I'm not sure I buy this. Again, this helps: {-# NOINLINE lock #-} lock :: MVar () lock = unsafePerformIO $ newMVar () trace s = withMVar lock $ const $ putStrLn s and then in read_ cmd <- read h trace trace is called _after_ all the timings in read so it should not affect the timings. You could basically say that the lock is at the end of read, after all the unpickling has been done. The other interesting thing is that replacing trace with delay _ = threadDelay 1 does not solve the issue. On Dec 21, 2005, at 2:33 PM, Branimir Maksimovic wrote:
In this code: do TOD time1 _ <- getClockTime (kind, ix1) <- unpickle puCmdType ptr ix TOD time2 _ <- getClockTime (cmd', _) <- unpickle (puCommand kind) ptr ix1 TOD time3 _ <- getClockTime you get time multiple times. So if you lock whole operation nothing else will be executed while in this code and therefore you don;t have timeouts. But, without lock more threads you have, more time have to wait for operation to finish and therefore timeouts.