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85 lines
2.5 KiB
C++
85 lines
2.5 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/type_check.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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/** Completion helper for implementing the extensible asynchronous model.
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This class template is used to transform caller-provided
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completion tokens in calls to asynchronous initiation
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functions. The transformation allows customization of
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the return type of the initiating function, and the type
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of the final handler.
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@tparam CompletionToken A CompletionHandler, 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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Usage:
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@code
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template<class CompletionToken>
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auto
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async_initfn(..., CompletionToken&& token)
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{
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async_completion<CompletionToken,
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void(error_code, std::size_t)> completion(token);
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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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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 CompletionToken, class Signature>
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struct async_completion
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{
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/** The type of the final handler.
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Objects of this type will be callable with the
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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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CompletionToken, Signature>::type;
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/** Construct the completion helper.
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@param token The completion token. Copies will be made as
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required. If `CompletionToken` is movable, it may also be moved.
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*/
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async_completion(std::remove_reference_t<CompletionToken>& token)
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: handler(std::forward<CompletionToken>(token))
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, result(handler)
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{
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static_assert(is_Handler<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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