100 lines
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100 lines
6.7 KiB
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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>Timer.1 - Using a timer synchronously</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="prev" href="../tutorial.html" title="Tutorial">
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<link rel="next" href="tuttimer1/src.html" title="Source listing for Timer.1">
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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="../tutorial.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u" href="../tutorial.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="tuttimer1/src.html"><img src="../../next.png" alt="Next"></a>
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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.tutorial.tuttimer1"></a><a class="link" href="tuttimer1.html" title="Timer.1 - Using a timer synchronously">Timer.1 - Using a timer synchronously</a>
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</h3></div></div></div>
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<p>
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This tutorial program introduces asio by showing how to perform a blocking
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wait on a timer.
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</p>
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<p>
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We start by including the necessary header files.
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</p>
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<p>
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All of the asio classes can be used by simply including the <code class="computeroutput"><span class="string">"asio.hpp"</span></code> header file.
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</p>
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<pre class="programlisting"><span class="special">#</span><span class="identifier">include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span>
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<span class="special">#</span><span class="identifier">include</span> <span class="special"><</span><span class="identifier">asio</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
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</pre>
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<p>
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All programs that use asio need to have at least one I/O execution context,
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such as an <a class="link" href="../reference/io_context.html" title="io_context">io_context</a> or
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<a class="link" href="../reference/thread_pool.html" title="thread_pool">thread_pool</a> object. An
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I/O execution context provides access to I/O functionality. We declare an
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object of type <a class="link" href="../reference/io_context.html" title="io_context">io_context</a>
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first thing in the main function.
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</p>
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<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
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<span class="special">{</span>
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<span class="identifier">asio</span><span class="special">::</span><span class="identifier">io_context</span> <span class="identifier">io</span><span class="special">;</span>
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</pre>
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<p>
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Next we declare an object of type asio::steady_timer. The core asio classes
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that provide I/O functionality (or as in this case timer functionality) always
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take an executor, or a reference to an execution context (such as <a class="link" href="../reference/io_context.html" title="io_context">io_context</a>),
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as their first constructor argument. The second argument to the constructor
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sets the timer to expire 5 seconds from now.
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</p>
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<pre class="programlisting"> <span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span> <span class="identifier">t</span><span class="special">(</span><span class="identifier">io</span><span class="special">,</span> <span class="identifier">asio</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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</pre>
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<p>
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In this simple example we perform a blocking wait on the timer. That is,
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the call to <a class="link" href="../reference/basic_waitable_timer/wait.html" title="basic_waitable_timer::wait">steady_timer::wait()</a>
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will not return until the timer has expired, 5 seconds after it was created
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(i.e. not from when the wait starts).
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</p>
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<p>
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A timer is always in one of two states: "expired" or "not
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expired". If the <a class="link" href="../reference/basic_waitable_timer/wait.html" title="basic_waitable_timer::wait">steady_timer::wait()</a>
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function is called on an expired timer, it will return immediately.
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</p>
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<pre class="programlisting"> <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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Finally we print the obligatory <code class="computeroutput"><span class="string">"Hello,
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world!"</span></code> message to show when the timer has expired.
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</p>
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<pre class="programlisting"> <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="string">"Hello, world!"</span> <span class="special"><<</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
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<span class="keyword">return</span> <span class="number">0</span><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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See the <a class="link" href="tuttimer1/src.html" title="Source listing for Timer.1">full source listing</a>
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</p>
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<p>
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Return to the <a class="link" href="../tutorial.html" title="Tutorial">tutorial index</a>
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</p>
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<p>
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Next: <a class="link" href="tuttimer2.html" title="Timer.2 - Using a timer asynchronously">Timer.2 - Using a timer asynchronously</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="../tutorial.html"><img src="../../prev.png" alt="Prev"></a><a accesskey="u" href="../tutorial.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="tuttimer1/src.html"><img src="../../next.png" alt="Next"></a>
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