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I have written a Forth Mandelbrot fractal plotter, and as much as a technical exercise as anything else I would like to try to speed it up with some parallel processing.

For the time being I would be happy if I could just use both of my cores (have one core do one half of the image and the other the other half).

I have noticed that Windows XP will quite happily manage two instances of Gforth and try use as much processor capacity as possible, so running two processes could be a start. However I am not sure if they can share memory, or if they can both write to a file at the same time (or how to tell one process to start writing at x bytes from the start of the file).

In summary, how can I do parallel processing using Gforth on Windows XP?

Peter Mortensen
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sheepez
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2 Answers2

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You could have each program do a grid of pixels rather than a single pixel, and then recombine them in the end.

AFAIK, pixels in Mandelbrot sets are independent of each other (someone correct me if I am wrong), however the computation of each of them is non-deterministic, making it a hard problem to properly parallelize, without having some kind of central dispatch thread (then again you run into potential problems with contention).

wmercer
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    I think you are right about the independence of pixels, though I am not sure in what way they are non-deterministic. In any case as far as I can tell gforth doesn't do system calls properly on Windows so I am a bit stuck. – sheepez Mar 16 '11 at 17:11
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See GForth Pipes.

Vijay Mathew
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  • This is probably a gap in my understanding, but how can I use pipes to help? – sheepez Dec 29 '10 at 15:01
  • @sheepez You can spawn a GForth instance from a running GForth, connect them with pipes and make them communicate through the pipes. Thus you can avoid the less reliable shared memory/file approach. – Vijay Mathew Dec 30 '10 at 10:07
  • @Vijay Mathew So far, my code calculates the colour of a pixel and the writes this to a bitmap file. Would I need to change the way that it operates to usefully incorporate pipes, I ask as keeping things synchronised looks tricky. – sheepez Dec 30 '10 at 13:57
  • @sheepez You may still have a race condition as both processes try to write to a single file, right? You could implement some-kind of channel communication on top of pipes and get rid of the synchronization problem. – Vijay Mathew Dec 31 '10 at 06:15
  • @Vijay Mathew Apologies for continuing to miss the point, could you possibly give an overview of how you would put something like this together? Just to clarify exactly what is sent through the pipes and what each process actually does. – sheepez Jan 01 '11 at 13:34
  • Some research makes me think that pipes and actually all system calls are non-functional on Windows. Do you have any experience to the contrary? – sheepez Jan 06 '11 at 18:45