X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=urcu-qsbr-static.h;h=c0467cd0e1606c87a522e56d2299716cf6402b3e;hb=6ee91d83a7a5b33160158f57f94dd75e6d0a67ed;hp=22a93b2fd7a823d21c76cbbd1ad5c6bf3b0495e4;hpb=47d2f29ead2c92123069ebf7b84c6e48cf91612a;p=urcu.git

diff --git a/urcu-qsbr-static.h b/urcu-qsbr-static.h
index 22a93b2..c0467cd 100644
--- a/urcu-qsbr-static.h
+++ b/urcu-qsbr-static.h
@@ -244,6 +244,22 @@ static inline void _rcu_thread_online(void)
 		STORE_SHARED(p, v);			\
 	})
 
+/**
+ * _rcu_cmpxchg_pointer - same as rcu_assign_pointer, but tests if the pointer
+ * is as expected by "old". If succeeds, returns the previous pointer to the
+ * data structure, which can be safely freed after waiting for a quiescent state
+ * using synchronize_rcu(). If fails (unexpected value), returns old (which
+ * should not be freed !).
+ */
+
+#define _rcu_cmpxchg_pointer(p, old, _new)		\
+	({						\
+		if (!__builtin_constant_p(_new) ||	\
+		    ((_new) != NULL))			\
+			wmb();				\
+		cmpxchg(p, old, _new);			\
+	})
+
 /**
  * _rcu_xchg_pointer - same as rcu_assign_pointer, but returns the previous
  * pointer to the data structure, which can be safely freed after waiting for a