How to Stop a Runnable Submitted to ExecutorService in Java

executorservicejava

I've implemented subscription in my Java app. When new subscriber added, the application creates new task (class which implements Runnable to be run in the separate thread) and it is added to the ExecutorService like:

public void Subscribe()
{
    es_.execute(new Subscriber(this, queueName, handler));
}

//...

private ExecutorService es_;

Application may register as many subscribers as you want. Now I want implement something like Unsubscribe so every subscriber has an ability to stop the message flow. Here I need a way to stop one of the tasks running in the ExecutorService. But I don't know how I can do this.

The ExecutorService.shutdown() and its variations are not for me: they terminates all the tasks, I want just terminate one of them. I'm searching for a solution. As simple as possible. Thanks.

Best Answer

You can use ExecutorService#submit instead of execute and use the returned Future object to try and cancel the task using Future#cancel

Example (Assuming Subscriber is a Runnable):

Future<?> future = es_.submit(new Subscriber(this, queueName, handler));
...
future.cancel(true); // true to interrupt if running

Important note from the comments:

If your task doesn't honour interrupts and it has already started, it will run to completion.

Related Solutions

Java Multithreading – Force Stopping ExecutorService Threads

Instant thread termination is never guaranteed, unless the thread checks periodically for isInterrupted() flag (or is waiting in interruptable method, i.e. which throws InterruptedException).

Consider implementing your worker threads in manner, when they check periodically for isInterrupted(). This may be something like that:

public void run() { 
  byte[] data;
  do {
     data = receiveDataChunk(timeout);
     processData(data);
  } while(!isInterrupted() && data != null);
}

Java stop Callable submitted to ExecutorService – How to

Future.cancel(true) and ExecutorService.shutdownNow() use thread interruption. As long as you don't make uninterruptable blocking calls in your task, all you need is to handle interrupted condition correctly, something like this:

for(int i = 0; i < 1000; i++){
    // Uses isInterrupted() to keep interrupted status set
    if (Thread.currentThread().isInterrupted()) {
        // Cannot use InterruptedException since it's checked
        throw new RuntimeException(); 
    }
    System.out.println(i);
}

If you make uninterruptable blocking calls (such as network IO), things become more complex, you need to interrupt them manually somehow, for example, by closing the underlying sockets.

Best Answer

Related Solutions

Java Multithreading – Force Stopping ExecutorService Threads

Java stop Callable submitted to ExecutorService – How to

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