[Boost-users] Serialization of boost::shared_ptr - wrong ref. count?

Subject: [Boost-users] Serialization of boost::shared_ptr - wrong ref. count?
From: Josef Uher (josef.uher_at_[hidden])
Date: 2015-04-13 04:49:06

Hi All,

I am using serialisation of boost::shared_ptr objects. Saving/loading works fine, except that I found out that all shared_ptr objects have reference count (use_count) minimum of 2 even though they should have 1!

Debugging into the boost’s code I found out that the ref. count is increased to value of 2 in “shared_ptr_helper.hpp”, line 181 where the pointer is stored inside map “m_o_sp”. This map however never gets deleted and hence the shared_ptr seems to be stored there for ever.

Please, am I doing something wrong or is there a bug? How to fix this?

The sample code I use is below. I would like to emphasise that I make sure the archives are deleted after being used. So it should release the resources.

I am using Mac OS X 10.10.2, boost version 1.57.0

Thank you for help,
Josef

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#include <boost/iostreams/device/file_descriptor.hpp>
#include <boost/iostreams/filtering_stream.hpp>
#include <boost/archive/xml_iarchive.hpp>
#include <boost/archive/xml_oarchive.hpp>
#include <boost/serialization/shared_ptr.hpp>
#include <boost/make_shared.hpp>

class SOBJ {
public:
    friend class boost::serialization::access;
    virtual void SerializationHelperFcn() {}
    SOBJ() {
        std::cout << "SOBJ Constructor" << std::endl;
    }

    virtual ~SOBJ() {
        std::cout << "SOBJ Destructor" << std::endl;
    }
    double value=0.;
    template<typename Archive> void serialize(Archive &ar, const unsigned int ver) {
        ar & boost::serialization::make_nvp("value", value);
    }
};

void shared_ptr_serialization_test() {
    boost::shared_ptr<SOBJ> out=boost::make_shared<SOBJ>();

    {
        boost::iostreams::filtering_ostream ofs;
        ofs.push(boost::iostreams::file_descriptor_sink("/Users/juhe/stest.xml"));
        boost::archive::xml_oarchive oa(ofs);
        oa << boost::serialization::make_nvp("tag", out);
    }

    boost::shared_ptr<SOBJ> in=nullptr;

    {
        boost::iostreams::filtering_istream ifs;
        ifs.push(boost::iostreams::file_descriptor_source("/Users/juhe/stest.xml"));
        boost::archive::xml_iarchive ia(ifs);
        ia >> boost::serialization::make_nvp("tag", in);
    }

    std::cout << "out.use_count()=" << out.use_count() << std::endl;
    std::cout << "in.use_count() =" << in.use_count() << std::endl;
}

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