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/cdefs.h> 39 __FBSDID("$FreeBSD$"); 40 41 #include <sys/param.h> 42 #include <sys/systm.h> 43 #include <sys/ktr.h> 44 #include <sys/condvar.h> 45 #include <sys/lock.h> 46 #include <sys/mutex.h> 47 #include <sys/sema.h> 48 49 void 50 sema_init(struct sema *sema, int value, const char *description) 51 { 52 53 KASSERT((value >= 0), ("%s(): negative value\n", __func__)); 54 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; 60 61 CTR4(KTR_LOCK, "%s(%p, %d, \"%s\")", __func__, sema, value, description); 62 } 63 64 void 65 sema_destroy(struct sema *sema) 66 { 67 68 CTR3(KTR_LOCK, "%s(%p) \"%s\"", __func__, sema, 69 cv_wmesg(&sema->sema_cv)); 70 71 KASSERT((sema->sema_waiters == 0), ("%s(): waiters\n", __func__)); 72 73 mtx_destroy(&sema->sema_mtx); 74 cv_destroy(&sema->sema_cv); 75 } 76 77 void 78 _sema_post(struct sema *sema, const char *file, int line) 79 { 80 81 mtx_lock(&sema->sema_mtx); 82 sema->sema_value++; 83 if (sema->sema_waiters && sema->sema_value > 0) 84 cv_signal(&sema->sema_cv); 85 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); 88 89 mtx_unlock(&sema->sema_mtx); 90 } 91 92 void 93 _sema_wait(struct sema *sema, const char *file, int line) 94 { 95 96 mtx_lock(&sema->sema_mtx); 97 while (sema->sema_value == 0) { 98 sema->sema_waiters++; 99 cv_wait(&sema->sema_cv, &sema->sema_mtx); 100 sema->sema_waiters--; 101 } 102 sema->sema_value--; 103 104 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema, 105 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line); 106 107 mtx_unlock(&sema->sema_mtx); 108 } 109 110 int 111 _sema_timedwait(struct sema *sema, int timo, const char *file, int line) 112 { 113 int error; 114 115 mtx_lock(&sema->sema_mtx); 116 117 /* 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 121 * long to wait. 122 */ 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--; 127 } 128 if (sema->sema_value > 0) { 129 /* Success. */ 130 sema->sema_value--; 131 error = 0; 132 133 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema, 134 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line); 135 } else { 136 CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema, 137 cv_wmesg(&sema->sema_cv), file, line); 138 } 139 140 mtx_unlock(&sema->sema_mtx); 141 return (error); 142 } 143 144 int 145 _sema_trywait(struct sema *sema, const char *file, int line) 146 { 147 int ret; 148 149 mtx_lock(&sema->sema_mtx); 150 151 if (sema->sema_value > 0) { 152 /* Success. */ 153 sema->sema_value--; 154 ret = 1; 155 156 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema, 157 cv_wmesg(&sema->sema_cv), sema->sema_value, file, line); 158 } else { 159 ret = 0; 160 161 CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema, 162 cv_wmesg(&sema->sema_cv), file, line); 163 } 164 165 mtx_unlock(&sema->sema_mtx); 166 return (ret); 167 } 168 169 int 170 sema_value(struct sema *sema) 171 { 172 int ret; 173 174 mtx_lock(&sema->sema_mtx); 175 ret = sema->sema_value; 176 mtx_unlock(&sema->sema_mtx); 177 return (ret); 178 } 179