Hi, > Could you at least ask Peter Dimov if he thinks the > dont_enable_shared_from_this patch could be generally useful? > Maybe he's OK adding it, then it wouldn't be a big deal > fixing Boost.Python, which would probably prevent a lot of > confusion and lost time in the future.
I stumbled once again on this problem, so I took some time to bother Peter Dimov with the patch suggestion. Here, is a copy of our exchange : Hello Peter, I wanted to contact you about a problem that was raised, on february, on c++-sig mailing list about a problem happening when wrapping classes derived from 'enable_shared_from_this' using boost.python library. The problem is briefly described in this post - including a patch to boost/shared_ptr.hpp that would allow to fix the problem. http://mail.python.org/pipermail/cplusplus-sig/2008-February/012973.html The original poster was encouraged by Ralf W. Grosse-Kunstleve to contact you about this, but we never heard from him on the list (http://mail.python.org/pipermail/cplusplus-sig/2008-February/013003.html). To make it short, boost.python creates shared_ptr objects, holding the wrapped c++ objects, with a custom deleter managing the python object reference count. This leads to something like that : #include <boost/enable_shared_from_this.hpp> namespace { class A : public boost::enable_shared_from_this<A> { public: ~A() {}; }; void my_deleter(void*) { } }; BOOST_AUTO_TEST_CASE( test_enable_shared_from_this ) { boost::shared_ptr<A> a( new A ); { boost::shared_ptr<A> ater = boost::shared_ptr<A>( a.get(), my_deleter ); // OP patch proposal :: boost::shared_ptr<A> ater = boost::shared_ptr<A>( a.get(), my_deleter // , boost::dont_enable_shared_from_this() ); BOOST_CHECK( a == ater ); } boost::shared_ptr<A> abug = a->shared_from_this(); // this throws bad_weak_ptr } Did you hear about this problem ? Do you think this patch is viable and could be applied in boost trunk ? Do you happen to have another idea of workaround that could be applied in client code and/or in shared_ptr ? Thanks for your time, best regards, Nicolas Lelong mgdesign Followed by Peter's answer that lead to Trac ticket #2584 : Yes, I am aware of this problem. It is possible today to emulate the proposed functionality by using the aliasing constructor, but I think that a more proper fix for the issue is to make enable_shared_from_this more intelligent so that it doesn't reinitialize itself in such scenarios. I'll appreciate it if you file a Trac ticket for this and assign it to me. I've a few pending enable_shared_from_this issues anyway, and I'll try to find the time to address them before the next release ships. -- Peter Dimov http://www.pdplayer.com
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