1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org> 5 * 6 * Redistribution and use in source and binary forms, with or without 7 * modification, are permitted provided that the following conditions 8 * are met: 9 * 1. Redistributions of source code must retain the above copyright 10 * notice, this list of conditions and the following disclaimer. 11 * 2. Redistributions in binary form must reproduce the above copyright 12 * notice, this list of conditions and the following disclaimer in the 13 * documentation and/or other materials provided with the distribution. 14 * 15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 25 * SUCH DAMAGE. 26 * 27 * $FreeBSD$ 28 */ 29 30 #ifndef __SYS_REFCOUNT_H__ 31 #define __SYS_REFCOUNT_H__ 32 33 #include <sys/limits.h> 34 #include <machine/atomic.h> 35 36 #ifdef _KERNEL 37 #include <sys/systm.h> 38 #else 39 #define KASSERT(exp, msg) /* */ 40 #endif 41 42 static __inline void 43 refcount_init(volatile u_int *count, u_int value) 44 { 45 46 *count = value; 47 } 48 49 static __inline void 50 refcount_acquire(volatile u_int *count) 51 { 52 53 KASSERT(*count < UINT_MAX, ("refcount %p overflowed", count)); 54 atomic_add_int(count, 1); 55 } 56 57 static __inline int 58 refcount_release(volatile u_int *count) 59 { 60 u_int old; 61 62 atomic_thread_fence_rel(); 63 old = atomic_fetchadd_int(count, -1); 64 KASSERT(old > 0, ("refcount %p is zero", count)); 65 if (old > 1) 66 return (0); 67 68 /* 69 * Last reference. Signal the user to call the destructor. 70 * 71 * Ensure that the destructor sees all updates. The fence_rel 72 * at the start of the function synchronized with this fence. 73 */ 74 atomic_thread_fence_acq(); 75 return (1); 76 } 77 78 /* 79 * This functions returns non-zero if the refcount was 80 * incremented. Else zero is returned. 81 */ 82 static __inline __result_use_check int 83 refcount_acquire_if_not_zero(volatile u_int *count) 84 { 85 u_int old; 86 87 old = *count; 88 for (;;) { 89 KASSERT(old < UINT_MAX, ("refcount %p overflowed", count)); 90 if (old == 0) 91 return (0); 92 if (atomic_fcmpset_int(count, &old, old + 1)) 93 return (1); 94 } 95 } 96 97 static __inline __result_use_check int 98 refcount_release_if_not_last(volatile u_int *count) 99 { 100 u_int old; 101 102 old = *count; 103 for (;;) { 104 KASSERT(old > 0, ("refcount %p is zero", count)); 105 if (old == 1) 106 return (0); 107 if (atomic_fcmpset_int(count, &old, old - 1)) 108 return (1); 109 } 110 } 111 112 #endif /* ! __SYS_REFCOUNT_H__ */ 113