How to wait for all threads to finish, using ExecutorService?

Question

I need to execute some amount of tasks 4 at a time, something like this:

ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
while(...) {
    tas         


        

Answer 1

You could use this code:

public class MyTask implements Runnable {

    private CountDownLatch countDownLatch;

    public MyTask(CountDownLatch countDownLatch {
         this.countDownLatch = countDownLatch;
    }

    @Override
    public void run() {
         try {
             //Do somethings
             //
             this.countDownLatch.countDown();//important
         } catch (InterruptedException ex) {
              Thread.currentThread().interrupt();
         }
     }
}

CountDownLatch countDownLatch = new CountDownLatch(NUMBER_OF_TASKS);
ExecutorService taskExecutor = Executors.newFixedThreadPool(4);
for (int i = 0; i < NUMBER_OF_TASKS; i++){
     taskExecutor.execute(new MyTask(countDownLatch));
}
countDownLatch.await();
System.out.println("Finish tasks");