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<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.steady_timer"></a><a class="link" href="steady_timer.html" title="steady_timer">steady_timer</a>
</h3></div></div></div>
<p>
<a class="indexterm" name="idm45773592997616"></a>
Typedef for a timer based on the steady clock.
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">basic_waitable_timer</span><span class="special"><</span> <span class="identifier">chrono</span><span class="special">::</span><span class="identifier">steady_clock</span> <span class="special">></span> <span class="identifier">steady_timer</span><span class="special">;</span>
</pre>
<h5>
<a name="boost_asio.reference.steady_timer.h0"></a>
<span class="phrase"><a name="boost_asio.reference.steady_timer.types"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_timer.types">Types</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/clock_type.html" title="basic_waitable_timer::clock_type"><span class="bold"><strong>clock_type</strong></span></a>
</p>
</td>
<td>
<p>
The clock type.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/duration.html" title="basic_waitable_timer::duration"><span class="bold"><strong>duration</strong></span></a>
</p>
</td>
<td>
<p>
The duration type of the clock.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/implementation_type.html" title="basic_waitable_timer::implementation_type"><span class="bold"><strong>implementation_type</strong></span></a>
</p>
</td>
<td>
<p>
The underlying implementation type of I/O object.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/service_type.html" title="basic_waitable_timer::service_type"><span class="bold"><strong>service_type</strong></span></a>
</p>
</td>
<td>
<p>
The type of the service that will be used to provide I/O operations.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/time_point.html" title="basic_waitable_timer::time_point"><span class="bold"><strong>time_point</strong></span></a>
</p>
</td>
<td>
<p>
The time point type of the clock.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/traits_type.html" title="basic_waitable_timer::traits_type"><span class="bold"><strong>traits_type</strong></span></a>
</p>
</td>
<td>
<p>
The wait traits type.
</p>
</td>
</tr>
</tbody>
</table></div>
<h5>
<a name="boost_asio.reference.steady_timer.h1"></a>
<span class="phrase"><a name="boost_asio.reference.steady_timer.member_functions"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_timer.member_functions">Member
Functions</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/async_wait.html" title="basic_waitable_timer::async_wait"><span class="bold"><strong>async_wait</strong></span></a>
</p>
</td>
<td>
<p>
Start an asynchronous wait on the timer.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/basic_waitable_timer.html" title="basic_waitable_timer::basic_waitable_timer"><span class="bold"><strong>basic_waitable_timer</strong></span></a>
</p>
</td>
<td>
<p>
Constructor.
</p>
<p>
Constructor to set a particular expiry time as an absolute time.
</p>
<p>
Constructor to set a particular expiry time relative to now.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/cancel.html" title="basic_waitable_timer::cancel"><span class="bold"><strong>cancel</strong></span></a>
</p>
</td>
<td>
<p>
Cancel any asynchronous operations that are waiting on the timer.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/cancel_one.html" title="basic_waitable_timer::cancel_one"><span class="bold"><strong>cancel_one</strong></span></a>
</p>
</td>
<td>
<p>
Cancels one asynchronous operation that is waiting on the timer.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/expires_at.html" title="basic_waitable_timer::expires_at"><span class="bold"><strong>expires_at</strong></span></a>
</p>
</td>
<td>
<p>
Get the timer's expiry time as an absolute time.
</p>
<p>
Set the timer's expiry time as an absolute time.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/expires_from_now.html" title="basic_waitable_timer::expires_from_now"><span class="bold"><strong>expires_from_now</strong></span></a>
</p>
</td>
<td>
<p>
Get the timer's expiry time relative to now.
</p>
<p>
Set the timer's expiry time relative to now.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/get_io_service.html" title="basic_waitable_timer::get_io_service"><span class="bold"><strong>get_io_service</strong></span></a>
</p>
</td>
<td>
<p>
Get the io_service associated with the object.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/wait.html" title="basic_waitable_timer::wait"><span class="bold"><strong>wait</strong></span></a>
</p>
</td>
<td>
<p>
Perform a blocking wait on the timer.
</p>
</td>
</tr>
</tbody>
</table></div>
<h5>
<a name="boost_asio.reference.steady_timer.h2"></a>
<span class="phrase"><a name="boost_asio.reference.steady_timer.protected_member_functions"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_timer.protected_member_functions">Protected
Member Functions</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/get_implementation.html" title="basic_waitable_timer::get_implementation"><span class="bold"><strong>get_implementation</strong></span></a>
</p>
</td>
<td>
<p>
Get the underlying implementation of the I/O object.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/get_service.html" title="basic_waitable_timer::get_service"><span class="bold"><strong>get_service</strong></span></a>
</p>
</td>
<td>
<p>
Get the service associated with the I/O object.
