Thoughts on OpenMP

This is a discussion on Thoughts on OpenMP within the C++ Programming forums, part of the General Programming Boards category; I am looking at OpenMP and it seems to me that while it is about time they added standardized multithreading ...

  1. #1
    Malum in se abachler's Avatar
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    Thoughts on OpenMP

    I am looking at OpenMP and it seems to me that while it is about time they added standardized multithreading capability to the language, that OpenMP is probably not the best solution. I may be biased of course, since I already know how to do everything OpenMP does by using exant Windows procedures. I do see it as having some use in converting existing code over to run faster on multicore systems or for programmers that don't 'get' threads, I do not think it would be the best choice for all/new applications. Another benefit of course would be portability. If it is added to the standard, then theoretically parallel code written for Win32 should also compile for linux.
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    I know some pretty heavy number crunching companies use OpenMP, so I guess it can't be "horrible".

    Like all multithreading, you need to get fairly large independent chunks of data to calculate in each thread - then the overhead of the mechanisms to present the work becomes less of an issue. If you have small chunks of work, no form of multithreading is really that efficient.

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    C++まいる!Cをこわせ! Elysia's Avatar
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    There's nothing wrong with it. It can pretty convenient. You could split a for loop into X threads very easily. I've only used it once, though, so I can't exactly say I'm an expert.
    So look forward to someone else's advice too.
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    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

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    Cat without Hat CornedBee's Avatar
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    It's very terse. Compare the code overhead for making a computation loop multi-threaded with OpenMP - one line, I think, perhaps two or three - with the overhead from doing it by hand - something on the order of a dozen lines or two, if you consider the final joining. And that doesn't consider that the OpenMP implementation probably has a thread pool for the computation, and a message dispatching mechanism to use it. If you have to implement this yourself, it will be a lot more than just two dozen lines.
    The job object API probably is a good alternative - I wouldn't be surprised if MS's OpenMP implementation used it internally.
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