[HOpenGL] HOpenGL and --enable-threaded-rts

[Simon Marlow]

> 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?).=20

Yes, these are all problems.  However, there is a nice abstraction of
the OS thread API in GHC's RTS, thanks to Sigbjorn.  So I'm sure this
API could be extended to include some thread-local state operations.

> 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 :-))

The trouble is, that is *way* too much overhead for a C call.  HOpenGL
does lots of these, and I strongly suspect that adding a full OS-thread
context switch (well two, including the return) for each one would be a
killer.

Cheers,
	Simon