I reviewed the patch today. It looks OK; however, since timer expiration is mostly a special case of cancel, expiration, cancellation and any other form of premature task termination can be handled through a single cancel(outcome, state) method. I have attached a new patch to JBPM-2537. Let me know what you all think.
On a different topic, I am not quite happy with the addition of the TimedActivityBehaviour interface and Execution.signal(String, boolean) method just to deliver a timer expiration signal. It should be possible to do it through the existing ExternalActivityBehavior and Execution.signal(String, Map) by passing a special parameter that indicates the cancellation state ("cancelled", "expired" or any other). I'm going to explore this path next week.