Java CountDownLatch Example Program.

import java.util.concurrent.CountDownLatch;

public class ThreadOnOffGate

{

    public static void main(String str[]) throws InterruptedException{

        int N = 10000 ;

        CountDownLatch startSignal = new CountDownLatch(1);

        CountDownLatch doneSignal = new CountDownLatch(N);

        

        for (int i = 0; i < N; ++i) // create and start threads

            new Thread(new Worker(startSignal, doneSignal)).start();

        

        System.out.println ("Main Thread will wait here") ;

        startSignal.countDown();      // let all threads proceed

        System.out.println(" Main thread waiting"); 

        doneSignal.await();           // wait for all to finish

        System.out.println(" Main thread work done.") ;

        

    }

}

class Worker implements Runnable {

    

    private CountDownLatch startCountDownLatch;

    private CountDownLatch doneCountDownLatch;

    Worker(CountDownLatch start, CountDownLatch done){

        this.startCountDownLatch = start ;

        this.doneCountDownLatch = done ;

    }

    /* (non-Javadoc)

     * @see java.lang.Runnable#run()

     */

    @Override

    public void run()

    {

        try {

            startCountDownLatch.await() ;

            doWork() ;

            doneCountDownLatch.countDown() ;

            

        }catch(InterruptedException e){

            

        }

    }

    /**

     * 

     */

    private void doWork()

    {

         System.out.println("Current Thread : " + Thread.currentThread().getName() + " working") ;      

    }

}