X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu%2Fref.h;h=74be50d6bbe4e46d28603ba4cb8de3db2ed7794a;hp=a422a9906fd787d1482210a5a61b6f3611b7f99c;hb=cd21955a846566b3cd7ca77d58cd3d006f3c533a;hpb=54fd78efce9aeddcdc7b35151ad6744b7ee629cb

diff --git a/urcu/ref.h b/urcu/ref.h
index a422a99..74be50d 100644
--- a/urcu/ref.h
+++ b/urcu/ref.h
@@ -15,6 +15,7 @@
  */
 
 #include <assert.h>
+#include <stdbool.h>
 #include <urcu/uatomic.h>
 
 struct urcu_ref {
@@ -45,4 +46,30 @@ static inline void urcu_ref_put(struct urcu_ref *ref,
 		release(ref);
 }
 
+/*
+ * urcu_ref_get_unless_zero
+ *
+ * Allows getting a reference atomically if the reference count is not
+ * zero. Returns true if the reference is taken, false otherwise. This
+ * needs to be used in conjunction with another synchronization
+ * technique (e.g.  RCU or mutex) to ensure existence of the reference
+ * count.
+ */
+static inline bool urcu_ref_get_unless_zero(struct urcu_ref *ref)
+{
+	long old, _new, res;
+
+	old = uatomic_read(&ref->refcount);
+	for (;;) {
+		if (old == 0)
+			return false;	/* Failure. */
+		_new = old + 1;
+		res = uatomic_cmpxchg(&ref->refcount, old, _new);
+		if (res == old) {
+			return true;	/* Success. */
+		}
+		old = res;
+	}
+}
+
 #endif /* _URCU_REF_H */