391 lines
18 KiB
HTML
391 lines
18 KiB
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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<title>execution_context</title>
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<link rel="stylesheet" href="../../boostbook.css" type="text/css">
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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="execution__submit.html" title="execution::submit">
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<link rel="next" href="execution_context/add_service.html" title="execution_context::add_service">
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<meta name="viewport" content="width=device-width, initial-scale=1">
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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="execution__submit.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="execution_context/add_service.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.execution_context"></a><a class="link" href="execution_context.html" title="execution_context">execution_context</a>
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</h3></div></div></div>
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<p>
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<a class="indexterm" name="asio.indexterm.execution_context"></a>
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</p>
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<p>
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A context for function object execution.
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</p>
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<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">execution_context</span> <span class="special">:</span>
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<span class="identifier">noncopyable</span>
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</pre>
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<h5>
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<a name="asio.reference.execution_context.h0"></a>
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<span><a name="asio.reference.execution_context.types"></a></span><a class="link" href="execution_context.html#asio.reference.execution_context.types">Types</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="execution_context__id.html" title="execution_context::id"><span class="bold"><strong>id</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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Class used to uniquely identify a service.
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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="execution_context__service.html" title="execution_context::service"><span class="bold"><strong>service</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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Base class for all io_context services.
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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="execution_context/fork_event.html" title="execution_context::fork_event"><span class="bold"><strong>fork_event</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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Fork-related event notifications.
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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.execution_context.h1"></a>
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<span><a name="asio.reference.execution_context.member_functions"></a></span><a class="link" href="execution_context.html#asio.reference.execution_context.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="execution_context/execution_context.html" title="execution_context::execution_context"><span class="bold"><strong>execution_context</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="execution_context/notify_fork.html" title="execution_context::notify_fork"><span class="bold"><strong>notify_fork</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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Notify the execution_context of a fork-related event.
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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="execution_context/_execution_context.html" title="execution_context::~execution_context"><span class="bold"><strong>~execution_context</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.execution_context.h2"></a>
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<span><a name="asio.reference.execution_context.protected_member_functions"></a></span><a class="link" href="execution_context.html#asio.reference.execution_context.protected_member_functions">Protected
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Member 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="execution_context/destroy.html" title="execution_context::destroy"><span class="bold"><strong>destroy</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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Destroys all services in the 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="execution_context/shutdown.html" title="execution_context::shutdown"><span class="bold"><strong>shutdown</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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Shuts down all services in the context.
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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.execution_context.h3"></a>
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<span><a name="asio.reference.execution_context.friends"></a></span><a class="link" href="execution_context.html#asio.reference.execution_context.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="execution_context/add_service.html" title="execution_context::add_service"><span class="bold"><strong>add_service</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 make_service().) Add a service object to the 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="execution_context/has_service.html" title="execution_context::has_service"><span class="bold"><strong>has_service</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 if an execution_context contains a specified service
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type.
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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="execution_context/make_service.html" title="execution_context::make_service"><span class="bold"><strong>make_service</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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Creates a service object and adds it to the 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="execution_context/use_service.html" title="execution_context::use_service"><span class="bold"><strong>use_service</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 service object corresponding to the given type.
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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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An execution context represents a place where function objects will be executed.
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An <code class="computeroutput"><span class="identifier">io_context</span></code> is an example
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of an execution context.
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</p>
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<h5>
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<a name="asio.reference.execution_context.h4"></a>
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<span><a name="asio.reference.execution_context.the_execution_context_class_and_services"></a></span><a class="link" href="execution_context.html#asio.reference.execution_context.the_execution_context_class_and_services">The
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execution_context class and services</a>
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</h5>
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<p>
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Class <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a>
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implements an extensible, type-safe, polymorphic set of services, indexed
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by service type.
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</p>
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<p>
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Services exist to manage the resources that are shared across an execution
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context. For example, timers may be implemented in terms of a single timer
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queue, and this queue would be stored in a service.
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</p>
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<p>
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Access to the services of an <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> is via three function
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templates, <code class="computeroutput"><span class="identifier">use_service</span><span class="special">()</span></code>,
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<code class="computeroutput"><span class="identifier">add_service</span><span class="special">()</span></code>
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and <code class="computeroutput"><span class="identifier">has_service</span><span class="special">()</span></code>.
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</p>
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<p>
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In a call to <code class="computeroutput"><span class="identifier">use_service</span><span class="special"><</span><span class="identifier">Service</span><span class="special">>()</span></code>, the type argument chooses a service,
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making available all members of the named type. If <code class="computeroutput"><span class="identifier">Service</span></code>
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is not present in an <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a>, an object of
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type <code class="computeroutput"><span class="identifier">Service</span></code> is created and
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added to the <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a>. A C++ program
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can check if an <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> implements a particular
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service with the function template <code class="computeroutput"><span class="identifier">has_service</span><span class="special"><</span><span class="identifier">Service</span><span class="special">>()</span></code>.
