Jonathan Cast wrote:
On Mon, 2007-11-05 at 20:12 +0000, Andrew Coppin wrote:
Hi folks.
Take a look at this:
render :: IOArray Point Colour -> (Point -> Colour) -> IO () render framebuffer fn = mapM_ (\p -> writeArray framebuffer p (fn p)) all_points
How do I alter this to compute fn in multiple threads in parallel? (As you can see from the type signature, the calculation is independent for each pixel.)
You can spark a thread for each computation of fn, like such:
writeArray framebuffer p `parApp` fn p where parApp f x = x `par` f x
Hmm, that may be a little *too* fine-grained. (But then, just because I spark 175,862 threads doesn't mean it will actually *run* that many at once, right?) I guess I'll try it and see...
Or, alternatively, since I believe IOArray is lazy, you could grab a list and hand it to parListChunk (from Parallel.Strategies) or there abouts:
xn <- getElems framebuffer evaluate $ parListChunk 100 rwhnf
or something (evaluate is from Control.Exception; rwhnf is also from Parallel.Strategies).
Yes, IOArray is lazy. The *real* array type I'm using is unboxed and therefore strict - however, the order in which pixels are written is of no interest to me. I will sit and have a think about this one too. Thanks.