The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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

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    1 /*-
    2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
    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 }

Cache object: 2134f6e4f9bd6157fb771f354f01390a


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