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);
51 * Attempt to handle reference count overflow and underflow. Force the counter
52 * to stay at the saturation value so that a counter overflow cannot trigger
53 * destruction of the containing object and instead leads to a less harmful
57 _refcount_update_saturated(volatile u_int *count)
60 panic("refcount %p wraparound", count);
62 atomic_store_int(count, REFCOUNT_SATURATION_VALUE);
67 refcount_init(volatile u_int *count, u_int value)
69 KASSERT(!REFCOUNT_SATURATED(value),
70 ("invalid initial refcount value %u", value));
75 refcount_acquire(volatile u_int *count)
79 old = atomic_fetchadd_int(count, 1);
80 if (__predict_false(REFCOUNT_SATURATED(old)))
81 _refcount_update_saturated(count);
87 refcount_acquiren(volatile u_int *count, u_int n)
91 KASSERT(n < REFCOUNT_SATURATION_VALUE / 2,
92 ("refcount_acquiren: n=%u too large", n));
93 old = atomic_fetchadd_int(count, n);
94 if (__predict_false(REFCOUNT_SATURATED(old)))
95 _refcount_update_saturated(count);
100 static __inline __result_use_check bool
101 refcount_acquire_checked(volatile u_int *count)
105 for (lcount = *count;;) {
106 if (__predict_false(REFCOUNT_SATURATED(lcount + 1)))
108 if (__predict_true(atomic_fcmpset_int(count, &lcount,
115 refcount_releasen(volatile u_int *count, u_int n)
119 KASSERT(n < REFCOUNT_SATURATION_VALUE / 2,
120 ("refcount_releasen: n=%u too large", n));
123 * Paired with acquire fence in refcount_release_last.
125 atomic_thread_fence_rel();
126 old = atomic_fetchadd_int(count, -n);
127 if (__predict_false(n >= REFCOUNT_COUNT(old) ||
128 REFCOUNT_SATURATED(old)))
129 return (refcount_release_last(count, n, old));
134 refcount_release(volatile u_int *count)
137 return (refcount_releasen(count, 1));
142 void _refcount_sleep(volatile u_int *count, struct lock_object *,
143 const char *wmesg, int prio);
146 refcount_sleep(volatile u_int *count, const char *wmesg, int prio)
149 _refcount_sleep(count, NULL, wmesg, prio);
152 #define refcount_sleep_interlock(count, lock, wmesg, prio) \
153 _refcount_sleep((count), (struct lock_object *)(lock), (wmesg), (prio))
156 refcount_wait(volatile u_int *count, const char *wmesg, int prio)
160 refcount_sleep(count, wmesg, prio);
165 * This functions returns non-zero if the refcount was
166 * incremented. Else zero is returned.
168 static __inline __result_use_check bool
169 refcount_acquire_if_gt(volatile u_int *count, u_int n)
175 if (REFCOUNT_COUNT(old) <= n)
177 if (__predict_false(REFCOUNT_SATURATED(old)))
179 if (atomic_fcmpset_int(count, &old, old + 1))
184 static __inline __result_use_check bool
185 refcount_acquire_if_not_zero(volatile u_int *count)
188 return refcount_acquire_if_gt(count, 0);
191 static __inline __result_use_check bool
192 refcount_release_if_gt(volatile u_int *count, u_int n)
197 ("refcount_release_if_gt: Use refcount_release for final ref"));
200 if (REFCOUNT_COUNT(old) <= n)
202 if (__predict_false(REFCOUNT_SATURATED(old)))
205 * Paired with acquire fence in refcount_release_last.
207 if (atomic_fcmpset_rel_int(count, &old, old - 1))
212 static __inline __result_use_check bool
213 refcount_release_if_not_last(volatile u_int *count)
216 return refcount_release_if_gt(count, 1);
218 #endif /* ! __SYS_REFCOUNT_H__ */