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<div class="section">
<div class="titlepage"><div><div><h3 class="title">
<a name="boost_asio.reference.high_resolution_timer"></a><a class="link" href="high_resolution_timer.html" title="high_resolution_timer">high_resolution_timer</a>
</h3></div></div></div>
<p>
<a class="indexterm" name="boost_asio.indexterm.high_resolution_timer"></a>
Typedef for
a timer based on the high resolution clock.
</p>
<pre class="programlisting">typedef basic_waitable_timer< chrono::high_resolution_clock > high_resolution_timer;
</pre>
<h5>
<a name="boost_asio.reference.high_resolution_timer.h0"></a>
<span class="phrase"><a name="boost_asio.reference.high_resolution_timer.types"></a></span><a class="link" href="high_resolution_timer.html#boost_asio.reference.high_resolution_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/executor_type.html" title="basic_waitable_timer::executor_type"><span class="bold"><strong>executor_type</strong></span></a>
</p>
</td>
<td>
<p>
The type of the executor associated with the object.
</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.high_resolution_timer.h1"></a>
<span class="phrase"><a name="boost_asio.reference.high_resolution_timer.member_functions"></a></span><a class="link" href="high_resolution_timer.html#boost_asio.reference.high_resolution_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. <br> <span class="silver"> —</span><br> Constructor to set a particular expiry
time as an absolute time. <br> <span class="silver"> —</span><br> Constructor to set a particular
expiry time relative to now. <br> <span class="silver"> —</span><br> Move-construct a basic_waitable_timer
from another.
</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.
<br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.) 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.
<br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.) Cancels
one asynchronous operation that is waiting on the timer.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/expires_after.html" title="basic_waitable_timer::expires_after"><span class="bold"><strong>expires_after</strong></span></a>
</p>
</td>
<td>
<p>
Set the timer's expiry time relative to now.
</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>
(Deprecated: Use expiry().) Get the timer's expiry time as an absolute
time. <br> <span class="silver"> —</span><br> Set the timer's expiry time as an absolute
time. <br> <span class="silver"> —</span><br> (Deprecated: Use non-error_code overload.)
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>
(Deprecated: Use expiry().) Get the timer's expiry time relative
to now. <br> <span class="silver"> —</span><br> (Deprecated: Use expires_after().) Set the
timer's expiry time relative to now.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/expiry.html" title="basic_waitable_timer::expiry"><span class="bold"><strong>expiry</strong></span></a>
</p>
</td>
<td>
<p>
Get the timer's expiry time as an absolute time.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/get_executor.html" title="basic_waitable_timer::get_executor"><span class="bold"><strong>get_executor</strong></span></a>
</p>
</td>
<td>
<p>
Get the executor associated with the object.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/get_io_context.html" title="basic_waitable_timer::get_io_context"><span class="bold"><strong>get_io_context</strong></span></a>
</p>
</td>
<td>
<p>
(Deprecated: Use get_executor().) Get the io_context associated
with the object.
</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>
(Deprecated: Use get_executor().) Get the io_context associated
with the object.
</p>
</td>
</tr>
<tr>
<td>
<p>
<a class="link" href="basic_waitable_timer/operator_eq_.html" title="basic_waitable_timer::operator="><span class="bold"><strong>operator=</strong></span></a>
</p>
</td>
<td>
<p>
Move-assign a basic_waitable_timer from another.
</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>
<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>
Destroys the timer.
</p>
</td>
</tr>
</tbody>
</table></div>
<p>
The <a class="link" href="basic_waitable_timer.html" title="basic_waitable_timer"><code class="computeroutput">basic_waitable_timer</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">wait()</code> or <code class="computeroutput">async_wait()</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">steady_timer</code></a>,
<a class="link" href="system_timer.html" title="system_timer"><code class="computeroutput">system_timer</code></a>
or <a class="link" href="high_resolution_timer.html" title="high_resolution_timer"><code class="computeroutput">high_resolution_timer</code></a>
typedefs.
</p>
<h5>
<a name="boost_asio.reference.high_resolution_timer.h2"></a>
<span class="phrase"><a name="boost_asio.reference.high_resolution_timer.remarks"></a></span><a class="link" href="high_resolution_timer.html#boost_asio.reference.high_resolution_timer.remarks">Remarks</a>
</h5>
<p>
This waitable timer functionality is for use with the C++11 standard library's
<code class="computeroutput"><chrono></code> facility, or with the Boost.Chrono library.
</p>
<h5>
<a name="boost_asio.reference.high_resolution_timer.h3"></a>
<span class="phrase"><a name="boost_asio.reference.high_resolution_timer.thread_safety"></a></span><a class="link" href="high_resolution_timer.html#boost_asio.reference.high_resolution_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.high_resolution_timer.h4"></a>
<span class="phrase"><a name="boost_asio.reference.high_resolution_timer.examples"></a></span><a class="link" href="high_resolution_timer.html#boost_asio.reference.high_resolution_timer.examples">Examples</a>
</h5>
<p>
Performing a blocking wait (C++11):
</p>
<pre class="programlisting">// Construct a timer without setting an expiry time.
boost::asio::steady_timer timer(io_context);
// Set an expiry time relative to now.
timer.expires_after(std::chrono::seconds(5));
// Wait for the timer to expire.
timer.wait();
</pre>
<p>
Performing an asynchronous wait (C++11):
</p>
<pre class="programlisting">void handler(const boost::system::error_code& error)
{
if (!error)
{
// Timer expired.
}
}
...
// Construct a timer with an absolute expiry time.
boost::asio::steady_timer timer(io_context,
std::chrono::steady_clock::now() + std::chrono::seconds(60));
// Start an asynchronous wait.
timer.async_wait(handler);
</pre>
<h5>
<a name="boost_asio.reference.high_resolution_timer.h5"></a>
<span class="phrase"><a name="boost_asio.reference.high_resolution_timer.changing_an_active_waitable_timer_s_expiry_time"></a></span><a class="link" href="high_resolution_timer.html#boost_asio.reference.high_resolution_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">void on_some_event()
{
if (my_timer.expires_after(seconds(5)) > 0)
{
// We managed to cancel the timer. Start new asynchronous wait.
my_timer.async_wait(on_timeout);
}
else
{
// Too late, timer has already expired!
}
}
void on_timeout(const boost::system::error_code& e)
{
if (e != boost::asio::error::operation_aborted)
{
// Timer was not cancelled, take necessary action.
}
}
</pre>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
The <code class="computeroutput">boost::asio::basic_waitable_timer::expires_after()</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">boost::asio::error::operation_aborted</code>.
</li>
</ul></div>
<p>
This typedef uses the C++11 <code class="computeroutput"><chrono></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">basic_waitable_timer</code></a>
template directly:
</p>
<pre class="programlisting">typedef basic_waitable_timer<boost::chrono::high_resolution_clock> timer;
</pre>
<h5>
<a name="boost_asio.reference.high_resolution_timer.h6"></a>
<span class="phrase"><a name="boost_asio.reference.high_resolution_timer.requirements"></a></span><a class="link" href="high_resolution_timer.html#boost_asio.reference.high_resolution_timer.requirements">Requirements</a>
</h5>
<p>
<span class="emphasis"><em>Header: </em></span><code class="literal">boost/asio/high_resolution_timer.hpp</code>
</p>
<p>
<span class="emphasis"><em>Convenience header: </em></span><code class="literal">boost/asio.hpp</code>
</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 © 2003-2018 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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