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(...) {     taskExecutor.execute(new MyTask()); } //...wait for completion somehow 

How can I get notified once all of them are complete? For now I can't think about anything better than setting some global task counter and decrease it at the end of every task, then monitor in infinite loop this counter to become 0; or get a list of Futures and in infinite loop monitor isDone for all of them. What are better solutions not involving infinite loops?

Thanks.

Answer 1

Basically on an ExecutorService you call shutdown() and then awaitTermination():

ExecutorService taskExecutor = Executors.newFixedThreadPool(4); while(...) {   taskExecutor.execute(new MyTask()); } taskExecutor.shutdown(); try {   taskExecutor.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS); } catch (InterruptedException e) {   ... } 

Answer 2

Use a CountDownLatch:

CountDownLatch latch = new CountDownLatch(totalNumberOfTasks); ExecutorService taskExecutor = Executors.newFixedThreadPool(4); while(...) {   taskExecutor.execute(new MyTask()); }  try {   latch.await(); } catch (InterruptedException E) {    // handle } 

and within your task (enclose in try / finally)

latch.countDown();