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<title>Issue 1219: unique_lock::lock and resource_deadlock_would_occur</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#Dup">Dup</a> status.</em></p>
<h3 id="1219"><a href="lwg-closed.html#1219">1219</a>. unique_lock::lock and resource_deadlock_would_occur</h3>
<p><b>Section:</b> 32.6.5.4.3 <a href="https://wg21.link/thread.lock.unique.locking">[thread.lock.unique.locking]</a> <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a>
 <b>Submitter:</b> Jeffrey Yasskin <b>Opened:</b> 2009-09-30 <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.lock.unique.locking">issues</a> in [thread.lock.unique.locking].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#Dup">Dup</a> status.</p>
<p><b>Duplicate of:</b> <a href="lwg-defects.html#1159" title="Unclear spec for resource_deadlock_would_occur (Status: C++11)">1159</a></p>
<p><b>Discussion:</b></p>



<p>
<code>unique_lock::lock</code> and friends raise
"<code>resource_deadlock_would_occur</code> -- if the current thread already
owns the mutex (i.e., on entry, <code>owns</code> is <code>true</code>)."  1)
The current thread owning a mutex is not the same as any particular
<code>unique_lock::owns</code> being <code>true</code>. 2) There's no need to
raise this exception for a <code>recursive_mutex</code> if <code>owns</code> is
<code>false</code>. 3) If <code>owns</code> is true, we need to raise some
exception or the unique_lock will lose track of whether to unlock itself
on destruction, but "deadlock" isn't it. For (3), s/bool owns/int
ownership_level/ would fix it.
</p>

<p><i>[
2009-11-11 Alisdair notes that this issue is very closely related to <a href="lwg-defects.html#1159" title="Unclear spec for resource_deadlock_would_occur (Status: C++11)">1159</a><sup><a href="https://cplusplus.github.io/LWG/issue1159" title="Latest snapshot">(i)</a></sup>,
if not a dup.
]</i></p>


<p><i>[
2009-11-14 Moved to Tentatively Dup after 5 positive votes on c++std-lib.
]</i></p>




<p id="res-1219"><b>Proposed resolution:</b></p>





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