Re: [Haskell-cafe] Implementing computations with timeout

7 Jan 2005


      Tomasz Zielonka  writes:
...
import Control.Concurrent (forkIO, threadDelay)
  import Control.Concurrent.STM
withTimeout :: Int -> STM a -> IO (Maybe a)
  withTimeout time fun = do
      mv <- atomically newEmptyTMVar
      tid <- forkIO $ do
          threadDelay time
          atomically (putTMVar mv ())
      x <- atomically (fmap Just fun `orElse` (takeTMVar mv >> return Nothing))
      killThread tid
      return x
Isn't this buggy if fun just keeps working without throwing an exception
or using retry? I meant wholly inside STM - if we use IO as the
signature then using the TMVar has few advantages over using an MVar.

- Einar Karttunen