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

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();

    }

}

main - waiting to be notified 2 times

Thread-1 - Task 2 done

Thread-0 - Task 1 done

main - notified