fork.html
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<title>Fork</title>
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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>
</h4></div></div></div>
<p>
Asio supports programs that utilise the <code class="computeroutput">fork()</code> system call.
Provided the program calls <code class="computeroutput">io_context.notify_fork()</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">io_context_.notify_fork(asio::io_context::fork_prepare);
if (fork() == 0)
{
io_context_.notify_fork(asio::io_context::fork_child);
...
}
else
{
io_context_.notify_fork(asio::io_context::fork_parent);
...
}
</pre>
<p>
User-defined services can also be made fork-aware by overriding the <code class="computeroutput">io_context::service::notify_fork()</code>
virtual function.
</p>
<p>
Note that any file descriptors accessible via Asio's public API (e.g. the
descriptors underlying <code class="computeroutput">basic_socket<></code>, <code class="computeroutput">posix::stream_descriptor</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>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2020 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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