[boost] Re: [shared_ptr] possible bug in sp_counted_base.hpp

14 Apr 2005


      Peter Dimov wrote:
...
Rene Rivera wrote:
...
I running the timing tests again, with some changes to see if I can
get more representative numbers.
If you can get the assembly version to outperform the generic Win32 
version, you mean ;-)
No.. just one that tests all three of the functions. The timing test you 
have only tests one of them.
...
But out of curiosity, what changes? I've been thinking to add a more 
representative shared_ptr and weak_ptr timing tests. The _mt versions 
aren't bad, though.
Well certainly an _mt timing test would be best. As it's not that useful 
to only time the non-contention cases.
...
...
...
//  detail/sp_counted_base_gcc_x86.hpp - g++ on 486+ or AMD64
You should probably fix this line...
...
...
//  Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd.
//  Copyright 2004-2005 Peter Dimov
... and add your name here.
Yes :-)


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#ifndef BOOST_DETAIL_SP_COUNTED_BASE_CW_X86_HPP_INCLUDED
#define BOOST_DETAIL_SP_COUNTED_BASE_CW_X86_HPP_INCLUDED

// MS compatible compilers support #pragma once

#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once
#endif

//
//  detail/sp_counted_base_cw_x86.hpp - CodeWarrion on 486+
//
//  Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd.
//  Copyright 2004-2005 Peter Dimov
//  Copyright 2005 Rene Rivera
//
//  Distributed under the Boost Software License, Version 1.0. (See
//  accompanying file LICENSE_1_0.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt)
//
//
//  Lock-free algorithm by Alexander Terekhov
//
//  Thanks to Ben Hitchings for the #weak + (#shared != 0)
//  formulation
//

#include <typeinfo>

namespace boost
{

namespace detail
{

inline int atomic_exchange_and_add( int * pw, int dv )
{
    // int r = *pw;
    // *pw += dv;
    // return r;

    asm
    {
        mov esi, [pw]
        mov eax, dv
        lock xadd dword ptr [esi], eax
    }
}

inline void atomic_increment( int * pw )
{
    //atomic_exchange_and_add( pw, 1 );

    asm
    {
        mov esi, [pw]
        lock inc dword ptr [esi]
    }
}

inline int atomic_conditional_increment( int * pw )
{
    // int rv = *pw;
    // if( rv != 0 ) ++*pw;
    // return rv;

    asm
    {
        mov esi, [pw]
        mov eax, dword ptr [esi]
    L0:
        test eax, eax
        je L1
        mov ebx, eax
        inc ebx
        lock cmpxchg dword ptr [esi], ebx
        jne L0
    L1:
    }
}

class sp_counted_base
{
private:

    sp_counted_base( sp_counted_base const & );
    sp_counted_base & operator= ( sp_counted_base const & );

    int use_count_;        // #shared
    int weak_count_;       // #weak + (#shared != 0)

public:

    sp_counted_base(): use_count_( 1 ), weak_count_( 1 )
    {
    }

    virtual ~sp_counted_base() // nothrow
    {
    }

    // dispose() is called when use_count_ drops to zero, to release
    // the resources managed by *this.

    virtual void dispose() = 0; // nothrow

    // destroy() is called when weak_count_ drops to zero.

    virtual void destroy() // nothrow
    {
        delete this;
    }

    virtual void * get_deleter( std::type_info const & ti ) = 0;

    void add_ref_copy()
    {
        atomic_increment( &use_count_ );
    }

    bool add_ref_lock() // true on success
    {
        return atomic_conditional_increment( &use_count_ ) != 0;
    }

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

    void weak_add_ref() // nothrow
    {
        atomic_increment( &weak_count_ );
    }

    void weak_release() // nothrow
    {
        if( atomic_exchange_and_add( &weak_count_, -1 ) == 1 )
        {
            destroy();
        }
    }

    long use_count() const // nothrow
    {
        return static_cast<int const volatile &>( use_count_ );
    }
};

} // namespace detail

} // namespace boost

#endif  // #ifndef BOOST_DETAIL_SP_COUNTED_BASE_GCC_X86_HPP_INCLUDED