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 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 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 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 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 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 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 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