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| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_asio.reference.io_service__strand"></a><a class="link" href="io_service__strand.html" title="io_service::strand">io_service::strand</a> |
| </h3></div></div></div> |
| <p> |
| Provides 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> |
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