[PyQt] [BUG] Issues with overriding QSGMaterialShader::attributeNames()

[Phil Thompson]

On 18/06/2015 7:49 pm, Vladimir Rutsky wrote:
> On Thu, Jun 18, 2015 at 8:43 PM, Phil Thompson
> <phil at riverbankcomputing.com> wrote:
>> On 02/06/2015 11:47 am, Vladimir Rutsky wrote:
>>> 
>>> Hello,
>>> 
>>> 1. Overrided in Python QSGMaterialShader::attributeNames() always
>>> returns NULL to Qt C++ code.
>>> 
>>> In PyQt-gpl-5.4.1/sip/QtQuick/qsgmaterial.sip code for
>>> attributeNames() method stores result in variable "result" and never
>>> touches "sipRes" variable, which is returned at the end of function.
>>> 
>>> Attached patch fixes this issue by assigning "sipRes" to "result" 
>>> (I'm
>>> not sure is this intented behavior in case of errors).
>>> 
>>> 2. Calling overriden in Python QSGMaterialShader::attributeNames()
>>> from Qt C++ code leads to memory leaks.
>>> 
>>> Each call to attributeNames() creates copy of strings
>>> (PyQt-gpl-5.4.1/sip/QtQuick/qsgmaterial.sip):
>>> 
>>>                 // Note that the converted value will leak.  This
>>> shouldn't matter
>>>                 // because the data should be static anyway.
>>>                 result = new char *[PyList_GET_SIZE(names) + 1];
>>>                 result[PyList_GET_SIZE(names)] = 0;
>>> 
>>> And attributeNames() is called e.g. in each
>>> Renderer::renderUnmergedBatch(), which can lead to unlimited memory
>>> leaks.
>> 
>> 
>> (1) is fixed but is it possible you could produce a short script that
>> demonstrates (2). I know it will leak but (as I'm not an OpenGL 
>> programmer)
>> it would be really useful to see how this method is normally called.
>> 
>> Thanks,
>> Phil
> 
> 
> I made example where attributeNames() are called approximately every
> 10 ms: https://gist.github.com/rutsky/380932afec27ff0f108e

Should be fixed in tonight's snapshot.

On OSX (at least) your script still leaks because the shader fails to 
compile because of the long name.

Thanks,
Phil