</p>
</td>
</tr>
</tbody>
</table></div>
<h5>
<a name="boost_asio.reference.steady_timer.h3"></a>
<span class="phrase"><a name="boost_asio.reference.steady_timer.protected_data_members"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_timer.protected_data_members">Protected
Data Members</a>
</h5>
<div class="informaltable"><table class="table">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Name
</p>
</th>
<th>
<p>
Description
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/implementation.html" title="basic_waitable_timer::implementation"><span class="bold"><strong>implementation</strong></span></a>
</p>
</td>
<td>
<p>
(Deprecated: Use get_implementation().) The underlying implementation
of the I/O object.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/service.html" title="basic_waitable_timer::service"><span class="bold"><strong>service</strong></span></a>
</p>
</td>
<td>
<p>
(Deprecated: Use get_service().) The service associated with the
I/O object.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
The <a class="link" href="basic_waitable_timer.html" title="basic_waitable_timer"><code class="computeroutput"><span class="identifier">basic_waitable_timer</span></code></a> class template
provides the ability to perform a blocking or asynchronous wait for a timer
to expire.
</p>
<p>
A waitable timer is always in one of two states: "expired" or "not
expired". If the <code class="computeroutput"><span class="identifier">wait</span><span class="special">()</span></code> or <code class="computeroutput"><span class="identifier">async_wait</span><span class="special">()</span></code> function is called on an expired timer,
the wait operation will complete immediately.
</p>
<p>
Most applications will use one of the <a class="link" href="steady_timer.html" title="steady_timer"><code class="computeroutput"><span class="identifier">steady_timer</span></code></a>, <a class="link" href="system_timer.html" title="system_timer"><code class="computeroutput"><span class="identifier">system_timer</span></code></a> or <a class="link" href="high_resolution_timer.html" title="high_resolution_timer"><code class="computeroutput"><span class="identifier">high_resolution_timer</span></code></a> typedefs.
</p>
<h5>
<a name="boost_asio.reference.steady_timer.h4"></a>
<span class="phrase"><a name="boost_asio.reference.steady_timer.remarks"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_timer.remarks">Remarks</a>
</h5>
<p>
This waitable timer functionality is for use with the C++11 standard library's
<code class="computeroutput"><span class="special"><</span><span class="identifier">chrono</span><span class="special">></span></code> facility, or with the Boost.Chrono library.
</p>
<h5>
<a name="boost_asio.reference.steady_timer.h5"></a>
<span class="phrase"><a name="boost_asio.reference.steady_timer.thread_safety"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_timer.thread_safety">Thread
Safety</a>
</h5>
<p>
<span class="emphasis"><em>Distinct</em></span> <span class="emphasis"><em>objects:</em></span> Safe.
</p>
<p>
<span class="emphasis"><em>Shared</em></span> <span class="emphasis"><em>objects:</em></span> Unsafe.
