1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Fork</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="../posix.html" title="POSIX-Specific Functionality"> 9<link rel="prev" href="stream_descriptor.html" title="Stream-Oriented File Descriptors"> 10<link rel="next" href="../windows.html" title="Windows-Specific Functionality"> 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="stream_descriptor.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../posix.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="../windows.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.posix.fork"></a><a class="link" href="fork.html" title="Fork">Fork</a> 28</h4></div></div></div> 29<p> 30 Boost.Asio supports programs that utilise the <code class="computeroutput">fork()</code> system 31 call. Provided the program calls <code class="computeroutput">io_context.notify_fork()</code> 32 at the appropriate times, Boost.Asio will recreate any internal file descriptors 33 (such as the "self-pipe trick" descriptor used for waking up 34 a reactor). The notification is usually performed as follows: 35 </p> 36<pre class="programlisting">io_context_.notify_fork(boost::asio::io_context::fork_prepare); 37if (fork() == 0) 38{ 39 io_context_.notify_fork(boost::asio::io_context::fork_child); 40 ... 41} 42else 43{ 44 io_context_.notify_fork(boost::asio::io_context::fork_parent); 45 ... 46} 47</pre> 48<p> 49 User-defined services can also be made fork-aware by overriding the <code class="computeroutput">io_context::service::notify_fork()</code> 50 virtual function. 51 </p> 52<p> 53 Note that any file descriptors accessible via Boost.Asio's public API (e.g. 54 the descriptors underlying <code class="computeroutput">basic_socket<></code>, <code class="computeroutput">posix::stream_descriptor</code>, 55 etc.) are not altered during a fork. It is the program's responsibility 56 to manage these as required. 57 </p> 58<h6> 59<a name="boost_asio.overview.posix.fork.h0"></a> 60 <span class="phrase"><a name="boost_asio.overview.posix.fork.see_also"></a></span><a class="link" href="fork.html#boost_asio.overview.posix.fork.see_also">See 61 Also</a> 62 </h6> 63<p> 64 <a class="link" href="../../reference/io_context/notify_fork.html" title="io_context::notify_fork">io_context::notify_fork()</a>, 65 <a class="link" href="../../reference/io_context/fork_event.html" title="io_context::fork_event">io_context::fork_event</a>, 66 <a class="link" href="../../reference/execution_context__service/notify_fork.html" title="execution_context::service::notify_fork">io_context::service::notify_fork()</a>, 67 <a class="link" href="../../examples/cpp03_examples.html#boost_asio.examples.cpp03_examples.fork">Fork examples</a>. 68 </p> 69</div> 70<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 71<td align="left"></td> 72<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 73 Kohlhoff<p> 74 Distributed under the Boost Software License, Version 1.0. (See accompanying 75 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>) 76 </p> 77</div></td> 78</tr></table> 79<hr> 80<div class="spirit-nav"> 81<a accesskey="p" href="stream_descriptor.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../posix.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="../windows.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a> 82</div> 83</body> 84</html> 85
