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88 lines
2.9 KiB
C++
88 lines
2.9 KiB
C++
//
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// Copyright (c) 2013-2016 Vinnie Falco (vinnie dot falco at gmail 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 BEAST_ASYNC_COMPLETION_HPP
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#define BEAST_ASYNC_COMPLETION_HPP
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#include <beast/core/handler_concepts.hpp>
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#include <boost/asio/async_result.hpp>
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#include <boost/asio/handler_type.hpp>
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#include <type_traits>
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#include <utility>
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namespace beast {
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/** Helper for customizing the return type of asynchronous initiation functions.
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This class template is used to transform caller-provided completion
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handlers in calls to asynchronous initiation functions. The transformation
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allows customization of the return type of the initiating function, and the
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function signature of the final handler.
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@tparam CompletionHandler A completion handler, or a user defined type
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with specializations for customizing the return type (for example,
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`boost::asio::use_future` or `boost::asio::yield_context`).
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@tparam Signature The callable signature of the final completion handler.
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Example:
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@code
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...
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template<class CompletionHandler>
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typename async_completion<CompletionHandler,
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void(boost::system::error_code)>::result_type
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async_initfn(..., CompletionHandler&& handler)
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{
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async_completion<CompletionHandler,
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void(boost::system::error_code)> completion(handler);
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...
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return completion.result.get();
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}
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@endcode
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@note See <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3896.pdf">
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Library Foundations For Asynchronous Operations</a>
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*/
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template <class CompletionHandler, class Signature>
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struct async_completion
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{
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/** The type of the final handler called by the asynchronous initiation function.
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Objects of this type will be callable with the specified signature.
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*/
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using handler_type =
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typename boost::asio::handler_type<
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CompletionHandler, Signature>::type;
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/// The type of the value returned by the asynchronous initiation function.
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using result_type = typename
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boost::asio::async_result<handler_type>::type;
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/** Construct the helper.
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@param token The completion handler. Copies will be made as
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required. If `CompletionHandler` is movable, it may also be moved.
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*/
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async_completion(typename std::remove_reference<CompletionHandler>::type& token)
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: handler(std::forward<CompletionHandler>(token))
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, result(handler)
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{
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static_assert(is_CompletionHandler<handler_type, Signature>::value,
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"Handler requirements not met");
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}
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/// The final completion handler, callable with the specified signature.
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handler_type handler;
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/// The return value of the asynchronous initiation function.
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boost::asio::async_result<handler_type> result;
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};
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} // beast
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#endif
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