So a part of the dependencies in the signal processing flow is only known to your sequencer, which leads to a situation where jack can not know, if all dependencies for running a certain client process function are satisfied? I personally would try to avoid that so that things will become easier, which means no need for ringbuffers (input and output buffers that depend on each other are passed together to the process function) and spinlocks (jack always calls the clients callback, if data is definitely available) for synchronization.