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    <p>The <a href="http://docs.python.org/library/multiprocessing.html" rel="noreferrer">python documentation for multiprocessing</a> blames the lack of os.fork() for the problems in Windows. It may be applicable here.</p> <p>See what happens when you import psyco. First, easy_install it:</p> <pre><code>C:\Users\hughdbrown&gt;\Python26\scripts\easy_install.exe psyco Searching for psyco Best match: psyco 1.6 Adding psyco 1.6 to easy-install.pth file Using c:\python26\lib\site-packages Processing dependencies for psyco Finished processing dependencies for psyco </code></pre> <p>Add this to the top of your python script:</p> <pre><code>import psyco psyco.full() </code></pre> <p>I get these results without:</p> <pre><code>serialrun took 1191.000 ms parallelrun took 3738.000 ms threadedrun took 2728.000 ms </code></pre> <p>I get these results with:</p> <pre><code>serialrun took 43.000 ms parallelrun took 3650.000 ms threadedrun took 265.000 ms </code></pre> <p>Parallel is still slow, but the others burn rubber.</p> <p>Edit: also, try it with the multiprocessing pool. (This is my first time trying this and it is so fast, I figure I must be missing something.)</p> <pre><code>@print_timing def parallelpoolrun(reps): pool = multiprocessing.Pool(processes=4) result = pool.apply_async(counter, (reps,)) </code></pre> <p>Results:</p> <pre><code>C:\Users\hughdbrown\Documents\python\StackOverflow&gt;python 1289813.py serialrun took 57.000 ms parallelrun took 3716.000 ms parallelpoolrun took 128.000 ms threadedrun took 58.000 ms </code></pre>
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    1. POpython multiprocessing vs threading for cpu bound work on windows and linux
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    1. CO+1 for the nice optimization.
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      1. USByron Whitlock
    2. COVery neat! Lowering the number of iterations (processes) while raising the count-to value shows that, as Byron told, that the parrallel slowness comes from the added setup time of Windows Processes.
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      1. USmanghole
    3. COThe Pool does not seem to wait for itself to complete, there is a join() method for Pool but it doesn't seem to do what I think it should do :P.
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