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

From: Rene Rivera (grafik.list_at_[hidden])
Date: 2005-04-14 15:21:34

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