//Implementation of classical, Dijkstra Semaphore
//Weakly Fair

//Course 02220 Concurrent Programming

//Hans Henrik Lovengreen   Sep 13, 2002

public class Semaphore {

    private int s = 0;

    public Semaphore(int s0) {
        if (s0 >= 0) 
            s = s0;
        else 
            throw new Error("Semaphore initialized to negative value: " + s0);
    }

    public synchronized void P() throws InterruptedException {
        while (s == 0) wait();
        s--;
    }

    public synchronized void V() {
        s++;
        notify();
    }

    public String toString() { // Give semaphore value (for debugging only)
        return ""+s;
    }

}