The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/sys/refcount.h

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    1 /*-
    2  * Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org>
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 3. Neither the name of the author nor the names of any co-contributors
   14  *    may be used to endorse or promote products derived from this software
   15  *    without specific prior written permission.
   16  *
   17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   27  * SUCH DAMAGE.
   28  *
   29  * $FreeBSD: releng/9.0/sys/sys/refcount.h 180763 2008-07-23 16:44:20Z des $
   30  */
   31 
   32 #ifndef __SYS_REFCOUNT_H__
   33 #define __SYS_REFCOUNT_H__
   34 
   35 #include <machine/atomic.h>
   36 
   37 #ifdef _KERNEL
   38 #include <sys/systm.h>
   39 #else
   40 #define KASSERT(exp, msg)       /* */
   41 #endif
   42 
   43 static __inline void
   44 refcount_init(volatile u_int *count, u_int value)
   45 {
   46 
   47         *count = value;
   48 }
   49 
   50 static __inline void
   51 refcount_acquire(volatile u_int *count)
   52 {
   53 
   54         atomic_add_acq_int(count, 1);   
   55 }
   56 
   57 static __inline int
   58 refcount_release(volatile u_int *count)
   59 {
   60         u_int old;
   61 
   62         /* XXX: Should this have a rel membar? */
   63         old = atomic_fetchadd_int(count, -1);
   64         KASSERT(old > 0, ("negative refcount %p", count));
   65         return (old == 1);
   66 }
   67 
   68 #endif  /* ! __SYS_REFCOUNT_H__ */

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