On a philosophical note, threads may be easier to model complex
hardware that includes a processor, for example our scsi card (and how
about using tcg as a jit to boost it :)
Yeah, it's hard to argue that script evaluation shouldn't be done in a
thread. But that doesn't prevent me from being very cautious about how
and where we use threading :-)
I agree that making script execution asynchronous is a good thing, however I'm
not convinced that (3) is the best way to do this. It's certainly the most
flexible model, however it also places responsibility for locking/correctness
on the device developer.
A more limited scheme (e.g. asynchronous callbacks) can actually be
significant advantage. By forcing the developer to solve the problem in a
particular way we significantly reduce the scope for race conditions, and
hopefully restrict all locking concerns to common code/APIs.