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<div class="titlepage"><div><div><h5 class="title">
<a name="asio.reference.basic_datagram_socket.cancel.overload2"></a><a class="link" href="overload2.html" title="basic_datagram_socket::cancel (2 of 2 overloads)">basic_datagram_socket::cancel
(2 of 2 overloads)</a>
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<p>
<span class="emphasis"><em>Inherited from basic_socket.</em></span>
</p>
<p>
Cancel all asynchronous operations associated with the socket.
</p>
<pre class="programlisting"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">cancel</span><span class="special">(</span>
<span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span> <span class="special">&</span> <span class="identifier">ec</span><span class="special">);</span>
</pre>
<p>
This function causes all outstanding asynchronous connect, send and receive
operations to finish immediately, and the handlers for cancelled operations
will be passed the <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error</span><span class="special">::</span><span class="identifier">operation_aborted</span></code>
error.
</p>
<a name="asio.reference.basic_datagram_socket.cancel.overload2.parameters"></a><h6>
<a name="id755816"></a>
<a class="link" href="overload2.html#asio.reference.basic_datagram_socket.cancel.overload2.parameters">Parameters</a>
</h6>
<div class="variablelist">
<p class="title"><b></b></p>
<dl>
<dt><span class="term">ec</span></dt>
<dd><p>
Set to indicate what error occurred, if any.
</p></dd>
</dl>
</div>
<a name="asio.reference.basic_datagram_socket.cancel.overload2.remarks"></a><h6>
<a name="id755856"></a>
<a class="link" href="overload2.html#asio.reference.basic_datagram_socket.cancel.overload2.remarks">Remarks</a>
</h6>
<p>
Calls to <code class="computeroutput"><span class="identifier">cancel</span><span class="special">()</span></code>
will always fail with <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error</span><span class="special">::</span><span class="identifier">operation_not_supported</span></code>
when run on Windows XP, Windows Server 2003, and earlier versions of
Windows, unless ASIO_ENABLE_CANCELIO is defined. However, the CancelIo
function has two issues that should be considered before enabling its
use:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
It will only cancel asynchronous operations that were initiated in
the current thread.
</li>
<li>
It can appear to complete without error, but the request to cancel
the unfinished operations may be silently ignored by the operating
system. Whether it works or not seems to depend on the drivers that
are installed.
</li>
</ul></div>
<p>
For portable cancellation, consider using one of the following alternatives:
</p>
<div class="itemizedlist"><ul type="disc">
<li>
Disable asio's I/O completion port backend by defining ASIO_DISABLE_IOCP.
</li>
<li>
Use the <code class="computeroutput"><span class="identifier">close</span><span class="special">()</span></code>
function to simultaneously cancel the outstanding operations and
close the socket.
</li>
</ul></div>
<p>
When running on Windows Vista, Windows Server 2008, and later, the CancelIoEx
function is always used. This function does not have the problems described
above.
</p>
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<td align="right"><div class="copyright-footer">Copyright © 2003 - 2010 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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