//@author: j.n.magee 11/11/96
//adapted by mh, 02/04/03


/********************************************************/
//
// The Semaphore Class
// up() is the V operation
// down() is the P operation
//
public class Semaphore {

    private int value;

    public Semaphore (int initial) {
	if (initial<0) {
	    System.exit(1); // out of range error
	} else {        
	    value = initial;
	} // if
    } // Semaphore

    synchronized public void up() {
        ++value;
        notify();    // notifyAll() ?
    } // up

    synchronized public void down() {
	try {        
	    while (value==0) {
	       wait();  
	    } // end while
        --value;
	} catch(InterruptedException e){}
    } // down

} // class Semaphore