`And how many hours a day did you do lessons?' said Alice, in a
hurry to change the subject.

  `Ten hours the first day,' said the Mock Turtle: `nine the
next, and so on.'

  `What a curious plan!' exclaimed Alice.

  `That's the reason they're called lessons,' the Gryphon
remarked:  `because they lessen from day to day.'

  `And how many hours a day did you do lessons?' said Alice, in a
hurry to change the subject.

  `Ten hours the first day,' said the Mock Turtle: `nine the
next, and so on.'

  `What a curious plan!' exclaimed Alice.

  `That's the reason they're called lessons,' the Gryphon
remarked:  `because they lessen from day to day.'

         * problems can exist with methods like FutureTask.done(), not to mention slow calls to
         * Thread.interrupt() (as discussed in InterruptibleTask). At the end of the day, it's
         * unlikely that cancel() will be slow, so we can probably get away with calling it while
         * holding a lock. Still, it would be nice to avoid somehow.
         */
        lock.lock();
        try {