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// boost/memory_order.hpp
//
// Defines enum boost::memory_order per the C++0x working draft
//
// Copyright (c) 2008, 2009 Peter Dimov
// Copyright (c) 2018, 2025 Andrey Semashev
//
// 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)
#ifndef BOOST_MEMORY_ORDER_HPP_INCLUDED
#define BOOST_MEMORY_ORDER_HPP_INCLUDED
#include <boost/config.hpp>
#if defined(BOOST_HAS_PRAGMA_ONCE)
#pragma once
#endif
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 class memory_order : unsigned int
{
relaxed = 0,
consume = 1,
acquire = 2,
release = 4,
acq_rel = 6, // acquire | release
seq_cst = 14 // acq_rel | 8
};
BOOST_INLINE_VARIABLE constexpr memory_order memory_order_relaxed = memory_order::relaxed;
BOOST_INLINE_VARIABLE constexpr memory_order memory_order_consume = memory_order::consume;
BOOST_INLINE_VARIABLE constexpr memory_order memory_order_acquire = memory_order::acquire;
BOOST_INLINE_VARIABLE constexpr memory_order memory_order_release = memory_order::release;
BOOST_INLINE_VARIABLE constexpr memory_order memory_order_acq_rel = memory_order::acq_rel;
BOOST_INLINE_VARIABLE constexpr memory_order memory_order_seq_cst = memory_order::seq_cst;
} // namespace boost
#endif // #ifndef BOOST_MEMORY_ORDER_HPP_INCLUDED
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