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 {
  26     __mo_relaxed,
  27     __mo_consume,
  28     __mo_acquire,
  29     __mo_release,
  30     __mo_acq_rel,
  31     __mo_seq_cst
  32 };
  33
  34 using __memory_order_underlying_t = underlying_type<__legacy_memory_order>::type;
  35
  36 #if _LIBCPP_STD_VER >= 20
  37
  38 enum class memory_order : __memory_order_underlying_t {
  39   relaxed = __mo_relaxed,
  40   consume = __mo_consume,
  41   acquire = __mo_acquire,
  42   release = __mo_release,
  43   acq_rel = __mo_acq_rel,
  44   seq_cst = __mo_seq_cst
  45 };
  46
  47 static_assert((is_same<underlying_type<memory_order>::type, __memory_order_underlying_t>::value),
  48   "unexpected underlying type for std::memory_order");
  49
  50 inline constexpr auto memory_order_relaxed = memory_order::relaxed;
  51 inline constexpr auto memory_order_consume = memory_order::consume;
  52 inline constexpr auto memory_order_acquire = memory_order::acquire;
  53 inline constexpr auto memory_order_release = memory_order::release;
  54 inline constexpr auto memory_order_acq_rel = memory_order::acq_rel;
  55 inline constexpr auto memory_order_seq_cst = memory_order::seq_cst;
  56
  57 #else
  58
  59 enum memory_order {
  60   memory_order_relaxed = __mo_relaxed,
  61   memory_order_consume = __mo_consume,
  62   memory_order_acquire = __mo_acquire,
  63   memory_order_release = __mo_release,
  64   memory_order_acq_rel = __mo_acq_rel,
  65   memory_order_seq_cst = __mo_seq_cst,
  66 };
  67
  68 #endif // _LIBCPP_STD_VER >= 20
  69
  70 _LIBCPP_END_NAMESPACE_STD
  71
  72 #endif // _LIBCPP___ATOMIC_MEMORY_ORDER_H