doc/html/boost_asio/reference/async_compose.html

   1 <html>
   2 <head>
   3 <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
   4 <title>async_compose</title>
   5 <link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css">
   6 <meta name="generator" content="DocBook XSL Stylesheets V1.79.1">
   7 <link rel="home" href="../../boost_asio.html" title="Boost.Asio">
   8 <link rel="up" href="../reference.html" title="Reference">
   9 <link rel="prev" href="async_completion/result.html" title="async_completion::result">
  10 <link rel="next" href="async_connect.html" title="async_connect">
  11 </head>
  12 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
  13 <table cellpadding="2" width="100%"><tr>
  14 <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td>
  15 <td align="center"><a href="../../../../index.html">Home</a></td>
  16 <td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td>
  17 <td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
  18 <td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
  19 <td align="center"><a href="../../../../more/index.htm">More</a></td>
  20 </tr></table>
  21 <hr>
  22 <div class="spirit-nav">
  23 <a accesskey="p" href="async_completion/result.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="async_connect.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
  24 </div>
  25 <div class="section">
  26 <div class="titlepage"><div><div><h3 class="title">
  27 <a name="boost_asio.reference.async_compose"></a><a class="link" href="async_compose.html" title="async_compose">async_compose</a>
  28 </h3></div></div></div>
  29 <p>
  30         <a class="indexterm" name="boost_asio.indexterm.async_compose"></a>
  31 Launch an asynchronous operation
  32         with a stateful implementation.
  33       </p>
  34 <pre class="programlisting">template&lt;
  35     typename CompletionToken,
  36     typename Signature,
  37     typename Implementation,
  38     typename... IoObjectsOrExecutors&gt;
  39 <a class="link" href="asynchronous_operations.html#boost_asio.reference.asynchronous_operations.automatic_deduction_of_initiating_function_return_type"><span class="emphasis"><em>DEDUCED</em></span></a> async_compose(
  40     Implementation &amp;&amp; implementation,
  41     CompletionToken &amp; token,
  42     IoObjectsOrExecutors &amp;&amp;... io_objects_or_executors);
  43 </pre>
  44 <p>
  45         The async_compose function simplifies the implementation of composed asynchronous
  46         operations automatically wrapping a stateful function object with a conforming
  47         intermediate completion handler.
  48       </p>
  49 <h5>
  50 <a name="boost_asio.reference.async_compose.h0"></a>
  51         <span class="phrase"><a name="boost_asio.reference.async_compose.parameters"></a></span><a class="link" href="async_compose.html#boost_asio.reference.async_compose.parameters">Parameters</a>
  52       </h5>
  53 <div class="variablelist">
  54 <p class="title"><b></b></p>
  55 <dl class="variablelist">
  56 <dt><span class="term">implementation</span></dt>
  57 <dd><p>
  58               A function object that contains the implementation of the composed
  59               asynchronous operation. The first argument to the function object is
  60               a non-const reference to the enclosing intermediate completion handler.
  61               The remaining arguments are any arguments that originate from the completion
  62               handlers of any asynchronous operations performed by the implementation.
  63             </p></dd>
  64 <dt><span class="term">token</span></dt>
  65 <dd><p>
  66               The completion token.
  67             </p></dd>
  68 <dt><span class="term">io_objects_or_executors</span></dt>
  69 <dd><p>
  70               Zero or more I/O objects or I/O executors for which outstanding work
  71               must be maintained.
  72             </p></dd>
  73 </dl>
  74 </div>
  75 <h5>
  76 <a name="boost_asio.reference.async_compose.h1"></a>
  77         <span class="phrase"><a name="boost_asio.reference.async_compose.example_"></a></span><a class="link" href="async_compose.html#boost_asio.reference.async_compose.example_">Example:</a>
  78       </h5>
  79 <pre class="programlisting">struct async_echo_implementation
  80 {
  81   tcp::socket&amp; socket_;
  82   boost::asio::mutable_buffer buffer_;
  83   enum { starting, reading, writing } state_;
  84
  85   template &lt;typename Self&gt;
  86   void operator()(Self&amp; self,
  87       boost::system::error_code error = {},
  88       std::size_t n = 0)
  89   {
  90     switch (state_)
  91     {
  92     case starting:
  93       state_ = reading;
  94       socket_.async_read_some(
  95           buffer_, std::move(self));
  96       break;
  97     case reading:
  98       if (error)
  99       {
 100         self.complete(error, 0);
 101       }
 102       else
 103       {
 104         state_ = writing;
 105         boost::asio::async_write(socket_, buffer_,
 106             boost::asio::transfer_exactly(n),
 107             std::move(self));
 108       }
 109       break;
 110     case writing:
 111       self.complete(error, n);
 112       break;
 113     }
 114   }
 115 };
 116
 117 template &lt;typename CompletionToken&gt;
 118 auto async_echo(tcp::socket&amp; socket,
 119     boost::asio::mutable_buffer buffer,
 120     CompletionToken&amp;&amp; token) -&gt;
 121   typename boost::asio::async_result&lt;
 122     typename std::decay&lt;CompletionToken&gt;::type,
 123       void(boost::system::error_code, std::size_t)&gt;::return_type
 124 {
 125   return boost::asio::async_compose&lt;CompletionToken,
 126     void(boost::system::error_code, std::size_t)&gt;(
 127       async_echo_implementation{socket, buffer,
 128         async_echo_implementation::starting},
 129       token, socket);
 130 }
 131 </pre>
 132 <h5>
 133 <a name="boost_asio.reference.async_compose.h2"></a>
 134         <span class="phrase"><a name="boost_asio.reference.async_compose.requirements"></a></span><a class="link" href="async_compose.html#boost_asio.reference.async_compose.requirements">Requirements</a>
 135       </h5>
 136 <p>
 137         <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/compose.hpp</code>
 138       </p>
 139 <p>
 140         <span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code>
 141       </p>
 142 </div>
 143 <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
 144 <td align="left"></td>
 145 <td align="right"><div class="copyright-footer">Copyright &#169; 2003-2019 Christopher M. Kohlhoff<p>
 146         Distributed under the Boost Software License, Version 1.0. (See accompanying
 147         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>)
 148       </p>
 149 </div></td>
 150 </tr></table>
 151 <hr>
 152 <div class="spirit-nav">
 153 <a accesskey="p" href="async_completion/result.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="async_connect.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a>
 154 </div>
 155 </body>
 156 </html>