[Boost-users] Best way to create a class using the singleton pattern and shared pointers?

From: Stephen Torri (storri_at_[hidden])
Date: 2007-05-16 18:52:24

Here is a function that I am trying to understand why its giving me a
error via valgrind of "Invalid read of size 4".

16:    Trace_State::ptr_t Trace_State::Instance()
17:    {
18:        // Lock the resource?
19:        if ( m_instance.get() == 0 )
20:            {
21:                m_instance = Trace_State::ptr_t ( new
Trace_State() );
22:            }
23:        
24:        // Unlock the resource?
25:        
26:        return m_instance;
27:    }

When I look at the full error report I see:

==10721== Invalid read of size 4
==10721==    at 0x41682E3: boost::detail::atomic_increment(int*) (sp_counted_base_gcc_x86.hpp:66)
==10721==    by 0x4168359: boost::detail::sp_counted_base::add_ref_copy() (sp_counted_base_gcc_x86.hpp:133)
==10721==    by 0x41684B1: boost::detail::shared_count::shared_count(boost::detail::shared_count const&) (shared_count.hpp:170)
==10721==    by 0x41775CF: boost::shared_ptr<libreverse::trace::Trace_State>::shared_ptr(boost::shared_ptr<libreverse::trace::Trace_State> const&) (shared_ptr.hpp:106)
==10721==    by 0x41772F0: libreverse::trace::Trace_State::Instance() (Trace.cpp:26)
==10721==    by 0x417731B: libreverse::trace::Trace::write_Trace(unsigned, std::string) (Trace.cpp:180)
==10721==    by 0x425E394: libreverse::elf_module::Elf_Reader<32>::~Elf_Reader() (Elf_Reader_T.cpp:52)
==10721==    by 0x423C8FD: void boost::checked_delete<libreverse::elf_module::Elf_Reader<32> >(libreverse::elf_module::Elf_Reader<32>*) (checked_delete.hpp:34)
==10721==    by 0x42480B8: boost::detail::sp_counted_impl_p<libreverse::elf_module::Elf_Reader<32> >::dispose() (sp_counted_impl.hpp:76)
==10721==    by 0x804C207: boost::detail::sp_counted_base::release() (sp_counted_base_gcc_x86.hpp:145)
==10721==    by 0x804C231: boost::detail::shared_count::~shared_count() (shared_count.hpp:159)
==10721==    by 0x423C171: boost::shared_ptr<libreverse::io::File_Reader>::~shared_ptr() (shared_ptr.hpp:106)
==10721==  Address 0x43F7A44 is 12 bytes inside a block of size 24 free'd
==10721==    at 0x40050FF: free (vg_replace_malloc.c:233)
==10721==    by 0x4185AC5: operator delete(void*) (sp_debug_hooks.cpp:205)
==10721==    by 0x417C9A4: boost::detail::sp_counted_impl_p<libreverse::trace::Trace_State>::~sp_counted_impl_p() (sp_counted_impl.hpp:52)
==10721==    by 0x4168337: boost::detail::sp_counted_base::destroy() (sp_counted_base_gcc_x86.hpp:126)
==10721==    by 0x804C1CD: boost::detail::sp_counted_base::weak_release() (sp_counted_base_gcc_x86.hpp:159)
==10721==    by 0x804C212: boost::detail::sp_counted_base::release() (sp_counted_base_gcc_x86.hpp:146)
==10721==    by 0x804C231: boost::detail::shared_count::~shared_count() (shared_count.hpp:159)
==10721==    by 0x4168EBB: boost::shared_ptr<libreverse::trace::Trace_State>::~shared_ptr() (shared_ptr.hpp:106)
==10721==    by 0x4176711: __tcf_1 (Trace.cpp:14)
==10721==    by 0x47BDCBE8: __cxa_finalize (in /lib/libc-2.5.so)
==10721==    by 0x4167192: (within /usr/local/lib/libreverse.so.0.0.0)
==10721==    by 0x429EE3B: (within /usr/local/lib/libreverse.so.0.0.0)
==10721==

The error is coming when the return of the Trace boost shared ptr. I am
wondering if I have made an error in the creation of the class. Here is
how the class is defined:

#ifndef LIBREVERSE_TRACE_H
#define LIBREVERSE_TRACE_H

#include <boost/cstdint.hpp>
#include <boost/shared_ptr.hpp>
#include <fstream>
#include "Reverse.h"

namespace libreverse { namespace trace {

    /* Idea taken from http://www.codeproject.com/debug/xytrace.asp
     * (28 Jan 2002 - Xiangyang Liu)
     *
     * I have modified this so that we don't use varargs and use constant types
     */
    class Trace_State {
    public:

        typedef boost::shared_ptr<Trace_State> ptr_t;

        virtual ~Trace_State();

        static Trace_State::ptr_t Instance();

        void set_Trace_File_Prefix ( std::string name );

        void set_Trace_Level ( boost::uint32_t level );

        void open_Trace_File ( void );

        std::string get_ID_String ( void );

        void close_Trace_File ( void );

        boost::uint32_t get_Trace_Level ( void ) const;

        void write_Message ( boost::uint32_t level, std::string msg );

    private:

        Trace_State();

        static Trace_State::ptr_t m_instance;
        
        std::string m_file_prefix;

        boost::uint32_t m_trace_level;

        //boost::recursive_mutex m_mutex;

        std::ofstream m_log_stream;
    };

    class Trace {
    public:

        static bool write_Trace ( boost::uint32_t level,
                                  std::string message );
    };

} /* namespace trace */
} /* namespace libreverse */

#endif /* LIBREVERSE_TRACE_H */

Is this an appropriate way to create a class using the singleton
pattern? Is the constructor assigning the boost shared_ptr?

Stephen