Enhance feature: ocl::setUseOpenCL(false) releases refcount/resources

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In OpenCV 4.5 or later and on all platforms…after any successful ocl::setUseOpenCL(true) and use of that OpenCL computing device, the managed OpenCL resources (buffers, queues, etc.) are not released when ocl::setUseOpenCL(false). The setUseOpenCL(false)` only sets a boolean flag. It doesn’t release resources or any refcount on them.

Goal → “OpenCV, please turn off OpenCL and release the used resources”.

I recommend the OpenCV API itself to be enhanced to somehow enable managed OpenCL resources to be released without requiring a new computing device. It is not possible to do alternatives like (pseudocode)

  • cv::ocl::OpenCLExecutionContext::getCurrentRef() = ocl::OpenCLExecutionContext() exposes a bug. It leaves the opencv TLS with empty .oclExecutionContext yet .execcontextinitialized=true.
  • ocl::OpenCLExecutionContext().bind() asserts because there is no impl
  • cv::ocl::OpenCLExecutionContext::getCurrentRef().release() fails later due to unmatched refcount decrement
  • cl_context = cv::ocl::Context::create("disabled"); cv::ocl::OpenCLExecutionContext::create(cl_context, cl_context.device(0)).bind(); asserts with no context or device

The only way to release managed OpenCL resources is to ocl::OpenCLExecutionContext.bind() to another OpenCL computing device – the old devices resources are released, and new resources are eventually allocated on the new computing device. But that is not the goal…and there might not be a 2nd OpenCL compute device to bind(). Somewhat related to Refcounts for ocl::Context::Impl not decremented when UMats out of scope · Issue #18919 · opencv/opencv · GitHub

I am confident I can update the API itself code to achieve the goal. However, I am unclear the approach to take. I’ll probably decrement the refcount for the current OpenCLExecutionContext. But…I’m not sure if I want to…

  1. create new static cv::ocl::OpenCLExecutionContext::unbind()
  2. allow binding a blank OpenCLExecutionContext
  3. allow assigning a blank to the current ref
  4. something else, etc…

Comments, ideas, alternatives?

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welcome.

you should take this to github and open an issue. no discussions of this kind take place here. actual Intel developers (who primarily run OpenCV) don’t frequent this forum.

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haha :grin: it was a draft github issue but then I thought…maybe the community wants to discuss before I have something clear enough for a PR. I’ll take your advice as moderator and go back. :heavy_check_mark:

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yeah I tried something similar here once. no reactions. trying to discuss that here makes no sense. this isn’t actually a community. this is unpaid first level support :wink:

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Hi
write an issue and wait for an answer and feel free to make a pr
setUseOpenCl is only to disable opencl function and does not release ressource
I think you should proposed a new name for this functionality