[LAD] Simple sound server design

Hello everyone, I am trying to understand how a simple sound server could be implemented. I will not necessarily develop this, but I'm trying to clarify my ideas. As in JACK, it would allow clients to register, and their process callback to be called with input and output buffers of a fixed size. The server would then mix all output data provided by clients and pass the result to the audio hardware. It would also read audio input from the hardware and dispatch it to the clients. There wouldn't be any ports, routing, etc.. as provided by JACK. The main purpose of a such server would be to allow several applications to record and play audio, without them acquiring exclusive access the audio hardware. In this regard it's similar to PulseAudio and many others. The server itself could have a realtime thread for accessing audio. Therefore, for a proof of concept, it could be developed on top of JACK. However, none of the client could run in realtime: this is a given of my problem. The clients would be standard applications, with very limited privileges. They wouldn't be able to increase their own thread priorities at all. Each client would run as an separated process. The only solution that came to my mind so far is to have the clients communicate with the server through shared memory. For each client, a shared memory region would be allocated, consisting of one lock-free ringbuffer for input, another for output, as well as a shared semaphore for server-to-client signaling. At each cycle, the server would read and write audio data from/to the ringbuffers of each registered clients, and then call sem_post() on all shared semaphores. A client side library would handle all client registering details, as well as thread creation. It would then sem_wait(), and when awaken, read from the input ringbuffer, call the client process callback with I/O buffers, and write to the output ringbuffer. Does this design sound good to you? Do you think it could achieve reliable I/O, and reasonable latency? Keeping latency as low as possible, what do you advise for the size of the ringbuffers? -- Olivier