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 47 void 48 sema_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 62 void 63 sema_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 75 void 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 90 void 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 } 107 108 int 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 } 141 142 int 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 } 166 167 int 168 sema_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