Cleanup: Re-organise source dir

[userspace-rcu.git] / include / urcu / ref.h

diff --git a/include/urcu/ref.h b/include/urcu/ref.h
new file mode 100644 (file)
index 0000000..e546da5
--- /dev/null
+++ b/include/urcu/ref.h
@@ -0,0 +1,98 @@
+#ifndef _URCU_REF_H
+#define _URCU_REF_H
+
+/*
+ * Userspace RCU - Reference counting
+ *
+ * Copyright (C) 2009 Novell Inc.
+ * Copyright (C) 2010 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * Author: Jan Blunck <jblunck@suse.de>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License version 2.1 as
+ * published by the Free  Software Foundation.
+ */
+
+#include <assert.h>
+#include <stdbool.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <urcu/uatomic.h>
+
+struct urcu_ref {
+       long refcount; /* ATOMIC */
+};
+
+static inline void urcu_ref_set(struct urcu_ref *ref, long val)
+{
+       uatomic_set(&ref->refcount, val);
+}
+
+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)
+{
+       if (!urcu_ref_get_safe(ref))
+               abort();
+}
+
+static inline void urcu_ref_put(struct urcu_ref *ref,
+                               void (*release)(struct urcu_ref *))
+{
+       long res = uatomic_sub_return(&ref->refcount, 1);
+       assert (res >= 0);
+       if (res == 0)
+               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 */