105 lines
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HTML
105 lines
5.4 KiB
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>Executors</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="../model.html" title="Asynchronous Model">
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<link rel="prev" href="child_agents.html" title="Child Agents">
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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="child_agents.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="allocators.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.executors"></a><a class="link" href="executors.html" title="Executors">Executors</a>
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</h4></div></div></div>
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<p>
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Every asynchronous agent has an associated <span class="emphasis"><em>executor</em></span>.
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An agent's executor determines how the agent's completion handlers are
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queued and ultimately run.
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</p>
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<p>
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Example uses of executors include:
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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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Coordinating a group of asynchronous agents that operate on shared
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data structures, ensuring that the agents' completion handlers never
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run concurrently<sup>[<a name="asio.overview.model.executors.f0" href="#ftn.asio.overview.model.executors.f0" class="footnote">5</a>]</sup>.
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</li>
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<li class="listitem">
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Ensuring that agents are run on specified execution resource (e.g.
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a CPU) that is proximal to data or an event source (e.g. a NIC).
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</li>
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<li class="listitem">
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Denoting a group of related agents, and so enabling dynamic thread
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pools to make smarter scheduling decisions (such as moving the agents
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between execution resources as a unit).
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</li>
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<li class="listitem">
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Queuing all completion handlers to run on a GUI application thread,
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so that they may safely update user interface elements.
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</li>
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<li class="listitem">
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Returning an asynchronous operation's default executor as-is, to run
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completion handlers as close as possible to the event that triggered
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the operation's completion.
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</li>
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<li class="listitem">
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Adapting an asynchronous operation's default executor, to run code
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before and after every completion handler, such as logging, user authorisation,
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or exception handling.
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</li>
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<li class="listitem">
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Specifying a priority for an asynchronous agent and its completion
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handlers.
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</li>
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</ul></div>
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<p>
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The asynchronous operations within an asynchronous agent use the agent's
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associated executor to:
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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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Track the existence of the work that the asynchronous operation represents,
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while the operation is outstanding.
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</li>
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<li class="listitem">
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Enqueue the completion handler for execution on completion of an operation.
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</li>
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<li class="listitem">
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Ensure that completion handlers do not run re-entrantly, if doing so
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might lead to inadvertent recursion and stack overflow.
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</li>
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</ul></div>
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<p>
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Thus, an asynchronous agent's associated executor represents a policy of
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how, where, and when the agent should run, specified as a cross-cutting
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concern to the code that makes up the 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.executors.f0" href="#asio.overview.model.executors.f0" class="para">5</a>] </sup>
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In Asio, this kind of executor is called a <a class="link" href="../core/strands.html" title="Strands: Use Threads Without Explicit Locking">strand</a>.
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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="child_agents.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="allocators.html"><img src="../../../next.png" alt="Next"></a>
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