ceph/src/boost/boost/asio/associated_executor.hpp

   1 //
   2 // associated_executor.hpp
   3 // ~~~~~~~~~~~~~~~~~~~~~~~
   4 //
   5 // Copyright (c) 2003-2020 Christopher M. Kohlhoff (chris at kohlhoff dot com)
   6 //
   7 // Distributed under the Boost Software License, Version 1.0. (See accompanying
   8 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   9 //
  10
  11 #ifndef BOOST_ASIO_ASSOCIATED_EXECUTOR_HPP
  12 #define BOOST_ASIO_ASSOCIATED_EXECUTOR_HPP
  13
  14 #if defined(_MSC_VER) && (_MSC_VER >= 1200)
  15 # pragma once
  16 #endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
  17
  18 #include <boost/asio/detail/config.hpp>
  19 #include <boost/asio/detail/type_traits.hpp>
  20 #include <boost/asio/execution/executor.hpp>
  21 #include <boost/asio/is_executor.hpp>
  22 #include <boost/asio/system_executor.hpp>
  23
  24 #include <boost/asio/detail/push_options.hpp>
  25
  26 namespace boost {
  27 namespace asio {
  28 namespace detail {
  29
  30 template <typename T, typename E, typename = void>
  31 struct associated_executor_impl
  32 {
  33   typedef void asio_associated_executor_is_unspecialised;
  34
  35   typedef E type;
  36
  37   static type get(const T&, const E& e = E()) BOOST_ASIO_NOEXCEPT
  38   {
  39     return e;
  40   }
  41 };
  42
  43 template <typename T, typename E>
  44 struct associated_executor_impl<T, E,
  45   typename void_type<typename T::executor_type>::type>
  46 {
  47   typedef typename T::executor_type type;
  48
  49   static type get(const T& t, const E& = E()) BOOST_ASIO_NOEXCEPT
  50   {
  51     return t.get_executor();
  52   }
  53 };
  54
  55 } // namespace detail
  56
  57 /// Traits type used to obtain the executor associated with an object.
  58 /**
  59  * A program may specialise this traits type if the @c T template parameter in
  60  * the specialisation is a user-defined type. The template parameter @c
  61  * Executor shall be a type meeting the Executor requirements.
  62  *
  63  * Specialisations shall meet the following requirements, where @c t is a const
  64  * reference to an object of type @c T, and @c e is an object of type @c
  65  * Executor.
  66  *
  67  * @li Provide a nested typedef @c type that identifies a type meeting the
  68  * Executor requirements.
  69  *
  70  * @li Provide a noexcept static member function named @c get, callable as @c
  71  * get(t) and with return type @c type.
  72  *
  73  * @li Provide a noexcept static member function named @c get, callable as @c
  74  * get(t,e) and with return type @c type.
  75  */
  76 template <typename T, typename Executor = system_executor>
  77 struct associated_executor
  78 #if !defined(GENERATING_DOCUMENTATION)
  79   : detail::associated_executor_impl<T, Executor>
  80 #endif // !defined(GENERATING_DOCUMENTATION)
  81 {
  82 #if defined(GENERATING_DOCUMENTATION)
  83   /// If @c T has a nested type @c executor_type, <tt>T::executor_type</tt>.
  84   /// Otherwise @c Executor.
  85   typedef see_below type;
  86
  87   /// If @c T has a nested type @c executor_type, returns
  88   /// <tt>t.get_executor()</tt>. Otherwise returns @c ex.
  89   static type get(const T& t,
  90       const Executor& ex = Executor()) BOOST_ASIO_NOEXCEPT;
  91 #endif // defined(GENERATING_DOCUMENTATION)
  92 };
  93
  94 /// Helper function to obtain an object's associated executor.
  95 /**
  96  * @returns <tt>associated_executor<T>::get(t)</tt>
  97  */
  98 template <typename T>
  99 inline typename associated_executor<T>::type
 100 get_associated_executor(const T& t) BOOST_ASIO_NOEXCEPT
 101 {
 102   return associated_executor<T>::get(t);
 103 }
 104
 105 /// Helper function to obtain an object's associated executor.
 106 /**
 107  * @returns <tt>associated_executor<T, Executor>::get(t, ex)</tt>
 108  */
 109 template <typename T, typename Executor>
 110 inline typename associated_executor<T, Executor>::type
 111 get_associated_executor(const T& t, const Executor& ex,
 112     typename enable_if<
 113       is_executor<Executor>::value || execution::is_executor<Executor>::value
 114     >::type* = 0) BOOST_ASIO_NOEXCEPT
 115 {
 116   return associated_executor<T, Executor>::get(t, ex);
 117 }
 118
 119 /// Helper function to obtain an object's associated executor.
 120 /**
 121  * @returns <tt>associated_executor<T, typename
 122  * ExecutionContext::executor_type>::get(t, ctx.get_executor())</tt>
 123  */
 124 template <typename T, typename ExecutionContext>
 125 inline typename associated_executor<T,
 126   typename ExecutionContext::executor_type>::type
 127 get_associated_executor(const T& t, ExecutionContext& ctx,
 128     typename enable_if<is_convertible<ExecutionContext&,
 129       execution_context&>::value>::type* = 0) BOOST_ASIO_NOEXCEPT
 130 {
 131   return associated_executor<T,
 132     typename ExecutionContext::executor_type>::get(t, ctx.get_executor());
 133 }
 134
 135 #if defined(BOOST_ASIO_HAS_ALIAS_TEMPLATES)
 136
 137 template <typename T, typename Executor = system_executor>
 138 using associated_executor_t = typename associated_executor<T, Executor>::type;
 139
 140 #endif // defined(BOOST_ASIO_HAS_ALIAS_TEMPLATES)
 141
 142 namespace detail {
 143
 144 template <typename T, typename E, typename = void>
 145 struct associated_executor_forwarding_base
 146 {
 147 };
 148
 149 template <typename T, typename E>
 150 struct associated_executor_forwarding_base<T, E,
 151     typename enable_if<
 152       is_same<
 153         typename associated_executor<T,
 154           E>::asio_associated_executor_is_unspecialised,
 155         void
 156       >::value
 157     >::type>
 158 {
 159   typedef void asio_associated_executor_is_unspecialised;
 160 };
 161
 162 } // namespace detail
 163 } // namespace asio
 164 } // namespace boost
 165
 166 #include <boost/asio/detail/pop_options.hpp>
 167
 168 #endif // BOOST_ASIO_ASSOCIATED_EXECUTOR_HPP