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  * $FreeBSD: releng/5.0/sys/kern/kern_sema.c 93818 2002-04-04 21:03:38Z jhb $
   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 ret, timed_out;
  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 (timed_out = 0; sema->sema_value == 0 && timed_out == 0;) {
  121                 sema->sema_waiters++;
  122                 timed_out = 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                 ret = 1;
  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                 ret = 0;
  134                 
  135                 CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
  136                     cv_wmesg(&sema->sema_cv), file, line);
  137         }
  138 
  139         mtx_unlock(&sema->sema_mtx);
  140         return (ret);
  141 }
  142 
  143 int
  144 _sema_trywait(struct sema *sema, const char *file, int line)
  145 {
  146         int ret;
  147 
  148         mtx_lock(&sema->sema_mtx);
  149 
  150         if (sema->sema_value > 0) {
  151                 /* Success. */
  152                 sema->sema_value--;
  153                 ret = 1;
  154 
  155                 CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
  156                     cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
  157         } else {
  158                 ret = 0;
  159 
  160                 CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
  161                     cv_wmesg(&sema->sema_cv), file, line);
  162         }
  163 
  164         mtx_unlock(&sema->sema_mtx);
  165         return (ret);
  166 }
  167 
  168 int
  169 sema_value(struct sema *sema)
  170 {
  171         int ret;
  172 
  173         mtx_lock(&sema->sema_mtx);
  174         ret = sema->sema_value;
  175         mtx_unlock(&sema->sema_mtx);
  176         return (ret);
  177 }

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

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sys/kern/kern_sema.c