[Haskell-cafe] Parallel executing of actions

Juan Carlos Arevalo Baeza jcab.lists at jcabs-rumblings.com
Tue Apr 17 20:49:11 EDT 2007

    I may be talking out of my other end here, but... if you want something  
like parMap to calculate all the pixels in parallel, then... can't you use  
parMap itself?

    Something like:

weirdParMap action = sequence_ . map action . parMap (id $!)

    This evaluates all the elements of the list using parMap (the expensive  
part, right?), and then sequentially applies the action on the current  


On Sun, 15 Apr 2007 12:56:02 -0700, Mitar <mmitar at gmail.com> wrote:

> Hi!
> On 4/15/07, Spencer Janssen <sjanssen at cse.unl.edu> wrote:
>> 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}
> OpenGL bindings successfully crash. The functional calculations in f
> should be done in parallel, but those few OpenGL actions should still
> be done sequentially. I am attaching the code in question. It is a
> simple voxel raycasting engine.
> (Any suggestions on other memory/performance improvements are more
> than welcome.)
> Mitar

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