2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (c) 2005 John Baldwin <jhb@FreeBSD.org>
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
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.
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
30 #ifndef __SYS_REFCOUNT_H__
31 #define __SYS_REFCOUNT_H__
33 #include <machine/atomic.h>
36 #include <sys/systm.h>
39 #define KASSERT(exp, msg) /* */
42 #define REFCOUNT_WAITER (1U << 31) /* Refcount has waiter. */
43 #define REFCOUNT_SATURATION_VALUE (3U << 29)
45 #define REFCOUNT_SATURATED(val) (((val) & (1U << 30)) != 0)
46 #define REFCOUNT_COUNT(x) ((x) & ~REFCOUNT_WAITER)
48 bool refcount_release_last(volatile u_int *count, u_int n, u_int old);
49 void refcount_sleep(volatile u_int *count, const char *wmesg, int prio);
52 * Attempt to handle reference count overflow and underflow. Force the counter
53 * to stay at the saturation value so that a counter overflow cannot trigger
54 * destruction of the containing object and instead leads to a less harmful
58 _refcount_update_saturated(volatile u_int *count)
61 panic("refcount %p wraparound", count);
63 atomic_store_int(count, REFCOUNT_SATURATION_VALUE);
68 refcount_init(volatile u_int *count, u_int value)
70 KASSERT(!REFCOUNT_SATURATED(value),
71 ("invalid initial refcount value %u", value));
76 refcount_acquire(volatile u_int *count)
80 old = atomic_fetchadd_int(count, 1);
81 if (__predict_false(REFCOUNT_SATURATED(old)))
82 _refcount_update_saturated(count);
88 refcount_acquiren(volatile u_int *count, u_int n)
92 KASSERT(n < REFCOUNT_SATURATION_VALUE / 2,
93 ("refcount_acquiren: n=%u too large", n));
94 old = atomic_fetchadd_int(count, n);
95 if (__predict_false(REFCOUNT_SATURATED(old)))
96 _refcount_update_saturated(count);
101 static __inline __result_use_check bool
102 refcount_acquire_checked(volatile u_int *count)
106 for (lcount = *count;;) {
107 if (__predict_false(REFCOUNT_SATURATED(lcount + 1)))
109 if (__predict_true(atomic_fcmpset_int(count, &lcount,
116 refcount_releasen(volatile u_int *count, u_int n)
120 KASSERT(n < REFCOUNT_SATURATION_VALUE / 2,
121 ("refcount_releasen: n=%u too large", n));
123 atomic_thread_fence_rel();
124 old = atomic_fetchadd_int(count, -n);
125 if (__predict_false(n >= REFCOUNT_COUNT(old) ||
126 REFCOUNT_SATURATED(old)))
127 return (refcount_release_last(count, n, old));
132 refcount_release(volatile u_int *count)
135 return (refcount_releasen(count, 1));
139 refcount_wait(volatile u_int *count, const char *wmesg, int prio)
143 refcount_sleep(count, wmesg, prio);
147 * This functions returns non-zero if the refcount was
148 * incremented. Else zero is returned.
150 static __inline __result_use_check bool
151 refcount_acquire_if_gt(volatile u_int *count, u_int n)
157 if (REFCOUNT_COUNT(old) <= n)
159 if (__predict_false(REFCOUNT_SATURATED(old)))
161 if (atomic_fcmpset_int(count, &old, old + 1))
166 static __inline __result_use_check bool
167 refcount_acquire_if_not_zero(volatile u_int *count)
170 return refcount_acquire_if_gt(count, 0);
173 static __inline __result_use_check bool
174 refcount_release_if_gt(volatile u_int *count, u_int n)
179 ("refcount_release_if_gt: Use refcount_release for final ref"));
182 if (REFCOUNT_COUNT(old) <= n)
184 if (__predict_false(REFCOUNT_SATURATED(old)))
186 if (atomic_fcmpset_int(count, &old, old - 1))
191 static __inline __result_use_check bool
192 refcount_release_if_not_last(volatile u_int *count)
195 return refcount_release_if_gt(count, 1);
197 #endif /* ! __SYS_REFCOUNT_H__ */