timer.h

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// timer.h 
//      Data structures to emulate a hardware timer.
//
//      A hardware timer generates a CPU interrupt every X milliseconds.
//      This means it can be used for implementing time-slicing, or for
//      having a thread go to sleep for a specific period of time. 
//
//      We emulate a hardware timer by scheduling an interrupt to occur
//      every time stats->totalTicks has increased by TimerTicks.
//
//      In order to introduce some randomness into time-slicing, if "doRandom"
//      is set, then the interrupt comes after a random number of ticks.
//
//  DO NOT CHANGE -- part of the machine emulation
//
// Copyright (c) 1992-1996 The Regents of the University of California.
// All rights reserved.  See copyright.h for copyright notice and limitation 
// of liability and disclaimer of warranty provisions.

#ifndef TIMER_H
#define TIMER_H

#include "copyright.h"
#include "utility.h"
#include "callback.h"

// The following class defines a hardware timer. 
class Timer : public CallBackObj {
  public:
    Timer(bool doRandom, CallBackObj *toCall);
                                // Initialize the timer, and callback to "toCall"
                                // every time slice.
    virtual ~Timer() {}
    
    void Disable() { disable = TRUE; }
                                // Turn timer device off, so it doesn't
                                // generate any more interrupts.

  private:
    bool randomize;             // set if we need to use a random timeout delay
    CallBackObj *callPeriodically; // call this every TimerTicks time units 
    bool disable;               // turn off the timer device after next
                                // interrupt.
    
    void CallBack();            // called internally when the hardware
                                // timer generates an interrupt

    void SetInterrupt();        // cause an interrupt to occur in the
                                // the future after a fixed or random
                                // delay
};

#endif // TIMER_H

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