cv::Mat Pointers, Scope and Threading

asked 2014-09-15 21:05:41 -0500

MRDaniel gravatar image


I would like to know about smart pointers and thread safety. If we take a simple example we create an image and pass it to two (hypothetical) 'threaded' functions. They use the cv::Mat, not a cv::Mat* or cv::Mat&, the idea being that when they go out of scope, they will be automatically released.

void functionX(cv::Mat image)
    //Do some threading things
    //Async long running.

void functionY(cv::Mat image)
    //Do some other threading things
    //Async long running.

    cv::Mat img = cv::imread('someImage.png',1);



Will the cv::Mat deallocate itself? I have read about smart pointers and they can make the object they are pointing to thread safe. With the std::shared_ptr() it is thread safe so long as two threads try not to write to the same shared_ptr() object, instead of two separate shared_ptrs to the base object.

Is this the case for OpenCV's cv::Mat?

When we call functionX or functionY, with the above call signatures, is a new cv::Mat header created for each of those functions? Headers that reference the same memory for the object img?

Will they be garbage collected when it goes out of scope?



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@StevenPuttemans is the guy to ask here me thinks. Any thoughts buddy?

MRDaniel gravatar imageMRDaniel ( 2014-09-15 21:09:14 -0500 )edit

Hmm not quite sure but afaik there is no thread safety for Mat objects and one should make sure that he uses a mutex structure to avoid two threads reading the same Mat which is essentially a pointer structure.

StevenPuttemans gravatar imageStevenPuttemans ( 2014-09-16 02:35:42 -0500 )edit