/*

 * Copyright (c) 2015, 2016, 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/g1/g1CollectedHeap.inline.hpp"

#include "gc/g1/g1CollectorPolicy.hpp"

#include "gc/g1/g1YoungRemSetSamplingThread.hpp"

#include "gc/g1/heapRegion.inline.hpp"

#include "gc/g1/heapRegionRemSet.hpp"

#include "gc/g1/suspendibleThreadSet.hpp"

#include "runtime/mutexLocker.hpp"

void G1YoungRemSetSamplingThread::run() {

  initialize_in_thread();

  wait_for_universe_init();

  run_service();

  terminate();

}

void G1YoungRemSetSamplingThread::stop() {

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

  {

    MutexLockerEx mu(Terminator_lock);

    _should_terminate = true;

  }

  stop_service();

  {

    MutexLockerEx mu(Terminator_lock);

    while (!_has_terminated) {

      Terminator_lock->wait();

    }

  }

}

G1YoungRemSetSamplingThread::G1YoungRemSetSamplingThread() :

    ConcurrentGCThread(),

    _monitor(Mutex::nonleaf,

             "G1YoungRemSetSamplingThread monitor",

             true,

             Monitor::_safepoint_check_never) {

  set_name("G1 Young RemSet Sampling");

  create_and_start();

}

void G1YoungRemSetSamplingThread::sleep_before_next_cycle() {

  MutexLockerEx x(&_monitor, Mutex::_no_safepoint_check_flag);

  if (!_should_terminate) {

    uintx waitms = G1ConcRefinementServiceIntervalMillis; // 300, really should be?

    _monitor.wait(Mutex::_no_safepoint_check_flag, waitms);

  }

}

void G1YoungRemSetSamplingThread::run_service() {

  double vtime_start = os::elapsedVTime();

  while (!_should_terminate) {

    sample_young_list_rs_lengths();

    if (os::supports_vtime()) {

      _vtime_accum = (os::elapsedVTime() - vtime_start);

    } else {

      _vtime_accum = 0.0;

    }

    sleep_before_next_cycle();

  }

}

void G1YoungRemSetSamplingThread::stop_service() {

  MutexLockerEx x(&_monitor, Mutex::_no_safepoint_check_flag);

  _monitor.notify();

}

void G1YoungRemSetSamplingThread::sample_young_list_rs_lengths() {

  SuspendibleThreadSetJoiner sts;

  G1CollectedHeap* g1h = G1CollectedHeap::heap();

  G1CollectorPolicy* g1p = g1h->g1_policy();

  if (g1p->adaptive_young_list_length()) {

    int regions_visited = 0;

    HeapRegion* hr = g1h->young_list()->first_region();

    size_t sampled_rs_lengths = 0;

    while (hr != NULL) {

      size_t rs_length = hr->rem_set()->occupied();

      sampled_rs_lengths += rs_length;

      // The current region may not yet have been added to the

      // incremental collection set (it gets added when it is

      // retired as the current allocation region).

      if (hr->in_collection_set()) {

        // Update the collection set policy information for this region

      }

      ++regions_visited;

      // we try to yield every time we visit 10 regions

      if (regions_visited == 10) {

        if (sts.should_yield()) {

          sts.yield();

          // A gc may have occurred and our sampling data is stale and further

          // traversal of the young list is unsafe

          return;

        }

        regions_visited = 0;

      }

      hr = hr->get_next_young_region();

    }

    g1p->revise_young_list_target_length_if_necessary(sampled_rs_lengths);

  }

}