6. CountDown Latches

Java Multithreading: Countdown Latches

A tutorial on using the excellent CountDownLatch Java class to synchronize your threads’ activities.

Code For This Tutorial

import java.util.concurrent.CountDownLatch;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

class Processor implements Runnable {

      private CountDownLatch latch;

      public Processor(CountDownLatch latch) {

            this.latch = latch;

      }

      public void run() {

            System.out.println("Started.");

            try {

                  Thread.sleep(3000);

            } catch (InterruptedException e) {

                  // TODO Auto-generated catch block

                  e.printStackTrace();

            }

            latch.countDown();

      }

}

public class App {

      public static void main(String[] args) {

            CountDownLatch latch = new CountDownLatch(3);

            ExecutorService executor = Executors.newFixedThreadPool(3);

            for (int i = 0; i < 3; i++) {

                  executor.submit(new Processor(latch));

            }

            try {

                  latch.await();

            } catch (InterruptedException e) {

                  // TODO Auto-generated catch block

                  e.printStackTrace();

            }

            System.out.println("Completed.");

      }

}

Output:

Started.

Started.

Started.

Completed.