75 lines
5.9 KiB
HTML
75 lines
5.9 KiB
HTML
<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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<title>Fork</title>
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<meta name="generator" content="DocBook XSL Stylesheets V1.75.2">
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../../asio.png"></td></tr></table>
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<a accesskey="p" href="stream_descriptor.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../posix.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="../windows.html"><img src="../../../next.png" alt="Next"></a>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h4 class="title">
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<a name="asio.overview.posix.fork"></a><a class="link" href="fork.html" title="Fork">Fork</a>
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</h4></div></div></div>
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<p>
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Asio supports programs that utilise the <code class="computeroutput"><span class="identifier">fork</span><span class="special">()</span></code> system call. Provided the program calls
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<code class="computeroutput"><span class="identifier">io_context</span><span class="special">.</span><span class="identifier">notify_fork</span><span class="special">()</span></code>
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at the appropriate times, Asio will recreate any internal file descriptors
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(such as the "self-pipe trick" descriptor used for waking up
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a reactor). The notification is usually performed as follows:
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</p>
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<pre class="programlisting"><span class="identifier">io_context_</span><span class="special">.</span><span class="identifier">notify_fork</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">fork_prepare</span><span class="special">);</span>
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<span class="keyword">if</span> <span class="special">(</span><span class="identifier">fork</span><span class="special">()</span> <span class="special">==</span> <span class="number">0</span><span class="special">)</span>
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<span class="special">{</span>
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<span class="identifier">io_context_</span><span class="special">.</span><span class="identifier">notify_fork</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">fork_child</span><span class="special">);</span>
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<span class="special">...</span>
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<span class="special">}</span>
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<span class="keyword">else</span>
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<span class="special">{</span>
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<span class="identifier">io_context_</span><span class="special">.</span><span class="identifier">notify_fork</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">fork_parent</span><span class="special">);</span>
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<span class="special">...</span>
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<span class="special">}</span>
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</pre>
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<p>
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User-defined services can also be made fork-aware by overriding the <code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">service</span><span class="special">::</span><span class="identifier">notify_fork</span><span class="special">()</span></code>
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virtual function.
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</p>
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<p>
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Note that any file descriptors accessible via Asio's public API (e.g. the
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descriptors underlying <code class="computeroutput"><span class="identifier">basic_socket</span><span class="special"><></span></code>, <code class="computeroutput"><span class="identifier">posix</span><span class="special">::</span><span class="identifier">stream_descriptor</span></code>,
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etc.) are not altered during a fork. It is the program's responsibility
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to manage these as required.
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</p>
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<h6>
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<a name="asio.overview.posix.fork.h0"></a>
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<span><a name="asio.overview.posix.fork.see_also"></a></span><a class="link" href="fork.html#asio.overview.posix.fork.see_also">See
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Also</a>
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</h6>
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<p>
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<a class="link" href="../../reference/io_context/notify_fork.html" title="io_context::notify_fork">io_context::notify_fork()</a>,
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<a class="link" href="../../reference/io_context/fork_event.html" title="io_context::fork_event">io_context::fork_event</a>,
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<a class="link" href="../../reference/execution_context__service/notify_fork.html" title="execution_context::service::notify_fork">io_context::service::notify_fork()</a>,
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<a class="link" href="../../examples/cpp03_examples.html#asio.examples.cpp03_examples.fork">Fork examples</a>.
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</p>
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</div>
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<div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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>)
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</p>
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</div>
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<hr>
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<div class="spirit-nav">
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