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<title>Issue 2185: Missing throws clause for future/shared_future::wait_for/wait_until</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#C++14">C++14</a> status.</em></p>
<h3 id="2185"><a href="lwg-defects.html#2185">2185</a>. Missing throws clause for <code>future/shared_future::wait_for/wait_until</code></h3>
<p><b>Section:</b> 32.10.7 <a href="https://wg21.link/futures.unique.future">[futures.unique.future]</a>, 32.10.8 <a href="https://wg21.link/futures.shared.future">[futures.shared.future]</a> <b>Status:</b> <a href="lwg-active.html#C++14">C++14</a>
 <b>Submitter:</b> Vicente J. Botet Escriba <b>Opened:</b> 2012-09-20 <b>Last modified:</b> 2021-06-06</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#futures.unique.future">issues</a> in [futures.unique.future].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++14">C++14</a> status.</p>
<p><b>Discussion:</b></p>

<p>
The functions <code>future::wait_for</code>, <code>future::wait_until</code>, <code>shared_future::wait_for</code>, and
<code>shared_future::wait_for</code> can throw any timeout-related exceptions. It would be better if the wording
could be more explicit. This is in line with the changes proposed in LWG <a href="lwg-defects.html#2093" title="Throws clause of condition_variable::wait with predicate (Status: C++14)">2093</a><sup><a href="https://cplusplus.github.io/LWG/issue2093" title="Latest snapshot">(i)</a></sup>'s <em>Throws</em> element
of <code>condition_variable::wait</code> with predicate.
</p>

<p><i>[2012, Portland: move to Review]</i></p>

<p>
The phrase timeout-related exception does not exist.
</p>
<p><a href="lwg-defects.html#2093" title="Throws clause of condition_variable::wait with predicate (Status: C++14)">2093</a><sup><a href="https://cplusplus.github.io/LWG/issue2093" title="Latest snapshot">(i)</a></sup> was put in review, and there is some dependency here with this issue.
</p>
<p>If you provide a user-defined clock that throws, we need to put back an exception to allow that to be done.
</p>
<p>
We will put this in review and say that this cannot go in before <a href="lwg-defects.html#2093" title="Throws clause of condition_variable::wait with predicate (Status: C++14)">2093</a><sup><a href="https://cplusplus.github.io/LWG/issue2093" title="Latest snapshot">(i)</a></sup>.
</p>

<p><i>[2013-04-20, Bristol]</i></p>

<p>Accepted for the working paper</p>



<p id="res-2185"><b>Proposed resolution:</b></p>
<p><i>[This resolution should not be adopted before resolving <a href="lwg-defects.html#2093" title="Throws clause of condition_variable::wait with predicate (Status: C++14)">2093</a><sup><a href="https://cplusplus.github.io/LWG/issue2093" title="Latest snapshot">(i)</a></sup>]</i></p>


<p><i>[This wording is relative to N3376.]</i></p>


<ol>
<li><p>Change  [futures.unique_future] as indicated:</p>
<blockquote><pre>
template &lt;class Rep, class Period&gt;
future_status wait_for(const chrono::duration&lt;Rep, Period&gt;&amp; rel_time) const;
</pre><blockquote><p>
-21- <i>Effects</i>: none if the shared state contains a deferred function (32.10.9 <a href="https://wg21.link/futures.async">[futures.async]</a>), otherwise
blocks until the shared state is ready or until the relative timeout (32.2.4 <a href="https://wg21.link/thread.req.timing">[thread.req.timing]</a>) specified by
<code>rel_time</code> has expired.
<p/>
-22- <i>Returns</i>: [&hellip;]
<p/>
<ins>-??- <i>Throws</i>: timeout-related exceptions (32.2.4 <a href="https://wg21.link/thread.req.timing">[thread.req.timing]</a>).</ins>
</p>
</blockquote><pre>
template &lt;class Clock, class Duration&gt;
future_status wait_until(const chrono::time_point&lt;Clock, Duration&gt;&amp; abs_time) const;
</pre><blockquote><p>
-23- <i>Effects</i>: none if the shared state contains a deferred function (32.10.9 <a href="https://wg21.link/futures.async">[futures.async]</a>), otherwise
blocks until the shared state is ready or until the absolute timeout (32.2.4 <a href="https://wg21.link/thread.req.timing">[thread.req.timing]</a>) specified by
<code>abs_time</code> has expired.
<p/>
-24- <i>Returns</i>: [&hellip;]
<p/>
<ins>-??- <i>Throws</i>: timeout-related exceptions (32.2.4 <a href="https://wg21.link/thread.req.timing">[thread.req.timing]</a>).</ins>
</p>
</blockquote></blockquote>
</li>

<li><p>Change  [futures.shared_future] as indicated:</p>
<blockquote><pre>
template &lt;class Rep, class Period&gt;
future_status wait_for(const chrono::duration&lt;Rep, Period&gt;&amp; rel_time) const;
</pre><blockquote><p>
-23- <i>Effects</i>: none if the shared state contains a deferred function (32.10.9 <a href="https://wg21.link/futures.async">[futures.async]</a>), otherwise
blocks until the shared state is ready or until the relative timeout (32.2.4 <a href="https://wg21.link/thread.req.timing">[thread.req.timing]</a>) specified by
<code>rel_time</code> has expired.
<p/>
-24- <i>Returns</i>: [&hellip;]
<p/>
<ins>-??- <i>Throws</i>: timeout-related exceptions (32.2.4 <a href="https://wg21.link/thread.req.timing">[thread.req.timing]</a>).</ins>
</p>
</blockquote><pre>
template &lt;class Clock, class Duration&gt;
future_status wait_until(const chrono::time_point&lt;Clock, Duration&gt;&amp; abs_time) const;
</pre><blockquote><p>
-25- <i>Effects</i>: none if the shared state contains a deferred function (32.10.9 <a href="https://wg21.link/futures.async">[futures.async]</a>), otherwise
blocks until the shared state is ready or until the absolute timeout (32.2.4 <a href="https://wg21.link/thread.req.timing">[thread.req.timing]</a>) specified by
<code>abs_time</code> has expired.
<p/>
-26- <i>Returns</i>: [&hellip;]
<p/>
<ins>-??- <i>Throws</i>: timeout-related exceptions (32.2.4 <a href="https://wg21.link/thread.req.timing">[thread.req.timing]</a>).</ins>
</p>
</blockquote></blockquote>
</li>

</ol>






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