Re: [Boost-users] Best way to create a class using the singletonpattern and shared pointers?

From: Hughes, James (jhughes_at_[hidden])
Date: 2007-05-17 05:16:01

> -----Original Message-----
> From: boost-users-bounces_at_[hidden] 
> [mailto:boost-users-bounces_at_[hidden]] On Behalf Of 
> Stephen Torri
> Sent: 16 May 2007 23:52
> To: boost-users
> Subject: [Boost-users] Best way to create a class using the 
> singletonpattern and shared pointers?
> 
> 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::share
> d_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_R
> eader<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_Stat
> e>::~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

Sorry, I don't have an answer to your specific question, but why would
you need to use a shared_ptr on a singleton anyway? You have no real
need to deallocate a singleton instance, so no need for a
shared_ptr....perhaps use a reference (See Meyers singletons)

Oh, hold on a sec....is it valid to call get() on an unassigned
shared_ptr, which you are doing in the instance function?

James

> 
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
> http://lists.boost.org/mailman/listinfo.cgi/boost-users
> 

This message (including any attachments) contains confidential 
and/or proprietary information intended only for the addressee.  
Any unauthorized disclosure, copying, distribution or reliance on 
the contents of this information is strictly prohibited and may 
constitute a violation of law.  If you are not the intended 
recipient, please notify the sender immediately by responding to 
this e-mail, and delete the message from your system.  If you 
have any questions about this e-mail please notify the sender 
immediately.