<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>defer (2 of 3 overloads)</title> <link rel="stylesheet" href="../../../boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.75.2"> <link rel="home" href="../../../index.html" title="Asio"> <link rel="up" href="../defer.html" title="defer"> <link rel="prev" href="overload1.html" title="defer (1 of 3 overloads)"> <link rel="next" href="overload3.html" title="defer (3 of 3 overloads)"> <meta name="viewport" content="width=device-width, initial-scale=1"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../../asio.png"></td></tr></table> <hr> <div class="spirit-nav"> <a accesskey="p" href="overload1.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../defer.html"><img src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png" alt="Home"></a><a accesskey="n" href="overload3.html"><img src="../../../next.png" alt="Next"></a> </div> <div class="section"> <div class="titlepage"><div><div><h4 class="title"> <a name="asio.reference.defer.overload2"></a><a class="link" href="overload2.html" title="defer (2 of 3 overloads)">defer (2 of 3 overloads)</a> </h4></div></div></div> <p> Submits a completion token or function object for execution. </p> <pre class="programlisting"><span class="keyword">template</span><span class="special"><</span> <span class="keyword">typename</span> <a class="link" href="../Executor1.html" title="Executor requirements">Executor</a><span class="special">,</span> <span class="keyword">typename</span> <a class="link" href="../NullaryToken.html" title="Nullary token requirements">NullaryToken</a> <span class="special">=</span> <a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a><span class="special">></span> <a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> <span class="identifier">defer</span><span class="special">(</span> <span class="keyword">const</span> <span class="identifier">Executor</span> <span class="special">&</span> <span class="identifier">ex</span><span class="special">,</span> <span class="identifier">NullaryToken</span> <span class="special">&&</span> <span class="identifier">token</span> <span class="special">=</span> <a class="link" href="../asynchronous_operations.html#asio.reference.asynchronous_operations.default_completion_tokens"><span class="emphasis"><em>DEFAULT</em></span></a><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">constraint</span><span class="special"><</span> <span class="special">(</span><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special"><</span> <span class="identifier">Executor</span> <span class="special">>::</span><span class="identifier">value</span> <span class="special">&&</span><span class="identifier">can_require</span><span class="special"><</span> <span class="identifier">Executor</span><span class="special">,</span> <span class="identifier">execution</span><span class="special">::</span><span class="identifier">blocking_t</span><span class="special">::</span><span class="identifier">never_t</span> <span class="special">>::</span><span class="identifier">value</span><span class="special">)||</span><span class="identifier">is_executor</span><span class="special"><</span> <span class="identifier">Executor</span> <span class="special">>::</span><span class="identifier">value</span> <span class="special">>::</span><span class="identifier">type</span> <span class="special">=</span> <span class="number">0</span><span class="special">);</span> </pre> <p> This function submits an object for execution using the specified executor. The function object is queued for execution, and is never called from the current thread prior to returning from <code class="computeroutput"><span class="identifier">defer</span><span class="special">()</span></code>. </p> <p> The use of <code class="computeroutput"><span class="identifier">defer</span><span class="special">()</span></code>, rather than <a class="link" href="../post.html" title="post"><code class="computeroutput"><span class="identifier">post</span></code></a>, indicates the caller's preference that the executor defer the queueing of the function object. This may allow the executor to optimise queueing for cases when the function object represents a continuation of the current call context. </p> <h6> <a name="asio.reference.defer.overload2.h0"></a> <span><a name="asio.reference.defer.overload2.parameters"></a></span><a class="link" href="overload2.html#asio.reference.defer.overload2.parameters">Parameters</a> </h6> <div class="variablelist"> <p class="title"><b></b></p> <dl> <dt><span class="term">ex</span></dt> <dd><p> The target executor. </p></dd> <dt><span class="term">token</span></dt> <dd> <p> The <a class="link" href="../../overview/model/completion_tokens.html" title="Completion Tokens">completion token</a> that will be used to produce a completion handler. The function signature of the completion handler must be: </p> <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">();</span> </pre> </dd> </dl> </div> <h6> <a name="asio.reference.defer.overload2.h1"></a> <span><a name="asio.reference.defer.overload2.return_value"></a></span><a class="link" href="overload2.html#asio.reference.defer.overload2.return_value">Return Value</a> </h6> <p> This function returns <code class="computeroutput"><span class="identifier">async_initiate</span><span class="special"><</span><span class="identifier">NullaryToken</span><span class="special">,</span> <span class="keyword">void</span><span class="special">()>(</span><span class="identifier">Init</span><span class="special">{</span><span class="identifier">ex</span><span class="special">},</span> <span class="identifier">token</span><span class="special">)</span></code>, where <code class="computeroutput"><span class="identifier">Init</span></code> is a function object type defined as: </p> <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">Init</span> <span class="special">{</span> <span class="keyword">public</span><span class="special">:</span> <span class="keyword">using</span> <span class="identifier">executor_type</span> <span class="special">=</span> <span class="identifier">Executor</span><span class="special">;</span> <span class="keyword">explicit</span> <span class="identifier">Init</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Executor</span><span class="special">&</span> <span class="identifier">ex</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">ex_</span><span class="special">(</span><span class="identifier">ex</span><span class="special">)</span> <span class="special">{}</span> <span class="identifier">executor_type</span> <span class="identifier">get_executor</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">ex_</span><span class="special">;</span> <span class="special">}</span> <span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">CompletionHandler</span><span class="special">></span> <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">CompletionHandler</span><span class="special">&&</span> <span class="identifier">completion_handler</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> <span class="keyword">private</span><span class="special">:</span> <span class="identifier">Executor</span> <span class="identifier">ex_</span><span class="special">;</span> <span class="comment">// exposition only</span> <span class="special">};</span> </pre> <p> The function call operator of <code