CyclicBarrier Example in Java

Here is a simple example of how and when to use CyclicBarrier in 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
	*/

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