P0982R1 Weaken Release Sequences

Author: jensmaurer

source/basic.tex

@@ -5069,17 +5069,13 @@
 \end{note}
 
 \pnum
-A \defn{release sequence} headed by a release operation \placeholder{A} on an atomic object
-\placeholder{M} is a maximal contiguous sub-sequence of
+A \defn{release sequence} headed
+by a release operation \placeholder{A} on an atomic object \placeholder{M}
+is a maximal contiguous sub-sequence of
 \indextext{side effects}%
-side effects in the
-modification order of \placeholder{M}, where the first operation is \tcode{A}, and
-every subsequent operation
-
-\begin{itemize}
-\item is performed by the same thread that performed \tcode{A}, or
-\item is an atomic read-modify-write operation.
-\end{itemize}
+side effects in the modification order of \placeholder{M},
+where the first operation is \placeholder{A}, and
+every subsequent operation is an atomic read-modify-write operation.
 
 \pnum
 Certain library calls \defn{synchronize with} other library calls performed by

source/compatibility.tex

@@ -1815,6 +1815,18 @@
 }
 \end{codeblock}
 
+\rSec2[diff.cpp17.basic]{\ref{basic}: basics}
+
+\diffref{intro.races}
+\change Except for the initial release operation,
+a release sequence consists solely of atomic read-modify-write operations.
+\rationale Removal of rarely used and confusing feature.
+\effect If a \tcode{memory_order_release} atomic store is followed
+by a \tcode{memory_order_relaxed} store to the same variable by the same thread,
+then reading the latter value with a \tcode{memory_order_acquire} load
+no longer provides any ``happens before'' guarantees,
+even in the absence of intervening stores by another thread.
+
 \rSec2[diff.cpp17.expr]{\ref{expr}: expressions}
 
 \diffref{expr.prim.lambda.capture}