[Numpy-discussion] Unreliable crash when converting using numpy.asarray via C buffer interface

[Hameer Abbasi]

Hey Friedrich,

If you can produce an MVCE that would be really helpful, along with your hardware and environment. Without that, it isn’t possible to be of much help.

https://matthewrocklin.com/blog/work/2018/02/28/minimal-bug-reports

Best Regards,
Hameer Abbasi

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> On Dienstag, Jan. 26, 2021 at 9:49 AM, Friedrich Romstedt <friedrichromstedt at gmail.com (mailto:friedrichromstedt at gmail.com)> wrote:
> Hi,
>
> This is with Python 3.8.2 64-bit and numpy 1.19.2 on Windows 10. I'd
> like to be able to convert some C++ extension type to a numpy array by
> using ``numpy.asarray``. The extension type implements the Python
> buffer interface to support this.
>
> The extension type, called "Image" here, holds some chunk of
> ``double``, C order, contiguous, 2 dimensions. It "owns" the buffer;
> the buffer is not shared with other objects. The following Python
> code crashes::
>
> image = <... Image production ...>
> ar = numpy.asarray(image)
>
> However, when I say::
>
> image = <... Image production ...>
> print("---")
> ar = numpy.asarray(image)
>
> the entire program is executing properly with correct data in the
> numpy ndarray produced using the buffer interface.
>
> The extension type permits reading the pixel values by a method;
> copying them over by a Python loop works fine. I am ``Py_INCREF``-ing
> the producer in the C++ buffer view creation function properly. The
> shapes and strides of the buffer view are ``delete[]``-ed upon
> releasing the buffer; avoiding this does not prevent the crash. I am
> catching ``std::exception`` in the view creation function; no such
> exception occurs. The shapes and strides are allocated by ``new
> Py_ssize_t[2]``, so they will survive the view creation function.
>
> I spent some hours trying to figure out what I am doing wrong. Maybe
> someone has an idea about this? I double-checked each line of code
> related to this problem and couldn't find any mistake. Probabaly I am
> not looking at the right aspect.
>
> Best,
> Friedrich
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