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  *
   14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   15  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   16  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   17  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   18  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   19  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   20  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   21  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   22  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   23  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   24  * SUCH DAMAGE.
   25  *
   26  * $FreeBSD: stable/11/sys/sys/refcount.h 339862 2018-10-29 14:37:27Z hselasky $
   27  */
   28 
   29 #ifndef __SYS_REFCOUNT_H__
   30 #define __SYS_REFCOUNT_H__
   31 
   32 #include <sys/limits.h>
   33 #include <machine/atomic.h>
   34 
   35 #ifdef _KERNEL
   36 #include <sys/systm.h>
   37 #else
   38 #define KASSERT(exp, msg)       /* */
   39 #endif
   40 
   41 static __inline void
   42 refcount_init(volatile u_int *count, u_int value)
   43 {
   44 
   45         *count = value;
   46 }
   47 
   48 static __inline void
   49 refcount_acquire(volatile u_int *count)
   50 {
   51 
   52         KASSERT(*count < UINT_MAX, ("refcount %p overflowed", count));
   53         atomic_add_int(count, 1);
   54 }
   55 
   56 static __inline int
   57 refcount_release(volatile u_int *count)
   58 {
   59         u_int old;
   60 
   61         atomic_thread_fence_rel();
   62         old = atomic_fetchadd_int(count, -1);
   63         KASSERT(old > 0, ("refcount %p is zero", count));
   64         if (old > 1)
   65                 return (0);
   66 
   67         /*
   68          * Last reference.  Signal the user to call the destructor.
   69          *
   70          * Ensure that the destructor sees all updates.  The fence_rel
   71          * at the start of the function synchronized with this fence.
   72          */
   73         atomic_thread_fence_acq();
   74         return (1);
   75 }
   76 
   77 /*
   78  * This functions returns non-zero if the refcount was
   79  * incremented. Else zero is returned.
   80  *
   81  * A temporary hack until refcount_* APIs are sorted out.
   82  */
   83 static __inline __result_use_check int
   84 refcount_acquire_if_not_zero(volatile u_int *count)
   85 {
   86         u_int old;
   87 
   88         old = *count;
   89         for (;;) {
   90                 KASSERT(old < UINT_MAX, ("refcount %p overflowed", count));
   91                 if (old == 0)
   92                         return (0);
   93                 if (atomic_fcmpset_int(count, &old, old + 1))
   94                         return (1);
   95         }
   96 }
   97 
   98 static __inline __result_use_check int
   99 refcount_release_if_not_last(volatile u_int *count)
  100 {
  101         u_int old;
  102 
  103         old = *count;
  104         for (;;) {
  105                 KASSERT(old > 0, ("refcount %p is zero", count));
  106                 if (old == 1)
  107                         return (0);
  108                 if (atomic_fcmpset_int(count, &old, old - 1))
  109                         return (1);
  110         }
  111 }
  112 
  113 #endif  /* ! __SYS_REFCOUNT_H__ */

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