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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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<div class="titlepage"><div><div><h4 class="title">
<a name="asio.overview.posix.fork"></a><a class="link" href="fork.html" title="Fork">Fork</a>
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<p>
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
<code class="computeroutput"><span class="identifier">io_context</span><span class="special">.</span><span class="identifier">notify_fork</span><span class="special">()</span></code>
at the appropriate times, Asio will recreate any internal file descriptors
(such as the "self-pipe trick" descriptor used for waking up
a reactor). The notification is usually performed as follows:
</p>
<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>
<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>
<span class="special">{</span>
<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>
<span class="special">...</span>
<span class="special">}</span>
<span class="keyword">else</span>
<span class="special">{</span>
<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>
<span class="special">...</span>
<span class="special">}</span>
</pre>
<p>
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>
virtual function.
</p>
<p>
Note that any file descriptors accessible via Asio's public API (e.g. the
descriptors underlying <code class="computeroutput"><span class="identifier">basic_socket</span><span class="special">&lt;&gt;</span></code>, <code class="computeroutput"><span class="identifier">posix</span><span class="special">::</span><span class="identifier">stream_descriptor</span></code>,
etc.) are not altered during a fork. It is the program's responsibility
to manage these as required.
</p>
<h6>
<a name="asio.overview.posix.fork.h0"></a>
<span><a name="asio.overview.posix.fork.see_also"></a></span><a class="link" href="fork.html#asio.overview.posix.fork.see_also">See
Also</a>
</h6>
<p>
<a class="link" href="../../reference/io_context/notify_fork.html" title="io_context::notify_fork">io_context::notify_fork()</a>,
<a class="link" href="../../reference/io_context/fork_event.html" title="io_context::fork_event">io_context::fork_event</a>,
<a class="link" href="../../reference/execution_context__service/notify_fork.html" title="execution_context::service::notify_fork">io_context::service::notify_fork()</a>,
<a class="link" href="../../examples/cpp03_examples.html#asio.examples.cpp03_examples.fork">Fork examples</a>.
</p>
</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>)
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