FutureTask.cancel() - can anyone explain the mechanism?

The Dude <matthewtyler04@googlemail.com>
Thu, 17 Sep 2009 07:09:02 -0700 (PDT)

I have a class which implements Callable<Integer> which is submitted
to an ExecutorService

two methods of interest are as follows

// Called from producer thread.
public void addMessage(final String message) {

   try {
   catch (InterruptedException ie) {
      // Log exception

// Implement Callable<Integer>
// Consume messages from blocking queue
public Integer call() {

   try {
      while (true) {
         final String message = blockingQueue.take();
   catch (Throwable t) {
      // log Throwable
   finally {
      // Log that Thread has been cancelled/stopped

   return 0;

When I submit the Callable to ExecutorService I receive a Future of
concrete class FutureTask.

If I invoke futureTask.cancel() I can see that I jump straight to the
finally clause of my call() method. No exceptions appear to be thrown.

Could someone explain to me

1. Why this happens.
2. If this is a safe mechanism for stopping my consumer thread.
3. If this is safe can I submit a Runnable instead of a callable and
safely cancel the Thread this way?

Many thanks for any help.

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