[boost] [asio] how detect deadline_timer expired state?

I'm performing an async_wait() on a deadline_timer. Based upon some independent event (e.g., a keystroke) I want to [re]set the timer and, if it was expired, 'fire' an event indicating that the system has changed state from not_running to running. Maybe I'm missing something obvious, but it seems that deadline_timer should have a method to test whether or not the timer had expired (i.e., bool expired() ). BTW: This library is a joy. When does the review period start? ;) Regards, Dick Bridges