1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org> 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 * 28 * $FreeBSD$ 29 */ 30 31 #ifndef __SYS_REFCOUNT_H__ 32 #define __SYS_REFCOUNT_H__ 33 34 #include <sys/limits.h> 35 #include <machine/atomic.h> 36 37 #ifdef _KERNEL 38 #include <sys/systm.h> 39 #else 40 #define KASSERT(exp, msg) /* */ 41 #endif 42 43 static __inline void 44 refcount_init(volatile u_int *count, u_int value) 45 { 46 47 *count = value; 48 } 49 50 static __inline void 51 refcount_acquire(volatile u_int *count) 52 { 53 54 KASSERT(*count < UINT_MAX, ("refcount %p overflowed", count)); 55 atomic_add_int(count, 1); 56 } 57 58 static __inline int 59 refcount_release(volatile u_int *count) 60 { 61 u_int old; 62 63 atomic_thread_fence_rel(); 64 old = atomic_fetchadd_int(count, -1); 65 KASSERT(old > 0, ("negative refcount %p", count)); 66 if (old > 1) 67 return (0); 68 69 /* 70 * Last reference. Signal the user to call the destructor. 71 * 72 * Ensure that the destructor sees all updates. The fence_rel 73 * at the start of the function synchronized with this fence. 74 */ 75 atomic_thread_fence_acq(); 76 return (1); 77 } 78 79 /* 80 * A temporary hack until refcount_* APIs are sorted out. 81 */ 82 static __inline int 83 refcount_acquire_if_not_zero(volatile u_int *count) 84 { 85 u_int old; 86 87 old = *count; 88 for (;;) { 89 if (old == 0) 90 return (0); 91 if (atomic_fcmpset_int(count, &old, old + 1)) 92 return (1); 93 } 94 } 95 96 static __inline int 97 refcount_release_if_not_last(volatile u_int *count) 98 { 99 u_int old; 100 101 old = *count; 102 for (;;) { 103 if (old == 1) 104 return (0); 105 if (atomic_fcmpset_int(count, &old, old - 1)) 106 return (1); 107 } 108 } 109 110 #endif /* ! __SYS_REFCOUNT_H__ */ 111