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| <div class="section"> |
| <div class="titlepage"><div><div><h3 class="title"> |
| <a name="boost_asio.overview.timers"></a><a class="link" href="timers.html" title="Timers">Timers</a> |
| </h3></div></div></div> |
| <p> |
| Long running I/O operations will often have a deadline by which they must |
| have completed. These deadlines may be expressed as absolute times, but are |
| often calculated relative to the current time. |
| </p> |
| <p> |
| As a simple example, to perform a synchronous wait operation on a timer using |
| a relative time one may write: |
| </p> |
| <pre class="programlisting"><span class="identifier">io_service</span> <span class="identifier">i</span><span class="special">;</span> |
| <span class="special">...</span> |
| <span class="identifier">deadline_timer</span> <span class="identifier">t</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span> |
| <span class="identifier">t</span><span class="special">.</span><span class="identifier">expires_from_now</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">posix_time</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">5</span><span class="special">));</span> |
| <span class="identifier">t</span><span class="special">.</span><span class="identifier">wait</span><span class="special">();</span> |
| </pre> |
| <p> |
| More commonly, a program will perform an asynchronous wait operation on a |
| timer: |
| </p> |
| <pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">system</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> |
| <span class="special">...</span> |
| <span class="identifier">io_service</span> <span class="identifier">i</span><span class="special">;</span> |
| <span class="special">...</span> |
| <span class="identifier">deadline_timer</span> <span class="identifier">t</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span> |
| <span class="identifier">t</span><span class="special">.</span><span class="identifier">expires_from_now</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">posix_time</span><span class="special">::</span><span class="identifier">milliseconds</span><span class="special">(</span><span class="number">400</span><span class="special">));</span> |
| <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> |
| <span class="special">...</span> |
| <span class="identifier">i</span><span class="special">.</span><span class="identifier">run</span><span class="special">();</span> |
| </pre> |
| <p> |
| The deadline associated with a timer may be also be obtained as a relative |
| time: |
| </p> |
| <pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">posix_time</span><span class="special">::</span><span class="identifier">time_duration</span> <span class="identifier">time_until_expiry</span> |
| <span class="special">=</span> <span class="identifier">t</span><span class="special">.</span><span class="identifier">expires_from_now</span><span class="special">();</span> |
| </pre> |
| <p> |
| or as an absolute time to allow composition of timers: |
| </p> |
| <pre class="programlisting"><span class="identifier">deadline_timer</span> <span class="identifier">t2</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span> |
| <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">expires_at</span><span class="special">()</span> <span class="special">+</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">posix_time</span><span class="special">::</span><span class="identifier">seconds</span><span class="special">(</span><span class="number">30</span><span class="special">));</span> |
| </pre> |
| <a name="boost_asio.overview.timers.see_also"></a><h5> |
| <a name="id772178"></a> |
| <a class="link" href="timers.html#boost_asio.overview.timers.see_also">See Also</a> |
| </h5> |
| <p> |
| <a class="link" href="../reference/basic_deadline_timer.html" title="basic_deadline_timer">basic_deadline_timer</a>, |
| <a class="link" href="../reference/deadline_timer.html" title="deadline_timer">deadline_timer</a>, |
| <a class="link" href="../reference/deadline_timer_service.html" title="deadline_timer_service">deadline_timer_service</a>, |
| <a class="link" href="../tutorial/tuttimer1.html" title="Timer.1 - Using a timer synchronously">timer tutorials</a>. |
| </p> |
| </div> |
| <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> |
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| <td align="right"><div class="copyright-footer">Copyright © 2003 - 2010 Christopher M. Kohlhoff<p> |
| Distributed under the Boost Software License, Version 1.0. (See accompanying |
| 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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