ceph/branches/marnberg/quota/common/DecayCounter.h

// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*- 
/*
 * Ceph - scalable distributed file system
 *
 * Copyright (C) 2004-2006 Sage Weil <sage@newdream.net>
 *
 * This is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License version 2.1, as published by the Free Software 
 * Foundation.  See file COPYING.
 * 
 */



#ifndef __DECAYCOUNTER_H
#define __DECAYCOUNTER_H

#include <math.h>
#include "Clock.h"

#include "config.h"

class DecayCounter {
 protected:
  double val;              // value

  double half_life;        // in seconds
  double k;                // k = ln(.5)/half_life

  utime_t last_decay;   // time of last decay

 public:
  DecayCounter() : val(0) {
    set_halflife( g_conf.mds_decay_halflife );
    reset();
  }
  /*
  DecayCounter(double hl) : val(0) {
    set_halflife(hl);
    reset();
  }
  */
  
  void adjust(double a) {
    decay();
    val += a;
  }
  void adjust_down(const DecayCounter& other) {
    // assume other has same time stamp as us...
    val -= other.val;
  }

  void set_halflife(double hl) {
    half_life = hl;
    k = log(.5) / hl;
  }

  void take(DecayCounter& other) {
    *this = other;
    other.reset();
  }

  void reset() {
    last_decay.sec_ref() = 0;
    last_decay.usec_ref() = 0;
    val = 0;
  }
  
  void decay() {
    utime_t el = g_clock.recent_now();
    el -= last_decay;
    if (el.sec() >= 1) {
      val = val * exp((double)el * k);
      if (val < .01) val = 0;
      last_decay = g_clock.recent_now();
    }
  }

  double get() {
    decay();
    return val;
  }

  double hit(double v = 1.0) {
    decay();
    val += v;
    return val;
  }

};


#endif