</p>
<h5>
<a name="boost_asio.reference.steady_timer.h6"></a>
<span class="phrase"><a name="boost_asio.reference.steady_timer.examples"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_timer.examples">Examples</a>
</h5>
<p>
Performing a blocking wait (C++11):
</p>
<pre class="programlisting"><span class="comment">// Construct a timer without setting an expiry time.</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span> <span class="identifier">timer</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">);</span>
<span class="comment">// Set an expiry time relative to now.</span>
<span class="identifier">timer</span><span class="special">.</span><span class="identifier">expires_from_now</span><span class="special">(</span><span class="identifier">std</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>
<span class="comment">// Wait for the timer to expire.</span>
<span class="identifier">timer</span><span class="special">.</span><span class="identifier">wait</span><span class="special">();</span>
</pre>
<p>
Performing an asynchronous wait (C++11):
</p>
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">handler</span><span class="special">(</span><span class="keyword">const</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="special">&</span> <span class="identifier">error</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">if</span> <span class="special">(!</span><span class="identifier">error</span><span class="special">)</span>
<span class="special">{</span>
<span class="comment">// Timer expired.</span>
<span class="special">}</span>
<span class="special">}</span>
<span class="special">...</span>
<span class="comment">// Construct a timer with an absolute expiry time.</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">steady_timer</span> <span class="identifier">timer</span><span class="special">(</span><span class="identifier">io_service</span><span class="special">,</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">steady_clock</span><span class="special">::</span><span class="identifier">now</span><span class="special">()</span> <span class="special">+</span> <span class="identifier">std</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">60</span><span class="special">));</span>
<span class="comment">// Start an asynchronous wait.</span>
<span class="identifier">timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">handler</span><span class="special">);</span>
</pre>
<h5>
<a name="boost_asio.reference.steady_timer.h7"></a>
<span class="phrase"><a name="boost_asio.reference.steady_timer.changing_an_active_waitable_timer_s_expiry_time"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_timer.changing_an_active_waitable_timer_s_expiry_time">Changing
an active waitable timer's expiry time</a>
</h5>
<p>
Changing the expiry time of a timer while there are pending asynchronous
waits causes those wait operations to be cancelled. To ensure that the action
associated with the timer is performed only once, use something like this:
used:
</p>
<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">on_some_event</span><span class="special">()</span>
<span class="special">{</span>
<span class="keyword">if</span> <span class="special">(</span><span class="identifier">my_timer</span><span class="special">.</span><span class="identifier">expires_from_now</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="special">></span> <span class="number">0</span><span class="special">)</span>
<span class="special">{</span>
<span class="comment">// We managed to cancel the timer. Start new asynchronous wait.</span>
<span class="identifier">my_timer</span><span class="special">.</span><span class="identifier">async_wait</span><span class="special">(</span><span class="identifier">on_timeout</span><span class="special">);</span>
<span class="special">}</span>
<span class="keyword">else</span>
<span class="special">{</span>
<span class="comment">// Too late, timer has already expired!</span>
<span class="special">}</span>
<span class="special">}</span>
<span class="keyword">void</span> <span class="identifier">on_timeout</span><span class="special">(</span><span class="keyword">const</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="special">&</span> <span class="identifier">e</span><span class="special">)</span>
<span class="special">{</span>
<span class="keyword">if</span> <span class="special">(</span><span class="identifier">e</span> <span class="special">!=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error</span><span class="special">::</span><span class="identifier">operation_aborted</span><span class="special">)</span>
<span class="special">{</span>
<span class="comment">// Timer was not cancelled, take necessary action.</span>
<span class="special">}</span>
<span class="special">}</span>
</pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
The <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">basic_waitable_timer</span><span class="special">::</span><span class="identifier">expires_from_now</span><span class="special">()</span></code>
function cancels any pending asynchronous waits, and returns the number
of asynchronous waits that were cancelled. If it returns 0 then you were
too late and the wait handler has already been executed, or will soon
be executed. If it returns 1 then the wait handler was successfully cancelled.
</li>
<li class="listitem">
If a wait handler is cancelled, the boost::system::error_code passed
to it contains the value <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">asio</span><span class="special">::</span><span class="identifier">error</span><span class="special">::</span><span class="identifier">operation_aborted</span></code>.
</li>
</ul></div>
<p>
This typedef uses the C++11 <code class="computeroutput"><span class="special"><</span><span class="identifier">chrono</span><span class="special">></span></code>
standard library facility, if available. Otherwise, it may use the Boost.Chrono
library. To explicitly utilise Boost.Chrono, use the <a class="link" href="basic_waitable_timer.html" title="basic_waitable_timer"><code class="computeroutput"><span class="identifier">basic_waitable_timer</span></code></a> template directly:
</p>
<pre class="programlisting"><span class="keyword">typedef</span> <span class="identifier">basic_waitable_timer</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">chrono</span><span class="special">::</span><span class="identifier">steady_clock</span><span class="special">></span> <span class="identifier">timer</span><span class="special">;</span>
</pre>
<h5>
<a name="boost_asio.reference.steady_timer.h8"></a>
<span class="phrase"><a name="boost_asio.reference.steady_timer.requirements"></a></span><a class="link" href="steady_timer.html#boost_asio.reference.steady_timer.requirements">Requirements</a>
</h5>
<p>
<span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/steady_timer.hpp</code>
</p>
<p>
<span class="emphasis"><em>Convenience header: </em></span>None
</p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
<td align="left"></td>
<td align="right"><div class="copyright-footer">Copyright © 2003-2015 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>)
</p>
</div></td>
</tr></table>
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