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<title>strand</title>
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<div class="section" title="strand">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.strand"></a><a class="link" href="strand.html" title="strand"> strand</a>
</h3></div></div></div>
<p>
<a class="indexterm" name="id1126054"></a>
Typedef for backwards compatibility.
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">strand</span> <span class="identifier">strand</span><span class="special">;</span>
</pre>
<a name="boost_asio.reference.strand.member_functions"></a><h5>
<a name="id1126122"></a>
<a class="link" href="strand.html#boost_asio.reference.strand.member_functions">Member Functions</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a class="link" href="io_service__strand/dispatch.html" title="io_service::strand::dispatch"><span class="bold"><strong>dispatch</strong></span></a>
</p>
</td>
<td>
<p>
Request the strand to invoke the given handler.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service__strand/get_io_service.html" title="io_service::strand::get_io_service"><span class="bold"><strong>get_io_service</strong></span></a>
</p>
</td>
<td>
<p>
Get the io_service associated with the strand.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service__strand/io_service.html" title="io_service::strand::io_service"><span class="bold"><strong>io_service</strong></span></a>
</p>
</td>
<td>
<p>
(Deprecated: use get_io_service().) Get the io_service associated
with the strand.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service__strand/post.html" title="io_service::strand::post"><span class="bold"><strong>post</strong></span></a>
</p>
</td>
<td>
<p>
Request the strand to invoke the given handler and return immediately.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service__strand/strand.html" title="io_service::strand::strand"><span class="bold"><strong>strand</strong></span></a>
</p>
</td>
<td>
<p>
Constructor.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service__strand/wrap.html" title="io_service::strand::wrap"><span class="bold"><strong>wrap</strong></span></a>
</p>
</td>
<td>
<p>
Create a new handler that automatically dispatches the wrapped handler
on the strand.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="io_service__strand/_strand.html" title="io_service::strand::~strand"><span class="bold"><strong>~strand</strong></span></a>
</p>
</td>
<td>
<p>
Destructor.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
The <a class="link" href="io_service__strand.html" title="io_service::strand"><code class="computeroutput"><span class="identifier">io_service</span><span class="special">::</span><span class="identifier">strand</span></code></a> class provides the ability
to post and dispatch handlers with the guarantee that none of those handlers
will execute concurrently.
</p>
<a name="boost_asio.reference.strand.order_of_handler_invocation"></a><h5>
<a name="id1126401"></a>
<a class="link" href="strand.html#boost_asio.reference.strand.order_of_handler_invocation">Order
of handler invocation</a>
</h5>
<p>
Given:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
a strand object s
</li>
<li class="listitem">
an object a meeting completion handler requirements
</li>
<li class="listitem">
an object a1 which is an arbitrary copy of a made by the implementation
</li>
<li class="listitem">
an object b meeting completion handler requirements
</li>
<li class="listitem">
an object b1 which is an arbitrary copy of b made by the implementation
</li>
</ul></div>
<p>
if any of the following conditions are true:
</p>
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
<li class="listitem">
s.post(a) happens-before s.post(b)
</li>
<li class="listitem">
s.post(a) happens-before s.dispatch(b), where the latter is performed outside
the strand
</li>
<li class="listitem">
s.dispatch(a) happens-before s.post(b), where the former is performed outside
the strand
</li>
<li class="listitem">
s.dispatch(a) happens-before s.dispatch(b), where both are performed outside
the strand
</li>
</ul></div>
<p>
then <code class="computeroutput"><span class="identifier">asio_handler_invoke</span><span class="special">(</span><span class="identifier">a1</span><span class="special">,</span>
<span class="special">&</span><span class="identifier">a1</span><span class="special">)</span></code> happens-before <code class="computeroutput"><span class="identifier">asio_handler_invoke</span><span class="special">(</span><span class="identifier">b1</span><span class="special">,</span>
<span class="special">&</span><span class="identifier">b1</span><span class="special">)</span></code>.
</p>
<p>
Note that in the following case:
</p>
<pre class="programlisting"><span class="identifier">async_op_1</span><span class="special">(...,</span> <span class="identifier">s</span><span class="special">.</span><span class="identifier">wrap</span><span class="special">(</span><span class="identifier">a</span><span class="special">));</span>
<span class="identifier">async_op_2</span><span class="special">(...,</span> <span class="identifier">s</span><span class="special">.</span><span class="identifier">wrap</span><span class="special">(</span><span class="identifier">b</span><span class="special">));</span>
</pre>
<p>
the completion of the first async operation will perform <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span class="identifier">dispatch</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span></code>,
and the second will perform <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span class="identifier">dispatch</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>,
but the order in which those are performed is unspecified. That is, you cannot
state whether one happens-before the other. Therefore none of the above conditions
are met and no ordering guarantee is made.
</p>
<a name="boost_asio.reference.strand.thread_safety"></a><h5>
<a name="id1126717"></a>
<a class="link" href="strand.html#boost_asio.reference.strand.thread_safety">Thread Safety</a>
</h5>
<p>
<span class="bold"><strong>Distinct</strong></span> <span class="bold"><strong>objects:</strong></span>
Safe.
</p>
<p>
<span class="bold"><strong>Shared</strong></span> <span class="bold"><strong>objects:</strong></span>
Safe.
</p>
<a name="boost_asio.reference.strand.requirements"></a><h5>
<a name="id1126768"></a>
<a class="link" href="strand.html#boost_asio.reference.strand.requirements">Requirements</a>
</h5>
<p>
<span class="bold"><strong>Header: </strong></span><code class="literal">boost/asio/strand.hpp</code>
</p>
<p>
<span class="bold"><strong>Convenience header: </strong></span><code class="literal">boost/asio.hpp</code>
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<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>)
</p>
</div></td>
</tr></table>
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