/*

 * Copyright (c) 2001, 2015, 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/g1MMUTracker.hpp"

#include "gc/shared/gcTrace.hpp"

#include "runtime/mutexLocker.hpp"

#include "utilities/ostream.hpp"

#define _DISABLE_MMU                             0

// can't rely on comparing doubles with tolerating a small margin for error

#define SMALL_MARGIN 0.0000001

#define is_double_leq_0(_value) ( (_value) < SMALL_MARGIN )

#define is_double_leq(_val1, _val2) is_double_leq_0((_val1) - (_val2))

#define is_double_geq(_val1, _val2) is_double_leq_0((_val2) - (_val1))

/***** ALL TIMES ARE IN SECS!!!!!!! *****/

G1MMUTracker::G1MMUTracker(double time_slice, double max_gc_time) :

  _time_slice(time_slice),

  _max_gc_time(max_gc_time) { }

G1MMUTrackerQueue::G1MMUTrackerQueue(double time_slice, double max_gc_time) :

  G1MMUTracker(time_slice, max_gc_time),

  _head_index(0),

  _tail_index(trim_index(_head_index+1)),

  _no_entries(0) { }

void G1MMUTrackerQueue::remove_expired_entries(double current_time) {

  double limit = current_time - _time_slice;

  while (_no_entries > 0) {

    if (is_double_geq(limit, _array[_tail_index].end_time())) {

      _tail_index = trim_index(_tail_index + 1);

      --_no_entries;

    } else

      return;

  }

  guarantee(_no_entries == 0, "should have no entries in the array");

}

double G1MMUTrackerQueue::calculate_gc_time(double current_time) {

  double gc_time = 0.0;

  double limit = current_time - _time_slice;

  for (int i = 0; i < _no_entries; ++i) {

    int index = trim_index(_tail_index + i);

    G1MMUTrackerQueueElem *elem = &_array[index];

    if (elem->end_time() > limit) {

      if (elem->start_time() > limit)

        gc_time += elem->duration();

      else

        gc_time += elem->end_time() - limit;

    }

  }

  return gc_time;

}

void G1MMUTrackerQueue::add_pause(double start, double end) {

  double duration = end - start;

  remove_expired_entries(end);

  if (_no_entries == QueueLength) {

    // OK, we've filled up the queue. There are a few ways

    // of dealing with this "gracefully"

    //   increase the array size (:-)

    //   remove the oldest entry (this might allow more GC time for

    //     the time slice than what's allowed) - this is what we

    //     currently do

    //   consolidate the two entries with the minimum gap between them

    //     (this might allow less GC time than what's allowed)

    // In the case where ScavengeALot is true, such overflow is not

    // uncommon; in such cases, we can, without much loss of precision

    // or performance (we are GC'ing most of the time anyway!),

    // simply overwrite the oldest entry in the tracker.

    _head_index = trim_index(_head_index + 1);

    assert(_head_index == _tail_index, "Because we have a full circular buffer");

    _tail_index = trim_index(_tail_index + 1);

  } else {

    _head_index = trim_index(_head_index + 1);

    ++_no_entries;

  }

  _array[_head_index] = G1MMUTrackerQueueElem(start, end);

  // Current entry needs to be added before calculating the value

  double slice_time = calculate_gc_time(end);

  G1MMUTracer::report_mmu(_time_slice, slice_time, _max_gc_time);

}

// basically the _internal call does not remove expired entries

// this is for trying things out in the future and a couple

// of other places (debugging)

double G1MMUTrackerQueue::when_sec(double current_time, double pause_time) {

  if (_DISABLE_MMU)

    return 0.0;

  MutexLockerEx x(MMUTracker_lock, Mutex::_no_safepoint_check_flag);

  remove_expired_entries(current_time);

  return when_internal(current_time, pause_time);

}

double G1MMUTrackerQueue::when_internal(double current_time,

                                        double pause_time) {

  // if the pause is over the maximum, just assume that it's the maximum

  double adjusted_pause_time =

    (pause_time > max_gc_time()) ? max_gc_time() : pause_time;

  double earliest_end = current_time + adjusted_pause_time;

  double limit = earliest_end - _time_slice;

  double gc_time = calculate_gc_time(earliest_end);

  double diff = gc_time + adjusted_pause_time - max_gc_time();

  if (is_double_leq_0(diff))

    return 0.0;

  int index = _tail_index;

  while ( 1 ) {

    G1MMUTrackerQueueElem *elem = &_array[index];

    if (elem->end_time() > limit) {

      if (elem->start_time() > limit)

        diff -= elem->duration();

      else

        diff -= elem->end_time() - limit;

      if (is_double_leq_0(diff))

        return  elem->end_time() + diff + _time_slice - adjusted_pause_time - current_time;

    }

    index = trim_index(index+1);

    guarantee(index != trim_index(_head_index + 1), "should not go past head");

  }

}