2 * Copyright (C) 2001 Jason Evans <jasone@freebsd.org>. All rights reserved.
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
7 * 1. Redistributions of source code must retain the above copyright
8 * notice(s), this list of conditions and the following disclaimer as
9 * the first lines of this file unmodified other than the possible
10 * addition of one or more copyright notices.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice(s), 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 COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
16 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
17 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
18 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
19 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
20 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
21 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
22 * 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 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/param.h>
39 #include <sys/systm.h>
41 #include <sys/condvar.h>
43 #include <sys/mutex.h>
47 sema_init(struct sema *sema, int value, const char *description)
50 KASSERT((value >= 0), ("%s(): negative value\n", __func__));
52 bzero(sema, sizeof(*sema));
53 mtx_init(&sema->sema_mtx, description, "sema backing lock",
54 MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
55 cv_init(&sema->sema_cv, description);
56 sema->sema_value = value;
58 CTR4(KTR_LOCK, "%s(%p, %d, \"%s\")", __func__, sema, value, description);
62 sema_destroy(struct sema *sema)
65 CTR3(KTR_LOCK, "%s(%p) \"%s\"", __func__, sema,
66 cv_wmesg(&sema->sema_cv));
68 KASSERT((sema->sema_waiters == 0), ("%s(): waiters\n", __func__));
70 mtx_destroy(&sema->sema_mtx);
71 cv_destroy(&sema->sema_cv);
75 _sema_post(struct sema *sema, const char *file, int line)
78 mtx_lock(&sema->sema_mtx);
80 if (sema->sema_waiters && sema->sema_value > 0)
81 cv_signal(&sema->sema_cv);
83 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
84 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
86 mtx_unlock(&sema->sema_mtx);
90 _sema_wait(struct sema *sema, const char *file, int line)
93 mtx_lock(&sema->sema_mtx);
94 while (sema->sema_value == 0) {
96 cv_wait(&sema->sema_cv, &sema->sema_mtx);
101 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
102 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
104 mtx_unlock(&sema->sema_mtx);
108 _sema_timedwait(struct sema *sema, int timo, const char *file, int line)
112 mtx_lock(&sema->sema_mtx);
115 * A spurious wakeup will cause the timeout interval to start over.
116 * This isn't a big deal as long as spurious wakeups don't occur
117 * continuously, since the timeout period is merely a lower bound on how
120 for (timed_out = 0; sema->sema_value == 0 && timed_out == 0;) {
121 sema->sema_waiters++;
122 timed_out = cv_timedwait(&sema->sema_cv, &sema->sema_mtx, timo);
123 sema->sema_waiters--;
125 if (sema->sema_value > 0) {
130 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
131 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
135 CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
136 cv_wmesg(&sema->sema_cv), file, line);
139 mtx_unlock(&sema->sema_mtx);
144 _sema_trywait(struct sema *sema, const char *file, int line)
148 mtx_lock(&sema->sema_mtx);
150 if (sema->sema_value > 0) {
155 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
156 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
160 CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
161 cv_wmesg(&sema->sema_cv), file, line);
164 mtx_unlock(&sema->sema_mtx);
169 sema_value(struct sema *sema)
173 mtx_lock(&sema->sema_mtx);
174 ret = sema->sema_value;
175 mtx_unlock(&sema->sema_mtx);