Example of using CyclicBarrier in Java

CyclicBarrierExample.java

package concurrency;

import java.util.concurrent.*;

public class CyclicBarrierExample {

    public static void main(String[] args) {
        //Define a barrier initialized with 3.
        CyclicBarrier barrier = new CyclicBarrier(3);

        //Create a new thread pool with 3 threads.
        ExecutorService executorService = Executors.newFixedThreadPool(3);

        for (int i = 0; i < 3; i++) {
            //Execute the runnable code using thread.
            executorService.submit(new CyclicBarrierTask(barrier, "Thread_" + i));

            //Introduce some delay between each thread call.
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        executorService.shutdown();
        System.out.println("All threads are done");

    }
}

class CyclicBarrierTask extends Thread {
    CyclicBarrier barrier;
    String threadName;

    public CyclicBarrierTask(CyclicBarrier barrier, String threadName) {
        this.barrier = barrier;
        this.threadName = threadName;
    }

    public void run() {
        System.out.println(threadName + " executing long running process");
        System.out.println("No. of threads already waiting at barrier: " + barrier.getNumberWaiting());
        while (true) {
            try {
                //Each thread gets blocked here till all the threads reach this point
                barrier.await();
                System.out.println(threadName + " doing post barrier work");
            } catch (InterruptedException | BrokenBarrierException e) {
                e.printStackTrace();
            }
        }
    }
}


/*
Output:
Thread_0 executing long running process
No. of threads waiting at barrier: 0
Thread_1 executing long running process
No. of threads waiting at barrier: 1
Thread_2 executing long running process
No. of threads waiting at barrier: 2
Waiting for threads to finish
All threads are done
Thread_0 doing post barrier work
Thread_1 doing post barrier work
Thread_2 doing post barrier work
*/