[Haskell-cafe] Timeouts that don't cause data growth.

[David Leimbach]

Is this just a problem of spawning too many forkIO resources that never
produce a result?

I was thinking of trying something like the following in System.Timeout's
place:

> module Main where

> import Control.Concurrent.MVar
> import Control.Concurrent
> import Data.Maybe


> timeout :: Int -> IO a -> IO (Maybe a)
> timeout time action = do
>   someMVar <- newEmptyMVar   -- MVar is a Maybe
>   timeoutThread <- forkIO $ nothingIzer time someMVar
>   forkIO $ actionRunner action someMVar timeoutThread
>   takeMVar someMVar >>= return
>     where
>       nothingIzer time mvar = threadDelay time >> putMVar mvar Nothing
>       actionRunner action mvar timeoutThread = do
>                         res <- action
>                         killThread timeoutThread
>                        putMVar mvar $ Just res

> main :: IO ()
> main = do
>  res <- timeout (5 * 10 ^ 6) (getLine >>= putStrLn)
>  case res of
>     Nothing -> putStrLn "Timeout"
>     Just x -> putStrLn "Success"



On Tue, Mar 23, 2010 at 11:31 AM, Roel van Dijk <vandijk.roel at gmail.com>wrote:

> I tried a few things. First I added another timeout to main, so the
> program kills itself after a few seconds.
>
> doit :: IO (Maybe ())
> doit = timeout 12000000 $ {- yield >> -} return ()
>
> main :: IO ()
> main = do _ <- timeout 5000000 $ forever doit
>          return ()
>
> This program failed to terminate. But when I compiled -with threaded
> and added a yield to doit, it worked (kinda). If the timeout in doit
> is not too long, like 200 milliseconds, the program has constant space
> usage. But when I increased the timeout in doit to 12 seconds I got a
> stack overflow.
>
> I'll investigate further when I have more time.
>
> Regards,
> Roel
>
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