 (G1Log::fine()) {
          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_old_marking_cycles_completed(true /* concurrent */);
    g1h->register_concurrent_cycle_end();
    _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);
}