201 lines
7.4 KiB
C++
201 lines
7.4 KiB
C++
//
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// defer.hpp
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// ~~~~~~~~~
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//
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// Copyright (c) 2003-2022 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_DEFER_HPP
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#define ASIO_DEFER_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/async_result.hpp"
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#include "asio/detail/type_traits.hpp"
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#include "asio/execution_context.hpp"
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#include "asio/execution/executor.hpp"
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#include "asio/is_executor.hpp"
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#include "asio/detail/push_options.hpp"
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namespace asio {
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/// Submits a completion token or function object for execution.
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/**
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* This function submits an object for execution using the object's associated
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* executor. The function object is queued for execution, and is never called
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* from the current thread prior to returning from <tt>defer()</tt>.
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*
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* The use of @c defer(), rather than @ref post(), indicates the caller's
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* preference that the executor defer the queueing of the function object. This
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* may allow the executor to optimise queueing for cases when the function
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* object represents a continuation of the current call context.
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*
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* @param token The @ref completion_token that will be used to produce a
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* completion handler. The function signature of the completion handler must be:
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* @code void handler(); @endcode
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*
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* @returns This function returns <tt>async_initiate<NullaryToken,
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* void()>(Init{}, token)</tt>, where @c Init is a function object type defined
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* as:
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*
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* @code class Init
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* {
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* public:
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* template <typename CompletionHandler>
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* void operator()(CompletionHandler&& completion_handler) const;
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* }; @endcode
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*
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* The function call operator of @c Init:
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*
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* @li Obtains the handler's associated executor object @c ex of type @c Ex by
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* performing @code auto ex = get_associated_executor(handler); @endcode
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*
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* @li Obtains the handler's associated allocator object @c alloc by performing
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* @code auto alloc = get_associated_allocator(handler); @endcode
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*
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* @li If <tt>execution::is_executor<Ex>::value</tt> is true, performs
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* @code execution::execute(
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* prefer(
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* require(ex, execution::blocking.never),
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* execution::relationship.continuation,
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* execution::allocator(alloc)),
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* std::forward<CompletionHandler>(completion_handler)); @endcode
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*
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* @li If <tt>execution::is_executor<Ex>::value</tt> is false, performs
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* @code ex.defer(
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* std::forward<CompletionHandler>(completion_handler),
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* alloc); @endcode
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*
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* @par Completion Signature
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* @code void() @endcode
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*/
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template <ASIO_COMPLETION_TOKEN_FOR(void()) NullaryToken>
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ASIO_INITFN_AUTO_RESULT_TYPE(NullaryToken, void()) defer(
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ASIO_MOVE_ARG(NullaryToken) token);
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/// Submits a completion token or function object for execution.
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/**
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* This function submits an object for execution using the specified executor.
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* The function object is queued for execution, and is never called from the
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* current thread prior to returning from <tt>defer()</tt>.
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*
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* The use of @c defer(), rather than @ref post(), indicates the caller's
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* preference that the executor defer the queueing of the function object. This
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* may allow the executor to optimise queueing for cases when the function
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* object represents a continuation of the current call context.
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*
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* @param ex The target executor.
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*
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* @param token The @ref completion_token that will be used to produce a
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* completion handler. The function signature of the completion handler must be:
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* @code void handler(); @endcode
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*
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* @returns This function returns <tt>async_initiate<NullaryToken,
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* void()>(Init{ex}, token)</tt>, where @c Init is a function object type
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* defined as:
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*
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* @code class Init
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* {
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* public:
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* using executor_type = Executor;
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* explicit Init(const Executor& ex) : ex_(ex) {}
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* executor_type get_executor() const noexcept { return ex_; }
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* template <typename CompletionHandler>
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* void operator()(CompletionHandler&& completion_handler) const;
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* private:
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* Executor ex_; // exposition only
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* }; @endcode
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*
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* The function call operator of @c Init:
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*
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* @li Obtains the handler's associated executor object @c ex1 of type @c Ex1 by
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* performing @code auto ex1 = get_associated_executor(handler, ex); @endcode
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*
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* @li Obtains the handler's associated allocator object @c alloc by performing
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* @code auto alloc = get_associated_allocator(handler); @endcode
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*
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* @li If <tt>execution::is_executor<Ex1>::value</tt> is true, constructs a
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* function object @c f with a member @c executor_ that is initialised with
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* <tt>prefer(ex1, execution::outstanding_work.tracked)</tt>, a member @c
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* handler_ that is a decay-copy of @c completion_handler, and a function call
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* operator that performs:
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* @code auto a = get_associated_allocator(handler_);
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* execution::execute(
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* prefer(executor_,
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* execution::blocking.possibly,
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* execution::allocator(a)),
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* std::move(handler_)); @endcode
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*
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* @li If <tt>execution::is_executor<Ex1>::value</tt> is false, constructs a
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* function object @c f with a member @c work_ that is initialised with
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* <tt>make_work_guard(ex1)</tt>, a member @c handler_ that is a decay-copy of
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* @c completion_handler, and a function call operator that performs:
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* @code auto a = get_associated_allocator(handler_);
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* work_.get_executor().dispatch(std::move(handler_), a);
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* work_.reset(); @endcode
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*
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* @li If <tt>execution::is_executor<Ex>::value</tt> is true, performs
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* @code execution::execute(
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* prefer(
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* require(ex, execution::blocking.never),
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* execution::relationship.continuation,
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* execution::allocator(alloc)),
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* std::move(f)); @endcode
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*
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* @li If <tt>execution::is_executor<Ex>::value</tt> is false, performs
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* @code ex.defer(std::move(f), alloc); @endcode
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*
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* @par Completion Signature
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* @code void() @endcode
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*/
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template <typename Executor,
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ASIO_COMPLETION_TOKEN_FOR(void()) NullaryToken
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ASIO_DEFAULT_COMPLETION_TOKEN_TYPE(Executor)>
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ASIO_INITFN_AUTO_RESULT_TYPE(NullaryToken, void()) defer(
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const Executor& ex,
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ASIO_MOVE_ARG(NullaryToken) token
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ASIO_DEFAULT_COMPLETION_TOKEN(Executor),
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typename constraint<
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execution::is_executor<Executor>::value || is_executor<Executor>::value
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>::type = 0);
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/// Submits a completion token or function object for execution.
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/**
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* @param ctx An execution context, from which the target executor is obtained.
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*
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* @param token The @ref completion_token that will be used to produce a
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* completion handler. The function signature of the completion handler must be:
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* @code void handler(); @endcode
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*
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* @returns <tt>defer(ctx.get_executor(), forward<NullaryToken>(token))</tt>.
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*
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* @par Completion Signature
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* @code void() @endcode
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*/
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template <typename ExecutionContext,
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ASIO_COMPLETION_TOKEN_FOR(void()) NullaryToken
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ASIO_DEFAULT_COMPLETION_TOKEN_TYPE(
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typename ExecutionContext::executor_type)>
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ASIO_INITFN_AUTO_RESULT_TYPE(NullaryToken, void()) defer(
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ExecutionContext& ctx,
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ASIO_MOVE_ARG(NullaryToken) token
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ASIO_DEFAULT_COMPLETION_TOKEN(
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typename ExecutionContext::executor_type),
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typename constraint<is_convertible<
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ExecutionContext&, execution_context&>::value>::type = 0);
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} // namespace asio
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#include "asio/detail/pop_options.hpp"
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#include "asio/impl/defer.hpp"
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#endif // ASIO_DEFER_HPP
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