On 02/03/2012 02:26 PM, Holger Brandsmeier wrote:
Dear list,Note: I am actually using Teuchos::RCP instead of boost::shared_ptr and boost::weak_ptr, but I already mirrored almost all the special treatments in boost::python, and have been successfully using this for a while. Everything that I write should actually apply to both implementations in the same way. I have a class that needs to store an RCP to itself to pass it along to some classes that it creates, which might later need the RCP to keep the original class alive. In C++ I implemented this by switching the constructor to procted, and by having a static create() method like this: static RCP<PfemSpaceT> create(RCP< MeshT> mesh, Point<int, meshdim> pol_deg_default) { RCP<PfemSpaceT> ret(new PfemSpaceT(mesh, pol_deg_default)); ret->setThisRCP(ret); ret->init(); return ret; } The function setThisRCP() stores the shared point as a weak pointer. When you call getThisRCP() the a strong RCP is returned from this weak RCP. This is what you want as otherwise the class will never be deleted. The problem starts now as the same class is extended from python. I mirror the same implementation in python as: def __init__(self, mesh, pol_deg, cb_setDofEntity): super(PfemSpaceStaticCond, self).__init__(mesh, pol_deg, False) self.setThisRCP(self) self.init() Now I get serious problems with this call: self.setThisRCP(self) My understanding is, that the following happens: 1) the from-python converter creates an RCP with the use count of one and a custom deletor (boost::python::converter::shared_ptr_deleter). 2) the function setThisRCP gets called and stores a weak RCP 3) the control gets back to python and the use count of the RCP drops to zero. The custom deletor dereferences the use count in python. Later calls to getThisRCP() that turn the weak RCP into a strong RCP are then invalid. When python no longer references the class, it gets deleted. Some C++ parts that used the RCP from getThisRCP() work on a class that has been deleted and at some point the program crashes. (Here maybe if I would use boost the program would crash already earlier). Do you have an idea how I can use the thisRCP paradigm together with C++ classes that are extended from python?
It sounds like you need to ensure that instances created in Python always use an RCP holder (even Python subclasses). I'd have thought passing RCP<Wrapper> as the holder template argument in the class_ definition would do that, but I'm not that familiar with how smart-pointer holders interact with wrapper classes.
The second part is that you'd need to make sure #1 is replaced by having Boost.Python look in the holder, find that it has an internal RCP, and use that instead of creating a new temporary one. I know Boost.Python can do that with shared_ptr at least some of the time, so I assume you've set it up so that's possible with RCP too. You might try having setThisRCP take a non-const reference to an RCP, so Boost.Python is forced to use an lvalue converter and hence a non-temporary RCP.
Good luck! Jim _______________________________________________ Cplusplus-sig mailing list Cplusplus-sig@python.org http://mail.python.org/mailman/listinfo/cplusplus-sig
