public boolean kill() {
        return owner.kill(this);
    }
Cancel the execution of this task and make sure it can never be
scheduled for execution again. After this method is invoked,
invoking the {@link #schedule schedule} and {@link #scheduleNow
scheduleNow} methods will have no effect.

@return true if the task was scheduled and we managed to avoid
        execution
jrt/src/com/yahoo/jrt/Task.java