83 lines
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83 lines
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<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
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<title>Customising Immediate Completion</title>
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<link rel="up" href="../composition.html" title="Composition and Completion Tokens">
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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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<div class="spirit-nav">
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<a accesskey="p" href="type_erasure.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u" href="../composition.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="../networking.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.composition.immediate_completion"></a><a class="link" href="immediate_completion.html" title="Customising Immediate Completion">Customising
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Immediate Completion</a>
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</h4></div></div></div>
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<p>
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The <code class="computeroutput"><span class="identifier">associated_immediate_executor</span></code>
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associator trait, along with the <code class="computeroutput"><span class="identifier">bind_immediate_executor</span></code>
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function, provide the ability to customise the execution of a completion
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handler when an asynchronous operation completes immediately.
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</p>
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<p>
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When a supported operation completes immediately (that is, within the initiating
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function) the associated immmediate executor is obtained, and the completion
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handler is delivered through that executor as if by using <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">dispatch</span></code> on that executor. By default,
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the immediate executor delivers the completion handler as if using <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span class="identifier">post</span></code> via the operation's I/O executor.
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</p>
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<p>
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For example, to allow a recursive call to the completion handler of an
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<code class="computeroutput"><span class="identifier">async_read_some</span></code> operation,
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we may specify that immediate completion is delivered via a <code class="computeroutput"><span class="identifier">system_executor</span></code>:
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</p>
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<pre class="programlisting"><span class="identifier">my_socket</span><span class="special">.</span><span class="identifier">async_read_some</span><span class="special">(</span><span class="identifier">my_buffer</span><span class="special">,</span>
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<span class="identifier">bind_immediate_executor</span><span class="special">(</span>
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<span class="identifier">system_executor</span><span class="special">(),</span>
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<span class="special">[](</span><span class="identifier">error_code</span> <span class="identifier">e</span><span class="special">,</span> <span class="identifier">size_t</span> <span class="identifier">n</span><span class="special">)</span>
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<span class="special">{</span>
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<span class="comment">// ...</span>
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<span class="special">}</span>
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<span class="special">)</span>
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<span class="special">);</span>
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</pre>
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<p>
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Immediate execution is currently supported for asynchronous operations
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on reactor-based sockets and descriptors, and for asynchronous operations
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on channels.
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</p>
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<p>
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<span class="bold"><strong>Note:</strong></span> When enabling the immediate execution
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of completion handlers, care must be taken to ensure that unbounded recursion
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and stack overflow do not occur. Furthermore, use of immediate completion
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may impact the fairness of completion handler scheduling, with a potential
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for starvation for other pending work.
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</p>
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<h6>
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<a name="asio.overview.composition.immediate_completion.h0"></a>
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<span><a name="asio.overview.composition.immediate_completion.see_also"></a></span><a class="link" href="immediate_completion.html#asio.overview.composition.immediate_completion.see_also">See Also</a>
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</h6>
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<p>
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<a class="link" href="../../reference/associated_immediate_executor.html" title="associated_immediate_executor">associated_immediate_executor</a>,
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<a class="link" href="../../reference/bind_immediate_executor.html" title="bind_immediate_executor">bind_immediate_executor</a>.
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</p>
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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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