[issue9990] PyMemoryView_FromObject alters the Py_buffer after calling PyObject_GetBuffer when ndim 1

[Nick Coghlan]

Nick Coghlan <ncoghlan at gmail.com> added the comment:

The alternative (if we declare that clients should treat Py_buffer contents as completely read-only) is to update memoryview to include a separate "orig_view" field that would never be touched. The GetBuffer and ReleaseBuffer calls would then use orig_view, with dup_buffer used to copy the data into the main view field before modifying it.

However, this approach greatly complicates the bf_getbuffer and bf_releasebuffer implementations, since memoryview could no longer pass the supplied Py_buffer pointer straight through to the underlying implementation.

Instead, for each call to bf_getbuffer, it would need to create a new Py_buffer struct, use that for the GetBuffer call to the underlying object, copy the contents over to the passed in buffer (modifying the shape information as appropriate for any slicing that is in effect), then, in bf_releasebuffer, use the passed in pointer to find the right Py_buffer struct to use in the ReleaseBuffer call.

Putting the onus on exporters to be suspicious of the contents of the Py_buffer objects handed to bf_releasebuffer implementations actually seems like the more robust approach in the long run.

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue9990>
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