[PyQt] sip: Member objects and GC

[Phil Thompson]

On Fri, 24 Feb 2012 17:13:11 +0100, Jonathan Kleinehellefort <jk at molb.org>
wrote:
> Hallo,
> 
> I was asked to debug memory corruption problem in some sip-based Python
> bindings, and what I found leads me to believe that sip is to blame.
> I'll try to explain the problem:
> 
> Let's say you have a C++ class that looks like this:
> 
>     struct C { M m; };
> 
> And then let's assume there is some Python code that accesses m after
> its containing c object is no longer referenced by Python, for example:
> 
>     C().m
> 
> The Python wrapper for m will then point inside the *deleted* c object,
> leading to memory corruption.
> 
> I have a more complete example at
> 
>     http://molb.org/~jk/siptest.tar.gz
> 
> First of all, I think this should be considered a bug in sip, since it
> easily can result in memory corruption, while there is not even a
> warning or even a mention of this problem in the documentation.  It
> might even be better for sip to refuse generating code for accessing
> members.
> 
> What I would like happen in this case is that when the m wrapper is
> created, the reference count for the c wrapper would be increased, and a
> reference to c is stored in m, so that c can be dereferenced when m is
> deleted.
> 
> However, I'm not sure how to achieve this.  I looked at the ownership
> stuff but I don't think this will help me.  So I'm asking for help on
> how to fix or work around this problem.

Fixed in tonight's snapshot.

Phil