112 lines
3.5 KiB
C++
112 lines
3.5 KiB
C++
//
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// handler_invoke_hook.hpp
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// ~~~~~~~~~~~~~~~~~~~~~~~
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//
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// Copyright (c) 2003-2023 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_HANDLER_INVOKE_HOOK_HPP
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#define ASIO_HANDLER_INVOKE_HOOK_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/push_options.hpp"
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namespace asio {
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/** @defgroup asio_handler_invoke asio::asio_handler_invoke
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*
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* @brief (Deprecated: Use the associated_executor trait.) Default invoke
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* function for handlers.
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*
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* Completion handlers for asynchronous operations are invoked by the
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* io_context associated with the corresponding object (e.g. a socket or
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* deadline_timer). Certain guarantees are made on when the handler may be
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* invoked, in particular that a handler can only be invoked from a thread that
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* is currently calling @c run() on the corresponding io_context object.
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* Handlers may subsequently be invoked through other objects (such as
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* io_context::strand objects) that provide additional guarantees.
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*
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* When asynchronous operations are composed from other asynchronous
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* operations, all intermediate handlers should be invoked using the same
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* method as the final handler. This is required to ensure that user-defined
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* objects are not accessed in a way that may violate the guarantees. This
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* hooking function ensures that the invoked method used for the final handler
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* is accessible at each intermediate step.
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*
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* Implement asio_handler_invoke for your own handlers to specify a custom
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* invocation strategy.
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*
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* This default implementation invokes the function object like so:
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* @code function(); @endcode
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* If necessary, the default implementation makes a copy of the function object
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* so that the non-const operator() can be used.
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*
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* @par Example
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* @code
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* class my_handler;
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*
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* template <typename Function>
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* void asio_handler_invoke(Function function, my_handler* context)
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* {
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* context->strand_.dispatch(function);
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* }
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* @endcode
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*/
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/*@{*/
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#if defined(ASIO_NO_DEPRECATED)
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// Places in asio that would have previously called the invocation hook to
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// execute a handler, now call it only to check whether the result type is this
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// type. If the result is not this type, it indicates that the user code still
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// has the old hooks in place, and if so we want to trigger a compile error.
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enum asio_handler_invoke_is_no_longer_used {};
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typedef asio_handler_invoke_is_no_longer_used
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asio_handler_invoke_is_deprecated;
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#else // defined(ASIO_NO_DEPRECATED)
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typedef void asio_handler_invoke_is_deprecated;
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#endif // defined(ASIO_NO_DEPRECATED)
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/// Default handler invocation hook used for non-const function objects.
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template <typename Function>
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inline asio_handler_invoke_is_deprecated
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asio_handler_invoke(Function& function, ...)
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{
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function();
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#if defined(ASIO_NO_DEPRECATED)
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return asio_handler_invoke_is_no_longer_used();
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#endif // defined(ASIO_NO_DEPRECATED)
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}
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/// Default handler invocation hook used for const function objects.
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template <typename Function>
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inline asio_handler_invoke_is_deprecated
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asio_handler_invoke(const Function& function, ...)
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{
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Function tmp(function);
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tmp();
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#if defined(ASIO_NO_DEPRECATED)
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return asio_handler_invoke_is_no_longer_used();
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#endif // defined(ASIO_NO_DEPRECATED)
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}
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/*@}*/
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} // namespace asio
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#include "asio/detail/pop_options.hpp"
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#endif // ASIO_HANDLER_INVOKE_HOOK_HPP
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