Does a Future timeout kill the Thread execution

Question

When using an ExecutorService and Future objects (when submitting Runnable tasks), if I specify a timeout value to the future's get function, does the underlying thread get killed when a TimeoutException is thrown?

Answer 1

It does not. Why would it? Unless you tell it to.

There is a very valid concern here in case of a Callable for example. If you waited for the result for say 20 seconds and you did not get it, then you are not interested in the result anymore. At that time you should cancel the task at all.

Something like this:

Future<?> future = service.submit(new MyCallable());
    try {
        future.get(100, TimeUnit.MILLISECONDS);
    } catch (Exception e){
        e.printStackTrace();
        future.cancel(true); //this method will stop the running underlying task
    }

Answer 2

No it doesnt. Morover there is even no attempt to interrupted the task. First of all Future.get with timeout doesn't say so. Secondly, try my test to see how it behaves

    ExecutorService ex = Executors.newSingleThreadExecutor();
    Future<?> f = ex.submit(new Runnable() {
        public void run() {
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("finished");
        }
    });
    f.get(1, TimeUnit.SECONDS);

in 1 sec it prints

Exception in thread "main" java.util.concurrent.TimeoutException
    at java.util.concurrent.FutureTask$Sync.innerGet(FutureTask.java:228)
    at java.util.concurrent.FutureTask.get(FutureTask.java:91)
    at Test1.main(Test1.java:23)

after another 1 sec the task successfullt finishes

finished

Answer 3

It seems that you need to kill, cancel or shutdown the task explicitly

Handling exceptions from Java ExecutorService tasks

How do I get FutureTask to return after TimeoutException?