/*

 * Copyright (c) 2015, 2019, 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/z/zMetronome.hpp"

#include "runtime/mutexLocker.hpp"

#include "runtime/timer.hpp"

#include "utilities/ticks.hpp"

ZMetronome::ZMetronome(uint64_t hz) :

    _monitor(Monitor::leaf, "ZMetronome", false, Monitor::_safepoint_check_never),

    _interval_ms(MILLIUNITS / hz),

    _start_ms(0),

    _nticks(0),

    _stopped(false) {}

bool ZMetronome::wait_for_tick() {

  if (_nticks++ == 0) {

    // First tick, set start time

    const Ticks now = Ticks::now();

    _start_ms = TimeHelper::counter_to_millis(now.value());

  }

  MonitorLocker ml(&_monitor, Monitor::_no_safepoint_check_flag);

  while (!_stopped) {

    // We might wake up spuriously from wait, so always recalculate

    // the timeout after a wakeup to see if we need to wait again.

    const Ticks now = Ticks::now();

    const uint64_t now_ms = TimeHelper::counter_to_millis(now.value());

    const uint64_t next_ms = _start_ms + (_interval_ms * _nticks);

    const int64_t timeout_ms = next_ms - now_ms;

    if (timeout_ms > 0) {

      // Wait

      ml.wait(timeout_ms);

    } else {

      // Tick

      if (timeout_ms < 0) {

        const uint64_t overslept = -timeout_ms;

        if (overslept > _interval_ms) {

          // Missed one or more ticks. Bump _nticks accordingly to

          // avoid firing a string of immediate ticks to make up

          // for the ones we missed.

          _nticks += overslept / _interval_ms;

        }

      }

      return true;

    }

  }

  // Stopped

  return false;

}

void ZMetronome::stop() {

  MonitorLocker ml(&_monitor, Monitor::_no_safepoint_check_flag);

  _stopped = true;

  ml.notify();

}