diff options
Diffstat (limited to 'sys/kern/kern_sema.c')
| -rw-r--r-- | sys/kern/kern_sema.c | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/sys/kern/kern_sema.c b/sys/kern/kern_sema.c new file mode 100644 index 0000000..61435bd --- /dev/null +++ b/sys/kern/kern_sema.c @@ -0,0 +1,177 @@ +/* + * 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. + * + * $FreeBSD$ + */ + +/* + * 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/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); +} |
