On Tue, 2010-03-16 at 20:56 +0100, Alexandre Hamez wrote: > On 16 mars 2010, at 13:12, Neal Becker wrote: > > > Alexandre Hamez wrote: > > > >> Hi all, > >> > >> I have a C++ library that needs to store in a hash map user's code, that > >> is, Python-extended objects. To make the C++ interface available to > >> Python, I use boost::python::wrapper, as stated in the tutorial > >> > > (http://www.boost.org/doc/libs/1_42_0/libs/python/doc/tutorial/doc/html/python/exposing.html#python.class_virtual_functions). > >> Because I store this extend objects, I need to tell Python that I've got a > >> reference on these objects. > >> A thread from 2007 > >> (http://mail.python.org/pipermail/cplusplus-sig/2007-March/011790.html) > >> states there is a problem for this particular use case, but in the end, no > >> solution is given. So my question is the following: as of today, what is > >> the correct way to tell Python we hold a reference to Python extend > >> objects of C++ classes, using the boost::python::wrapper mechanism? > >> > >> Thanks, > >> --------------------- > >> Alexandre Hamez > > > > Thanks for answering so quickly. > > I've use 2 methods: > > > > 1) with_custodian_and_ward > OK, I didn't think of this method. Seems a good way to do it. > > > 2) boost::shared_ptr > > For this point, do you mean you just take the objects that should seen they > references increased by a shared_ptr? Just after having asked this question, > I tried with this simple solution, and it seems to work. I hope there is no > hidden potential crash :-) >
If you get a boost::shared_ptr to a Python object (either by wrapping a function taking a shared_ptr or by using boost::python::extract), that shared_ptr will properly manage the Python reference count via a custom deleter that decref's the PyObject* when it goes out of scope. The only catch is that shared_ptr doesn't do garbage collection, so you can get cycles that don't get deleted if your shared_ptrs own other shared_ptrs. Other than that, you're should be safe if you just use shared_ptr everywhere. This will work differently internally if you declare your wrapped classes to have shared_ptr storage (that's generally what I do), but the effects should be mostly the same. Note that you can also declare your storage to be shared_ptr to a wrapper class. > Do you use these two methods conjointly in the same project? Or did you > identify some use cases which favor a method rather the other one? > I generally use shared_ptr storage for everything, but I often mix that with with_custodian_and_ward and its cousins (return_internal_reference, in particular) when I don't have access to a shared_ptr on the C++ side. Jim Bosch _______________________________________________ Cplusplus-sig mailing list Cplusplus-sig@python.org http://mail.python.org/mailman/listinfo/cplusplus-sig
