1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Stackless Coroutines</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="../core.html" title="Core Concepts and Functionality"> 9<link rel="prev" href="concurrency_hint.html" title="Concurrency Hints"> 10<link rel="next" href="spawn.html" title="Stackful Coroutines"> 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="concurrency_hint.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../core.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="spawn.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h4 class="title"> 27<a name="boost_asio.overview.core.coroutine"></a><a class="link" href="coroutine.html" title="Stackless Coroutines">Stackless Coroutines</a> 28</h4></div></div></div> 29<p> 30 The <a class="link" href="../../reference/coroutine.html" title="coroutine"><code class="computeroutput">coroutine</code></a> 31 class provides support for stackless coroutines. Stackless coroutines enable 32 programs to implement asynchronous logic in a synchronous manner, with 33 minimal overhead, as shown in the following example: 34 </p> 35<pre class="programlisting">struct session : boost::asio::coroutine 36{ 37 boost::shared_ptr<tcp::socket> socket_; 38 boost::shared_ptr<std::vector<char> > buffer_; 39 40 session(boost::shared_ptr<tcp::socket> socket) 41 : socket_(socket), 42 buffer_(new std::vector<char>(1024)) 43 { 44 } 45 46 void operator()(boost::system::error_code ec = boost::system::error_code(), std::size_t n = 0) 47 { 48 if (!ec) reenter (this) 49 { 50 for (;;) 51 { 52 yield socket_->async_read_some(boost::asio::buffer(*buffer_), *this); 53 yield boost::asio::async_write(*socket_, boost::asio::buffer(*buffer_, n), *this); 54 } 55 } 56 } 57}; 58</pre> 59<p> 60 The <code class="computeroutput">coroutine</code> class is used in conjunction with the pseudo-keywords 61 <code class="computeroutput">reenter</code>, <code class="computeroutput">yield</code> and <code class="computeroutput">fork</code>. These are 62 preprocessor macros, and are implemented in terms of a <code class="computeroutput">switch</code> 63 statement using a technique similar to Duff's Device. The <a class="link" href="../../reference/coroutine.html" title="coroutine"><code class="computeroutput">coroutine</code></a> 64 class's documentation provides a complete description of these pseudo-keywords. 65 </p> 66<h6> 67<a name="boost_asio.overview.core.coroutine.h0"></a> 68 <span class="phrase"><a name="boost_asio.overview.core.coroutine.see_also"></a></span><a class="link" href="coroutine.html#boost_asio.overview.core.coroutine.see_also">See 69 Also</a> 70 </h6> 71<p> 72 <a class="link" href="../../reference/coroutine.html" title="coroutine">coroutine</a>, <a class="link" href="../../examples/cpp03_examples.html#boost_asio.examples.cpp03_examples.http_server_4">HTTP Server 73 4 example</a>, <a class="link" href="spawn.html" title="Stackful Coroutines">Stackful 74 Coroutines</a>. 75 </p> 76</div> 77<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 78<td align="left"></td> 79<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 80 Kohlhoff<p> 81 Distributed under the Boost Software License, Version 1.0. (See accompanying 82 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>) 83 </p> 84</div></td> 85</tr></table> 86<hr> 87<div class="spirit-nav"> 88<a accesskey="p" href="concurrency_hint.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../core.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="spawn.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 89</div> 90</body> 91</html> 92
