Boost Python - C++ class' private static data blown away before accessing in Python?

Stodge stodge at gmail.com
Wed Jul 9 17:44:27 CEST 2008


I wonder if it's a DLL boundary problem.

On Jul 5, 11:14 pm, Giuseppe Ottaviano <giu... at gmail.com> wrote:
> > In Python, I retrive an Entity from the EntityList:
>
> > elist = EntityList()
> > elist.append(Entity())
> > elist.append(Entity())
>
> > entity = elist.get_at(0)
>
> > entity.foo()
>
> > But it crashes inside foo() as the private static data is empty; or
> > rather the string array is empty. I know before that point that the
> > private static data is valid when accessed earlier by the C++ code as
> > the program works fine. It just won't work from Python, so somehow the
> > private static data has been blown away but I can't work out where or
> > why.
>
> Probably it is a problem of lifetime. What is the signature of append?  
> Who deletes the appended Entity in C++ code?
> If append takes a raw pointer, Boost.Python copies the pointer but  
> destroys the Entity object because it is a temporary and its reference  
> count went to zero. So the pointer in the list is referring to a  
> destroyed object, which results in undefined behaviour.
>
> Did you have a look at the lifetime policies of Boost.Python? The  
> simplest way to workaround the problem is using const reference  
> arguments, and always use value semantics. If it can result in a  
> performance penalty, another simple way is using shared_ptr's, which  
> have their own reference count (different from the one in CPython  
> lib), but Boost.Python does the magic to make them work together.
>
> HTH,
> Giuseppe




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