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Turn on/off multithreading?

asked 2014-07-01 12:19:19 -0500

ben2316 gravatar image

I just noticed that GridAdaptedFeatureDetector::detectImpl (in modules/features2d/src/detectors.cpp) uses cv::parallel_for_ in its implementation. I'm assuming that means that it uses multithreading to speed up the feature detection process. My question is: is there a way I can force this to run in serial? The motivation to turn off multithreading is to do performance testing, to see how my code runs faster or slower, serially, based on different code changes. Is there a compile flag or function call I need to do?

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it's all done in the cmake stage, when building the libs. if you don't enable anything (like openmp or similar) there, it will run single-threaded anyway.

berak gravatar imageberak ( 2014-07-01 14:18:36 -0500 )edit

How about if I didn't compile OpenCV from source?

ben2316 gravatar imageben2316 ( 2014-07-01 19:39:40 -0500 )edit
sturkmen gravatar imagesturkmen ( 2020-07-06 12:38:05 -0500 )edit

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answered 2014-07-02 03:37:55 -0500

If your OpenCV version was compiled with TBB, then the answer is no way, I suppose. Because in that case, there is some where in the compiled code, the task_scheduler_init initialized the number of threads based on your hardware configuration (it is usually with more than 1 core) and due to the information from this link, other calls will be ignored, this means you can not change that number. In case your OpenCV was compiled with OpenMP, the code below may be a try:

int num_threads = 1;
omp_set_dynamic(0);
omp_set_num_threads(num_threads);
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Does anyone know if the OpenCV pre-built Windows libraries are compiled with TBB?

ben2316 gravatar imageben2316 ( 2014-07-02 11:20:19 -0500 )edit
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Asked: 2014-07-01 12:19:19 -0500

Seen: 4,467 times

Last updated: Jul 02 '14