29a0e4d380
argument from a mutex to a lock_object. Add cv_*wait*() wrapper macros that accept either a mutex, rwlock, or sx lock as the second argument and convert it to a lock_object and then call _cv_*wait*(). Basically, the visible difference is that you can now use rwlocks and sx locks with condition variables using the same API as with mutexes.
209 lines
5.0 KiB
Groff
209 lines
5.0 KiB
Groff
.\"
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.\" Copyright (C) 2000 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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.Dd March 21, 2007
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.Dt CONDVAR 9
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.Os
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.Sh NAME
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.Nm condvar ,
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.Nm cv_init ,
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.Nm cv_destroy ,
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.Nm cv_wait ,
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.Nm cv_wait_sig ,
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.Nm cv_wait_unlock ,
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.Nm cv_timedwait ,
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.Nm cv_timedwait_sig ,
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.Nm cv_signal ,
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.Nm cv_broadcast ,
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.Nm cv_broadcastpri ,
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.Nm cv_wmesg
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.Nd kernel condition variable
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/proc.h
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.In sys/condvar.h
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.Ft void
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.Fn cv_init "struct cv *cvp" "const char *desc"
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.Ft void
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.Fn cv_destroy "struct cv *cvp"
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.Ft void
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.Fn cv_wait "struct cv *cvp" "lock"
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.Ft int
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.Fn cv_wait_sig "struct cv *cvp" "lock"
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.Ft void
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.Fn cv_wait_unlock "struct cv *cvp" "lock"
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.Ft int
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.Fn cv_timedwait "struct cv *cvp" "lock" "int timo"
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.Ft int
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.Fn cv_timedwait_sig "struct cv *cvp" "lock" "int timo"
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.Ft void
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.Fn cv_signal "struct cv *cvp"
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.Ft void
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.Fn cv_broadcast "struct cv *cvp"
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.Ft void
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.Fn cv_broadcastpri "struct cv *cvp" "int pri"
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.Ft const char *
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.Fn cv_wmesg "struct cv *cvp"
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.Sh DESCRIPTION
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Condition variables are used in conjunction with mutexes to wait for conditions
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to occur.
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Condition variables are created with
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.Fn cv_init ,
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where
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.Fa cvp
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is a pointer to space for a
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.Vt struct cv ,
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and
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.Fa desc
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is a pointer to a null-terminated character string that describes the condition
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variable.
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Condition variables are destroyed with
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.Fn cv_destroy .
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Threads wait on condition variables by calling
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.Fn cv_wait ,
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.Fn cv_wait_sig ,
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.Fn cv_wait_unlock ,
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.Fn cv_timedwait ,
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or
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.Fn cv_timedwait_sig .
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Threads unblock waiters by calling
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.Fn cv_signal
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to unblock one waiter, or
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.Fn cv_broadcast
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or
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.Fn cv_broadcastpri
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to unblock all waiters.
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In addition to waking waiters,
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.Fn cv_broadcastpri
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ensures that all of the waiters have a priority of at least
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.Fa pri
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by raising the priority of any threads that do not.
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.Fn cv_wmesg
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returns the description string of
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.Fa cvp ,
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as set by the initial call to
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.Fn cv_init .
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.Pp
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The
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.Fa lock
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argument is a pointer to either a
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.Xr mutex 9 ,
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.Xr rwlock 9 ,
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or
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.Xr sx 9
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lock.
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A thread must hold
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.Fa lock
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before calling
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.Fn cv_wait ,
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.Fn cv_wait_sig ,
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.Fn cv_wait_unlock ,
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.Fn cv_timedwait ,
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or
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.Fn cv_timedwait_sig .
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When a thread waits on a condition,
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.Fa lock
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is atomically released before the thread is blocked, then reacquired
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before the function call returns.
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The
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.Fn cv_wait_unlock
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function does not reacquire the lock before returning.
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All waiters must pass the same
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.Fa lock
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in conjunction with
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.Fa cvp .
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.Pp
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When
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.Fn cv_wait ,
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.Fn cv_wait_sig ,
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.Fn cv_wait_unlock ,
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.Fn cv_timedwait ,
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and
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.Fn cv_timedwait_sig
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unblock, their calling threads are made runnable.
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.Fn cv_timedwait
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and
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.Fn cv_timedwait_sig
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wait for at most
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.Fa timo
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/
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.Dv HZ
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seconds before being unblocked and returning
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.Er EWOULDBLOCK ;
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otherwise, they return 0.
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.Fn cv_wait_sig
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and
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.Fn cv_timedwait_sig
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return prematurely with a value of
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.Er EINTR
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or
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.Er ERESTART
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if a signal is caught, or 0 if signaled via
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.Fn cv_signal
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or
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.Fn cv_broadcast .
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.Sh RETURN VALUES
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If successful,
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.Fn cv_wait_sig ,
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.Fn cv_timedwait ,
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and
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.Fn cv_timedwait_sig
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return 0.
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Otherwise, a non-zero error code is returned.
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.Pp
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.Fn cv_wmesg
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returns the description string that was passed to
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.Fn cv_init .
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.Sh ERRORS
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.Fn cv_wait_sig
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and
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.Fn cv_timedwait_sig
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EINTR
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A signal was caught and the system call should be interrupted.
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.It Bq Er ERESTART
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A signal was caught and the system call should be restarted.
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.El
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.Pp
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.Fn cv_timedwait
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and
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.Fn cv_timedwait_sig
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will fail if:
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.Bl -tag -width Er
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.It Bq Er EWOULDBLOCK
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Timeout expired.
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.El
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.Sh SEE ALSO
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.Xr mtx_pool 9 ,
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.Xr mutex 9 ,
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.Xr rwlock 9 ,
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.Xr sema 9 ,
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.Xr sleep 9 ,
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.Xr sx 9
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