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
>
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