ExecutorService, how to know when all threads finished without blocking the main thread?

Question

I have a multithreaded implementation where i create an ExecutorService and submit tasks to be executed, i want to know when all the threads is submited have finished without blocking the main thread and the UI. I've tried ExecutorService.awaitTermination() but it blocks the main thread and the UI. I've searched alot but i can't seem to find an elegant way of doing this. I'm currently thinking about creating another thread that counts the amount of threads finished and launches an event when they all finished, but that doesn't to be a good approach and i wanted a better solution!

What is your main thread doing that it can't be blocked? – user207421 Mar 20 '12 at 00:42 — user207421, Mar 20 '12 at 00:42

Dev · Answer 1 · 2015-03-07T19:37:45.103

7

Use a SwingWorker to shutdown the thread pool and call awaitTermination(). This will prevent the UI from blocking and call done() from the Event Dispatch Thread on your SwingWorker implementation which you can use to trigger the whatever UI changes you need.

If you desire to keep track of the threads running via a UI update you can use the the worker thread to monitor this in a loop and call publish() with arguments which then get passed to your implementation of process() on the EDT.

edited Mar 07 '15 at 19:37

answered Mar 20 '12 at 00:35

Dev

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He never mentions that this is a Swing application, and if not, then a SwingWorker would not be appropriate. – Hovercraft Full Of Eels Mar 20 '12 at 00:37
1

I forgot to mention that it is a Swing application! – Trota Mar 20 '12 at 00:44
After reading more on SwingWorker i realized that this is a fairly simple solution to my problem! Thank you Dev! – Trota Mar 20 '12 at 00:50
Well slap my knee and shut my mouth! I stand corrected. 1+. And @user1220585: that's kind of important information you know and should be in the original post. – Hovercraft Full Of Eels Mar 20 '12 at 01:23

score 4 · Answer 2 · answered Mar 20 '12 at 00:36

4

Why not use a CountDownLatch and then notify the main thread when the latch has been completed.

answered Mar 20 '12 at 00:36

Hovercraft Full Of Eels

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Good idea; there's a nice example cited [here](http://stackoverflow.com/a/3588523/230513). – trashgod Mar 20 '12 at 05:09
1

@trashgod just commented in your post: the example has a small glitch in accessing the textComponent off the EDT – kleopatra Mar 20 '12 at 11:20

score 2 · Answer 3 · answered Apr 06 '12 at 04:23

You can maintain a separate thread to track when the executor service instance shuts down:

    final ExecutorService execSvc = ...;
    execSvc.submit(task1);
    ...
    execSvc.submit(taskN);
    // important to request the exec service to shut down :)
    execSvc.shutdown();

    new Thread(new Runnable() {

        public void run() {
            while (!execSvc.isTerminated()) {
                try {
                    execSvc.awaitTermination(60, TimeUnit.SECONDS);
                } catch (InterruptedException e) {
                    // ignore exception
                }
            }
            System.out.println("ExecSvc.run: exec service has terminated!");
            // possibly submit a task using SwingUtilities.invokeLater() to update the UI
        }

    }).start();

score 2 · Answer 4 · edited May 23 '17 at 10:32

Using 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();

Or on 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) {
  ...
}

Also have a look at THIS answer

Unless I'm mistaken in my understanding, neither of these solutions are addressing the OP's fundamental question which is to avoid blocking on the main thread. — Trevor, Jun 22 '14 at 12:41

score 2 · Answer 5 · answered Mar 20 '12 at 00:12

2

isTerminated() will do

note however that both awaitTermination and isTerminated will only give you a meaningful result after you have called shutdown

answered Mar 20 '12 at 00:12

ratchet freak

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I've found some things about isTerminated() but still, i think i need to run it on a "side thread" to constantly check if it returns true which brings me to my initial solution! – Trota Mar 20 '12 at 00:15

ExecutorService, how to know when all threads finished without blocking the main thread?

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