I would not expect Plack to have such a thing.   The signal (whatever it is...) comes in once, and you are just carrying-out one or more actions in response to it.   (Hardware interrupt service routines in operating-systems routinely adopt a similar strategy, made necessary in part by the “sharing” of a limited number of IRQs, and in part by there simply being a variable number of “interested listeners.”)

Packages like POE do have some logic along these lines ... whether to be literally-used or to be studied as a possible example.   These are the basis for “reactive,” “event-driven” systems which would treat “shutdown request” as just another type of event that can happen.   Food for thought, maybe.