cutils: add simple reference counter

Change-Id: Iefb34abc864cb4ca2da2f1c85c45f89af8c7fe8b

include/cutils/aref.h

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2013 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _CUTILS_AREF_H_
+#define _CUTILS_AREF_H_
+
+#include <stddef.h>
+#include <sys/cdefs.h>
+
+#ifdef ANDROID_SMP
+#include <cutils/atomic-inline.h>
+#else
+#include <cutils/atomic.h>
+#endif
+
+__BEGIN_DECLS
+
+#define AREF_TO_ITEM(aref, container, member) \
+    (container *) (((char*) (aref)) - offsetof(container, member))
+
+struct aref
+{
+    volatile int32_t count;
+};
+
+static inline void aref_init(struct aref *r)
+{
+    r->count = 1;
+}
+
+static inline int32_t aref_count(struct aref *r)
+{
+    return r->count;
+}
+
+static inline void aref_get(struct aref *r)
+{
+    android_atomic_inc(&r->count);
+}
+
+static inline void aref_put(struct aref *r, void (*release)(struct aref *))
+{
+    if (android_atomic_dec(&r->count) == 1)
+        release(r);
+}
+
+__END_DECLS
+
+#endif // _CUTILS_AREF_H_