title: Wait for cancel() on FutureTask
body: <p>I want to cancel a FutureTask that I get from a ThreadPoolExecutor but I want to be sure that Callable on the thread pool has stopped its work.</p>
  <p>If I call FutureTask#cancel(false) and then get() (to block until completion) I get a CancelledException. Is this exception thrown immediately or after the task has stopped executing?</p>