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+/* 
+ * Copyright (c) 1995-1993 The University of Utah and
+ * the Computer Systems Laboratory at the University of Utah (CSL).
+ * All rights reserved.
+ *
+ * Permission to use, copy, modify and distribute this software is hereby
+ * granted provided that (1) source code retains these copyright, permission,
+ * and disclaimer notices, and (2) redistributions including binaries
+ * reproduce the notices in supporting documentation, and (3) all advertising
+ * materials mentioning features or use of this software display the following
+ * acknowledgement: ``This product includes software developed by the
+ * Computer Systems Laboratory at the University of Utah.''
+ *
+ * THE UNIVERSITY OF UTAH AND CSL ALLOW FREE USE OF THIS SOFTWARE IN ITS "AS
+ * IS" CONDITION.  THE UNIVERSITY OF UTAH AND CSL DISCLAIM ANY LIABILITY OF
+ * ANY KIND FOR ANY DAMAGES WHATSOEVER RESULTING FROM THE USE OF THIS SOFTWARE.
+ *
+ * CSL requests users of this software to return to csl-dist@cs.utah.edu any
+ * improvements that they make and grant CSL redistribution rights.
+ *
+ *      Author: Bryan Ford, University of Utah CSL
+ */
+/*
+ *	File:	refcount.h
+ *
+ *	This defines the system-independent atomic reference count data type.
+ *	(This file will often be overridden
+ *	by better machine-dependent implementations.)
+ *
+ */
+
+#ifndef	_KERN_REF_COUNT_H_
+#define _KERN_REF_COUNT_H_
+
+#include <mach/macro_help.h>
+
+#include "simple_lock.h"
+
+
+struct ref_count {
+	decl_simple_lock_data(,lock)	/* lock for reference count */
+	int		count;		/* number of references */
+};
+
+#define ref_count_init(refcount, refs)			\
+	MACRO_BEGIN					\
+		simple_lock_init(&(refcount)->lock);	\
+		((refcount)->count = (refs));		\
+	MACRO_END
+
+#define ref_count_take(refcount)			\
+	MACRO_BEGIN					\
+		simple_lock(&(refcount)->lock);		\
+		(refcount)->count++;			\
+		simple_unlock(&(refcount)->lock);	\
+	MACRO_END
+
+#define ref_count_drop(refcount, func)			\
+	MACRO_BEGIN					\
+		int new_value;				\
+		simple_lock(&(refcount)->lock);		\
+		new_value = --(refcount)->count;	\
+		simple_unlock(&(refcount)->lock);	\
+		if (new_value == 0) { func; }		\
+	MACRO_END
+
+
+#endif _KERN_REF_COUNT_H_