From d6fe50b6b9aed17f7a6847f8b3da2f3a5d088b29 Mon Sep 17 00:00:00 2001
From: John Baldwin <jhb@FreeBSD.org>
Date: Tue, 27 Sep 2005 18:01:33 +0000
Subject: [PATCH] Add a simple reference count API that is simply a thin
 wrapper API around atomic operations on ints.

Reviewed by:	arch@
MFC after:	1 week
---
 sys/sys/refcount.h | 59 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 sys/sys/refcount.h

diff --git a/sys/sys/refcount.h b/sys/sys/refcount.h
new file mode 100644
index 00000000000..5316dd938f7
--- /dev/null
+++ b/sys/sys/refcount.h
@@ -0,0 +1,59 @@
+/*-
+ * Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of the author nor the names of any co-contributors
+ *    may be used to endorse or promote products derived from this software
+ *    without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef __SYS_REFCOUNT_H__
+#define __SYS_REFCOUNT_H__
+
+#include <machine/atomic.h>
+
+static __inline void
+refcount_init(volatile u_int *count, u_int value)
+{
+
+	*count = value;
+}
+
+static __inline void
+refcount_acquire(volatile u_int *count)
+{
+
+	atomic_add_acq_int(count, 1);	
+}
+
+static __inline int
+refcount_release(volatile u_int *count)
+{
+
+	/* XXX: Should this have a rel membar? */
+	return (atomic_fetchadd_int(count, -1) == 1);
+}
+
+#endif	/* ! __SYS_REFCOUNT_H__ */
-- 
2.45.2