Hello list I am trying to use STM for shared access to a file I first used a TVar to to accumulate the text returned by the threads and write TVar's content to a file after a delay (how do you ensure all threads have terminated by the way, that would be more robust than using an arbitrary delay) -- this works main = do let fname = "store.txt" store <- atomically $ newTVar "" forkIO $ 10 `replicateM_` (thread store) threadDelay 800000 txt <- atomically (readTVar store) writeFile fname txt thread :: TVar (String) -> IO () thread store = atomically ( readTVar store >>= writeTVar store . (++ " some text ")) But when I try to concurrently write to the file, I get into troubles. I keep the file handle in a TMVar, hoping than just one thread at a time will be able to use that handle but nothing gets written to "store.txt" ? Is my IO too lazy ? -- this does not work main = do let fname = "store.txt" fh <- openFile fname ReadWriteMode store <- atomically $ newTMVar fh forkIO $ 10 `replicateM_` (writeTo store) writeTo :: TMVar (Handle) -> IO () writeTo store = do fh <- atomically $ takeTMVar store text <- hGetContents fh hPutStr fh (text ++ " some text ") atomically $ putTMVar store fh Thank you -- Emmanuel Delaborde ----------------------------------------------------------------------------------------------- This e-mail (and any attachments) is confidential and may contain personal views which are not the views of Cimex Media Ltd and any affiliated companies, unless specifically stated. It is intended for the use of the individual or group to whom it is addressed. If you have received it in error, please delete it from your system, do not use, copy or disclose the information in any way nor act in reliance on it and please notify postmaster@cimex.com A company registered in England Wales. Company Number 03765711 Registered Office : The Olde Bakehouse, 156 Watling Street East, Towcester, Northants NN12 6DB This email was scanned by Postini, the leading provider in Managed Email Security.