1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>Timers</title> 5<link rel="stylesheet" href="../../../../doc/src/boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../../boost_asio.html" title="Boost.Asio"> 8<link rel="up" href="../overview.html" title="Overview"> 9<link rel="prev" href="networking/bsd_sockets.html" title="The BSD Socket API and Boost.Asio"> 10<link rel="next" href="serial_ports.html" title="Serial Ports"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr> 14<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../boost.png"></td> 15<td align="center"><a href="../../../../index.html">Home</a></td> 16<td align="center"><a href="../../../../libs/libraries.htm">Libraries</a></td> 17<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 18<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 19<td align="center"><a href="../../../../more/index.htm">More</a></td> 20</tr></table> 21<hr> 22<div class="spirit-nav"> 23<a accesskey="p" href="networking/bsd_sockets.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../overview.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="serial_ports.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 24</div> 25<div class="section"> 26<div class="titlepage"><div><div><h3 class="title"> 27<a name="boost_asio.overview.timers"></a><a class="link" href="timers.html" title="Timers">Timers</a> 28</h3></div></div></div> 29<p> 30 Long running I/O operations will often have a deadline by which they must 31 have completed. These deadlines may be expressed as absolute times, but are 32 often calculated relative to the current time. 33 </p> 34<p> 35 As a simple example, to perform a synchronous wait operation on a timer using 36 a relative time one may write: 37 </p> 38<pre class="programlisting">io_context i; 39... 40deadline_timer t(i); 41t.expires_from_now(boost::posix_time::seconds(5)); 42t.wait(); 43</pre> 44<p> 45 More commonly, a program will perform an asynchronous wait operation on a 46 timer: 47 </p> 48<pre class="programlisting">void handler(boost::system::error_code ec) { ... } 49... 50io_context i; 51... 52deadline_timer t(i); 53t.expires_from_now(boost::posix_time::milliseconds(400)); 54t.async_wait(handler); 55... 56i.run(); 57</pre> 58<p> 59 The deadline associated with a timer may also be obtained as a relative time: 60 </p> 61<pre class="programlisting">boost::posix_time::time_duration time_until_expiry 62 = t.expires_from_now(); 63</pre> 64<p> 65 or as an absolute time to allow composition of timers: 66 </p> 67<pre class="programlisting">deadline_timer t2(i); 68t2.expires_at(t.expires_at() + boost::posix_time::seconds(30)); 69</pre> 70<h5> 71<a name="boost_asio.overview.timers.h0"></a> 72 <span class="phrase"><a name="boost_asio.overview.timers.see_also"></a></span><a class="link" href="timers.html#boost_asio.overview.timers.see_also">See 73 Also</a> 74 </h5> 75<p> 76 <a class="link" href="../reference/basic_deadline_timer.html" title="basic_deadline_timer">basic_deadline_timer</a>, 77 <a class="link" href="../reference/deadline_timer.html" title="deadline_timer">deadline_timer</a>, 78 <a class="link" href="../tutorial/tuttimer1.html" title="Timer.1 - Using a timer synchronously">timer tutorials</a>. 79 </p> 80</div> 81<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 82<td align="left"></td> 83<td align="right"><div class="copyright-footer">Copyright © 2003-2020 Christopher M. 84 Kohlhoff<p> 85 Distributed under the Boost Software License, Version 1.0. (See accompanying 86 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>) 87 </p> 88</div></td> 89</tr></table> 90<hr> 91<div class="spirit-nav"> 92<a accesskey="p" href="networking/bsd_sockets.html"><img src="../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../overview.html"><img src="../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../boost_asio.html"><img src="../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="serial_ports.html"><img src="../../../../doc/src/images/next.png" alt="Next"></a> 93</div> 94</body> 95</html> 96
