Stream default to Stream::Null() when no default in function prototype

[r2d3]

this corrects bug #16592 where a Stream is created at
each GpuMat::load(arr,stream) call

a correct solution would have been to add a default to GpuMat::load
but due to circular dependence between Stream and GpuMat, this is not possible

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or other license that is incompatible with OpenCV
• The PR is proposed to proper branch
• There is reference to original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

force_builders=Custom
buildworker:Custom=linux-4,linux-6
build_image:Custom=ubuntu-cuda:18.04

[alalek]

Thank you for contribution!

It would be nice if you could add simple test here: https://github.com/opencv/opencv/blob/4.5.2/modules/python/test/test_cuda.py

[r2d3]

Hello @alalek

what kind of test do you need ?

1. that the patch does not break mat_device.upload(mat_host, stream) ?
2. that the patch correct the issue ? to test that the issue is corrected, we need to use nvprof from the CUDA Toolkit for launching the test.

I have a second question. My fix looks like a hack. Here is the problem creating the bug.
The generated Python code for GpuMat::upload is declaring Stream stream variables to parse the stream parameter. But the default ctor creates a new stream by calling cudaStreamCreate. The fix is to have Stream stream=Stream::Null() in the Python bindings code.

Other functions are using a default value in the C++ function prototype:
CV_EXPORTS_W void resize(InputArray src, OutputArray dst, Size dsize, double fx=0, double fy=0, int interpolation = INTER_LINEAR, Stream& stream = Stream::Null());

But this is not possible for GpuMat::upload because there is a circular dependency between GpuMat and Stream classes.

So patching gen2.py is the only solution I found to generate the correct stream parameter parsing.

[r2d3]

jenkins cn please retry a build

[alalek]

There is already .upload check. More accurate test is hard to write.

The patch looks good to me 👍

[alalek]

Please remove "WIP: " when patch is ready (BTW, you can use GitHub's "drafts" instead)

[r2d3]

Hello @alalek

I added a test_cuda_upload_download_stream to test_cuda.py as the current upload/download test were not using stream.

Running nvprof python3.6 test_cuda.py allows to see if cudaStreamCreate is called only 2 times.