Something like this. If someone inserts a timer while we are doing our checking we can always catch it on the next iteration of the loop. --- Now runs unblocked checkTimers :: IO () checkTimers = do t <- readMVar timers -- takes it and puts it back case M.size t of -- no timers 0 -> threadDelay timeout -- some timers n -> do let (key@(time, name), io) = M.findMin t now <- getClockTime if (time <= now) then do modifyMVar_ timers $ \a -> return $! M.delete key a try $ io -- don't think we care return () else threadDelay timeout checkTimers On Dec 15, 2005, at 9:39 AM, Tomasz Zielonka wrote:
Perhaps you could use modifyMVar:
http://www.haskell.org/ghc/docs/latest/html/libraries/base/Control- Concurrent-MVar.html#v%3AmodifyMVar
modifyMVar_ :: MVar a -> (a -> IO a) -> IO ()
A safe wrapper for modifying the contents of an MVar. Like withMVar, modifyMVar will replace the original contents of the MVar if an exception is raised during the operation.