#include <iostream>
#include <unistd.h>
#include <signal.h>

using namespace std;

const int TIMESLICE=3;
bool alarmFired = false;

/*
 * void sigalarm_handler(int signum)
 * 	User defined signal handler for the signal number that is registered
 * 	using signal(unsigned int signum, sighandler_t)
 * @param signum: signal number of the signal that caused the handler to fire.
 */
void sigalarm_handler(int signum)
{
    // To simulate a preemptive, timesliced scheduling system, a signal handler
    // must be registered that simulates the CPU timer that fires whenever the
    // system has to schedule another process.
    cout << "got signal " <<  signum << endl;
    alarmFired = true;
}

/*
 * main(void)
 * 	Demonstrates the use of signal to register a signal handler for a signal
 * 	as well as the use of alarm to set an alarm for TIMESLICE seconds. Then
 * 	the process sleeps for some arbitrary amount of time. The process awakens
 * 	due to the alarm since the sleep time is greater than the alarm time.
 */
int main(void)
{
	int timeRemaining = 16;
    signal(SIGALRM, sigalarm_handler);
    cout << "pid is " << getpid() << endl;
	
    while (timeRemaining > 0)
    {
        // Set the alarm each time through for the prescribed number of seconds.
        alarm(TIMESLICE);

        // Simulate CPU time with either sleep(int seconds) or 
        // settimer(ITIMER_REAL, const struct itimerval *newval, struct itimerval *oldval)
        // Get the sleep seconds from the remaining process time.
        sleep(timeRemaining);
        cout << "ProcessName " << timeRemaining << endl; 

        // If alarm has fired, then timeslice expired,
        // otherwise remaining time expired.
        if (alarmFired == true)
            timeRemaining -= TIMESLICE;
        else
            timeRemaining -= timeRemaining;

        // Print that process is finished if no time remaining.
        if (timeRemaining == 0)
            cout << "ProcessName finished" << endl;

        // Reset alarmFired.
        alarmFired = false;
    }
}