384 lines
8.7 KiB
C
384 lines
8.7 KiB
C
/* $NetBSD: kern_condvar.c,v 1.16 2008/03/17 16:54:51 ad Exp $ */
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/*-
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* Copyright (c) 2006, 2007, 2008 The NetBSD Foundation, Inc.
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* All rights reserved.
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*
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* This code is derived from software contributed to The NetBSD Foundation
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* by Andrew Doran.
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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, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, 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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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by the NetBSD
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* Foundation, Inc. and its contributors.
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* 4. Neither the name of The NetBSD Foundation nor the names of its
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* contributors may be used to endorse or promote products derived
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* from this software without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*/
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/*
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* Kernel condition variable implementation, modeled after those found in
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* Solaris, a description of which can be found in:
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*
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* Solaris Internals: Core Kernel Architecture, Jim Mauro and
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* Richard McDougall.
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*/
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#include <sys/cdefs.h>
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__KERNEL_RCSID(0, "$NetBSD: kern_condvar.c,v 1.16 2008/03/17 16:54:51 ad Exp $");
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#include <sys/param.h>
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#include <sys/proc.h>
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#include <sys/sched.h>
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#include <sys/systm.h>
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#include <sys/condvar.h>
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#include <sys/sleepq.h>
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static u_int cv_unsleep(lwp_t *, bool);
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static syncobj_t cv_syncobj = {
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SOBJ_SLEEPQ_SORTED,
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cv_unsleep,
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sleepq_changepri,
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sleepq_lendpri,
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syncobj_noowner,
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};
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static const char deadcv[] = "deadcv";
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/*
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* cv_init:
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*
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* Initialize a condition variable for use.
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*/
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void
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cv_init(kcondvar_t *cv, const char *wmesg)
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{
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KASSERT(wmesg != NULL);
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cv->cv_wmesg = wmesg;
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cv->cv_waiters = 0;
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}
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/*
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* cv_destroy:
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*
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* Tear down a condition variable.
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*/
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void
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cv_destroy(kcondvar_t *cv)
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{
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#ifdef DIAGNOSTIC
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KASSERT(cv_is_valid(cv));
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cv->cv_wmesg = deadcv;
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cv->cv_waiters = -3;
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#endif
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}
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/*
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* cv_enter:
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*
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* Look up and lock the sleep queue corresponding to the given
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* condition variable, and increment the number of waiters.
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*/
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static inline sleepq_t *
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cv_enter(kcondvar_t *cv, kmutex_t *mtx, lwp_t *l)
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{
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sleepq_t *sq;
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KASSERT(cv_is_valid(cv));
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KASSERT((l->l_pflag & LP_INTR) == 0 || panicstr != NULL);
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l->l_cv_signalled = 0;
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l->l_kpriority = true;
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sq = sleeptab_lookup(&sleeptab, cv);
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cv->cv_waiters++;
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sleepq_enter(sq, l);
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sleepq_enqueue(sq, cv, cv->cv_wmesg, &cv_syncobj);
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mutex_exit(mtx);
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return sq;
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}
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/*
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* cv_exit:
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*
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* After resuming execution, check to see if we have been restarted
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* as a result of cv_signal(). If we have, but cannot take the
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* wakeup (because of eg a pending Unix signal or timeout) then try
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* to ensure that another LWP sees it. This is necessary because
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* there may be multiple waiters, and at least one should take the
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* wakeup if possible.
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*/
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static inline int
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cv_exit(kcondvar_t *cv, kmutex_t *mtx, lwp_t *l, const int error)
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{
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mutex_enter(mtx);
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if (__predict_false(error != 0) && l->l_cv_signalled != 0)
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cv_signal(cv);
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KASSERT(cv_is_valid(cv));
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return error;
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}
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/*
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* cv_unsleep:
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*
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* Remove an LWP from the condition variable and sleep queue. This
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* is called when the LWP has not been awoken normally but instead
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* interrupted: for example, when a signal is received. Must be
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* called with the LWP locked, and must return it unlocked.
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*/
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static u_int
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cv_unsleep(lwp_t *l, bool cleanup)
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{
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kcondvar_t *cv;
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cv = (kcondvar_t *)(uintptr_t)l->l_wchan;
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KASSERT(l->l_wchan != NULL);
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KASSERT(lwp_locked(l, l->l_sleepq->sq_mutex));
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KASSERT(cv_is_valid(cv));
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KASSERT(cv->cv_waiters > 0);
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cv->cv_waiters--;
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return sleepq_unsleep(l, cleanup);
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}
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/*
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* cv_wait:
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*
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* Wait non-interruptably on a condition variable until awoken.
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*/
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void
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cv_wait(kcondvar_t *cv, kmutex_t *mtx)
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{
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lwp_t *l = curlwp;
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sleepq_t *sq;
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KASSERT(mutex_owned(mtx));
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if (sleepq_dontsleep(l)) {
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(void)sleepq_abort(mtx, 0);
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return;
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}
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sq = cv_enter(cv, mtx, l);
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(void)sleepq_block(0, false);
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(void)cv_exit(cv, mtx, l, 0);
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}
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/*
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* cv_wait_sig:
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*
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* Wait on a condition variable until a awoken or a signal is received.
