03. CountDownLatch.md

CountDownLatch

• CountDownLatch is used to when you want a thread to wait until one or more events have occurred.
• It is initially created with a count of the number of events that must occur before the latch is released.
• Each time an event happens, the count is decremented. and the latch is opened when the count reaches to zero.

import java.util.concurrent.CountDownLatch;

class Task implements Runnable {
    CountDownLatch cdl;

    Task(CountDownLatch cdl){
        this.cdl = cdl;
    }

    /**
     * Runs this operation.
     */
    @Override
    public void run() {
        String name = Thread.currentThread().getName();
        try {
            for(int i=1;i<=3;i++){
                Thread.sleep(10);
                System.out.println("Event >> " + i);
                cdl.countDown(); // decrement count
            }
        } catch (InterruptedException ex) {
            System.out.println("thread interrupted");
        }
    }
}

public class Main {

    public static void main(String[] args) {
        CountDownLatch cdl = new CountDownLatch(3); // latch that requires 3 events to occur before it opens

       new Thread(new Task(cdl)).start();

        try {
           cdl.await();
        } catch (InterruptedException e) {
            System.out.println("Exception occurred");
        }
    }
}