It would be good if there were a way of telling GHC's RTS scheduler "Please don't run any other threads apart from this one until further notice".
It seems like you're only worried about the threads which interact with your servers. A thread which continues printing prime numbers or whatever to the screen probably wouldn't cause problems. It also sounds like you want to be able to tell the RTS 'and if one of the other threads is already talking to the servers, let it finish first'. In other words, it sounds like the right thing is to protect access to the servers with some kind of lock (MVar, Semaphore, etc.). Is there a reason why this won't work? [I'm currently working on a system which lets you define your own scheduler hierarchy. Each scheduler has different consequences for preemption and, hence, the kind of locks that its children may or may not need to protect themselves from their siblings. Reasoning about which locks to use where is... challenging. I'd be interested if your program cannot be solved with a carefully placed lock but can be solved with a novel scheduler hierarchy. Not that it'd do _you_ any good though - the scheduler hierarchy is for embedded systems which tend not to be written in Haskell...] -- Alastair Reid alastair@reid-consulting-uk.ltd.uk Reid Consulting (UK) Limited http://www.reid-consulting-uk.ltd.uk/alastair/