Java Executors: how can I stop submitted tasks?

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Just because you call cancel() on Future doesn’t mean that the task will stop automatically. You have to do some work within the task to make sure that it will stop:

  • Use cancel(true) so that an interrupt is sent to the task.
  • Handle InterruptedException. If a function in your task throws an InterruptedException, make sure you exit gracefully as soon as possible upon catching the exception.
  • Periodically check Thread.currentThread().isInterrupted() if the task does continuous computation.

For example:

class LongTask implements Callable<Double> {
    public Double call() {
        
         // Sleep for a while; handle InterruptedException appropriately
         try {
             Thread.sleep(10000);
         } catch (InterruptedException ex) {
             System.out.println("Exiting gracefully!");
             return null;
         }


         // Compute for a while; check Thread.isInterrupted() periodically
         double sum = 0.0;
         for (long i = 0; i < 10000000; i++) {
             sum += 10.0
             if (Thread.currentThread().isInterrupted()) {
                 System.out.println("Exiting gracefully");
                 return null;
             }
         }

         return sum;
    } 
}

Also, as other posts have mentioned: ConcurrentModificationException can be thrown even if using the thread-safe Vector class, because iterators you obtain from Vector are not thread-safe, and thus need to be synchronized. The enhanced for-loop uses iterators, so watch out:

final Vector<Double> vector = new Vector<Double>();
vector.add(1.0);
vector.add(2.0);

// Not thread safe!  If another thread modifies "vector" during the loop, then
// a ConcurrentModificationException will be thrown.
for (Double num : vector) {
    System.out.println(num);
}

// You can try this as a quick fix, but it might not be what you want:
synchronized (vector) {    // "vector" must be final
    for (Double num : vector) {
        System.out.println(num);
    }
}

More Related Contents:

  1. How to wait for all threads to finish, using ExecutorService?
  2. ExecutorService, how to wait for all tasks to finish
  3. ExecutorService that interrupts tasks after a timeout
  4. Handling exceptions from Java ExecutorService tasks
  5. How to properly shutdown java ExecutorService
  6. Executors.newCachedThreadPool() versus Executors.newFixedThreadPool()
  7. Choose between ExecutorService’s submit and ExecutorService’s execute
  8. How to properly use Java Executor?
  9. What are the advantages of using an ExecutorService?
  10. Java’s Fork/Join vs ExecutorService – when to use which?
  11. Turning an ExecutorService to daemon in Java
  12. Is ExecutorService (specifically ThreadPoolExecutor) thread safe?
  13. Impossible to make a cached thread pool with a size limit?
  14. ThreadPoolExecutor Block When Queue Is Full?
  15. Java ExecutorService: awaitTermination of all recursively created tasks
  16. How to use invokeAll() to let all thread pool do their task?
  17. How to shutdown an ExecutorService?
  18. FixedThreadPool vs CachedThreadPool: the lesser of two evils
  19. ThreadPoolExecutor Block When its Queue Is Full?
  20. How to stop all runnable thread in java executor class?
  21. ExecutorService vs Casual Thread Spawner
  22. How to pause/resume all threads in an ExecutorService in Java?
  23. Removing all queued tasks of an ThreadPoolExecutor
  24. Shutdown ExecutorService gracefully in webapp?
  25. Dynamic Thread Pool
  26. ExecutorCompletionService? Why do need one if we have invokeAll?
  27. I have wondered why ‘new Thread(new Thread(),”string”);’ is running correctly
  28. java.lang.IllegalStateException: Not on FX application thread; currentThread = Thread-4
  29. Propagating ThreadLocal to a new Thread fetched from a ExecutorService
  30. Updating your UI and forcibly waiting before continuing JavaFX

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