Ticket #9567: test_shared_from_this.cpp

// This demonstrates a problem with boost::serialization and boost::enable_shared_from_this.
// (boost version 1.53)
//
// Given the following class structure:
//    Base is a simple class
//    Derived inherits from Base
//    Derived also inherits from boost::enable_shared_from_this<Derived>
//    Base and Derived implement boost::serialization
//
// When deserializing an instance of Derived into a vector of boost::shared_ptr<Derived>:
//    Base and Derived members are reconstructed correctly.
//        Derived::shared_from_this() works as expected.
//
// But when deserializing an instance of Derived into a vector of boost::shared_ptr<Base>:
//    Base and Derived members are still reconstructed correctly.
//        Derived::shared_from_this() throws a bad_weak_ptr exception.
//    This is because enable_shared_from_this::weak_ptr is NOT reconstructed - It is zero.
#define BOOST_TEST_MAIN
#include <boost/test/unit_test.hpp>
#include <boost/test/output_test_stream.hpp>
#include <vector>
#include <boost/shared_ptr.hpp>
#include <boost/enable_shared_from_this.hpp>
#include <boost/serialization/shared_ptr.hpp>
#include <boost/archive/xml_oarchive.hpp>
#include <boost/archive/xml_iarchive.hpp>
#include <boost/serialization/vector.hpp>
#include <boost/serialization/export.hpp>

class Base {
public:
        Base() {}
        virtual ~Base() {}              // "virtual" forces RTTI, to enable serialization of Derived from Base pointer
        int m_base;

        template<class Archive>
        void serialize(Archive & ar, const unsigned int version)
        {
                ar & BOOST_SERIALIZATION_NVP(m_base);
        }
};

class Derived : public Base, public boost::enable_shared_from_this<Derived> {
public:
        Derived() {}
        ~Derived() {}
        boost::shared_ptr<Derived> SharedPtr() { return shared_from_this(); }
        int m_derived;

        template<class Archive>
        void serialize(Archive & ar, const unsigned int version)
        {
                ar & BOOST_SERIALIZATION_BASE_OBJECT_NVP(Base);
                ar & BOOST_SERIALIZATION_NVP(m_derived);
        }
};
// The following is required to enable serialization from Base pointer
BOOST_CLASS_EXPORT(Derived)

BOOST_AUTO_TEST_SUITE(test_shared_from_this)

// This test passes
BOOST_AUTO_TEST_CASE(deserialize_pointer_Derived)
{
        std::stringstream ss;

        {
                // Create a vector of shared_ptr<Derived> containing an instance of shared_ptr<Derived> 
                std::vector<boost::shared_ptr<Derived>> vec_d;
                boost::shared_ptr<Derived> d(new Derived());
                d->m_base = 1;
                d->m_derived = 2;
                vec_d.push_back(d);
                d.reset();

                // Get a raw pointer to Derived
                Derived* raw_d = vec_d[0].get();

                // Verify base and derived members
                BOOST_CHECK(raw_d->m_base==1);
                BOOST_CHECK(raw_d->m_derived==2);

                // verify shared_from_this
                d = raw_d->SharedPtr();
                BOOST_CHECK(d == vec_d[0]);

                // Serialize the vector
                boost::archive::xml_oarchive oa(ss);
                oa & BOOST_SERIALIZATION_NVP(vec_d);
        }
        {
                // Deserialize it back into a vector of shared_ptr<Derived>
                std::vector<boost::shared_ptr<Derived>> vec_d;
                ss.seekg(0);
                boost::archive::xml_iarchive ia(ss);
                ia & BOOST_SERIALIZATION_NVP(vec_d);

                // Get a raw pointer to Derived
                Derived* raw_d = vec_d[0].get();

                // Verify base and derived members
                BOOST_CHECK(raw_d->m_base==1);
                BOOST_CHECK(raw_d->m_derived==2);

                // verify shared_from_this
                boost::shared_ptr<Derived> d = raw_d->SharedPtr();
                BOOST_CHECK(d == vec_d[0]);
        }
}

// This test fails
BOOST_AUTO_TEST_CASE(deserialize_vector_Base)
{
        std::stringstream ss;

        {
                // Create a vector of shared_ptr<Base> containing an instance of shared_ptr<Derived> 
                std::vector<boost::shared_ptr<Base>> vec_b;
                boost::shared_ptr<Derived> d(new Derived());
                d->m_base = 1;
                d->m_derived = 2;
                vec_b.push_back(d);
                d.reset();

                // Get a raw pointer to Derived via shared_ptr<Base>
                Derived* raw_d = static_cast<Derived*>(vec_b[0].get());

                // Verify base and derived members
                BOOST_CHECK(raw_d->m_base==1);
                BOOST_CHECK(raw_d->m_derived==2);

                // verify shared_from_this
                d = raw_d->SharedPtr();
                BOOST_CHECK(d == vec_b[0]);

                // Serialize the vector
                boost::archive::xml_oarchive oa(ss);
                oa & BOOST_SERIALIZATION_NVP(vec_b);
        }
        {
                // Deserialize it back into a vector of shared_ptr<Base>
                std::vector<boost::shared_ptr<Base>> vec_b;
                ss.seekg(0);
                boost::archive::xml_iarchive ia(ss);
                ia & BOOST_SERIALIZATION_NVP(vec_b);

                // Get a raw pointer to Derived via shared_ptr<Base>
                Derived* raw_d = static_cast<Derived*>(vec_b[0].get());
                // Verify base and derived members
                BOOST_CHECK(raw_d->m_base==1);
                BOOST_CHECK(raw_d->m_derived==2);

                // verify shared_from_this
                // FAIL: The following line throws bad_weak_ptr exception 
                boost::shared_ptr<Derived> d = raw_d->SharedPtr();
                BOOST_CHECK(d == vec_b[0]);
        }
}

BOOST_AUTO_TEST_SUITE_END()