sys/kern/kern_sema.c

   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 }