SPP_TP34_exo1

package ex1;
import java.util.concurrent.locks.ReentrantReadWriteLock;;

public class MySemaphore implements SemaphoreInterface {

    private int slots;
    private int waitingThreads;
    private ReentrantReadWriteLock l;

    public MySemaphore() {
        this.slots = 0;
        this.waitingThreads = 0;
        this.l = new ReentrantReadWriteLock();
    }

    @Override
    public synchronized void up() {
        l.writeLock().lock();
        slots++;
        l.writeLock().unlock();

        l.readLock().lock();
        int waiting = waitingThreads;
        l.readLock().unlock();

        if(waiting > 0) {
            l.writeLock().lock();
            waitingThreads--;
            l.writeLock().unlock();
        }

        notify(); // Notifying thread to wake up
    }

    @Override
    public synchronized void down() {
        l.readLock().lock();
        int s = slots;
        l.readLock().unlock();

        while (s == 0) {
            try {
                l.writeLock().lock();
                waitingThreads++;
                l.writeLock().unlock();

                wait(); // Blocking current thread
                } catch (InterruptedException exception) {
                    exception.printStackTrace();
                }

                l.readLock().lock();
                s = slots;
                l.readLock().unlock();
            }
            l.writeLock().lock();
            slots--;
            l.writeLock().unlock();
    }

    @Override
    public synchronized int releaseAll() {
        l.readLock().lock();
        int tmp = waitingThreads;
        int waiting = waitingThreads;
        l.readLock().unlock();

        while(waiting > 0) {
            notify();

            l.writeLock().lock();
            waiting--;
            l.writeLock().unlock();
        }

        l.writeLock().lock();
        waitingThreads = 0;
        l.writeLock().unlock();

        l.writeLock().lock();
        slots += tmp;
        l.writeLock().unlock();

        return tmp;
    }

}