sp_counted_base_gcc_x86.hpp

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#ifndef BOOST_SMART_PTR_DETAIL_SP_COUNTED_BASE_GCC_X86_HPP_INCLUDED
#define BOOST_SMART_PTR_DETAIL_SP_COUNTED_BASE_GCC_X86_HPP_INCLUDED
 
// MS compatible compilers support #pragma once
 
#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once
#endif
 
//
//  detail/sp_counted_base_gcc_x86.hpp - g++ on 486+ or AMD64
//
//  Copyright (c) 2001, 2002, 2003 Peter Dimov and Multi Media Ltd.
//  Copyright 2004-2005 Peter Dimov
//
//  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 <boost/detail/sp_typeinfo.hpp>
 
namespace boost
{
 
namespace detail
{
 
inline int atomic_exchange_and_add( int * pw, int dv )
{
    // int r = *pw;
    // *pw += dv;
    // return r;
 
    int r;
 
    __asm__ __volatile__
    (
        "lock\n\t"
        "xadd %1, %0":
        "=m"( *pw ), "=r"( r ): // outputs (%0, %1)
        "m"( *pw ), "1"( dv ): // inputs (%2, %3 == %1)
        "memory", "cc" // clobbers
    );
 
    return r;
}
 
inline void atomic_increment( int * pw )
{
    //atomic_exchange_and_add( pw, 1 );
 
    __asm__
    (
        "lock\n\t"
        "incl %0":
        "=m"( *pw ): // output (%0)
        "m"( *pw ): // input (%1)
        "cc" // clobbers
    );
}
 
inline int atomic_conditional_increment( int * pw )
{
    // int rv = *pw;
    // if( rv != 0 ) ++*pw;
    // return rv;
 
    int rv, tmp;
 
    __asm__
    (
        "movl %0, %%eax\n\t"
        "0:\n\t"
        "test %%eax, %%eax\n\t"
        "je 1f\n\t"
        "movl %%eax, %2\n\t"
        "incl %2\n\t"
        "lock\n\t"
        "cmpxchgl %2, %0\n\t"
        "jne 0b\n\t"
        "1:":
        "=m"( *pw ), "=&a"( rv ), "=&r"( tmp ): // outputs (%0, %1, %2)
        "m"( *pw ): // input (%3)
        "cc" // clobbers
    );
 
    return rv;
}
 
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( sp_typeinfo const & ti ) = 0;
    virtual void * get_untyped_deleter() = 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_SMART_PTR_DETAIL_SP_COUNTED_BASE_GCC_X86_HPP_INCLUDED