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LumiGuide / haskell-opencv

Haskell binding to OpenCV-3.x
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Non-thread-safety in inemcode #132

Closed nh2 closed 5 years ago

nh2 commented 5 years ago

For imencode, there's this warning:

https://github.com/LumiGuide/haskell-opencv/blob/dd51d7cfb1513e03516706465c246164e33fb589/opencv/src/OpenCV/ImgCodecs.hs#L83

Where does the non-thread-safety come from?

I'm investigating a memory leak reported by valgrind and am wondering if this is relevant for it.

roelvandijk commented 5 years ago

I believe I wrote that comment based on the C++ implementation. Upon closer inspection I believe it is actually thread safe.

Internally it uses some ImageEncoder, which is a Ptr<BaseImageEncoder>. It changes some properties of this encoder object when you invoke imencode. But it does so on a copy of the original object. I think I missed the copy part when I wrote the comment stating it is not thread safe.

roelvandijk commented 5 years ago

Did you look into using valgrind suppression files for opencv?

https://github.com/opencv/opencv/tree/master/platforms/scripts

nh2 commented 5 years ago

Thanks for the explanations. If the function is actually thread safe, we probably want to remove the comment.

Did you look into using valgrind suppression files for opencv?

No, so far I haven't needed to reduce the number of messages emitted.

By now I believe my potential memory leak doesn't exist and it's simply a reference I hold from Haskell (my ForeignPtr with finalizer hasn't been GC'd yet, I'll retest that with performMajorGC).

roelvandijk commented 5 years ago

Fixed by 28b22ed35f793cf62d938545f9f973cca66e6827