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 <sys/systm.h>          /* wakeup() */
  36 #include <machine/atomic.h>
  37
  38 #define REFCNTF_WAITING 0x40000000
  39
  40 void _refcount_wait(volatile u_int *countp, const char *wstr);
  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) & ~REFCNTF_WAITING) == 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) & ~REFCNTF_WAITING) == 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  * NOTE: Presence of waiters clears the WAITING bit asynchronously from the
  84  *       1->0 transition.
  85  */
  86 static __inline int
  87 refcount_release_wakeup(volatile u_int *countp)
  88 {
  89         u_int n;
  90
  91         n = atomic_fetchadd_int(countp, -1);
  92         if (n == (REFCNTF_WAITING | 1)) {
  93                 atomic_clear_int(countp, REFCNTF_WAITING);
  94                 wakeup(countp);
  95                 n &= ~REFCNTF_WAITING;
  96         }
  97         return (n == 1);
  98 }
  99
 100 static __inline int
 101 refcount_release_wakeup_n(volatile u_int *countp, u_int i)
 102 {
 103         u_int n;
 104
 105         n = atomic_fetchadd_int(countp, -i);
 106         if (n == (REFCNTF_WAITING | i)) {
 107                 atomic_clear_int(countp, REFCNTF_WAITING);
 108                 wakeup(countp);
 109                 n &= ~REFCNTF_WAITING;
 110         }
 111         return (n == i);
 112 }
 113
 114 /*
 115  * Wait for all refs on *countp to go away.
 116  *
 117  * WARNING!  If this function is used then all releases on countp MUST
 118  *           use refcount_release_wakeup() instead of refcount_release().
 119  */
 120 static __inline void
 121 refcount_wait(volatile u_int *countp, const char *wstr)
 122 {
 123         if (*countp)
 124                 _refcount_wait(countp, wstr);
 125 }
 126
 127 #endif  /* ! _SYS_REFCOUNT_H_ */