1 //  boost/memory_order.hpp
2 //
3 //  Defines enum boost::memory_order per the C++0x working draft
4 //
5 //  Copyright (c) 2008, 2009 Peter Dimov
6 //  Copyright (c) 2018 Andrey Semashev
7 //
8 //  Distributed under the Boost Software License, Version 1.0.
9 //  See accompanying file LICENSE_1_0.txt or copy at
10 //  http://www.boost.org/LICENSE_1_0.txt)
11 
12 #ifndef BOOST_MEMORY_ORDER_HPP_INCLUDED
13 #define BOOST_MEMORY_ORDER_HPP_INCLUDED
14 
15 #include <boost/config.hpp>
16 
17 #if defined(BOOST_HAS_PRAGMA_ONCE)
18 # pragma once
19 #endif
20 
21 namespace boost
22 {
23 
24 //
25 // Enum values are chosen so that code that needs to insert
26 // a trailing fence for acquire semantics can use a single
27 // test such as:
28 //
29 // if( mo & memory_order_acquire ) { ...fence... }
30 //
31 // For leading fences one can use:
32 //
33 // if( mo & memory_order_release ) { ...fence... }
34 //
35 // Architectures such as Alpha that need a fence on consume
36 // can use:
37 //
38 // if( mo & ( memory_order_acquire | memory_order_consume ) ) { ...fence... }
39 //
40 // The values are also in the order of increasing "strength"
41 // of the fences so that success/failure orders can be checked
42 // efficiently in compare_exchange methods.
43 //
44 
45 #if !defined(BOOST_NO_CXX11_SCOPED_ENUMS)
46 
47 enum class memory_order : unsigned int
48 {
49     relaxed = 0,
50     consume = 1,
51     acquire = 2,
52     release = 4,
53     acq_rel = 6, // acquire | release
54     seq_cst = 14 // acq_rel | 8
55 };
56 
57 #if !defined(BOOST_NO_CXX17_INLINE_VARIABLES)
58 #define BOOST_MEMORY_ORDER_INLINE_VARIABLE inline
59 #else
60 #define BOOST_MEMORY_ORDER_INLINE_VARIABLE
61 #endif
62 
63 BOOST_MEMORY_ORDER_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST memory_order memory_order_relaxed = memory_order::relaxed;
64 BOOST_MEMORY_ORDER_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST memory_order memory_order_consume = memory_order::consume;
65 BOOST_MEMORY_ORDER_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST memory_order memory_order_acquire = memory_order::acquire;
66 BOOST_MEMORY_ORDER_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST memory_order memory_order_release = memory_order::release;
67 BOOST_MEMORY_ORDER_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST memory_order memory_order_acq_rel = memory_order::acq_rel;
68 BOOST_MEMORY_ORDER_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST memory_order memory_order_seq_cst = memory_order::seq_cst;
69 
70 #undef BOOST_MEMORY_ORDER_INLINE_VARIABLE
71 
72 #else // !defined(BOOST_NO_CXX11_SCOPED_ENUMS)
73 
74 enum memory_order
75 {
76     memory_order_relaxed = 0,
77     memory_order_consume = 1,
78     memory_order_acquire = 2,
79     memory_order_release = 4,
80     memory_order_acq_rel = 6, // acquire | release
81     memory_order_seq_cst = 14 // acq_rel | 8
82 };
83 
84 #endif // !defined(BOOST_NO_CXX11_SCOPED_ENUMS)
85 
86 } // namespace boost
87 
88 #endif // #ifndef BOOST_MEMORY_ORDER_HPP_INCLUDED
89