//Basic implementation of Alley class
//CP Lab 3
//Course 02158 Concurrent Programming, DTU

//Hans Henrik Lovengreen

public class BasicAlley extends Alley {

    int up = 0, down = 0;
    
    BasicAlley() {
    }

    @Override
    /* Block until car no. may enter alley */
    public synchronized void enter(int no) throws InterruptedException {
        if (no < 5) {
            while (up   > 0) { wait(); }
            down++;
        } else {
            while (down > 0) { wait(); }
            up++;
        }
     }

    @Override
    /* Register that car no. has left the alley */
    public synchronized void leave(int no) {
        if (no < 5) {
            down--; 
            if (down == 0) notifyAll();
        } else {
            up--; 
            if (up   == 0) notifyAll();
        }
    }

}