id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
4415,"Posible ""Segmentation Fault"" in shared_ptr destructor",Takenori Sato <takenori.sato@…>,Peter Dimov,"Hi, 

I got Segmentation Fault as follows, and found a possible bug. 


{{{
Program terminated with signal 11, Segmentation fault.
#0  0x0000000000401227 in boost::detail::atomic_exchange_and_add (pw=Cannot access memory at address 0x7fff2ee2dff8
)
    at /home/takenori/workspace_native/Boost/boost/smart_ptr/detail/sp_counted_base_gcc_x86.hpp:36
36      {
(gdb) bt
#0  0x0000000000401227 in boost::detail::atomic_exchange_and_add (pw=Cannot access memory at address 0x7fff2ee2dff8
)
    at /home/takenori/workspace_native/Boost/boost/smart_ptr/detail/sp_counted_base_gcc_x86.hpp:36
#1  0x000000000040137b in boost::detail::sp_counted_base::release (
    this=0xd921130)
    at /home/takenori/workspace_native/Boost/boost/smart_ptr/detail/sp_counted_base_gcc_x86.hpp:143
#2  0x000000000040142b in boost::detail::shared_count::~shared_count (
    this=0xd9210c0, __in_chrg=<value optimized out>)
    at /home/takenori/workspace_native/Boost/boost/smart_ptr/detail/shared_count.hpp:217
#3  0x00000000004014be in boost::shared_ptr<SPIntSLLNode>::~shared_ptr (
    this=0xd9210b8, __in_chrg=<value optimized out>)
    at /home/takenori/workspace_native/Boost/boost/smart_ptr/shared_ptr.hpp:163
}}}

Here's I doubt. 

{{{
    ~shared_count() // nothrow
    {
        if( pi_ != 0 ) pi_->release();
#if defined(BOOST_SP_ENABLE_DEBUG_HOOKS)
        id_ = 0;
#endif
    }
}}}

sp_count_base

{{{
    void release() // nothrow
    {
        if( atomic_exchange_and_add( &use_count_, -1 ) == 1 )
        {
            dispose();
            weak_release();
        }
    }
}}}


The two last threads can enter release(), the latter encounters Segmentation Fault on &use_count_. 

Fairly large singly linked list with shared_ptr easily reproduce this issue at its destruction.

Cheers, 
Takenori ",Bugs,closed,Boost 1.44.0,smart_ptr,Boost 1.44.0,Problem,invalid,,