> (It would be nice to have some concurrency in nhc98, of course, but > I don't foresee that happening soon.)
I remember implementing cooperative concurrency in Hugs as being rather easy. Of course, that was building on a base which already used a continuation passing IO monad... If you want to try, I could dig out some details but the main issues are: 1) When you have a choice of which thread to wake next, it matters which you wake next. IIRC, waking the wrong one makes it impossible to implement a producer-consumer pattern. 2) There's a lot of interaction with non-deterministic exception handling. 3) unsafePerformIO foo had better not block since we have no way to block the non-monadic code that invoked it. In that case, we raise an exception or give up (don't remember which). > Actually, I'm just wondering whether I can use the GC as a > poor-man's scheduler. If a finaliser blocks on an MVar, save its > state, keep the finaliser in the pending queue, and return to the > main thread. Then on the next GC, try the same finaliser again, ad > infinitum until it succeeds. The finalizer won't become runnable until someone does a putMVar so you can deal with this case by storing the finalizer's state in a queue of blocked threads attached to the MVar and having putMVar do a context switch to the thread at the head of the MVar's queue of blocked threads. If you want finalizers to have priority over other threads, have two queues: one for finalizers, one for normal threads. -- Alastair _______________________________________________ FFI mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/ffi
