On Sun, 15 Apr 2007 18:01:44 +0200
Mitar <[EMAIL PROTECTED]> wrote:
> Hi!
>
> Is there a parallel version of mapM_? Like it is for map (parMap)?
This version will fork a new thread for each action:
\begin{code}
import Control.Concurrent
import Control.Monad
parSequence_ xs = do
m <- newEmptyMVar
mapM_ (\x -> forkIO x >> putMVar m ()) xs
replicateM_ (length xs) (takeMVar m)
parMapM_ f xs = parSequence_ $ map f xs
\end{code}
> I would like to execute actions in parallel as the computation of
> necessary data for actions is quite computational heavy. But it does
> not matter in which order those actions are executed. (I am rendering
> pixels with OpenGL and it does not matter in which order I draw them,
> but it matters that for one pixel it takes some time to calculate its
> color.)
>
> The example would be:
>
> main :: IO ()
> main = do
> -- the order of printed characters is not important
> -- instead of putStrLn there will be a computationally big function
> -- so it would be great if those computations would be done in
> parallel -- and results printed out as they come
> mapM_ rwhnf (putStrLn) ["a","b","c","d"]
>
> Is this possible? Without unsafe functions? And without changing the
> semantics of the program.
Of course the semantics of the program will change, the order in which
the actions are executed is unknown!
Cheers,
Spencer Janssen
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