1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (C) 2001 Jason Evans <jasone@freebsd.org>. All rights reserved.
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(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.
16 *
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
27 * DAMAGE.
28 */
29
30 /*
31 * Counting semaphores.
32 *
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.
36 */
37
38 #include <sys/param.h>
39 #include <sys/systm.h>
40 #include <sys/ktr.h>
41 #include <sys/condvar.h>
42 #include <sys/lock.h>
43 #include <sys/mutex.h>
44 #include <sys/sema.h>
45
46 void
sema_init(struct sema * sema,int value,const char * description)47 sema_init(struct sema *sema, int value, const char *description)
48 {
49
50 KASSERT((value >= 0), ("%s(): negative value\n", __func__));
51
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;
57
58 CTR4(KTR_LOCK, "%s(%p, %d, \"%s\")", __func__, sema, value, description);
59 }
60
61 void
sema_destroy(struct sema * sema)62 sema_destroy(struct sema *sema)
63 {
64
65 CTR3(KTR_LOCK, "%s(%p) \"%s\"", __func__, sema,
66 cv_wmesg(&sema->sema_cv));
67
68 KASSERT((sema->sema_waiters == 0), ("%s(): waiters\n", __func__));
69
70 mtx_destroy(&sema->sema_mtx);
71 cv_destroy(&sema->sema_cv);
72 }
73
74 void
_sema_post(struct sema * sema,const char * file,int line)75 _sema_post(struct sema *sema, const char *file, int line)
76 {
77
78 mtx_lock(&sema->sema_mtx);
79 sema->sema_value++;
80 if (sema->sema_waiters && sema->sema_value > 0)
81 cv_signal(&sema->sema_cv);
82
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);
85
86 mtx_unlock(&sema->sema_mtx);
87 }
88
89 void
_sema_wait(struct sema * sema,const char * file,int line)90 _sema_wait(struct sema *sema, const char *file, int line)
91 {
92
93 mtx_lock(&sema->sema_mtx);
94 while (sema->sema_value == 0) {
95 sema->sema_waiters++;
96 cv_wait(&sema->sema_cv, &sema->sema_mtx);
97 sema->sema_waiters--;
98 }
99 sema->sema_value--;
100
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);
103
104 mtx_unlock(&sema->sema_mtx);
105 }
106
107 int
_sema_timedwait(struct sema * sema,int timo,const char * file,int line)108 _sema_timedwait(struct sema *sema, int timo, const char *file, int line)
109 {
110 int error;
111
112 mtx_lock(&sema->sema_mtx);
113
114 /*
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
118 * long to wait.
119 */
120 for (error = 0; sema->sema_value == 0 && error == 0;) {
121 sema->sema_waiters++;
122 error = cv_timedwait(&sema->sema_cv, &sema->sema_mtx, timo);
123 sema->sema_waiters--;
124 }
125 if (sema->sema_value > 0) {
126 /* Success. */
127 sema->sema_value--;
128 error = 0;
129
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);
132 } else {
133 CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
134 cv_wmesg(&sema->sema_cv), file, line);
135 }
136
137 mtx_unlock(&sema->sema_mtx);
138 return (error);
139 }
140
141 int
_sema_trywait(struct sema * sema,const char * file,int line)142 _sema_trywait(struct sema *sema, const char *file, int line)
143 {
144 int ret;
145
146 mtx_lock(&sema->sema_mtx);
147
148 if (sema->sema_value > 0) {
149 /* Success. */
150 sema->sema_value--;
151 ret = 1;
152
153 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
154 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
155 } else {
156 ret = 0;
157
158 CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
159 cv_wmesg(&sema->sema_cv), file, line);
160 }
161
162 mtx_unlock(&sema->sema_mtx);
163 return (ret);
164 }
165
166 int
sema_value(struct sema * sema)167 sema_value(struct sema *sema)
168 {
169 int ret;
170
171 mtx_lock(&sema->sema_mtx);
172 ret = sema->sema_value;
173 mtx_unlock(&sema->sema_mtx);
174 return (ret);
175 }
176