libcxx/include/__atomic/memory_order.h

   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.
  25 enum __legacy_memory_order { __mo_relaxed, __mo_consume, __mo_acquire, __mo_release, __mo_acq_rel, __mo_seq_cst };
  26
  27 using __memory_order_underlying_t = underlying_type<__legacy_memory_order>::type;
  28
  29 #if _LIBCPP_STD_VER >= 20
  30
  31 enum 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
  40 static_assert(is_same<underlying_type<memory_order>::type, __memory_order_underlying_t>::value,
  41               "unexpected underlying type for std::memory_order");
  42
  43 inline constexpr auto memory_order_relaxed = memory_order::relaxed;
  44 inline constexpr auto memory_order_consume = memory_order::consume;
  45 inline constexpr auto memory_order_acquire = memory_order::acquire;
  46 inline constexpr auto memory_order_release = memory_order::release;
  47 inline constexpr auto memory_order_acq_rel = memory_order::acq_rel;
  48 inline constexpr auto memory_order_seq_cst = memory_order::seq_cst;
  49
  50 #else
  51
  52 enum 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