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* Will also return early if the process is exiting. Returns zero if
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* awoken normallly, ERESTART if a signal was received and the system
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* call is restartable, or EINTR otherwise.
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*/
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int
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cv_wait_sig(kcondvar_t *cv, kmutex_t *mtx)
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{
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lwp_t *l = curlwp;
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sleepq_t *sq;
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int error;
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KASSERT(mutex_owned(mtx));
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if (sleepq_dontsleep(l))
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return sleepq_abort(mtx, 0);
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sq = cv_enter(cv, mtx, l);
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error = sleepq_block(0, true);
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return cv_exit(cv, mtx, l, error);
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}
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/*
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* cv_timedwait:
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*
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* Wait on a condition variable until awoken or the specified timeout
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* expires. Returns zero if awoken normally or EWOULDBLOCK if the
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* timeout expired.
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*/
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int
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cv_timedwait(kcondvar_t *cv, kmutex_t *mtx, int timo)
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{
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lwp_t *l = curlwp;
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sleepq_t *sq;
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int error;
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KASSERT(mutex_owned(mtx));
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if (sleepq_dontsleep(l))
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return sleepq_abort(mtx, 0);
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sq = cv_enter(cv, mtx, l);
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error = sleepq_block(timo, false);
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return cv_exit(cv, mtx, l, error);
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}
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/*
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* cv_timedwait_sig:
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*
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* Wait on a condition variable until a timeout expires, awoken or a
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* signal is received. Will also return early if the process is
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* exiting. Returns zero if awoken normallly, EWOULDBLOCK if the
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* timeout expires, ERESTART if a signal was received and the system
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* call is restartable, or EINTR otherwise.
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*/
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int
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cv_timedwait_sig(kcondvar_t *cv, kmutex_t *mtx, int timo)
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{
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lwp_t *l = curlwp;
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sleepq_t *sq;
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int error;
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KASSERT(mutex_owned(mtx));
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if (sleepq_dontsleep(l))
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return sleepq_abort(mtx, 0);
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sq = cv_enter(cv, mtx, l);
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error = sleepq_block(timo, true);
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return cv_exit(cv, mtx, l, error);
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}
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/*
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* cv_signal:
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*
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* Wake the highest priority LWP waiting on a condition variable.
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* Must be called with the interlocking mutex held.
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*/
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void
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cv_signal(kcondvar_t *cv)
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{
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lwp_t *l;
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sleepq_t *sq;
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KASSERT(cv_is_valid(cv));
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if (cv->cv_waiters == 0)
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return;
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/*
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* cv->cv_waiters may be stale and have dropped to zero, but
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* while holding the interlock (the mutex passed to cv_wait()
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* and similar) we will see non-zero values when it matters.
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*/
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sq = sleeptab_lookup(&sleeptab, cv);
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if (cv->cv_waiters != 0) {
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cv->cv_waiters--;
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l = sleepq_wake(sq, cv, 1);
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l->l_cv_signalled = 1;
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} else
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sleepq_unlock(sq);
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KASSERT(cv_is_valid(cv));
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}
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/*
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* cv_broadcast:
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*
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* Wake all LWPs waiting on a condition variable. Must be called
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* with the interlocking mutex held.
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*/
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void
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cv_broadcast(kcondvar_t *cv)
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{
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sleepq_t *sq;
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u_int cnt;
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KASSERT(cv_is_valid(cv));
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if (cv->cv_waiters == 0)
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return;
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sq = sleeptab_lookup(&sleeptab, cv);
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if ((cnt = cv->cv_waiters) != 0) {
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cv->cv_waiters = 0;
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sleepq_wake(sq, cv, cnt);
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} else
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sleepq_unlock(sq);
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KASSERT(cv_is_valid(cv));
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}
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/*
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* cv_wakeup:
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*
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* Wake all LWPs waiting on a condition variable. For cases
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* where the address may be waited on by mtsleep()/tsleep().
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* Not a documented call.
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*/
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void
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cv_wakeup(kcondvar_t *cv)
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{
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sleepq_t *sq;
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KASSERT(cv_is_valid(cv));
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sq = sleeptab_lookup(&sleeptab, cv);
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cv->cv_waiters = 0;
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sleepq_wake(sq, cv, (u_int)-1);
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KASSERT(cv_is_valid(cv));
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}
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/*
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* cv_has_waiters:
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*
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* For diagnostic assertions: return non-zero if a condition
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* variable has waiters.
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*/
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bool
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cv_has_waiters(kcondvar_t *cv)
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{
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/* No need to interlock here */
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return cv->cv_waiters != 0;
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}
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/*
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* cv_is_valid:
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*
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* For diagnostic assertions: return non-zero if a condition
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* variable appears to be valid. No locks need be held.
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*/
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bool
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cv_is_valid(kcondvar_t *cv)
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{
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if (cv->cv_wmesg == deadcv || cv->cv_wmesg == NULL)
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return false;
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if ((cv->cv_waiters & 0xff000000) != 0) {
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/* Arbitrary: invalid number of waiters. */
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return false;
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}
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return cv->cv_waiters >= 0;
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}
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