The GHC documentation on QSem is very sparse. I would like to give a thread exclusive access to a resource. My *guess* based on the documentation is that I can create an exclusive lock using: logSem <- newQSem 1 And then any thread that wants to lock the resource uses: withLogSem x = do waitQSem logSem; y <- x; signalQSem logSem; return y as follows: withLogSem $ rotate curLogPos Am I misunderstanding QSem? -Alex- _________________________________________________________________ S. Alexander Jacobson mailto:me@alexjacobson.com tel:917-770-6565 http://alexjacobson.com