[Stackless] PySide problem, take #2: typeobject clash

John Ehresman jpe at wingware.com
Mon Oct 21 22:10:08 CEST 2013

On 10/21/13 1:07 PM, Christian Tismer wrote:
> No, it is about the type layout, there are (ah, here came the word frame
> again?! ) there are type fields in CPython that stackless does not have.
> Well, and because these structures are different in size, pyside must
> be compiled using stackless, otherwise it crashes ugly.

I think I see the problem; to me, at least, it's useful to see the 
stackless version of object.h at 
http://www.stackless.com/browser/Include/object.h  It looks like 
stackless moves the fields defined in PyHeapTypeObject into 
PyTypeObject, adds at least one additional field, and then #define's 
PyHeapTypeObject to PyTypeObject.  This leads to two problems, which are 
somewhat separable --

1) When compiling, there is no ht_type field in PyHeapTypeObject.  This 
is what Christian's patch addresses.

2) At runtime, both pyside and stackless assume they can store 
additional type data in the same place after the PyTypeObject data. 
pyside stores a pointer to a separate structure here.

I think it might be worth trying to fix #2 as well as #1 so there's no 
need for separate pyside builds for stackless.  It may be possible to 
allocate these type objects on the heap so the length of the base object 
can be determined at runtime.  I haven't thought this all the way 
through, but think it might work, though it might or might not require 
an ABI break.

As for the current patch, I think it needs motivating comments to at 
least point developers who aren't familiar with the stackless changes to 
PyTypeObject in the right direction.



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