Handler backpressure

[neverfox]

Is there a way to apply backpressure on incoming messages to a handler? I am using some core.async logic in some of my components and, in order to keep buffers from getting overwhelmed or having to guess at appropriate buffer sizes, it would be nice to limit the rate of incoming messages to a handler (which you could match to your internal buffers for tuning). If there's not already some facility to do this, perhaps it means implementing ack/nack + prefetch count model.