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: src/sys/sys/refcount.h,v 1.1 2005/09/27 18:01:33 jhb Exp $
   30  */
   31 
   32 #ifndef _SYS_REFCOUNT_H_
   33 #define _SYS_REFCOUNT_H_
   34 
   35 #include <machine/atomic.h>
   36 
   37 #define REFCNTF_WAITING 0x40000000
   38 
   39 void _refcount_wait(volatile u_int *countp, const char *wstr);
   40 int _refcount_release_wakeup_n(volatile u_int *countp, u_int i);
   41 
   42 static __inline void
   43 refcount_init(volatile u_int *countp, u_int value)
   44 {
   45         *countp = value;
   46 }
   47 
   48 static __inline void
   49 refcount_acquire(volatile u_int *countp)
   50 {
   51         atomic_add_acq_int(countp, 1);
   52 }
   53 
   54 static __inline void
   55 refcount_acquire_n(volatile u_int *countp, u_int i)
   56 {
   57         atomic_add_acq_int(countp, i);
   58 }
   59 
   60 static __inline int
   61 refcount_release(volatile u_int *countp)
   62 {
   63         return (atomic_fetchadd_int(countp, -1) == 1);
   64 }
   65 
   66 static __inline int
   67 refcount_release_n(volatile u_int *countp, u_int i)
   68 {
   69         return (atomic_fetchadd_int(countp, -i) == i);
   70 }
   71 
   72 /*
   73  * Release a refcount and also handle waiters who have (atomically)
   74  * set the REFCNTF_WAITING flag.  If the flag was set the atomic op
   75  * will fail (because the 'old' value we pass it is with the flag
   76  * cleared).  The atomic op can also fail on a race so the helper
   77  * function deals with all cases.
   78  *
   79  * This function returns TRUE(1) on the last release and FALSE(0) otherwise.
   80  *
   81  * NOTE: (i) must be non-zero.
   82  */
   83 static __inline int
   84 refcount_release_wakeup(volatile u_int *countp)
   85 {
   86         u_int n = *countp & ~REFCNTF_WAITING;
   87         if (!atomic_cmpset_int(countp, n, n - 1))
   88                 return(_refcount_release_wakeup_n(countp, 1));
   89         return(n == 1);
   90 }
   91 
   92 static __inline int
   93 refcount_release_wakeup_n(volatile u_int *countp, u_int i)
   94 {
   95         u_int n = *countp & ~REFCNTF_WAITING;
   96         if (!atomic_cmpset_int(countp, n, n - i))
   97                 return(_refcount_release_wakeup_n(countp, i));
   98         return(n == i);
   99 }
  100 
  101 /*
  102  * Wait for all refs on *countp to go away.
  103  *
  104  * WARNING!  If this function is used then all releases on countp MUST
  105  *           use refcount_release_wakeup() instead of refcount_release().
  106  */
  107 static __inline void
  108 refcount_wait(volatile u_int *countp, const char *wstr)
  109 {
  110         if (*countp)
  111                 _refcount_wait(countp, wstr);
  112 }
  113 
  114 #endif  /* ! _SYS_REFCOUNT_H_ */

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