150 lines
4.3 KiB
C++
150 lines
4.3 KiB
C++
//
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// associated_executor.hpp
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// ~~~~~~~~~~~~~~~~~~~~~~~
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//
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// Copyright (c) 2003-2018 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#ifndef ASIO_ASSOCIATED_EXECUTOR_HPP
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#define ASIO_ASSOCIATED_EXECUTOR_HPP
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#if defined(_MSC_VER) && (_MSC_VER >= 1200)
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# pragma once
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#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
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#include "asio/detail/config.hpp"
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#include "asio/detail/type_traits.hpp"
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#include "asio/is_executor.hpp"
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#include "asio/system_executor.hpp"
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#include "asio/detail/push_options.hpp"
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namespace asio {
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namespace detail {
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template <typename>
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struct associated_executor_check
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{
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typedef void type;
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};
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template <typename T, typename E, typename = void>
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struct associated_executor_impl
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{
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typedef E type;
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static type get(const T&, const E& e) ASIO_NOEXCEPT
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{
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return e;
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}
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};
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template <typename T, typename E>
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struct associated_executor_impl<T, E,
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typename associated_executor_check<typename T::executor_type>::type>
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{
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typedef typename T::executor_type type;
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static type get(const T& t, const E&) ASIO_NOEXCEPT
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{
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return t.get_executor();
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}
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};
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} // namespace detail
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/// Traits type used to obtain the executor associated with an object.
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/**
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* A program may specialise this traits type if the @c T template parameter in
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* the specialisation is a user-defined type. The template parameter @c
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* Executor shall be a type meeting the Executor requirements.
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*
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* Specialisations shall meet the following requirements, where @c t is a const
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* reference to an object of type @c T, and @c e is an object of type @c
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* Executor.
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*
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* @li Provide a nested typedef @c type that identifies a type meeting the
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* Executor requirements.
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*
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* @li Provide a noexcept static member function named @c get, callable as @c
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* get(t) and with return type @c type.
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*
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* @li Provide a noexcept static member function named @c get, callable as @c
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* get(t,e) and with return type @c type.
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*/
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template <typename T, typename Executor = system_executor>
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struct associated_executor
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{
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/// If @c T has a nested type @c executor_type, <tt>T::executor_type</tt>.
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/// Otherwise @c Executor.
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#if defined(GENERATING_DOCUMENTATION)
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typedef see_below type;
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#else // defined(GENERATING_DOCUMENTATION)
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typedef typename detail::associated_executor_impl<T, Executor>::type type;
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#endif // defined(GENERATING_DOCUMENTATION)
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/// If @c T has a nested type @c executor_type, returns
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/// <tt>t.get_executor()</tt>. Otherwise returns @c ex.
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static type get(const T& t,
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const Executor& ex = Executor()) ASIO_NOEXCEPT
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{
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return detail::associated_executor_impl<T, Executor>::get(t, ex);
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}
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};
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/// Helper function to obtain an object's associated executor.
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/**
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* @returns <tt>associated_executor<T>::get(t)</tt>
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*/
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template <typename T>
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inline typename associated_executor<T>::type
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get_associated_executor(const T& t) ASIO_NOEXCEPT
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{
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return associated_executor<T>::get(t);
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}
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/// Helper function to obtain an object's associated executor.
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/**
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* @returns <tt>associated_executor<T, Executor>::get(t, ex)</tt>
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*/
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template <typename T, typename Executor>
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inline typename associated_executor<T, Executor>::type
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get_associated_executor(const T& t, const Executor& ex,
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typename enable_if<is_executor<
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Executor>::value>::type* = 0) ASIO_NOEXCEPT
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{
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return associated_executor<T, Executor>::get(t, ex);
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}
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/// Helper function to obtain an object's associated executor.
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/**
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* @returns <tt>associated_executor<T, typename
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* ExecutionContext::executor_type>::get(t, ctx.get_executor())</tt>
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*/
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template <typename T, typename ExecutionContext>
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inline typename associated_executor<T,
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typename ExecutionContext::executor_type>::type
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get_associated_executor(const T& t, ExecutionContext& ctx,
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typename enable_if<is_convertible<ExecutionContext&,
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execution_context&>::value>::type* = 0) ASIO_NOEXCEPT
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{
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return associated_executor<T,
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typename ExecutionContext::executor_type>::get(t, ctx.get_executor());
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}
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#if defined(ASIO_HAS_ALIAS_TEMPLATES)
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template <typename T, typename Executor = system_executor>
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using associated_executor_t = typename associated_executor<T, Executor>::type;
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#endif // defined(ASIO_HAS_ALIAS_TEMPLATES)
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} // namespace asio
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#include "asio/detail/pop_options.hpp"
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#endif // ASIO_ASSOCIATED_EXECUTOR_HPP
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