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    CWG Issue 1176</TITLE>
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<P><EM>This is an unofficial snapshot of the ISO/IEC JTC1 SC22 WG21
  Core Issues List revision 118b.
  See http://www.open-std.org/jtc1/sc22/wg21/ for the official
  list.</EM></P>
<P>2025-09-28</P>
<HR>
<A NAME="1176"></A><H4>1176.
  
Definition of release sequence
</H4>
<B>Section: </B>6.10.2&#160; [<A href="https://wg21.link/intro.multithread">intro.multithread</A>]
 &#160;&#160;&#160;

 <B>Status: </B>C++11
 &#160;&#160;&#160;

 <B>Submitter: </B>CA, GB
 &#160;&#160;&#160;

 <B>Date: </B>2010-08-10<BR><BR>


<P>[Voted into the WP at the November, 2010 meeting as part of paper
N3196.]</P>

<A href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3296.html#CA12">N3092 comment
  CA&#160;12<BR></A>
<A href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2011/n3296.html#GB9">N3092 comment
  GB&#160;9<BR></A>

<P>The current wording of the standard suggests
that release sequences are maximal with respect to
sequence inclusion, i.e. that if there are two release
operations in the modification order,</P>

<PRE>
mod       mod
rel1-----&gt;rel2-----&gt;w
</PRE>

<P>then <TT>[rel1;rel2;w]</TT> is the only release sequence, as the
other candidate <TT>[rel2;w]</TT> is included in it. This
interpretation precludes synchronizing with releases which have other
releases sequenced-before them. We believe that the intention is
actually to define the maximal release sequence from a particular
release operation, which would admit both <TT>[rel1;rel2;w]</TT> and
<TT>[rel2;w]</TT>.</P>

<P><B>Proposed resolution (August, 2010):</B></P>

<P>Change 6.10.2 [<A href="https://wg21.link/intro.multithread#6">intro.multithread</A>] paragraph 6 as follows:</P>

<BLOCKQUOTE>

<P>A <I>release sequence</I> <INS>from a release operation
<I>A</I></INS> on an atomic object <I>M</I> is a maximal contiguous
sub-sequence of side effects in the modification order of
<I>M</I>, where the first operation is <DEL>a release</DEL>
<INS><I>A</I></INS>, and every subsequent operation</P>

<UL>
<LI><P>is performed by the same thread that performed the release,
or</P></LI>

<LI><P>is an atomic read-modify-write operation.</P></LI>

</UL>

</BLOCKQUOTE>

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