Folks, I need to move away from STM (unfortunately) until I profile my program to my satisfaction. Profiling is somewhat crippled with STM in 6.4.1. I cannot do void and drag profiling, for examplel. I decided to abstract my mailboxes in a Queue module so that I could switch between STM and non-STM as needed. Please let me know what you think of this bounded queue implementation. --- module Queue where import Control.Monad import Control.Concurrent data Queue a = Queue !QSem !(Chan a) newQ :: Int -> IO (Queue a) newQ size = do sem <- newQSem size q <- newChan return $! Queue sem q writeQ :: Queue a -> a -> IO () writeQ (Queue sem q) x = do waitQSem sem writeChan q x readQ :: Queue a -> IO a readQ (Queue sem q) = do x <- readChan q signalQSem sem return x Thank, Joel -- http://wagerlabs.com/