public class MyProg
{ public static void main( String args[] )
{ Semaphore sem0=new Semaphore(1);
    Semaphore sem1=new Semaphore(1);
    Worker myThread0=new Worker ("Worker0", sem0, sem1);
    Worker myThread1=new Worker ("Worker1", sem0, sem1);
    myThread0.start();
    myThread1.start();
}
}
class Worker extends Thread
{ private Semaphore sem0, sem1;

    public Worker(String n, Semaphore s0, Semaphore s1)
    {super(n);
        sem0=s0;
        sem1=s1;
    }

    public void run()
    {for (int i=1; i<=3; i++)
    {int x=(int)(Math.random()*2);
        System.err.println("x="+x);
        if (x==0)
        {System.err.println(this.getName()+" calls sem0.P()");
            sem0.P();
            criticalSection0();
            System.err.println(this.getName()+" calls sem1.P()");
            sem1.P();
            criticalSection1();
            System.err.println(this.getName()+" calls sem1.V()");
            sem1.V();
            System.err.println(this.getName()+" calls sem0.V()");
            sem0.V();}
        else
        {System.err.println(this.getName()+" calls sem1.P()");
            sem1.P();
            criticalSection1();
            System.err.println(this.getName()+" calls sem0.P()");
            sem0.P();
            criticalSection0();
            System.err.println(this.getName()+" calls sem0.V()");
            sem0.V();
            System.err.println(this.getName()+" calls sem1.V()");
            sem1.V();}
    }
        System.err.println( this.getName()+": THE END");
    }

    public void criticalSection0()
    {System.err.println(this.getName()+"  ENTERS THE CRITICAL SECTION 0");
        try
        {Thread.sleep((int)(Math.random()*3000));}
        catch (InterruptedException e) {}
        System.err.println(this.getName()+"  EXITS FROM CRITICAL SECTION 0");
    }
    public void criticalSection1()
    {System.err.println(this.getName()+"  ENTERS THE CRITICAL SECTION 1");
        try
        {Thread.sleep((int)(Math.random()*3000));}
        catch (InterruptedException e) {}
        System.err.println(this.getName()+"  EXITS FROM CRITICAL SECTION 1");
    }
}

class Semaphore
{
    public Semaphore(int v)
    { value = v; }

    public void P()
    { while (value <= 0);
        value --;
    }

    public void V()
    { ++value;  }

    private int value;
}