Java Thread: How to execute a statement simultaneously

Question

Consider I have a run method as below, I am trying to create four threads for MyThread. Statement 1 to 3 can either run at same time by threads or differently. But I want Statement 4 to be executed by threads at a same time. Can I pool all threads before statement 4 and execute statement 4 at a same time by all threads?

class MyThread extends Thread
{ 
    public void run()
    {
        //Statement 1
    //Statement 2
    //Statement 3
    //Statement 4
    }

}

Answer 1

Use CyclicBarrier, it is best suited for your requirement.

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;

public class CyclicBarrierUsage {

    private static final int NUMBER_OF_THREADS = 2;

    public static void main(String[] args) {
        CyclicBarrier barrier = new CyclicBarrier(NUMBER_OF_THREADS);

        Thread t1 = new Thread(new PrimaryParty(barrier));
        Thread t2 = new Thread(new PrimaryParty(barrier));

        t1.start();
        t2.start();    
    }
}

class PrimaryParty implements Runnable {

    private CyclicBarrier barrier;

    public PrimaryParty(CyclicBarrier barrier) {
        this.barrier = barrier;
    }

    @Override
    public void run() {
        //Statement 1
        //Statement 2
        //Statement 3

        try {
            barrier.await();
        } catch (InterruptedException | BrokenBarrierException e) {
            e.printStackTrace();
        }

        //Statement 4
    }
}

Answer 2

There are a few ways to do what you want. Perhaps the easiest way is by using Java's implementation of Future . You can define one (or more) Futures which will execute on separate threads, block until they are all done with Future.get() , and then complete your other tasks based on the results.