Need Urgent Help!!!!

[needHelp123]

"Implement an Alarm class. Threads will call your Pause(int time) to go to sleep for a period of time. You can use the Java Timer class. When timer interrupt goes off, the Timer interrupt handler must wake up any thread sleeping in Pause whose interval has expired. It is not required that an awakened thread starts running immediately after the interval expires. Just have them wake up after they have waited for at least the specified interval, time"

How do I approach this? Please help me! It's very urgent.
Does it need to be synchronized? Why? How?

[Hack]

Welcome to DevX

What have you got so far?

(Is this a school assignment?)

[needHelp123]

Yes, it is a school assignment.
I found the following, which I believe must be close to what's required but I don't fully understand what the following piece of code does. I don't know what's missing there. I don't understand where the sychronization should take place and how. If you can give me a brief explanation I'd really appreciate it. Thank you.

http://www.koders.com/java/fid22FAD8...%3asemap*.java

package nachos.threads;

import nachos.machine.*;

/**
 * Uses the hardware timer to provide preemption, and to allow threads to sleep
 * until a certain time.
 */
public class Alarm {
    /**
     * Allocate a new Alarm. Set the machine's timer interrupt handler to this
     * alarm's callback.
     *
     * <p><b>Note</b>: Nachos will not function correctly with more than one
     * alarm.
     */
    public Alarm() {
	Machine.timer().setInterruptHandler(new Runnable() {
		public void run() { timerInterrupt(); }
	    });
    }

    /**
     * The timer interrupt handler. This is called by the machine's timer
     * periodically (approximately every 500 clock ticks). Causes the current
     * thread to yield, forcing a context switch if there is another thread
     * that should be run.
     */
    public void timerInterrupt() {
	KThread.currentThread().yield();
    }

    /**
     * Put the current thread to sleep for at least <i>x</i> ticks,
     * waking it up in the timer interrupt handler. The thread must be
     * woken up (placed in the scheduler ready set) during the first timer
     * interrupt where
     *
     * <p><blockquote>
     * (current time) >= (WaitUntil called time)+(x)
     * </blockquote>
     *
     * @param	x	the minimum number of clock ticks to wait.
     *
     * @see	nachos.machine.Timer#getTime()
     */
    public void waitUntil(long x) {
	// for now, cheat just to get something working (busy waiting is bad)
	long wakeTime = Machine.timer().getTime() + x;
	while (wakeTime > Machine.timer().getTime())
	    KThread.yield();
    }
}