Initial Commit

include/asio/dispatch.hpp

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+//
+// dispatch.hpp
+// ~~~~~~~~~~~~
+//
+// Copyright (c) 2003-2025 Christopher M. Kohlhoff (chris at kohlhoff dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+
+#ifndef ASIO_DISPATCH_HPP
+#define ASIO_DISPATCH_HPP
+
+#if defined(_MSC_VER) && (_MSC_VER >= 1200)
+# pragma once
+#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
+
+#include "asio/detail/config.hpp"
+#include "asio/async_result.hpp"
+#include "asio/detail/initiate_dispatch.hpp"
+#include "asio/detail/type_traits.hpp"
+#include "asio/execution_context.hpp"
+#include "asio/execution/executor.hpp"
+#include "asio/is_executor.hpp"
+
+#include "asio/detail/push_options.hpp"
+
+namespace asio {
+
+/// Submits a completion token or function object for execution.
+/**
+ * This function submits an object for execution using the object's associated
+ * executor. The function object may be called from the current thread prior to
+ * returning from <tt>dispatch()</tt>. Otherwise, it is queued for execution.
+ *
+ * @param token The @ref completion_token that will be used to produce a
+ * completion handler. The function signature of the completion handler must be:
+ * @code void handler(); @endcode
+ *
+ * @returns This function returns <tt>async_initiate<NullaryToken,
+ * void()>(Init{}, token)</tt>, where @c Init is a function object type defined
+ * as:
+ *
+ * @code class Init
+ * {
+ * public:
+ *   template <typename CompletionHandler>
+ *     void operator()(CompletionHandler&& completion_handler) const;
+ * }; @endcode
+ *
+ * The function call operator of @c Init:
+ *
+ * @li Obtains the handler's associated executor object @c ex of type @c Ex by
+ * performing @code auto ex = get_associated_executor(handler); @endcode
+ *
+ * @li Obtains the handler's associated allocator object @c alloc by performing
+ * @code auto alloc = get_associated_allocator(handler); @endcode
+ *
+ * @li If <tt>execution::is_executor<Ex>::value</tt> is true, performs
+ * @code prefer(ex, execution::allocator(alloc)).execute(
+ *     std::forward<CompletionHandler>(completion_handler)); @endcode
+ *
+ * @li If <tt>execution::is_executor<Ex>::value</tt> is false, performs
+ * @code ex.dispatch(
+ *     std::forward<CompletionHandler>(completion_handler),
+ *     alloc); @endcode
+ *
+ * @par Completion Signature
+ * @code void() @endcode
+ */
+template <ASIO_COMPLETION_TOKEN_FOR(void()) NullaryToken>
+inline auto dispatch(NullaryToken&& token)
+  -> decltype(
+    async_initiate<NullaryToken, void()>(
+      declval<detail::initiate_dispatch>(), token))
+{
+  return async_initiate<NullaryToken, void()>(
+      detail::initiate_dispatch(), token);
+}
+
+/// Submits a completion token or function object for execution.
+/**
+ * This function submits an object for execution using the specified executor.
+ * The function object may be called from the current thread prior to returning
+ * from <tt>dispatch()</tt>. Otherwise, it is queued for execution.
+ *
+ * @param ex The target executor.
