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
46void
47sema_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
61void
62sema_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
74void
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
89void
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
107int
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
141int
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
166int
167sema_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