1 //
2 // execution/execute.hpp
3 // ~~~~~~~~~~~~~~~~~~~~~
4 //
5 // Copyright (c) 2003-2021 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_EXECUTION_EXECUTE_HPP
12 #define BOOST_ASIO_EXECUTION_EXECUTE_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/detail/as_invocable.hpp>
21 #include <boost/asio/execution/detail/as_receiver.hpp>
22 #include <boost/asio/traits/execute_member.hpp>
23 #include <boost/asio/traits/execute_free.hpp>
24 
25 #include <boost/asio/detail/push_options.hpp>
26 
27 #if defined(GENERATING_DOCUMENTATION)
28 
29 namespace boost {
30 namespace asio {
31 namespace execution {
32 
33 /// A customisation point that executes a function on an executor.
34 /**
35  * The name <tt>execution::execute</tt> denotes a customisation point object.
36  *
37  * For some subexpressions <tt>e</tt> and <tt>f</tt>, let <tt>E</tt> be a type
38  * such that <tt>decltype((e))</tt> is <tt>E</tt> and let <tt>F</tt> be a type
39  * such that <tt>decltype((f))</tt> is <tt>F</tt>. The expression
40  * <tt>execution::execute(e, f)</tt> is ill-formed if <tt>F</tt> does not model
41  * <tt>invocable</tt>, or if <tt>E</tt> does not model either <tt>executor</tt>
42  * or <tt>sender</tt>. Otherwise, it is expression-equivalent to:
43  *
44  * @li <tt>e.execute(f)</tt>, if that expression is valid. If the function
45  *   selected does not execute the function object <tt>f</tt> on the executor
46  *   <tt>e</tt>, the program is ill-formed with no diagnostic required.
47  *
48  * @li Otherwise, <tt>execute(e, f)</tt>, if that expression is valid, with
49  *   overload resolution performed in a context that includes the declaration
50  *   <tt>void execute();</tt> and that does not include a declaration of
51  *   <tt>execution::execute</tt>. If the function selected by overload
52  *   resolution does not execute the function object <tt>f</tt> on the executor
53  *   <tt>e</tt>, the program is ill-formed with no diagnostic required.
54  */
55 inline constexpr unspecified execute = unspecified;
56 
57 /// A type trait that determines whether a @c execute expression is well-formed.
58 /**
59  * Class template @c can_execute is a trait that is derived from
60  * @c true_type if the expression <tt>execution::execute(std::declval<T>(),
61  * std::declval<F>())</tt> is well formed; otherwise @c false_type.
62  */
63 template <typename T, typename F>
64 struct can_execute :
65   integral_constant<bool, automatically_determined>
66 {
67 };
68 
69 } // namespace execution
70 } // namespace asio
71 } // namespace boost
72 
73 #else // defined(GENERATING_DOCUMENTATION)
74 
75 namespace boost {
76 namespace asio {
77 namespace execution {
78 
79 template <typename T, typename R>
80 struct is_sender_to;
81 
82 namespace detail {
83 
84 template <typename S, typename R>
85 void submit_helper(BOOST_ASIO_MOVE_ARG(S) s, BOOST_ASIO_MOVE_ARG(R) r);
86 
87 } // namespace detail
88 } // namespace execution
89 } // namespace asio
90 } // namespace boost
91 namespace asio_execution_execute_fn {
92 
93 using boost::asio::conditional;
94 using boost::asio::decay;
95 using boost::asio::declval;
96 using boost::asio::enable_if;
97 using boost::asio::execution::detail::as_receiver;
98 using boost::asio::execution::detail::is_as_invocable;
99 using boost::asio::execution::is_sender_to;
100 using boost::asio::false_type;
101 using boost::asio::result_of;
102 using boost::asio::traits::execute_free;
103 using boost::asio::traits::execute_member;
104 using boost::asio::true_type;
105 using boost::asio::void_type;
106 
107 void execute();
108 
109 enum overload_type
110 {
111   call_member,
112   call_free,
113   adapter,
114   ill_formed
115 };
116 
117 template <typename Impl, typename T, typename F, typename = void,
118     typename = void, typename = void, typename = void, typename = void>
119 struct call_traits
120 {
121   BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = ill_formed);
122 };
123 
124 template <typename Impl, typename T, typename F>
125 struct call_traits<Impl, T, void(F),
126   typename enable_if<
127     execute_member<typename Impl::template proxy<T>::type, F>::is_valid
128   >::type> :
129   execute_member<typename Impl::template proxy<T>::type, F>
130 {
131   BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_member);
132 };
133 
134 template <typename Impl, typename T, typename F>
135 struct call_traits<Impl, T, void(F),
136   typename enable_if<
137     !execute_member<typename Impl::template proxy<T>, F>::is_valid
138   >::type,
139   typename enable_if<
140     execute_free<T, F>::is_valid
141   >::type> :
142   execute_free<T, F>
143 {
144   BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = call_free);
145 };