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</p>
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<p>
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Service objects may be explicitly added to an <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> using the function
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template <code class="computeroutput"><span class="identifier">add_service</span><span class="special"><</span><span class="identifier">Service</span><span class="special">>()</span></code>.
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If the <code class="computeroutput"><span class="identifier">Service</span></code> is already
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present, the <a class="link" href="service_already_exists.html" title="service_already_exists"><code class="computeroutput"><span class="identifier">service_already_exists</span></code></a> exception
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is thrown. If the owner of the service is not the same object as the <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a>
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parameter, the <a class="link" href="invalid_service_owner.html" title="invalid_service_owner"><code class="computeroutput"><span class="identifier">invalid_service_owner</span></code></a> exception
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is thrown.
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</p>
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<p>
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Once a service reference is obtained from an <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> object by calling
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<code class="computeroutput"><span class="identifier">use_service</span><span class="special">()</span></code>,
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that reference remains usable as long as the owning <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> object exists.
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</p>
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<p>
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All service implementations have <a class="link" href="execution_context__service.html" title="execution_context::service"><code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="identifier">service</span></code></a> as a public base class.
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Custom services may be implemented by deriving from this class and then added
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to an <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a>
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using the facilities described above.
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</p>
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<h5>
|
||
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<a name="asio.reference.execution_context.h5"></a>
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||
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<span><a name="asio.reference.execution_context.the_execution_context_as_a_base_class"></a></span><a class="link" href="execution_context.html#asio.reference.execution_context.the_execution_context_as_a_base_class">The
|
||
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|
execution_context as a base class</a>
|
||
|
|
</h5>
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||
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|
<p>
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||
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Class <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a>
|
||
|
|
may be used only as a base class for concrete execution context types. The
|
||
|
|
<code class="computeroutput"><span class="identifier">io_context</span></code> is an example
|
||
|
|
of such a derived type.
|
||
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|
</p>
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||
|
|
<p>
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||
|
|
On destruction, a class that is derived from <a class="link" href="execution_context.html" title="execution_context"><code class="computeroutput"><span class="identifier">execution_context</span></code></a> must perform
|
||
|
|
<code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="identifier">shutdown</span><span class="special">()</span></code>
|
||
|
|
followed by <code class="computeroutput"><span class="identifier">execution_context</span><span class="special">::</span><span class="identifier">destroy</span><span class="special">()</span></code>.
|
||
|
|
</p>
|
||
|
|
<p>
|
||
|
|
This destruction sequence permits programs to simplify their resource management
|
||
|
|
by using <code class="computeroutput"><span class="identifier">shared_ptr</span><span class="special"><></span></code>.
|
||
|
|
Where an object's lifetime is tied to the lifetime of a connection (or some
|
||
|
|
other sequence of asynchronous operations), a <code class="computeroutput"><span class="identifier">shared_ptr</span></code>
|
||
|
|
to the object would be bound into the handlers for all asynchronous operations
|
||
|
|
associated with it. This works as follows:
|
||
|
|
</p>
|
||
|
|
<div class="itemizedlist"><ul class="itemizedlist" type="disc">
|
||
|
|
<li class="listitem">
|
||
|
|
When a single connection ends, all associated asynchronous operations
|
||
|
|
complete. The corresponding handler objects are destroyed, and all <code class="computeroutput"><span class="identifier">shared_ptr</span></code> references to the objects
|
||
|
|
are destroyed.
|
||
|
|
</li>
|
||
|
|
<li class="listitem">
|
||
|
|
To shut down the whole program, the <a class="link" href="io_context.html" title="io_context"><code class="computeroutput"><span class="identifier">io_context</span></code></a> function stop() is
|
||
|
|
called to terminate any run() calls as soon as possible. The <a class="link" href="io_context.html" title="io_context"><code class="computeroutput"><span class="identifier">io_context</span></code></a> destructor calls
|
||
|
|
<code class="computeroutput"><span class="identifier">shutdown</span><span class="special">()</span></code>
|
||
|
|
and <code class="computeroutput"><span class="identifier">destroy</span><span class="special">()</span></code>
|
||
|
|
to destroy all pending handlers, causing all <code class="computeroutput"><span class="identifier">shared_ptr</span></code>
|
||
|
|
references to all connection objects to be destroyed.
|
||
|
|
</li>
|
||
|
|
</ul></div>
|
||
|
|
<h5>
|
||
|
|
<a name="asio.reference.execution_context.h6"></a>
|
||
|
|
<span><a name="asio.reference.execution_context.requirements"></a></span><a class="link" href="execution_context.html#asio.reference.execution_context.requirements">Requirements</a>
|
||
|
|
</h5>
|
||
|
|
<p>
|
||
|
|
<span class="emphasis"><em>Header: </em></span><code class="literal">asio/execution_context.hpp</code>
|
||
|
|
</p>
|
||
|
|
<p>
|
||
|
|
<span class="emphasis"><em>Convenience header: </em></span><code class="literal">asio/execution.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>
|
||
|
|
</div>
|
||
|
|
<hr>
|
||
|
|
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