Boost C++ Libraries

boost/memory_order.hpp

#ifndef BOOST_MEMORY_ORDER_HPP_INCLUDED
#define BOOST_MEMORY_ORDER_HPP_INCLUDED

// MS compatible compilers support #pragma once

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

//  boost/memory_order.hpp
//
//  Defines enum boost::memory_order per the C++0x working draft
//
//  Copyright (c) 2008, 2009 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)


namespace boost
{

//
// Enum values are chosen so that code that needs to insert
// a trailing fence for acquire semantics can use a single
// test such as:
//
// if( mo & memory_order_acquire ) { ...fence... }
//
// For leading fences one can use:
//
// if( mo & memory_order_release ) { ...fence... }
//
// Architectures such as Alpha that need a fence on consume
// can use:
//
// if( mo & ( memory_order_acquire | memory_order_consume ) ) { ...fence... }
//
// The values are also in the order of increasing "strength"
// of the fences so that success/failure orders can be checked
// efficiently in compare_exchange methods.
//

enum memory_order
{
    memory_order_relaxed = 0,
    memory_order_consume = 1,
    memory_order_acquire = 2,
    memory_order_release = 4,
    memory_order_acq_rel = 6, // acquire | release
    memory_order_seq_cst = 14 // acq_rel | 8
};

} // namespace boost

#endif // #ifndef BOOST_MEMORY_ORDER_HPP_INCLUDED