+ *
+ * @param token The @ref completion_token that will be used to produce a
+ * completion handler. The function signature of the completion handler must be:
+ * @code void handler(); @endcode
+ *
+ * @returns This function returns <tt>async_initiate<NullaryToken,
+ * void()>(Init{ex}, token)</tt>, where @c Init is a function object type
+ * defined as:
+ *
+ * @code class Init
+ * {
+ * public:
+ *   using executor_type = Executor;
+ *   explicit Init(const Executor& ex) : ex_(ex) {}
+ *   executor_type get_executor() const noexcept { return ex_; }
+ *   template <typename CompletionHandler>
+ *     void operator()(CompletionHandler&& completion_handler) const;
+ * private:
+ *   Executor ex_; // exposition only
+ * }; @endcode
+ *
+ * The function call operator of @c Init:
+ *
+ * @li Obtains the handler's associated executor object @c ex1 of type @c Ex1 by
+ * performing @code auto ex1 = get_associated_executor(handler, ex); @endcode
+ *
+ * @li Obtains the handler's associated allocator object @c alloc by performing
+ * @code auto alloc = get_associated_allocator(handler); @endcode
+ *
+ * @li If <tt>execution::is_executor<Ex1>::value</tt> is true, constructs a
+ * function object @c f with a member @c executor_ that is initialised with
+ * <tt>prefer(ex1, execution::outstanding_work.tracked)</tt>, a member @c
+ * handler_ that is a decay-copy of @c completion_handler, and a function call
+ * operator that performs:
+ * @code auto a = get_associated_allocator(handler_);
+ * prefer(executor_, execution::allocator(a)).execute(std::move(handler_));
+ * @endcode
+ *
+ * @li If <tt>execution::is_executor<Ex1>::value</tt> is false, constructs a
+ * function object @c f with a member @c work_ that is initialised with
+ * <tt>make_work_guard(ex1)</tt>, a member @c handler_ that is a decay-copy of
+ * @c completion_handler, and a function call operator that performs:
+ * @code auto a = get_associated_allocator(handler_);
+ * work_.get_executor().dispatch(std::move(handler_), a);
+ * work_.reset(); @endcode
+ *
+ * @li If <tt>execution::is_executor<Ex>::value</tt> is true, performs
+ * @code prefer(ex, execution::allocator(alloc)).execute(std::move(f)); @endcode
+ *
+ * @li If <tt>execution::is_executor<Ex>::value</tt> is false, performs
+ * @code ex.dispatch(std::move(f), alloc); @endcode
+ *
+ * @par Completion Signature
+ * @code void() @endcode
+ */
+template <typename Executor,
+    ASIO_COMPLETION_TOKEN_FOR(void()) NullaryToken
+      = default_completion_token_t<Executor>>
+inline auto dispatch(const Executor& ex,
+    NullaryToken&& token = default_completion_token_t<Executor>(),
+    constraint_t<
+      execution::is_executor<Executor>::value || is_executor<Executor>::value
+    > = 0)
+  -> decltype(
+    async_initiate<NullaryToken, void()>(
+      declval<detail::initiate_dispatch_with_executor<Executor>>(), token))
+{
+  return async_initiate<NullaryToken, void()>(
+      detail::initiate_dispatch_with_executor<Executor>(ex), token);
+}
+
+/// Submits a completion token or function object for execution.
+/**
+ * @param ctx An execution context, from which the target executor is obtained.
+ *
+ * @param token The @ref completion_token that will be used to produce a
+ * completion handler. The function signature of the completion handler must be:
+ * @code void handler(); @endcode
+ *
+ * @returns <tt>dispatch(ctx.get_executor(),
+ * forward<NullaryToken>(token))</tt>.
+ *
+ * @par Completion Signature
+ * @code void() @endcode
+ */
+template <typename ExecutionContext,
+    ASIO_COMPLETION_TOKEN_FOR(void()) NullaryToken
+      = default_completion_token_t<typename ExecutionContext::executor_type>>
+inline auto dispatch(ExecutionContext& ctx,
+    NullaryToken&& token = default_completion_token_t<
+      typename ExecutionContext::executor_type>(),
+    constraint_t<
+      is_convertible<ExecutionContext&, execution_context&>::value
+    > = 0)
+  -> decltype(
+    async_initiate<NullaryToken, void()>(
+      declval<detail::initiate_dispatch_with_executor<
+        typename ExecutionContext::executor_type>>(), token))
+{
+  return async_initiate<NullaryToken, void()>(
+      detail::initiate_dispatch_with_executor<
+        typename ExecutionContext::executor_type>(
+          ctx.get_executor()), token);
+}
+
+} // namespace asio
+
+#include "asio/detail/pop_options.hpp"
+
+#endif // ASIO_DISPATCH_HPP