BUG/MINOR: threads: fix multiple use of argument inside HA_ATOMIC_CAS()
When threads are disabled, HA_ATOMIC_CAS() becomes a simple compound
expression. However this expression presents a problem, which is that
its arguments are evaluated multiple times, once for the comparison
and once again for the assignement. This presents a risk of performing
some side-effect operations twice in the non-threaded case (e.g. in
case of auto-increment or function return).
The macro was rewritten using local copies for arguments like the
other macros do.
Fortunately a complete inspection of the code indicates that this case
currently never happens. It was however responsible for the strict-aliasing
warning emitted when building fd.c without threads but with 64-bit CAS.
This may be backported as far as 1.8 though it will not fix any existing
bug and is more of a long-term safety measure in case a future fix would
depend on this behavior.
diff --git a/include/common/hathreads.h b/include/common/hathreads.h
index 95dfb05..1350f19 100644
--- a/include/common/hathreads.h
+++ b/include/common/hathreads.h
@@ -77,7 +77,12 @@
#define __decl_rwlock(lock)
#define __decl_aligned_rwlock(lock)
-#define HA_ATOMIC_CAS(val, old, new) ({((*val) == (*old)) ? (*(val) = (new) , 1) : (*(old) = *(val), 0);})
+#define HA_ATOMIC_CAS(val, old, new) \
+ ({ \
+ typeof(val) _v = (val); \
+ typeof(old) _o = (old); \
+ (*_v == *_o) ? ((*_v = (new)), 1) : ((*_o = *_v), 0); \
+ })
/* warning, n is a pointer to the double value for dwcas */
#define HA_ATOMIC_DWCAS(val, o, n) \