349 lines
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349 lines
16 KiB
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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<title>io_context::strand</title>
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<meta name="generator" content="DocBook XSL Stylesheets V1.75.2">
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<link rel="home" href="../../index.html" title="Asio">
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<link rel="up" href="../reference.html" title="Reference">
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<link rel="prev" href="io_context__service/_service.html" title="io_context::service::~service">
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<link rel="next" href="io_context__strand/context.html" title="io_context::strand::context">
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</head>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../asio.png"></td></tr></table>
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<hr>
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<div class="spirit-nav">
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<a accesskey="p" href="io_context__service/_service.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u" href="../reference.html"><img src="../../up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../home.png" alt="Home"></a><a accesskey="n" href="io_context__strand/context.html"><img src="../../next.png" alt="Next"></a>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h3 class="title">
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<a name="asio.reference.io_context__strand"></a><a class="link" href="io_context__strand.html" title="io_context::strand">io_context::strand</a>
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</h3></div></div></div>
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<p>
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<a class="indexterm" name="asio.indexterm.io_context__strand"></a>
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</p>
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<p>
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Provides serialised handler execution.
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</p>
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<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">strand</span>
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</pre>
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<h5>
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<a name="asio.reference.io_context__strand.h0"></a>
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<span><a name="asio.reference.io_context__strand.member_functions"></a></span><a class="link" href="io_context__strand.html#asio.reference.io_context__strand.member_functions">Member
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Functions</a>
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</h5>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>
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<p>
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Name
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</p>
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</th>
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<th>
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<p>
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Description
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</p>
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</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/context.html" title="io_context::strand::context"><span class="bold"><strong>context</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Obtain the underlying execution context.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/defer.html" title="io_context::strand::defer"><span class="bold"><strong>defer</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Request the strand to invoke the given function object.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/dispatch.html" title="io_context::strand::dispatch"><span class="bold"><strong>dispatch</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Request the strand to invoke the given function object. <br>
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<span class="silver"> —</span><br> (Deprecated: Use asio::dispatch().) Request the strand to
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invoke the given handler.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/on_work_finished.html" title="io_context::strand::on_work_finished"><span class="bold"><strong>on_work_finished</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Inform the strand that some work is no longer outstanding.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/on_work_started.html" title="io_context::strand::on_work_started"><span class="bold"><strong>on_work_started</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Inform the strand that it has some outstanding work to do.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/post.html" title="io_context::strand::post"><span class="bold"><strong>post</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Request the strand to invoke the given function object. <br>
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<span class="silver"> —</span><br> (Deprecated: Use asio::post().) Request the strand to invoke
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the given handler and return immediately.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/running_in_this_thread.html" title="io_context::strand::running_in_this_thread"><span class="bold"><strong>running_in_this_thread</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Determine whether the strand is running in the current thread.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/strand.html" title="io_context::strand::strand"><span class="bold"><strong>strand</strong></span></a> <span class="silver">[constructor]</span>
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</p>
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</td>
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<td>
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<p>
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Constructor.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/wrap.html" title="io_context::strand::wrap"><span class="bold"><strong>wrap</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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(Deprecated: Use asio::bind_executor().) Create a new handler that
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automatically dispatches the wrapped handler on the strand.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/_strand.html" title="io_context::strand::~strand"><span class="bold"><strong>~strand</strong></span></a> <span class="silver">[destructor]</span>
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</p>
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</td>
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<td>
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<p>
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Destructor.
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</p>
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</td>
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</tr>
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</tbody>
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</table></div>
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<h5>
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<a name="asio.reference.io_context__strand.h1"></a>
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<span><a name="asio.reference.io_context__strand.friends"></a></span><a class="link" href="io_context__strand.html#asio.reference.io_context__strand.friends">Friends</a>
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</h5>
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<div class="informaltable"><table class="table">
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<colgroup>
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<col>
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<col>
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</colgroup>
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<thead><tr>
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<th>
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<p>
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Name
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</p>
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</th>
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<th>
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<p>
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Description
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</p>
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</th>
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</tr></thead>
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<tbody>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/operator_not__eq_.html" title="io_context::strand::operator!="><span class="bold"><strong>operator!=</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Compare two strands for inequality.
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</p>
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</td>
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</tr>
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<tr>
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<td>
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<p>
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<a class="link" href="io_context__strand/operator_eq__eq_.html" title="io_context::strand::operator=="><span class="bold"><strong>operator==</strong></span></a>
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</p>
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</td>
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<td>
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<p>
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Compare two strands for equality.
