<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=US-ASCII"> <title>io_service::strand</title> <link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> <meta name="generator" content="DocBook XSL Stylesheets V1.78.1"> <link rel="home" href="../../boost_asio.html" title="Boost.Asio"> <link rel="up" href="../reference.html" title="Reference"> <link rel="prev" href="io_service__service/shutdown_service.html" title="io_service::service::shutdown_service"> <link rel="next" href="io_service__strand/dispatch.html" title="io_service::strand::dispatch"> </head> <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> <table cellpadding="2" width="100%"><tr> <td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td> <td align="center"><a href="../../../../index.html">Home</a></td> <td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td> <td 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serialised handler execution. </p> <pre class="programlisting"><span class="keyword">class</span> <span class="identifier">strand</span> </pre> <h5> <a name="boost_asio.reference.io_service__strand.h0"></a> <span class="phrase"><a name="boost_asio.reference.io_service__strand.member_functions"></a></span><a class="link" href="io_service__strand.html#boost_asio.reference.io_service__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/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/running_in_this_thread.html" title="io_service::strand::running_in_this_thread"><span class="bold"><strong>running_in_this_thread</strong></span></a> </p> </td> <td> <p> Determine whether the strand is running in the current thread. </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> <h5> <a name="boost_asio.reference.io_service__strand.h1"></a> <span class="phrase"><a name="boost_asio.reference.io_service__strand.order_of_handler_invocation"></a></span><a class="link" href="io_service__strand.html#boost_asio.reference.io_service__strand.order_of_handler_invocation">Order of handler invocation</a> </h5> <p> Given: </p> <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"> a strand object <code class="computeroutput"><span class="identifier">s</span></code> </li> <li class="listitem"> an object <code class="computeroutput"><span class="identifier">a</span></code> meeting completion handler requirements </li> <li class="listitem"> an object <code class="computeroutput"><span class="identifier">a1</span></code> which is an arbitrary copy of <code class="computeroutput"><span class="identifier">a</span></code> made by the implementation </li> <li class="listitem"> an object <code class="computeroutput"><span class="identifier">b</span></code> meeting completion handler requirements </li> <li class="listitem"> an object <code class="computeroutput"><span class="identifier">b1</span></code> which is an arbitrary copy of <code class="computeroutput"><span class="identifier">b</span></code> made by the implementation </li> </ul></div> <p> if any of the following conditions are true: </p> <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "> <li class="listitem"> <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span class="identifier">post</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span></code> happens-before <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span class="identifier">post</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code> </li> <li class="listitem"> <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span class="identifier">post</span><span class="special">(</span><span class="identifier">a</span><span class="special">)</span></code> happens-before <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>, where the latter is performed outside the strand </li> <li class="listitem"> <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> happens-before <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span class="identifier">post</span><span class="special">(</span><span class="identifier">b</span><span class="special">)</span></code>, where the former is performed outside the strand </li> <li class="listitem"> <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> happens-before <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>, 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> <h5> <a name="boost_asio.reference.io_service__strand.h2"></a> <span class="phrase"><a name="boost_asio.reference.io_service__strand.remarks"></a></span><a class="link" href="io_service__strand.html#boost_asio.reference.io_service__strand.remarks">Remarks</a> </h5> <p> The implementation makes no guarantee that handlers posted or dispatched through different <code class="computeroutput"><span class="identifier">strand</span></code> objects will be invoked concurrently. </p> <h5> <a name="boost_asio.reference.io_service__strand.h3"></a> <span class="phrase"><a name="boost_asio.reference.io_service__strand.thread_safety"></a></span><a class="link" href="io_service__strand.html#boost_asio.reference.io_service__strand.thread_safety">Thread Safety</a> </h5> <p> <span class="emphasis"><em>Distinct</em></span> <span class="emphasis"><em>objects:</em></span> Safe. </p> <p> <span class="emphasis"><em>Shared</em></span> <span class="emphasis"><em>objects:</em></span> Safe. </p> <h5> <a name="boost_asio.reference.io_service__strand.h4"></a> <span class="phrase"><a name="boost_asio.reference.io_service__strand.requirements"></a></span><a class="link" href="io_service__strand.html#boost_asio.reference.io_service__strand.requirements">Requirements</a> </h5> <p> <span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/strand.hpp</code> </p> <p> <span class="emphasis"><em>Convenience header: </em></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 © 2003-2015 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> <hr> <div class="spirit-nav"> <a accesskey="p" href="io_service__service/shutdown_service.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="io_service__strand/dispatch.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> </div> </body> </html>