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_ */ 128