sys/sys/refcount.h

   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_ */