WaitTraits.html
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<div class="titlepage"><div><div><h3 class="title">
<a name="asio.reference.WaitTraits"></a><a class="link" href="WaitTraits.html" title="Wait traits requirements">Wait traits requirements</a>
</h3></div></div></div>
<p>
The <code class="computeroutput">basic_waitable_timer</code> template uses wait traits to allow
programs to customize <code class="computeroutput">wait</code> and <code class="computeroutput">async_wait</code> behavior.
[<span class="emphasis"><em>Note:</em></span> Possible uses of wait traits include:<br> — To
enable timers based on non-realtime clocks.<br> — Determining how quickly
wallclock-based timers respond to system time changes.<br> — Correcting for
errors or rounding timeouts to boundaries.<br> — Preventing duration overflow.
That is, a program may set a timer's expiry <code class="computeroutput">e</code> to be <code class="computeroutput">Clock::max()</code>
(meaning never reached) or <code class="computeroutput">Clock::min()</code> (meaning always in the
past). As a result, computing the duration until timer expiry as <code class="computeroutput">e
- Clock::now()</code> may cause overflow. —<span class="emphasis"><em>end note</em></span>]
</p>
<p>
For a type <code class="computeroutput">Clock</code> meeting the <code class="computeroutput">Clock</code> requirements
(C++Std [time.clock.req]), a type <code class="computeroutput">X</code> meets the <code class="computeroutput">WaitTraits</code>
requirements if it satisfies the requirements listed below.
</p>
<p>
In the table below, <code class="computeroutput">t</code> denotes a (possibly const) value of type
<code class="computeroutput">Clock::time_point</code>; and <code class="computeroutput">d</code> denotes a (possibly const)
value of type <code class="computeroutput">Clock::duration</code>.
</p>
<div class="table">
<a name="asio.reference.WaitTraits.t0"></a><p class="title"><b>Table 33. WaitTraits requirements</b></p>
<div class="table-contents"><table class="table" summary="WaitTraits requirements">
<colgroup>
<col>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
expression
</p>
</th>
<th>
<p>
return type
</p>
</th>
<th>
<p>
assertion/note<br> pre/post-condition
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<code class="computeroutput">X::to_wait_duration(d)</code>
</p>
</td>
<td>
<p>
<code class="computeroutput">Clock::duration</code>
</p>
</td>
<td>
<p>
Returns a <code class="computeroutput">Clock::duration</code> value to be used in a <code class="computeroutput">wait</code>
or <code class="computeroutput">async_wait</code> operation. [<span class="emphasis"><em>Note:</em></span>
The return value is typically representative of the duration <code class="computeroutput">d</code>.
—<span class="emphasis"><em>end note</em></span>]
</p>
</td>
</tr>
<tr>
<td>
<p>
<code class="computeroutput">X::to_wait_duration(t)</code>
</p>
</td>
<td>
<p>
<code class="computeroutput">Clock::duration</code>
</p>
</td>
<td>
<p>
Returns a <code class="computeroutput">Clock::duration</code> value to be used in a <code class="computeroutput">wait</code>
or <code class="computeroutput">async_wait</code> operation. [<span class="emphasis"><em>Note:</em></span>
The return value is typically representative of the duration from
<code class="computeroutput">Clock::now()</code> until the time point <code class="computeroutput">t</code>.
—<span class="emphasis"><em>end note</em></span>]
</p>
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</tbody>
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<td align="right"><div class="copyright-footer">Copyright © 2003-2020 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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