161 lines
4.2 KiB
C
161 lines
4.2 KiB
C
/*
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* Copyright (C) 2001 Jason Evans <jasone@freebsd.org>. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice(s), this list of conditions and the following disclaimer as
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* the first lines of this file unmodified other than the possible
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* addition of one or more copyright notices.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice(s), this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER(S) ``AS IS'' AND ANY
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* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER(S) BE LIABLE FOR ANY
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* DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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* (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH
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* DAMAGE.
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*
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* $FreeBSD$
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*/
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/*
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* Shared/exclusive locks. This implementation assures deterministic lock
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* granting behavior, so that slocks and xlocks are interleaved.
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*
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* Priority propagation will not generally raise the priority of lock holders,
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* so should not be relied upon in combination with sx locks.
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*
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* The witness code can not detect lock cycles.
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*
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* slock --> xlock (deadlock)
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* slock --> slock (slock recursion, not fatal)
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* xlock --> xlock (deadlock)
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* xlock --> slock (deadlock)
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*/
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#include <sys/param.h>
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#include <sys/systm.h>
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#include <sys/ktr.h>
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#include <sys/condvar.h>
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#include <sys/mutex.h>
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#include <sys/sx.h>
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void
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sx_init(struct sx *sx, const char *description)
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{
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mtx_init(&sx->sx_lock, description, MTX_DEF);
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sx->sx_cnt = 0;
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cv_init(&sx->sx_shrd_cv, description);
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sx->sx_shrd_wcnt = 0;
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cv_init(&sx->sx_excl_cv, description);
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sx->sx_excl_wcnt = 0;
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}
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void
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sx_destroy(struct sx *sx)
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{
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KASSERT((sx->sx_cnt == 0 && sx->sx_shrd_wcnt == 0 && sx->sx_excl_wcnt ==
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0), ("%s: holders or waiters\n", __FUNCTION__));
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mtx_destroy(&sx->sx_lock);
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cv_destroy(&sx->sx_shrd_cv);
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cv_destroy(&sx->sx_excl_cv);
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}
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void
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sx_slock(struct sx *sx)
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{
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mtx_lock(&sx->sx_lock);
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/*
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* Loop in case we lose the race for lock acquisition.
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*/
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while (sx->sx_cnt < 0) {
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sx->sx_shrd_wcnt++;
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cv_wait(&sx->sx_shrd_cv, &sx->sx_lock);
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sx->sx_shrd_wcnt--;
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}
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/* Acquire a shared lock. */
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sx->sx_cnt++;
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mtx_unlock(&sx->sx_lock);
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}
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void
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sx_xlock(struct sx *sx)
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{
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mtx_lock(&sx->sx_lock);
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/* Loop in case we lose the race for lock acquisition. */
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while (sx->sx_cnt != 0) {
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sx->sx_excl_wcnt++;
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cv_wait(&sx->sx_excl_cv, &sx->sx_lock);
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sx->sx_excl_wcnt--;
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}
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/* Acquire an exclusive lock. */
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sx->sx_cnt--;
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mtx_unlock(&sx->sx_lock);
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}
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void
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sx_sunlock(struct sx *sx)
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{
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mtx_lock(&sx->sx_lock);
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KASSERT((sx->sx_cnt > 0), ("%s: lacking slock\n", __FUNCTION__));
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/* Release. */
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sx->sx_cnt--;
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/*
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* If we just released the last shared lock, wake any waiters up, giving
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* exclusive lockers precedence. In order to make sure that exclusive
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* lockers won't be blocked forever, don't wake shared lock waiters if
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* there are exclusive lock waiters.
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*/
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if (sx->sx_excl_wcnt > 0) {
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if (sx->sx_cnt == 0)
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cv_signal(&sx->sx_excl_cv);
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} else if (sx->sx_shrd_wcnt > 0)
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cv_broadcast(&sx->sx_shrd_cv);
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mtx_unlock(&sx->sx_lock);
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}
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void
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sx_xunlock(struct sx *sx)
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{
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mtx_lock(&sx->sx_lock);
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KASSERT((sx->sx_cnt == -1), ("%s: lacking xlock\n", __FUNCTION__));
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/* Release. */
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sx->sx_cnt++;
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/*
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* Wake up waiters if there are any. Give precedence to slock waiters.
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*/
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if (sx->sx_shrd_wcnt > 0)
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cv_broadcast(&sx->sx_shrd_cv);
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else if (sx->sx_excl_wcnt > 0)
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cv_signal(&sx->sx_excl_cv);
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mtx_unlock(&sx->sx_lock);
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}
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