mpd/src/system/PeriodClock.hxx

/*
 * Copyright (C) 2003-2014 The Music Player Daemon Project
 * http://www.musicpd.org
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program 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 for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */

#ifndef MPD_PERIOD_CLOCK_HXX
#define MPD_PERIOD_CLOCK_HXX

#include "Clock.hxx"

/**
 * This is a stopwatch which saves the timestamp of an event, and can
 * check whether a specified time span has passed since then.
 */
class PeriodClock {
protected:
  typedef unsigned Stamp;

private:
  Stamp last;

public:
  /**
   * Initializes the object, setting the last time stamp to "0",
   * i.e. a Check() will always succeed.  If you do not want this
   * default behaviour, call Update() immediately after creating the
   * object.
   */
  constexpr
  PeriodClock():last(0) {}

protected:
  static Stamp GetNow() {
    return MonotonicClockMS();
  }

  constexpr int Elapsed(Stamp now) const {
    return last == 0
      ? -1
      : now - last;
  }

  constexpr bool Check(Stamp now, unsigned duration) const {
    return now >= last + duration;
  }

  void Update(Stamp now) {
    last = now;
  }

public:
  bool IsDefined() const {
    return last != 0;
  }

  /**
   * Resets the clock.
   */
  void Reset() {
    last = 0;
  }

  /**
   * Returns the number of milliseconds elapsed since the last
   * update().  Returns -1 if update() was never called.
   */
  int Elapsed() const {
    return Elapsed(GetNow());
  }

  /**
   * Combines a call to Elapsed() and Update().
   */
  int ElapsedUpdate() {
    const auto now = GetNow();
    int result = Elapsed(now);
    Update(now);
    return result;
  }

  /**
   * Checks whether the specified duration has passed since the last
   * update.
   *
   * @param duration the duration in milliseconds
   */
  bool Check(unsigned duration) const {
    return Check(GetNow(), duration);
  }

  /**
   * Updates the time stamp, setting it to the current clock.
   */
  void Update() {
    Update(GetNow());
  }

  /**
   * Updates the time stamp, setting it to the current clock plus the
   * specified offset.
   */
  void UpdateWithOffset(int offset) {
    Update(GetNow() + offset);
  }

  /**
   * Checks whether the specified duration has passed since the last
   * update.  If yes, it updates the time stamp.
   *
   * @param duration the duration in milliseconds
   */
  bool CheckUpdate(unsigned duration) {
    Stamp now = GetNow();
    if (Check(now, duration)) {
      Update(now);
      return true;
    } else
      return false;
  }

  /**
   * Checks whether the specified duration has passed since the last
   * update.  After that, it updates the time stamp.
   *
   * @param duration the duration in milliseconds
   */
  bool CheckAlwaysUpdate(unsigned duration) {
    Stamp now = GetNow();
    bool ret = Check(now, duration);
    Update(now);
    return ret;
  }
};

#endif