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<title>Issue 1489: unlock functions and unlock mutex requirements are inconsistent</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_Editorial">NAD Editorial</a> status.</em></p>
<h3 id="1489"><a href="lwg-closed.html#1489">1489</a>. <code>unlock</code> functions and unlock mutex requirements are inconsistent</h3>
<p><b>Section:</b> 32.6 <a href="https://wg21.link/thread.mutex">[thread.mutex]</a> <b>Status:</b> <a href="lwg-active.html#NAD_Editorial">NAD Editorial</a>
 <b>Submitter:</b> Switzerland <b>Opened:</b> 2010-08-25 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#thread.mutex">issues</a> in [thread.mutex].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD Editorial">NAD Editorial</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses CH-26</b></p>

<p>
Specifications of <code>unlock</code> member functions and <code>unlock</code>
mutex requirements are inconsistent wrt to exceptions and
pre- and postconditions.
</p>

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

<blockquote><p>
<code>unlock</code> should specifiy the precondition that the
current thread "owns the lock", this will make calls
without holding the locks "undefined behavior".
<code>unlock</code> in  [mutex.requirements] should either be
<code>noexcept(true)</code> or be allowed to throw
<code>system_error</code> like <code>unique_lock::unlock</code>, or the latter
should be <code>nothrow(true)</code> and have the precondition
<code>owns == true</code>.
Furthermore <code>unique_lock</code>'s postcondition is wrong
in the case of a recursive mutex where <code>owns</code>
might stay true, when it is not the last <code>unlock</code>
needed to be called.
</p></blockquote>



<p id="res-1489"><b>Proposed resolution:</b></p>





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