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<title>Issue 1443: Imposed happens-before edges are not made transitive</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="1443"><a href="lwg-closed.html#1443">1443</a>. Imposed happens-before edges are not made transitive</h3>
<p><b>Section:</b> 32 <a href="https://wg21.link/thread">[thread]</a> <b>Status:</b> <a href="lwg-active.html#Dup">Dup</a>
 <b>Submitter:</b> BSI <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">issues</a> in [thread].</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-closed.html#1442" title="&quot;happens-before&quot; should be &quot;synchronizes-with&quot; (Status: NAD Editorial)">1442</a></p>
<p><b>Discussion:</b></p>


<p><b>Addresses GB-122</b></p>

<p>At various points in the standard new edges are added to
happens-before, for example 27.2.3:2 adds happens-before edges between
writes and reads from a stream:</p>

<p>If one thread makes a library call a that writes a value to a
stream and, as a result, another thread reads this value from the
stream through a library call b such that this does not result in a
data race, then a happens before b.</p>

<p>Happens-before is defined in 1.10:11 in a deliberate way that makes it
not explicitly transitively closed. Adding edges to happens-before
directly, as in 27.2.3:2, does not provide transitivity with
sequenced-before or any other existing happens-before edge. This lack
of transitivity seems to be unintentional. In order to achieve
transitivity we suggest each edge be added to
inter-thread-happens-before as a synchronises-with edge (as per
conversation with Hans Boehm). In the standard, each use of the words
"happens-before" should be replaced with the words "synchronizes-with"
in the following sentences:</p>

<p>27.2.3:2,
30.3.1.2:6,
30.3.1.5:7,
30.6.4:7,
30.6.9:5,
30.6.10.1:23</p>


<p id="res-1443"><b>Proposed resolution:</b></p>
<p>
Request the concurrency working group to
determine if changes are needed
</p>





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