1//===----------------------------------------------------------------------===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8
9#ifndef _LIBCPP___ATOMIC_MEMORY_ORDER_H
10#define _LIBCPP___ATOMIC_MEMORY_ORDER_H
11
12#include <__config>
13#include <__type_traits/is_same.h>
14#include <__type_traits/underlying_type.h>
15
16#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
17#  pragma GCC system_header
18#endif
19
20_LIBCPP_BEGIN_NAMESPACE_STD
21
22// Figure out what the underlying type for `memory_order` would be if it were
23// declared as an unscoped enum (accounting for -fshort-enums). Use this result
24// to pin the underlying type in C++20.
25enum __legacy_memory_order { __mo_relaxed, __mo_consume, __mo_acquire, __mo_release, __mo_acq_rel, __mo_seq_cst };
26
27using __memory_order_underlying_t = underlying_type<__legacy_memory_order>::type;
28
29#if _LIBCPP_STD_VER >= 20
30
31enum class memory_order : __memory_order_underlying_t {
32  relaxed = __mo_relaxed,
33  consume = __mo_consume,
34  acquire = __mo_acquire,
35  release = __mo_release,
36  acq_rel = __mo_acq_rel,
37  seq_cst = __mo_seq_cst
38};
39
40static_assert((is_same<underlying_type<memory_order>::type, __memory_order_underlying_t>::value),
41              "unexpected underlying type for std::memory_order");
42
43inline constexpr auto memory_order_relaxed = memory_order::relaxed;
44inline constexpr auto memory_order_consume = memory_order::consume;
45inline constexpr auto memory_order_acquire = memory_order::acquire;
46inline constexpr auto memory_order_release = memory_order::release;
47inline constexpr auto memory_order_acq_rel = memory_order::acq_rel;
48inline constexpr auto memory_order_seq_cst = memory_order::seq_cst;
49
50#else
51
52enum memory_order {
53  memory_order_relaxed = __mo_relaxed,
54  memory_order_consume = __mo_consume,
55  memory_order_acquire = __mo_acquire,
56  memory_order_release = __mo_release,
57  memory_order_acq_rel = __mo_acq_rel,
58  memory_order_seq_cst = __mo_seq_cst,
59};
60
61#endif // _LIBCPP_STD_VER >= 20
62
63_LIBCPP_END_NAMESPACE_STD
64
65#endif // _LIBCPP___ATOMIC_MEMORY_ORDER_H
66