public class Elaborato {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        int N=2;
        int M=3;

        Monitor m = new Monitor(N,M);

        Generator g = new Generator(m, M, N);
        g.start();

        Avg[] avg = new Avg[N];
        for (int i=0; i<N; i++){
            avg[i]=new Avg(i, m, M);
            avg[i].start();


        }
    }

}

public class Generator extends Thread {

    private Monitor m;
    int M,N;

    public Generator(Monitor m, int M, int N) {
        this.m = m;
        this.M=M;
        this.N=N;
    }

    public void run() {
        int i= 0;
        try {
            do {
                m.startWrite();
                //scrive sul db
                for (int j=i; j<i+M*N; j++)
                    m.doWrite(j);
                i+=M*N;
                m.endWrite();
                Thread.sleep(500);
            } while (true);
        } catch (InterruptedException ie) {
        }
    }

}

public class Avg extends Thread {

    private int id;
    private Monitor m;
    private int M;

    public Avg(int id, Monitor m, int M) {
        this.id = id;
        this.m = m;
        this.M = M;
    }

    @Override
    public void run() {
        try {
            do {
                m.startRead();
                //gestisce le medie
                float q = m.doRead(id);
                q = q / (float) M;
                System.out.println("Avg " + id + " : " + q);
                m.endRead();
                Thread.sleep(500);
            } while (true);
        } catch (InterruptedException ie) {
        }
    }
}


public class Monitor {

    private int nReaders;
    private int nWriters;
    private int[] numbers;
    private int N;

    public Monitor(int N, int M) {
        nReaders = 0;
        nWriters = 0;
        this.N=N;
        numbers = new int[N * M];

    }

    public synchronized void startRead() throws InterruptedException {
        while (nWriters > 0) {
            wait();
        }
        nReaders++;
        notifyAll();
    }

    public synchronized void endRead() throws InterruptedException {
        nReaders--;
        notifyAll();
    }

    public synchronized void startWrite() throws InterruptedException {
        while (nReaders > 0) {
            wait();
        }
        nWriters++;
        notifyAll();
    }

    public synchronized void endWrite() {
        nWriters--;
        notifyAll();
    }

    public void doWrite(int i){
        numbers[i%(numbers.length)]=i;
    }

    public int doRead(int id){
        int sum=0;
        for(int i=0; i<numbers.length; i++)
            if (i%(N)==id)
                sum+=numbers[i];
        return sum;
    }
}