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</p>
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</td>
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</tr>
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</tbody>
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</table></div>
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<p>
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The <a class="link" href="io_context__strand.html" title="io_context::strand"><code class="computeroutput"><span class="identifier">io_context</span><span class="special">::</span><span class="identifier">strand</span></code></a>
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class provides the ability to post and dispatch handlers with the guarantee
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that none of those handlers will execute concurrently.
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</p>
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<h5>
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<a name="asio.reference.io_context__strand.h2"></a>
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<span><a name="asio.reference.io_context__strand.order_of_handler_invocation"></a></span><a class="link" href="io_context__strand.html#asio.reference.io_context__strand.order_of_handler_invocation">Order
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of handler invocation</a>
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</h5>
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<p>
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Given:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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a strand object <code class="computeroutput"><span class="identifier">s</span></code>
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</li>
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<li class="listitem">
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an object <code class="computeroutput"><span class="identifier">a</span></code> meeting completion
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handler requirements
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</li>
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<li class="listitem">
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an object <code class="computeroutput"><span class="identifier">a1</span></code> which is
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an arbitrary copy of <code class="computeroutput"><span class="identifier">a</span></code>
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made by the implementation
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</li>
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<li class="listitem">
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an object <code class="computeroutput"><span class="identifier">b</span></code> meeting completion
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handler requirements
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</li>
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<li class="listitem">
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an object <code class="computeroutput"><span class="identifier">b1</span></code> which is
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an arbitrary copy of <code class="computeroutput"><span class="identifier">b</span></code>
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made by the implementation
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</li>
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</ul></div>
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<p>
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if any of the following conditions are true:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" type="disc">
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<li class="listitem">
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<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>
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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>
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</li>
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<li class="listitem">
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<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>
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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>,
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where the latter is performed outside the strand
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</li>
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<li class="listitem">
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<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>
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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>,
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where the former is performed outside the strand
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</li>
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<li class="listitem">
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<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>
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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>,
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where both are performed outside the strand
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</li>
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</ul></div>
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<p>
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then <code class="computeroutput"><span class="identifier">asio_handler_invoke</span><span class="special">(</span><span class="identifier">a1</span><span class="special">,</span>
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<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>
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<span class="special">&</span><span class="identifier">b1</span><span class="special">)</span></code>.
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</p>
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<p>
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Note that in the following case:
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</p>
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<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>
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<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>
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</pre>
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<p>
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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>,
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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>,
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but the order in which those are performed is unspecified. That is, you cannot
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state whether one happens-before the other. Therefore none of the above conditions
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are met and no ordering guarantee is made.
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</p>
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<h5>
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<a name="asio.reference.io_context__strand.h3"></a>
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<span><a name="asio.reference.io_context__strand.remarks"></a></span><a class="link" href="io_context__strand.html#asio.reference.io_context__strand.remarks">Remarks</a>
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</h5>
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<p>
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The implementation makes no guarantee that handlers posted or dispatched
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through different <code class="computeroutput"><span class="identifier">strand</span></code>
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objects will be invoked concurrently.
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</p>
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<h5>
|
||
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<a name="asio.reference.io_context__strand.h4"></a>
|
||
|
|
<span><a name="asio.reference.io_context__strand.thread_safety"></a></span><a class="link" href="io_context__strand.html#asio.reference.io_context__strand.thread_safety">Thread
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Safety</a>
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||
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</h5>
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||
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<p>
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||
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<span class="emphasis"><em>Distinct</em></span> <span class="emphasis"><em>objects:</em></span> Safe.
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||
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|
</p>
|
||
|
|
<p>
|
||
|
|
<span class="emphasis"><em>Shared</em></span> <span class="emphasis"><em>objects:</em></span> Safe.
|
||
|
|
</p>
|
||
|
|
<h5>
|
||
|
|
<a name="asio.reference.io_context__strand.h5"></a>
|
||
|
|
<span><a name="asio.reference.io_context__strand.requirements"></a></span><a class="link" href="io_context__strand.html#asio.reference.io_context__strand.requirements">Requirements</a>
|
||
|
|
</h5>
|
||
|
|
<p>
|
||
|
|
<span class="emphasis"><em>Header: </em></span><code class="literal">asio/io_context_strand.hpp</code>
|
||
|
|
</p>
|
||
|
|
<p>
|
||
|
|
<span class="emphasis"><em>Convenience header: </em></span><code class="literal">asio.hpp</code>
|
||
|
|
</p>
|
||
|
|
</div>
|
||
|
|
<div class="copyright-footer">Copyright © 2003-2023 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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</div>
|
||
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