109 lines
5.6 KiB
HTML
109 lines
5.6 KiB
HTML
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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>Child Agents</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="../model.html" title="Asynchronous Model">
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<link rel="prev" href="associators.html" title="Associated Characteristics and Associators">
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<link rel="next" href="executors.html" title="Executors">
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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="associators.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../model.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="executors.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><h4 class="title">
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<a name="asio.overview.model.child_agents"></a><a class="link" href="child_agents.html" title="Child Agents">Child Agents</a>
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</h4></div></div></div>
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<p>
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The asynchronous operations within an agent may themselves be implemented
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in terms of child agents.<sup>[<a name="asio.overview.model.child_agents.f0" href="#ftn.asio.overview.model.child_agents.f0" class="footnote">3</a>]</sup> As far as the parent agent is concerned, it is waiting for
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the completion of a single asynchronous operation. The asynchronous operations
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that constitute the child agent run in sequence, and when the final completion
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handler runs the parent agent is resumed.
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</p>
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<p>
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<span class="inlinemediaobject"><img src="../../../async_child_agent_chain.png" width="802"></span>
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</p>
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<p>
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As with individual asynchronous operations, the asynchronous operations
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built on child agents must release their temporary resources prior to calling
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the completion handler. We may also think of these child agents as resources
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that end their lifetimes before the completion handler is invoked.
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</p>
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<p>
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When an asynchronous operation creates a child agent, it may propagate<sup>[<a name="asio.overview.model.child_agents.f1" href="#ftn.asio.overview.model.child_agents.f1" class="footnote">4</a>]</sup> the associated characteristics of the parent agent to the child
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agent. These associated characteristics may then be recursively propagated
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through further layers of asynchronous operations and child agents. This
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stacking of asynchronous operations replicates another property of synchronous
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operations.
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</p>
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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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Property of synchronous operations
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</p>
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</th>
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<th>
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<p>
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Equivalent property of asynchronous operations
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</p>
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</th>
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</tr></thead>
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<tbody><tr>
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<td>
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<p>
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Compositions of synchronous operations may be refactored to use
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child functions that run on the same thread (i.e. are simply
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called) without altering functionality.
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</p>
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</td>
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<td>
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<p>
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Asynchronous agents may be refactored to use asynchronous operations
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and child agents that share the associated characteristics of
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the parent agent, without altering functionality.
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</p>
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</td>
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</tr></tbody>
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</table></div>
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<p>
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Finally, some asynchronous operations may be implemented in terms of multiple
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child agents that run concurrently. In this case, the asynchronous operation
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may choose to selectively propagate the associated characteristics of the
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parent agent.
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</p>
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<div class="footnotes">
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<br><hr width="100" align="left">
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<div class="footnote"><p><sup>[<a name="ftn.asio.overview.model.child_agents.f0" href="#asio.overview.model.child_agents.f0" class="para">3</a>] </sup>
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In Asio these asynchronous operations are referred to as <span class="emphasis"><em>composed
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operations</em></span>.
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</p></div>
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<div class="footnote"><p><sup>[<a name="ftn.asio.overview.model.child_agents.f1" href="#asio.overview.model.child_agents.f1" class="para">4</a>] </sup>
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Typically, by specialising the associator trait and forwarding to the
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outer completion handler.
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</p></div>
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</div>
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</div>
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<div class="copyright-footer">Copyright © 2003-2023 Christopher M. Kohlhoff<p>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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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>)
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</p>
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</div>
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<hr>
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<div class="spirit-nav">
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<a accesskey="p" href="associators.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../model.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="executors.html"><img src="../../../next.png" alt="Next"></a>
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</div>
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</body>
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</html>
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