X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu%2Fref.h;h=e546da567120e086e5773950ac135d510900b4fc;hp=a422a9906fd787d1482210a5a61b6f3611b7f99c;hb=2af1c19e6a553878fcb2a5106f050d5ed7ac0f54;hpb=9d2614f07691a813a3c560a6c0bcd0a7be854ed5

diff --git a/urcu/ref.h b/urcu/ref.h
index a422a99..e546da5 100644
--- a/urcu/ref.h
+++ b/urcu/ref.h
@@ -15,6 +15,9 @@
  */
 
 #include <assert.h>
+#include <stdbool.h>
+#include <limits.h>
+#include <stdlib.h>
 #include <urcu/uatomic.h>
 
 struct urcu_ref {
@@ -31,9 +34,29 @@ static inline void urcu_ref_init(struct urcu_ref *ref)
 	urcu_ref_set(ref, 1);
 }
 
+static inline bool  __attribute__((warn_unused_result))
+		urcu_ref_get_safe(struct urcu_ref *ref)
+{
+	long old, _new, res;
+
+	old = uatomic_read(&ref->refcount);
+	for (;;) {
+		if (old == LONG_MAX) {
+			return false;	/* Failure. */
+		}
+		_new = old + 1;
+		res = uatomic_cmpxchg(&ref->refcount, old, _new);
+		if (res == old) {
+			return true;	/* Success. */
+		}
+		old = res;
+	}
+}
+
 static inline void urcu_ref_get(struct urcu_ref *ref)
 {
-	uatomic_add(&ref->refcount, 1);
+	if (!urcu_ref_get_safe(ref))
+		abort();
 }
 
 static inline void urcu_ref_put(struct urcu_ref *ref,
@@ -45,4 +68,31 @@ 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. False is also returned in case incrementing the refcount would
+ * result in an overflow.
+ */
+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 || old == LONG_MAX)
+			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 */