[Cython] tp_clear() of buffer client objects

[Stefan Behnel]

mark florisson, 23.04.2012 11:10:
> On 23 April 2012 09:42, Stefan Behnel wrote:
>> Stefan Behnel, 23.04.2012 10:23:
>>> mark florisson, 22.04.2012 16:41:
>>>> On 22 April 2012 15:31, mark florisson wrote:
>>>>> I think the problem here
>>>>> is that a single memoryview object is traversed multiple times through
>>>>> different traverse functions, and that the refcount doesn't match the
>>>>> number of traverses. Indeed, the refcount is only one, as the actual
>>>>> count is the acquisition count. So we shouldn't traverse the
>>>>> memoryview objects in memoryview slices, i.e. not
>>>>> _memoryviewslice.from_slice.memview. I'll come up with a commit
>>>>> shortly, would you be willing to test it?
>>>>
>>>> BTW, tp_clear calls Py_CLEAR on Py_buffer.obj, shouldn't it call
>>>> releasebuffer instead?
>>>
>>> Where is that? The memoryview class calls __Pyx_ReleaseBuffer() here.
>>
>> Ah, found it. Yes, tp_clear() would be called before __dealloc__() in
>> reference cycles, so that's a problem. I'm not sure tp_clear should do
>> something as (potentially) involved as freeing the buffer, but if the
>> Py_buffer is owned by the object, then I guess it just has to do that.
>> Otherwise, it would leak the buffer.
>>
>> The problem is that this also impacts user code, though, so a change might
>> break code, e.g. when it needs to do some cleanup on its own before freeing
>> the buffer. It would make the code more correct, sure, but it would still
>> break it. Guess we have to take that route, though...
>
> It also seems that tp_clear is only generated for object attributes,
> and then it includes freeing the object of Py_buffers (so only a
> Py_buffer attribute doesn't result in a tp_clear function). Finally,
> tp_dealloc doesn't deallocate buffers either, which it should. So both
> tp_clear and tp_dealloc should call release buffer

Good call.


> (it can be called
> multiple times on the same buffer).

I guess calling it the first time would set "obj" to NULL and the second
time would recognise it and do nothing, right? That's fine.

Stefan