boost/asio/associated_immediate_executor.hpp
// // associated_immediate_executor.hpp // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ // // Copyright (c) 2003-2024 Christopher M. Kohlhoff (chris at kohlhoff dot com) // // Distributed under the Boost Software License, Version 1.0. (See accompanying // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) // #ifndef BOOST_ASIO_ASSOCIATED_IMMEDIATE_EXECUTOR_HPP #define BOOST_ASIO_ASSOCIATED_IMMEDIATE_EXECUTOR_HPP #if defined(_MSC_VER) && (_MSC_VER >= 1200) # pragma once #endif // defined(_MSC_VER) && (_MSC_VER >= 1200) #include <boost/asio/detail/config.hpp> #include <boost/asio/associator.hpp> #include <boost/asio/detail/functional.hpp> #include <boost/asio/detail/type_traits.hpp> #include <boost/asio/execution/blocking.hpp> #include <boost/asio/execution/executor.hpp> #include <boost/asio/execution_context.hpp> #include <boost/asio/is_executor.hpp> #include <boost/asio/require.hpp> #include <boost/asio/detail/push_options.hpp> namespace boost { namespace asio { template <typename T, typename Executor> struct associated_immediate_executor; namespace detail { template <typename T, typename = void> struct has_immediate_executor_type : false_type { }; template <typename T> struct has_immediate_executor_type<T, void_t<typename T::immediate_executor_type>> : true_type { }; template <typename E, typename = void, typename = void> struct default_immediate_executor { typedef decay_t<require_result_t<E, execution::blocking_t::never_t>> type; static auto get(const E& e) noexcept -> decltype(boost::asio::require(e, execution::blocking.never)) { return boost::asio::require(e, execution::blocking.never); } }; template <typename E> struct default_immediate_executor<E, enable_if_t< !execution::is_executor<E>::value >, enable_if_t< is_executor<E>::value >> { class type : public E { public: template <typename Executor1> explicit type(const Executor1& e, constraint_t< conditional_t< !is_same<Executor1, type>::value, is_convertible<Executor1, E>, false_type >::value > = 0) noexcept : E(e) { } type(const type& other) noexcept : E(static_cast<const E&>(other)) { } type(type&& other) noexcept : E(static_cast<E&&>(other)) { } template <typename Function, typename Allocator> void dispatch(Function&& f, const Allocator& a) const { this->post(static_cast<Function&&>(f), a); } friend bool operator==(const type& a, const type& b) noexcept { return static_cast<const E&>(a) == static_cast<const E&>(b); } friend bool operator!=(const type& a, const type& b) noexcept { return static_cast<const E&>(a) != static_cast<const E&>(b); } }; static type get(const E& e) noexcept { return type(e); } }; template <typename T, typename E, typename = void, typename = void> struct associated_immediate_executor_impl { typedef void asio_associated_immediate_executor_is_unspecialised; typedef typename default_immediate_executor<E>::type type; static auto get(const T&, const E& e) noexcept -> decltype(default_immediate_executor<E>::get(e)) { return default_immediate_executor<E>::get(e); } }; template <typename T, typename E> struct associated_immediate_executor_impl<T, E, void_t<typename T::immediate_executor_type>> { typedef typename T::immediate_executor_type type; static auto get(const T& t, const E&) noexcept -> decltype(t.get_immediate_executor()) { return t.get_immediate_executor(); } }; template <typename T, typename E> struct associated_immediate_executor_impl<T, E, enable_if_t< !has_immediate_executor_type<T>::value >, void_t< typename associator<associated_immediate_executor, T, E>::type >> : associator<associated_immediate_executor, T, E> { }; } // namespace detail /// Traits type used to obtain the immediate executor associated with an object. /** * A program may specialise this traits type if the @c T template parameter in * the specialisation is a user-defined type. The template parameter @c * Executor shall be a type meeting the Executor requirements. * * Specialisations shall meet the following requirements, where @c t is a const * reference to an object of type @c T, and @c e is an object of type @c * Executor. * * @li Provide a nested typedef @c type that identifies a type meeting the * Executor requirements. * * @li Provide a noexcept static member function named @c get, callable as @c * get(t) and with return type @c type or a (possibly const) reference to @c * type. * * @li Provide a noexcept static member function named @c get, callable as @c * get(t,e) and with return type @c type or a (possibly const) reference to @c * type. */ template <typename T, typename Executor> struct associated_immediate_executor #if !defined(GENERATING_DOCUMENTATION) : detail::associated_immediate_executor_impl<T, Executor> #endif // !defined(GENERATING_DOCUMENTATION) { #if defined(GENERATING_DOCUMENTATION) /// If @c T has a nested type @c immediate_executor_type, // <tt>T::immediate_executor_type</tt>. Otherwise @c Executor. typedef see_below type; /// If @c T has a nested type @c immediate_executor_type, returns /// <tt>t.get_immediate_executor()</tt>. Otherwise returns /// <tt>boost::asio::require(ex, boost::asio::execution::blocking.never)</tt>. static decltype(auto) get(const T& t, const Executor& ex) noexcept; #endif // defined(GENERATING_DOCUMENTATION) }; /// Helper function to obtain an object's associated executor. /** * @returns <tt>associated_immediate_executor<T, Executor>::get(t, ex)</tt> */ template <typename T, typename Executor> BOOST_ASIO_NODISCARD inline auto get_associated_immediate_executor( const T& t, const Executor& ex, constraint_t< is_executor<Executor>::value || execution::is_executor<Executor>::value > = 0) noexcept -> decltype(associated_immediate_executor<T, Executor>::get(t, ex)) { return associated_immediate_executor<T, Executor>::get(t, ex); } /// Helper function to obtain an object's associated executor. /** * @returns <tt>associated_immediate_executor<T, typename * ExecutionContext::executor_type>::get(t, ctx.get_executor())</tt> */ template <typename T, typename ExecutionContext> BOOST_ASIO_NODISCARD inline typename associated_immediate_executor<T, typename ExecutionContext::executor_type>::type get_associated_immediate_executor(const T& t, ExecutionContext& ctx, constraint_t< is_convertible<ExecutionContext&, execution_context&>::value > = 0) noexcept { return associated_immediate_executor<T, typename ExecutionContext::executor_type>::get(t, ctx.get_executor()); } template <typename T, typename Executor> using associated_immediate_executor_t = typename associated_immediate_executor<T, Executor>::type; namespace detail { template <typename T, typename E, typename = void> struct associated_immediate_executor_forwarding_base { }; template <typename T, typename E> struct associated_immediate_executor_forwarding_base<T, E, enable_if_t< is_same< typename associated_immediate_executor<T, E>::asio_associated_immediate_executor_is_unspecialised, void >::value >> { typedef void asio_associated_immediate_executor_is_unspecialised; }; } // namespace detail /// Specialisation of associated_immediate_executor for /// @c std::reference_wrapper. template <typename T, typename Executor> struct associated_immediate_executor<reference_wrapper<T>, Executor> #if !defined(GENERATING_DOCUMENTATION) : detail::associated_immediate_executor_forwarding_base<T, Executor> #endif // !defined(GENERATING_DOCUMENTATION) { /// Forwards @c type to the associator specialisation for the unwrapped type /// @c T. typedef typename associated_immediate_executor<T, Executor>::type type; /// Forwards the request to get the executor to the associator specialisation /// for the unwrapped type @c T. static auto get(reference_wrapper<T> t, const Executor& ex) noexcept -> decltype(associated_immediate_executor<T, Executor>::get(t.get(), ex)) { return associated_immediate_executor<T, Executor>::get(t.get(), ex); } }; } // namespace asio } // namespace boost #include <boost/asio/detail/pop_options.hpp> #endif // BOOST_ASIO_ASSOCIATED_IMMEDIATE_EXECUTOR_HPP