Thread synchronization with multiple objects

Question

I have been facing this problem for many days, Please help me out. I am implementing producer-consumer example using thread synchronization. I have made some twist in this traditional program. Instead of using only one queue object, i have used two Queue objects. But program is not working.. (PS- I know i can make this program work by using only one object of queue, But what if i want to use two queue objects ?? )

class Queue {

static int value;

static boolean valueSet = false;

public static final Object obj;

static {

    obj = new Object();
}


void push() {

    synchronized(Queue.obj) {

        while( Queue.valueSet ) {

            try {
            Thread.sleep(1000);
            }catch(Exception e) {}
        }

        System.out.print("\n\n Push:-  " + (++(Queue.value)));
        Queue.valueSet = true;

        return;

    }

}

void pop() {

    synchronized(Queue.obj) {

        while(!(Queue.valueSet)) {

            try {
            Thread.sleep(1000);
            }catch(Exception e) {}
        }

        System.out.print("\n\n Pop:-   " + Queue.value);

        Queue.valueSet = false;

        return;

    }

}

}

class Producer implements Runnable {

Queue Q;
Thread P;


Producer(Queue Q) {

    this.Q = Q;
    P = new Thread(this);
    P.start();

}

public void run() {

    while(true) {

        Q.push();

    }
}

}

class Consumer implements Runnable {

Queue Q;
Thread C;

Consumer(Queue Q) {

    this.Q = Q;
    C = new Thread(this);
    C.start();


}

public void run() {

    while(true) {

        Q.pop();

    }
}

}

public class TestQueue {

public static void main(String[] args) {

    Queue Q1 = new Queue();
    Queue Q2 = new Queue();

    Object obj = new Object();


    Producer p = new Producer(Q1);
    Consumer c = new Consumer(Q2);
}

}

Answer 1

I got the answer. My misconception was wait,notify and notifyall methods are of thread class. So i was invoking them on thread object.

Solution is to just invoke wait and notify method on shared static object other than thread.

Answer:-

class Queue {

static int value;

static boolean valueSet = false;

public static final Object obj;

static {

    obj = new Object();
}


void push() {

    synchronized(Queue.obj) {

        while( Queue.valueSet ) {

            try {
            Queue.obj.wait();
            Thread.sleep(1000);
            }catch(Exception e) {

                e.printStackTrace();
            }
        }

        System.out.print("\n\n Push:-  " + (++(Queue.value)));
        Queue.valueSet = true;
        Queue.obj.notify();
    }

}

void pop() {

    synchronized(Queue.obj) {

        while(!(Queue.valueSet)) {

            try {
            Queue.obj.wait();
                Thread.sleep(1000);
            }catch(Exception e) {

                e.printStackTrace();
            }
        }

        System.out.print("\n\n Pop:-   " + Queue.value);

        Queue.valueSet = false;
        Queue.obj.notify();
    }

}

}

class Producer implements Runnable {

Queue Q;
Thread P;


Producer(Queue Q) {

    this.Q = Q;
    P = new Thread(this);
    P.start();

}

public void run() {

    while(true) {

        Q.push();

    }
}

}

class Consumer implements Runnable {

Queue Q;
Thread C;

Consumer(Queue Q) {

    this.Q = Q;
    C = new Thread(this);
    C.start();


}

public void run() {

    while(true) {

        Q.pop();

    }
}

}

public class TestQueue {

public static void main(String[] args) {

    Queue Q1 = new Queue();
    Queue Q2 = new Queue();

    Producer p = new Producer(Q1);
    Consumer c = new Consumer(Q2);
}

}