Re: [pygccxml-development] Parameter passing, ownership semantics

[Gustavo C. <gjc...@gm...>]

On 2/18/07, Roman Yakovenko <rom...@gm...> wrote:
>
> On 2/18/07, Gustavo Carneiro <gjc...@gm...> wrote:
> >   Take this program, where Simulator and EventImpl are C++ classes
> wrapped
> > by Py++ / boost python:
> >
> > class MyEvent(EventImpl):
> >
> >     def Notify(self, *args):
> >          print "Notify!", args
> >
> >
> >  ev = MyEvent()
> > t1 = Seconds(1)
> >  Simulator.Schedule(t1, ev)
> > Simulator.Run()
> >
> >   There's a memory error here because 'ev' is passed into Simulator,
> which
> > takes ownership of the value and eventually calls delete on C++
> counterpart
> > to 'ev'.  valgrind says that Address 0xsomething is 8 bytes inside the
> > object allocated by boost python.
> >
> >   If, OTOH, I do "Simulator.Schedule(Seconds(1), MyEvent())", then the
> > python objects are prematurely destroyed, and another memory error
> occurs .
> >
> >   I notice that Py++ "call policies" are always related to the return
> value;
> > I don't see how to customize the parameter passing aspect of it all.
> >
> >   Any advice is appreciated.  Thanks in advance.
>
> I don't fully understand your situation. Take a look on this FAQ(
> http://boost.org/libs/python/doc/v2/faq.html#ownership )
>
> Does it help?


  Yes, it seems to match my problem.

  Now, trying to  implement the advice I stumble upon the "Make sure the C++
object is held by auto_ptr" part, which I have no idea how to do.  How do I
tell Py++ to do that?

If not, please describe your situation with some C++ code.
>
> If it do help, than you can use "function transformation" feature to
> create the wrapper.
>
> (
> http://language-binding.net/pyplusplus/documentation/functions/transformation/built_in/built_in.html
> )


  That doesn't seem to help; I don't know enough of Py++ internals to be
able to my own function transformation in useful time.

-- 
Gustavo J. A. M. Carneiro
"The universe is always one step beyond logic."