2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (C) 2001 Jason Evans <jasone@freebsd.org>. All rights reserved.
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(s), this list of conditions and the following disclaimer as
11 * the first lines of this file unmodified other than the possible
12 * addition of one or more copyright notices.
13 * 2. Redistributions in binary form must reproduce the above copyright
14 * notice(s), this list of conditions and the following disclaimer in the
15 * documentation and/or other materials provided with the distribution.
17 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
18 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
19 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
20 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
21 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
22 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
23 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
24 * 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 SUCH
31 * Counting semaphores.
33 * Priority propagation will not generally raise the priority of semaphore
34 * "owners" (a misnomer in the context of semaphores), so should not be relied
35 * upon in combination with semaphores.
38 #include <sys/cdefs.h>
39 __FBSDID("$FreeBSD$");
41 #include <sys/param.h>
42 #include <sys/systm.h>
44 #include <sys/condvar.h>
46 #include <sys/mutex.h>
50 sema_init(struct sema *sema, int value, const char *description)
53 KASSERT((value >= 0), ("%s(): negative value\n", __func__));
55 bzero(sema, sizeof(*sema));
56 mtx_init(&sema->sema_mtx, description, "sema backing lock",
57 MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
58 cv_init(&sema->sema_cv, description);
59 sema->sema_value = value;
61 CTR4(KTR_LOCK, "%s(%p, %d, \"%s\")", __func__, sema, value, description);
65 sema_destroy(struct sema *sema)
68 CTR3(KTR_LOCK, "%s(%p) \"%s\"", __func__, sema,
69 cv_wmesg(&sema->sema_cv));
71 KASSERT((sema->sema_waiters == 0), ("%s(): waiters\n", __func__));
73 mtx_destroy(&sema->sema_mtx);
74 cv_destroy(&sema->sema_cv);
78 _sema_post(struct sema *sema, const char *file, int line)
81 mtx_lock(&sema->sema_mtx);
83 if (sema->sema_waiters && sema->sema_value > 0)
84 cv_signal(&sema->sema_cv);
86 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
87 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
89 mtx_unlock(&sema->sema_mtx);
93 _sema_wait(struct sema *sema, const char *file, int line)
96 mtx_lock(&sema->sema_mtx);
97 while (sema->sema_value == 0) {
99 cv_wait(&sema->sema_cv, &sema->sema_mtx);
100 sema->sema_waiters--;
104 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
105 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
107 mtx_unlock(&sema->sema_mtx);
111 _sema_timedwait(struct sema *sema, int timo, const char *file, int line)
115 mtx_lock(&sema->sema_mtx);
118 * A spurious wakeup will cause the timeout interval to start over.
119 * This isn't a big deal as long as spurious wakeups don't occur
120 * continuously, since the timeout period is merely a lower bound on how
123 for (error = 0; sema->sema_value == 0 && error == 0;) {
124 sema->sema_waiters++;
125 error = cv_timedwait(&sema->sema_cv, &sema->sema_mtx, timo);
126 sema->sema_waiters--;
128 if (sema->sema_value > 0) {
133 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
134 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
136 CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
137 cv_wmesg(&sema->sema_cv), file, line);
140 mtx_unlock(&sema->sema_mtx);
145 _sema_trywait(struct sema *sema, const char *file, int line)
149 mtx_lock(&sema->sema_mtx);
151 if (sema->sema_value > 0) {
156 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
157 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
161 CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
162 cv_wmesg(&sema->sema_cv), file, line);
165 mtx_unlock(&sema->sema_mtx);
170 sema_value(struct sema *sema)
174 mtx_lock(&sema->sema_mtx);
175 ret = sema->sema_value;
176 mtx_unlock(&sema->sema_mtx);