SimonM:
Yes, my guess is that this will probably have to be done by manipulating the thread-local state in the RTS - grab the current thread-local state whenever a call is made into Haskell, and whenever we run a Haskell thread we have to set the appropriate thread-local state. Perhaps it should be stored in the TSO and inherited by child threads too.
The trouble is that there isn't a single object representing the whole thread-local state. Does OpenGL use pthread_getspecific() and pthread_setspecific() to access its thread-local state?
This sounds like a lot of work and a porting nightmare (what do you mean Linux/Win32/HPUX/... doesn't have thread manipulation function X, it's available on FreeBSD/Win32/... What if there are other forms of thread-local state (e.g., errno)? What about setjmp/longjmp?). The only viable solution I can see is to provide a way to capture the calling thread (as a first class entity) when you call into Haskell and to explicitly specify whcih thread to use when you call out from Haskell. (Hmmm, sounds like callcc for C :-)) Off the top of my head, this might look like this: foreign export "static capture_thread" mycallback :: HsThread -> Int -> Char which would provide a C function with this prototype: HsChar mycallback(HsInt); and, on the callout side: foreign import "static with_thread" foo :: HsThread -> Float -> IO Double which would invoke a C function with this type: HsDouble foo(HsFloat); -- Alastair Reid reid@cs.utah.edu http://www.cs.utah.edu/~reid/