87 lines
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87 lines
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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>Timers</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="../overview.html" title="Overview">
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<link rel="prev" href="networking/bsd_sockets.html" title="The BSD Socket API and Asio">
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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="networking/bsd_sockets.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u" href="../overview.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="files.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.overview.timers"></a><a class="link" href="timers.html" title="Timers">Timers</a>
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</h3></div></div></div>
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<p>
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Long running I/O operations will often have a deadline by which they must
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have completed. These deadlines may be expressed as absolute times, but are
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often calculated relative to the current time.
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</p>
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<p>
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As a simple example, to perform a synchronous wait operation on a timer using
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a relative time one may write:
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</p>
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<pre class="programlisting"><span class="identifier">io_context</span> <span class="identifier">i</span><span class="special">;</span>
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<span class="special">...</span>
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<span class="identifier">steady_timer</span> <span class="identifier">t</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>
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<span class="identifier">t</span><span class="special">.</span><span class="identifier">expires_after</span><span class="special">(</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">5</span><span class="special">));</span>
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<span class="identifier">t</span><span class="special">.</span><span class="identifier">wait</span><span class="special">();</span>
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</pre>
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<p>
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More commonly, a program will perform an asynchronous wait operation on a
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timer:
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</p>
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<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error_code</span> <span class="identifier">ec</span><span class="special">)</span> <span class="special">{</span> <span class="special">...</span> <span class="special">}</span>
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<span class="special">...</span>
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<span class="identifier">io_context</span> <span class="identifier">i</span><span class="special">;</span>
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<span class="special">...</span>
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<span class="identifier">steady_timer</span> <span class="identifier">t</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>
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<span class="identifier">t</span><span class="special">.</span><span class="identifier">expires_after</span><span class="special">(</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">milliseconds</span><span class="special">(</span><span class="number">400</span><span class="special">));</span>
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<span class="identifier">t</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">handler</span><span class="special">);</span>
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<span class="special">...</span>
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<span class="identifier">i</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span>
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</pre>
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<p>
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The deadline associated with a timer may also be obtained as an absolute
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time:
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</p>
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<pre class="programlisting"><span class="identifier">steady_timer</span><span class="special">::</span><span class="identifier">time_point</span> <span class="identifier">time_of_expiry</span> <span class="special">=</span> <span class="identifier">t</span><span class="special">.</span><span class="identifier">expiry</span><span class="special">();</span>
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</pre>
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<p>
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which allows composition of timers:
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</p>
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<pre class="programlisting"><span class="identifier">steady_timer</span> <span class="identifier">t2</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span>
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<span class="identifier">t2</span><span class="special">.</span><span class="identifier">expires_at</span><span class="special">(</span><span class="identifier">t</span><span class="special">.</span><span class="identifier">expiry</span><span class="special">()</span> <span class="special">+</span> <span class="identifier">chrono</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">30</span><span class="special">));</span>
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</pre>
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<h5>
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<a name="asio.overview.timers.h0"></a>
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<span><a name="asio.overview.timers.see_also"></a></span><a class="link" href="timers.html#asio.overview.timers.see_also">See
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Also</a>
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</h5>
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<p>
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<a class="link" href="../reference/basic_waitable_timer.html" title="basic_waitable_timer">basic_waitable_timer</a>,
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<a class="link" href="../reference/steady_timer.html" title="steady_timer">steady_timer</a>, <a class="link" href="../reference/system_timer.html" title="system_timer">system_timer</a>,
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<a class="link" href="../reference/high_resolution_timer.html" title="high_resolution_timer">high_resolution_timer</a>,
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<a class="link" href="../tutorial/tuttimer1.html" title="Timer.1 - Using a timer synchronously">timer tutorials</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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<div class="spirit-nav">
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<a accesskey="p" href="networking/bsd_sockets.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u" href="../overview.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="files.html"><img src="../../next.png" alt="Next"></a>
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