[LAD] file and communications for RT audio

I have an idea in mind for an application that would involve a core audio callback responsible for playing several sounds at the same time, each being streamed in by some as-yet-undetermined means. Before I get too far into it, I have a few questions about the best method for ensuring that the audio callback is not interrupted for lengthy disk access, etc. Obviously I am not planning on doing the main disk I/O in the callback, but I am thinking about the best means for the callback to communicate with the rest of the application. Possibly I might like to support having some of these streams come from external processes, opened through popen() for example. So, the idea for an RT audio callback is that it should not wait on data, (whether it comes from a file or process), but continue processing the other streams if audio data is not immediately available. There are a few ways to do this in Linux: 1) Have a secondary thread responsible for passing data to the audio callback through a wait-free ring buffer. 2) Read from a pipe, FIFO, or socket from another process (e.g. popen), using select() or poll() to check when there is actually data to read. 3) Read from a file, using select()? 4) The async I/O API. 5) Interprocess shared memory, presumably using a semaphore of some kind. I guess this is similar to (1) but for inter-process communication. The question is, which one of these methods is the most "real-time friendly"? Under what conditions, if any, can I be sure a read() will not block? Is there any advantage to threads vs. processes? Using async I/O I suppose I could avoid either one. Are there any general guidelines somewhere for dealing with I/O in audio applications? thanks in advance, Steve