1/*-
2 * Copyright (C) 2001 Jason Evans <jasone@freebsd.org>.  All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
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.
14 *
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
25 * DAMAGE.
26 */
27
28/*
29 * Counting semaphores.
30 *
31 * Priority propagation will not generally raise the priority of semaphore
32 * "owners" (a misnomer in the context of semaphores), so should not be relied
33 * upon in combination with semaphores.
34 */
35
36#include <sys/cdefs.h>
37__FBSDID("$FreeBSD$");
38
39#include <sys/param.h>
40#include <sys/systm.h>
41#include <sys/ktr.h>
42#include <sys/condvar.h>
43#include <sys/lock.h>
44#include <sys/mutex.h>
45#include <sys/sema.h>
46
47void
48sema_init(struct sema *sema, int value, const char *description)
49{
50
51	KASSERT((value >= 0), ("%s(): negative value\n", __func__));
52
53	bzero(sema, sizeof(*sema));
54	mtx_init(&sema->sema_mtx, description, "sema backing lock",
55	    MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
56	cv_init(&sema->sema_cv, description);
57	sema->sema_value = value;
58
59	CTR4(KTR_LOCK, "%s(%p, %d, \"%s\")", __func__, sema, value, description);
60}
61
62void
63sema_destroy(struct sema *sema)
64{
65
66	CTR3(KTR_LOCK, "%s(%p) \"%s\"", __func__, sema,
67	    cv_wmesg(&sema->sema_cv));
68
69	KASSERT((sema->sema_waiters == 0), ("%s(): waiters\n", __func__));
70
71	mtx_destroy(&sema->sema_mtx);
72	cv_destroy(&sema->sema_cv);
73}
74
75void
76_sema_post(struct sema *sema, const char *file, int line)
77{
78
79	mtx_lock(&sema->sema_mtx);
80	sema->sema_value++;
81	if (sema->sema_waiters && sema->sema_value > 0)
82		cv_signal(&sema->sema_cv);
83
84	CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
85	    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
86
87	mtx_unlock(&sema->sema_mtx);
88}
89
90void
91_sema_wait(struct sema *sema, const char *file, int line)
92{
93
94	mtx_lock(&sema->sema_mtx);
95	while (sema->sema_value == 0) {
96		sema->sema_waiters++;
97		cv_wait(&sema->sema_cv, &sema->sema_mtx);
98		sema->sema_waiters--;
99	}
100	sema->sema_value--;
101
102	CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
103	    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
104
105	mtx_unlock(&sema->sema_mtx);
106}
107
108int
109_sema_timedwait(struct sema *sema, int timo, const char *file, int line)
110{
111	int error;
112
113	mtx_lock(&sema->sema_mtx);
114
115	/*
116	 * A spurious wakeup will cause the timeout interval to start over.
117	 * This isn't a big deal as long as spurious wakeups don't occur
118	 * continuously, since the timeout period is merely a lower bound on how
119	 * long to wait.
120	 */
121	for (error = 0; sema->sema_value == 0 && error == 0;) {
122		sema->sema_waiters++;
123		error = cv_timedwait(&sema->sema_cv, &sema->sema_mtx, timo);
124		sema->sema_waiters--;
125	}
126	if (sema->sema_value > 0) {
127		/* Success. */
128		sema->sema_value--;
129		error = 0;
130
131		CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
132		    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
133	} else {
134		CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
135		    cv_wmesg(&sema->sema_cv), file, line);
136	}
137
138	mtx_unlock(&sema->sema_mtx);
139	return (error);
140}
141
142int
143_sema_trywait(struct sema *sema, const char *file, int line)
144{
145	int ret;
146
147	mtx_lock(&sema->sema_mtx);
148
149	if (sema->sema_value > 0) {
150		/* Success. */
151		sema->sema_value--;
152		ret = 1;
153
154		CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
155		    cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
156	} else {
157		ret = 0;
158
159		CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
160		    cv_wmesg(&sema->sema_cv), file, line);
161	}
162
163	mtx_unlock(&sema->sema_mtx);
164	return (ret);
165}
166
167int
168sema_value(struct sema *sema)
169{
170	int ret;
171
172	mtx_lock(&sema->sema_mtx);
173	ret = sema->sema_value;
174	mtx_unlock(&sema->sema_mtx);
175	return (ret);
176}
177