Thank you for your reply, I'd come up with the following:
timed :: Int → IO a → b → IO (Either b a)
timed max act def = do
r ← new
t ← forkIO $ do
a ← act
r ≔ Right a
s ← forkIO $ do
wait max
e ← em r
case e of
True → do
kill t
r ≔ Left def
False → return ()
takeMVar r
---------------------
*Network.Port.Scan> timed 500 (wait 50000 >> return 0) 'x'
Left 'x'
*Network.Port.Scan> timed 500000 (wait 50000 >> return 0) 'x'
Right 0
---------------------
before reading your reply:
timed timeout act fallback = do
res <- newEmptyMVar
tid <- forkIO $ act >>= writeMVar res
threadDelay timeout
stillRunning <- isEmptyMVar res
if stillRunning then killThread tid >> return fallback else takeMVar res
---------------------
*Network.Port.Scan> timed2 500 (wait 50000 >> return 0) 'x'
<interactive>:1:33:
No instance for (Num Char)
arising from the literal `0' at <interactive>:1:33
Possible fix: add an instance declaration for (Num Char)
In the first argument of `return', namely `0'
In the second argument of `(>>)', namely `return 0'
In the second argument of `timed2', namely
`(wait 50000 >> return 0)'
Regards,
Cetin Sert
2009/5/30 Sebastian Sylvan <[email protected]>
>
>
> 2009/5/30 Cetin Sert <[email protected]>
>
>> Hi how could one implement a function in concurrent haskell that either
>> returns 'a' successfully or due timeout 'b'?
>>
>> timed :: Int → IO a → b → IO (Either a b)
>> timed max act def = do
>>
>
>
> Something like (warning, untested code - no compiler atm).
>
> timed timeout act fallback = do
> res <- newEmptyMVar
> tid <- forkIO $ act >>= writeMVar res
> threadDelay timeout
> stillRunning <- isEmptyMVar res
> if stillRunning then killThread tid >> return fallback else takeMVar res
>
> --
> Sebastian Sylvan
> +44(0)7857-300802
> UIN: 44640862
>
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