Java concurrency - avoid busy wait using CountDownLatch (inter-thread communication)

In this article we would like to show to to avoid busy wait in java using CountDownLatch.

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;

public class CountDownLatchExample {

    private final CountDownLatch countDownLatch = new CountDownLatch(2);

    private void executeTasks() throws InterruptedException {

        // Task 1
        Thread thread1 = new Thread(() -> {
            try {
                simulateTask(300);
            } finally {
                countDownLatch.countDown();
                System.out.println(getThreadName() + " - Task 1 done");
            }
        });

        // Task 2
        Thread thread2 = new Thread(() -> {
            try {
                simulateTask(100);
            } finally {
                countDownLatch.countDown();
                System.out.println(getThreadName() + " - Task 2 done");
            }
        });

        thread1.start();
        thread2.start();

        System.out.println(getThreadName() + " - waiting to be notified 2 times");

        // Causes the current thread to wait until the latch has counted down
        // to zero, unless the thread is interrupted.
        // If the current count is zero then this method returns immediately.
        countDownLatch.await();
        System.out.println(getThreadName() + " - notified");
    }

    private String getThreadName() {
        return Thread.currentThread().getName();
    }

    private void simulateTask(int timeout) {
        sleep(timeout);
    }

    private void sleep(int timeout) {
        try {
            TimeUnit.MILLISECONDS.sleep(timeout);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new CountDownLatchExample().executeTasks();
    }
}

Output:

main - waiting to be notified 2 times
Thread-1 - Task 2 done
Thread-0 - Task 1 done
main - notified

See also

1. What is busy waiting lock?