We can't currently allow several Haskell threads to really run simultaneosly [e.g. on two separate processors, or preemtively scheduled on a single processor], because they always mutate the same global heap. Currently, GHC switches its green threads only at times when the heap is in a defined state [not truly preemptively]. There seems to be some SMP support in the RTS, I don't know if it ever worked. If anyone wants to fix/finish it, that would be great, but it's not what I'm proposing here.

The SMP support is an experiment that was never finished. There are serious issues to be solved regarding reducing the locking overhead on a shared-memory heap.

My proposal is only a minimum solution intended to resolve the inherent incompatibility between the "threaded RTS" and libraries like OpenGL, which require thread-local-state.

I think I'm happy with that, although I don't have the whole context swapped in. That seems to be the conclusion we came to at the last discussion, though: http://www.haskell.org/pipermail/glasgow-haskell-users/2002-June/003592. html Cheers, Simon