CyclicBarrier in Java

CyclicBarrier in Java

1. Description
   A synchronization aid that allows a set of threads to all wait for each other to reach a common barrier point. CyclicBarriers are useful in programs involving a fixed sized party of threads that must occasionally wait for each other. The barrier is called cyclic because it can be re-used after the waiting threads are released.


The threads wait for each other by calling the await() method on the CyclicBarrier. Once N threads are waiting at the CyclicBarrier, all threads are released and can continue running

2. API

int	await() Waits until all parties have invoked await on this barrier.
int	await(long timeout, TimeUnit unit) Waits until all parties have invoked await on this barrier.
int	getNumberWaiting() Returns the number of parties currently waiting at the barrier.
int	getParties() Returns the number of parties required to trip this barrier.
boolean	isBroken() Queries if this barrier is in a broken state.
void	reset() Resets the barrier to its initial state.

3. Sample

public   class  CyclicBarrierRunnable  implements  Runnable {

    CyclicBarrier barrier1 = null;
    CyclicBarrier barrier2 = null;

    public CyclicBarrierRunnable(
            CyclicBarrier barrier1,
            CyclicBarrier barrier2) {

        this.barrier1 = barrier1;
        this.barrier2 = barrier2;
    }

    public void run() {
        try {
            Thread.sleep(1000);
            System.out.println(Thread.currentThread().getName() +
                                " waiting at barrier 1");
            this.barrier1.await();

            Thread.sleep(1000);
            System.out.println(Thread.currentThread().getName() +
                                " waiting at barrier 2");
            this.barrier2.await();

            System.out.println(Thread.currentThread().getName() +
                                " done!");

        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (BrokenBarrierException e) {
            e.printStackTrace();
        }
    }
}


public   class  CyclicBarrierMain  {
    
    public static void main(String[] args){
        Runnable barrier1Action = new Runnable() {
            public void run() {
                System.out.println("BarrierAction 1 executed ");
            }
        };
        Runnable barrier2Action = new Runnable() {
            public void run() {
                System.out.println("BarrierAction 2 executed ");
            }
        };

        CyclicBarrier barrier1 = new CyclicBarrier(2, barrier1Action);
        CyclicBarrier barrier2 = new CyclicBarrier(2, barrier2Action);

        CyclicBarrierRunnable barrierRunnable1 =
                new CyclicBarrierRunnable(barrier1, barrier2);

        CyclicBarrierRunnable barrierRunnable2 =
                new CyclicBarrierRunnable(barrier1, barrier2);

        new Thread(barrierRunnable1).start();
        new Thread(barrierRunnable2).start();

    }
    Runnable barrier1Action = new Runnable() {
        public void run() {
            System.out.println("BarrierAction 1 executed ");
        }
    };
    Runnable barrier2Action = new Runnable() {
        public void run() {
            System.out.println("BarrierAction 2 executed ");
        }
    };
}