A3.java

import java.lang.Math;
import java.util.Arrays;

class A3 extends Thread {

    private static final int N = 3;
    private int myid = 0;
    public volatile static Integer array[] = {0,0,0};

    A3(int i)
    {
        myid = i;
    }


    public void run()
    {
        rand_sleep();
        access();
    }

    /* accessing both tools */
    public void access()
    {
        int lefttool = get_left();

        /*locking left tool */
        get_left_tool(1);
        System.out.println(myid + " nimmt linken schluessel " +  Arrays.toString(array));
        get_right_tool(1);
        System.out.println(myid + " nimmt rechten schluessel " +  Arrays.toString(array));

        System.out.println(myid + " arbeitet mit beiden schluesseln "+  Arrays.toString(array));
        rand_sleep();

        get_right_tool(-1);
        System.out.println(myid + " legt rechten schluessel zurueck " +  Arrays.toString(array));
        get_left_tool(-1);
        System.out.println(myid + " legt linken schluessel zurueck " +  Arrays.toString(array));
    }


    /* simple random sleep func */
    private void rand_sleep()
    {
        try
        {
            Thread.sleep((long)(Math.random()*1000));
        }
        catch(Exception e) {}
    }


    /* calculates left tool position */
    private int get_left()
    {
        if (myid!=0)
        {
            return myid-1;
        }
        else
        {
            return N-1;
        }
    }


    /* gets left tool */
    private void get_left_tool(int inc)
    {
        int left_tool_pos = get_left();

        /* Wait till available */
        while(array[left_tool_pos] != 0) { /* wait */ }

        synchronized(array[left_tool_pos])
        {
            array[left_tool_pos]+=inc;
        }
    }

    /* gets right tool */
    private void get_right_tool(int inc)
    {
        /* Wait till available */
        while(array[myid] != 0) { /* wait */ }

        synchronized(array[myid])
        {
            array[myid]+=inc;
        }
    }

    public static void main (String [] args)
    {
        A3 mech[] = new A3[N];

        for (int i=0; i<N ; ++i)
        {
            mech[i] = new A3(i);
            mech[i].start();
        }

        for (int i=0 ;i<N ;++i )
        {
            try{
                mech[i].join(); 
            }
            catch(Exception e)
            {}

        }
    }
}