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/*
* Copyright (C) 2001 Jason Evans <jasone@freebsd.org>. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice(s), this list of conditions and the following disclaimer as
* the first lines of this file unmodified other than the possible
* addition of one or more copyright notices.
* 2. Redistributions in binary form must reproduce the above copyright
* notice(s), this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
* DAMAGE.
*/
/*
* Counting semaphores.
*
* Priority propagation will not generally raise the priority of semaphore
* "owners" (a misnomer in the context of semaphores), so should not be relied
* upon in combination with semaphores.
*/
#include <sys/cdefs.h>
__FBSDID("$FreeBSD$");
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/ktr.h>
#include <sys/condvar.h>
#include <sys/lock.h>
#include <sys/mutex.h>
#include <sys/sema.h>
void
sema_init(struct sema *sema, int value, const char *description)
{
KASSERT((value >= 0), ("%s(): negative value\n", __func__));
bzero(sema, sizeof(*sema));
mtx_init(&sema->sema_mtx, description, "sema backing lock",
MTX_DEF | MTX_NOWITNESS | MTX_QUIET);
cv_init(&sema->sema_cv, description);
sema->sema_value = value;
CTR4(KTR_LOCK, "%s(%p, %d, \"%s\")", __func__, sema, value, description);
}
void
sema_destroy(struct sema *sema)
{
CTR3(KTR_LOCK, "%s(%p) \"%s\"", __func__, sema,
cv_wmesg(&sema->sema_cv));
KASSERT((sema->sema_waiters == 0), ("%s(): waiters\n", __func__));
mtx_destroy(&sema->sema_mtx);
cv_destroy(&sema->sema_cv);
}
void
_sema_post(struct sema *sema, const char *file, int line)
{
mtx_lock(&sema->sema_mtx);
sema->sema_value++;
if (sema->sema_waiters && sema->sema_value > 0)
cv_signal(&sema->sema_cv);
CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
mtx_unlock(&sema->sema_mtx);
}
void
_sema_wait(struct sema *sema, const char *file, int line)
{
mtx_lock(&sema->sema_mtx);
while (sema->sema_value == 0) {
sema->sema_waiters++;
cv_wait(&sema->sema_cv, &sema->sema_mtx);
sema->sema_waiters--;
}
sema->sema_value--;
CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
mtx_unlock(&sema->sema_mtx);
}
int
_sema_timedwait(struct sema *sema, int timo, const char *file, int line)
{
int ret, timed_out;
mtx_lock(&sema->sema_mtx);
/*
* A spurious wakeup will cause the timeout interval to start over.
* This isn't a big deal as long as spurious wakeups don't occur
* continuously, since the timeout period is merely a lower bound on how
* long to wait.
*/
for (timed_out = 0; sema->sema_value == 0 && timed_out == 0;) {
sema->sema_waiters++;
timed_out = cv_timedwait(&sema->sema_cv, &sema->sema_mtx, timo);
sema->sema_waiters--;
}
if (sema->sema_value > 0) {
/* Success. */
sema->sema_value--;
ret = 1;
CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
} else {
ret = 0;
CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
cv_wmesg(&sema->sema_cv), file, line);
}
mtx_unlock(&sema->sema_mtx);
return (ret);
}
int
_sema_trywait(struct sema *sema, const char *file, int line)
{
int ret;
mtx_lock(&sema->sema_mtx);
if (sema->sema_value > 0) {
/* Success. */
sema->sema_value--;
ret = 1;
CTR6(KTR_LOCK, "%s(%p) \"%s\" v = %d at %s:%d", __func__, sema,
cv_wmesg(&sema->sema_cv), sema->sema_value, file, line);
} else {
ret = 0;
CTR5(KTR_LOCK, "%s(%p) \"%s\" fail at %s:%d", __func__, sema,
cv_wmesg(&sema->sema_cv), file, line);
}
mtx_unlock(&sema->sema_mtx);
return (ret);
}
int
sema_value(struct sema *sema)
{
int ret;
mtx_lock(&sema->sema_mtx);
ret = sema->sema_value;
mtx_unlock(&sema->sema_mtx);
return (ret);
}
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