146 
147 template <typename Impl, typename T, typename F>
148 struct call_traits<Impl, T, void(F),
149   typename enable_if<
150     !execute_member<typename Impl::template proxy<T>::type, F>::is_valid
151   >::type,
152   typename enable_if<
153     !execute_free<T, F>::is_valid
154   >::type,
155   typename void_type<
156    typename result_of<typename decay<F>::type&()>::type
157   >::type,
158   typename enable_if<
159     !is_as_invocable<typename decay<F>::type>::value
160   >::type,
161   typename enable_if<
162     is_sender_to<T, as_receiver<typename decay<F>::type, T> >::value
163   >::type>
164 {
165   BOOST_ASIO_STATIC_CONSTEXPR(overload_type, overload = adapter);
166   BOOST_ASIO_STATIC_CONSTEXPR(bool, is_valid = true);
167   BOOST_ASIO_STATIC_CONSTEXPR(bool, is_noexcept = false);
168   typedef void result_type;
169 };
170 
171 struct impl
172 {
173   template <typename T>
174   struct proxy
175   {
176 #if defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
177     struct type
178     {
179       template <typename F>
180       auto execute(BOOST_ASIO_MOVE_ARG(F) f)
181         noexcept(
182           noexcept(
183             declval<typename conditional<true, T, F>::type>().execute(
184               BOOST_ASIO_MOVE_CAST(F)(f))
185           )
186         )
187         -> decltype(
188           declval<typename conditional<true, T, F>::type>().execute(
189             BOOST_ASIO_MOVE_CAST(F)(f))
190         );
191     };
192 #else // defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
193     typedef T type;
194 #endif // defined(BOOST_ASIO_HAS_DEDUCED_EXECUTE_MEMBER_TRAIT)
195   };
196 
197   template <typename T, typename F>
198   BOOST_ASIO_CONSTEXPR typename enable_if<
199     call_traits<impl, T, void(F)>::overload == call_member,
200     typename call_traits<impl, T, void(F)>::result_type
201   >::type
operator ()asio_execution_execute_fn::impl202   operator()(
203       BOOST_ASIO_MOVE_ARG(T) t,
204       BOOST_ASIO_MOVE_ARG(F) f) const
205     BOOST_ASIO_NOEXCEPT_IF((
206       call_traits<impl, T, void(F)>::is_noexcept))
207   {
208     return BOOST_ASIO_MOVE_CAST(T)(t).execute(BOOST_ASIO_MOVE_CAST(F)(f));
209   }
210 
211   template <typename T, typename F>
212   BOOST_ASIO_CONSTEXPR typename enable_if<
213     call_traits<impl, T, void(F)>::overload == call_free,
214     typename call_traits<impl, T, void(F)>::result_type
215   >::type
operator ()asio_execution_execute_fn::impl216   operator()(
217       BOOST_ASIO_MOVE_ARG(T) t,
218       BOOST_ASIO_MOVE_ARG(F) f) const
219     BOOST_ASIO_NOEXCEPT_IF((
220       call_traits<impl, T, void(F)>::is_noexcept))
221   {
222     return execute(BOOST_ASIO_MOVE_CAST(T)(t), BOOST_ASIO_MOVE_CAST(F)(f));
223   }
224 
225   template <typename T, typename F>
226   BOOST_ASIO_CONSTEXPR typename enable_if<
227     call_traits<impl, T, void(F)>::overload == adapter,
228     typename call_traits<impl, T, void(F)>::result_type
229   >::type
operator ()asio_execution_execute_fn::impl230   operator()(
231       BOOST_ASIO_MOVE_ARG(T) t,
232       BOOST_ASIO_MOVE_ARG(F) f) const
233     BOOST_ASIO_NOEXCEPT_IF((
234       call_traits<impl, T, void(F)>::is_noexcept))
235   {
236     return boost::asio::execution::detail::submit_helper(
237         BOOST_ASIO_MOVE_CAST(T)(t),
238         as_receiver<typename decay<F>::type, T>(
239           BOOST_ASIO_MOVE_CAST(F)(f), 0));
240   }
241 };
242 
243 template <typename T = impl>
244 struct static_instance
245 {
246   static const T instance;
247 };
248 
249 template <typename T>
250 const T static_instance<T>::instance = {};
251 
252 } // namespace asio_execution_execute_fn
253 namespace boost {
254 namespace asio {
255 namespace execution {
256 namespace {
257 
258 static BOOST_ASIO_CONSTEXPR const asio_execution_execute_fn::impl&
259   execute = asio_execution_execute_fn::static_instance<>::instance;
260 
261 } // namespace
262 
263 typedef asio_execution_execute_fn::impl execute_t;
264 
265 template <typename T, typename F>
266 struct can_execute :
267   integral_constant<bool,
268     asio_execution_execute_fn::call_traits<
269       execute_t, T, void(F)>::overload !=
270         asio_execution_execute_fn::ill_formed>
271 {
272 };
273 
274 #if defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
275 
276 template <typename T, typename F>
277 constexpr bool can_execute_v = can_execute<T, F>::value;
278 
279 #endif // defined(BOOST_ASIO_HAS_VARIABLE_TEMPLATES)
280 
281 } // namespace execution
282 } // namespace asio
283 } // namespace boost
284 
285 #endif // defined(GENERATING_DOCUMENTATION)
286 
287 #include <boost/asio/detail/pop_options.hpp>
288 
289 #endif // BOOST_ASIO_EXECUTION_EXECUTE_HPP
290