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

[David Leimbach]

Actually this isn't good enough either as I'm potentially leaving the
"action" thread in a state where it never times out...  I guess I have to do
all thread killing in the main thread.

On Tue, Mar 23, 2010 at 12:23 PM, David Leimbach <leimy2k at gmail.com> wrote:

> 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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