[suraj]

It is possible to use Swift on audio thread. You have to be careful not to use any reference counted (i.e. class) objects. If you do need to perform allocations (e.g. creating CMSampleBuffer instances), use a custom allocator.

[lfnoise]

I had someone on the Swift compiler team tell me unequivocally that they make no real time guarantees. Unless you can point to somewhere in the language documentation that the runtime is guaranteed not to ever do X, then I would not assume that you could. (me: former Apple CoreAudio engineer)