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<title>Issue 1499: Condition variables preclude wakeup optimization</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#NAD">NAD</a> status.</em></p>
<h3 id="1499"><a href="lwg-closed.html#1499">1499</a>. Condition variables preclude wakeup optimization</h3>
<p><b>Section:</b> 32.7 <a href="https://wg21.link/thread.condition">[thread.condition]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> INCITS <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2019-02-26</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#thread.condition">issues</a> in [thread.condition].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses US-193</b></p>

<p>
Condition variables preclude a wakeup optimization.
</p>

<p><i>[
Resolution proposed by ballot comment:
]</i></p>


<blockquote><p>
Change condition_variable to allow such
optimization. See Appendix 1 - Additional Details
</p></blockquote>

<p><i>[
2010 Batavia
]</i></p>

<p>
The Concurrency subgroup reviewed the issue, and deemed it an extension to be handled after C++0x.
</p>

<p><b>Rationale:</b></p><p>The LWG does not wish to make the change at this time.</p>

<p><i>[LEWG Kona 2017]</i></p>

<p>Recommend NAD: (N4618 numbering) 30.5.1[thread.condition.condvar] p10.3 allows spurious wakeups. This issue is out of date.</p>

<p><i>[2017-03-01, Kona]</i></p>

<p>
SG1 recommends: Close as NAD
<p/>
The approach suggested there raises all sorts of issues about <code>thread_locals</code>, etc. It's probably way too late 
to change this anyway, but this would have required a careful paper.
</p>



<p id="res-1499"><b>Proposed resolution:</b></p>





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