+/*
+ * 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;
+ }
+}
+