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FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_sema.c

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    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: releng/7.4/sys/kern/kern_sema.c 139804 2005-01-06 23:35:40Z imp $");
   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 }

Cache object: 49ba87f6a2169fd50f22121052666764


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