CyclicBarrier

A CyclicBarrier is a synchronization aid that allows a set of threads to wait for each other to reach a common barrier point. Unlike CountDownLatch, it can be reset and reused recursively.

CyclicBarrier vs. CountDownLatch

Let's compare these two coordination utilities:

• Reusability: CyclicBarrier can be reset and reused (hence "cyclic"). CountDownLatch is a one-shot utility.
• Waiting Threads: In CyclicBarrier, the worker threads call await() to block themselves. In CountDownLatch, the workers call countDown() (non-blocking) and a coordinator thread calls await().
• Barrier Action: CyclicBarrier allows running an optional callback task when the barrier opens.

Code Walkthrough

This program demonstrates worker threads syncing at a barrier checkpoint before completing their tasks.

import java.util.concurrent.CyclicBarrier;
public class CalculationPipeline {
    public static void main(String[] args) {
        Runnable barrierAction = () -> System.out.println("All workers arrived! Merging data...");
        CyclicBarrier barrier = new CyclicBarrier(3, barrierAction);
Runnable worker = () -> {
            try {
                System.out.println(Thread.currentThread().getName() + " working on Phase 1...");
                Thread.sleep(1000);
System.out.println(Thread.currentThread().getName() + " waiting at checkpoint...");
                barrier.await(); // Block until all 3 workers arrive
System.out.println(Thread.currentThread().getName() + " working on Phase 2...");
            } catch (Exception e) {
                // Handle BrokenBarrierException or InterruptedException
            }
        };
new Thread(worker, "Worker-1").start();
        new Thread(worker, "Worker-2").start();
        new Thread(worker, "Worker-3").start();
    }
}

Interview-Relevant Information