class="computeroutput"><span class="identifier">Init</span><span class="special">:</span></code> </p> <div class="itemizedlist"><ul class="itemizedlist" type="disc"> <li class="listitem"> <p class="simpara"> Obtains the handler's associated executor object <code class="computeroutput"><span class="identifier">ex1</span></code> of type <code class="computeroutput"><span class="identifier">Ex1</span></code> by performing </p> <pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">ex1</span> <span class="special">=</span> <span class="identifier">get_associated_executor</span><span class="special">(</span><span class="identifier">handler</span><span class="special">,</span> <span class="identifier">ex</span><span class="special">);</span> </pre> </li> <li class="listitem"> <p class="simpara"> Obtains the handler's associated allocator object <code class="computeroutput"><span class="identifier">alloc</span></code> by performing </p> <pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">alloc</span> <span class="special">=</span> <span class="identifier">get_associated_allocator</span><span class="special">(</span><span class="identifier">handler</span><span class="special">);</span> </pre> </li> <li class="listitem"> <p class="simpara"> If <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special"><</span><span class="identifier">Ex1</span><span class="special">>::</span><span class="identifier">value</span></code> is true, constructs a function object <code class="computeroutput"><span class="identifier">f</span></code> with a member <code class="computeroutput"><span class="identifier">executor_</span></code> that is initialised with <code class="computeroutput"><span class="identifier">prefer</span><span class="special">(</span><span class="identifier">ex1</span><span class="special">,</span> <span class="identifier">execution</span><span class="special">::</span><span class="identifier">outstanding_work</span><span class="special">.</span><span class="identifier">tracked</span><span class="special">)</span></code>, a member <code class="computeroutput"><span class="identifier">handler_</span></code> that is a decay-copy of <code class="computeroutput"><span class="identifier">completion_handler</span></code>, and a function call operator that performs: </p> <pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">a</span> <span class="special">=</span> <span class="identifier">get_associated_allocator</span><span class="special">(</span><span class="identifier">handler_</span><span class="special">);</span> <span class="identifier">prefer</span><span class="special">(</span><span class="identifier">executor_</span><span class="special">,</span> <span class="identifier">execution</span><span class="special">::</span><span class="identifier">allocator</span><span class="special">(</span><span class="identifier">a</span><span class="special">)).</span><span class="identifier">execute</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">handler_</span><span class="special">));</span> </pre> </li> <li class="listitem"> <p class="simpara"> If <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special"><</span><span class="identifier">Ex1</span><span class="special">>::</span><span class="identifier">value</span></code> is false, constructs a function object <code class="computeroutput"><span class="identifier">f</span></code> with a member <code class="computeroutput"><span class="identifier">work_</span></code> that is initialised with <code class="computeroutput"><span class="identifier">make_work_guard</span><span class="special">(</span><span class="identifier">ex1</span><span class="special">)</span></code>, a member <code class="computeroutput"><span class="identifier">handler_</span></code> that is a decay-copy of <code class="computeroutput"><span class="identifier">completion_handler</span></code>, and a function call operator that performs: </p> <pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">a</span> <span class="special">=</span> <span class="identifier">get_associated_allocator</span><span class="special">(</span><span class="identifier">handler_</span><span class="special">);</span> <span class="identifier">work_</span><span class="special">.</span><span class="identifier">get_executor</span><span class="special">().</span><span class="identifier">dispatch</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">handler_</span><span class="special">),</span> <span class="identifier">a</span><span class="special">);</span> <span class="identifier">work_</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span> </pre> </li> <li class="listitem"> <p class="simpara"> If <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special"><</span><span class="identifier">Ex</span><span class="special">>::</span><span class="identifier">value</span></code> is true, performs </p> <pre class="programlisting"><span class="identifier">prefer</span><span class="special">(</span> <span class="identifier">require</span><span class="special">(</span><span class="identifier">ex</span><span class="special">,</span> <span class="identifier">execution</span><span class="special">::</span><span class="identifier">blocking</span><span class="special">.</span><span class="identifier">never</span><span class="special">),</span> <span class="identifier">execution</span><span class="special">::</span><span class="identifier">relationship</span><span class="special">.</span><span class="identifier">continuation</span><span class="special">,</span> <span class="identifier">execution</span><span class="special">::</span><span class="identifier">allocator</span><span class="special">(</span><span class="identifier">alloc</span><span class="special">)</span> <span class="special">).</span><span class="identifier">execute</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">f</span><span class="special">));</span> </pre> </li> <li class="listitem"> <p class="simpara"> If <code class="computeroutput"><span class="identifier">execution</span><span class="special">::</span><span class="identifier">is_executor</span><span class="special"><</span><span class="identifier">Ex</span><span class="special">>::</span><span class="identifier">value</span></code> is false, performs </p> <pre class="programlisting"><span class="identifier">ex</span><span class="special">.</span><span class="identifier">defer</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">f</span><span class="special">),</span> <span class="identifier">alloc</span><span class="special">);</span> </pre> </li> </ul></div> <h6> <a name="asio.reference.defer.overload2.h2"></a> <span><a name="asio.reference.defer.overload2.completion_signature"></a></span><a class="link" href="overload2.html#asio.reference.defer.overload2.completion_signature">Completion Signature</a> </h6> <pre class="programlisting"><span class="keyword">void</span><span class="special">()</span> </pre> </div> <div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p> Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) </p> </div> <hr> <div class="spirit-nav"> <a accesskey="p" href="overload1.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../defer.html"><img src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png" alt="Home"></a><a accesskey="n" href="overload3.html"><img src="../../../next.png" alt="Next"></a> </div> </body> </html>