204 lines
5.1 KiB
Groff
204 lines
5.1 KiB
Groff
.\"
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.\" Copyright (c) 1996 Joerg Wunsch
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.\"
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.\" 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, 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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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd December 17, 1998
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.Os
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.Dt SLEEP 9
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.Sh NAME
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.Nm msleep ,
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.Nm msleep_spin ,
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.Nm tsleep ,
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.Nm wakeup
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.Nd wait for events
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/systm.h
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.In sys/proc.h
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.Ft int
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.Fn tsleep "void *chan" "int priority" "const char *wmesg" "int timo"
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.Ft int
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.Fn msleep "void *chan" "struct mtx *mtx" "int priority" "const char *wmesg" "int timo"
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.Ft int
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.Fn msleep_spin "void *chan" "struct mtx *mtx" "const char *wmesg" "int timo"
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.Ft void
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.Fn wakeup "void *chan"
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.Ft void
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.Fn wakeup_one "void *chan"
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.Sh DESCRIPTION
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The functions
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.Fn tsleep
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and
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.Fn wakeup
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handle event-based process blocking.
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If a process must wait for an
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external event, it is put on sleep by
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.Fn tsleep .
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The parameter
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.Fa chan
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is an arbitrary address that uniquely identifies the event on which
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the process is being asleep.
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All processes sleeping on a single
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.Fa chan
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are woken up later by
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.Fn wakeup ,
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often called from inside an interrupt routine, to indicate that the
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resource the process was blocking on is available now.
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.Pp
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The parameter
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.Fa wmesg
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is a string describing the sleep condition for tools like
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.Xr ps 1 .
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Due to the limited space of those programs to display arbitrary strings,
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this message should not be longer than 6 characters.
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.Pp
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The
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.Fn wakeup_one
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function is used to make the first process in the queue that is
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sleeping on the parameter
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.Fa chan
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runnable.
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This can prevent the system from becoming saturated
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when a large number of processes are sleeping on the same address,
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but only one of them can actually do any useful work when made
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runnable.
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.Pp
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The
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.Fn tsleep
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function is the general sleep call.
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Suspends the current process until a wakeup is
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performed on the specified identifier.
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The process will then be made
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runnable with the specified
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.Fa priority .
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Sleeps at most
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.Fa timo
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\&/ hz seconds (0 means no timeout).
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If the
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.Va Giant
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lock is not held and
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.Fa mtx
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is
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.Dv NULL ,
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then
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.Fa timo
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must be non-zero.
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If
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.Fa priority
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includes the
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.Dv PCATCH
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flag, signals are checked before and after sleeping, otherwise signals are
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not checked.
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Returns 0 if awakened,
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.Er EWOULDBLOCK
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if the timeout expires.
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If
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.Dv PCATCH
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is set and a signal needs to be delivered,
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.Er ERESTART
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is returned if the current system call should be restarted if
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possible, and
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.Er EINTR
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is returned if the system call should be interrupted by the signal
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(return
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.Er EINTR ) .
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.Pp
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The
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.Fn msleep
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function is a variation on tsleep.
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The parameter
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.Fa mtx
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is a mutex which will be released before sleeping and reacquired before
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.Fn msleep
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returns.
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If
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.Fa priority
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includes the
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.Dv PDROP
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flag, the
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.Fa mtx
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parameter will not be reacquired before returning.
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The mutex is
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used to ensure that a condition can be checked atomically, and
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that the current process can be suspended without missing a
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change to the condition, or an associated wakeup.
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.Pp
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The
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.Fn msleep_spin
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function is another variation on
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.Fn tsleep
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similar to
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.Fn msleep .
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Unlike
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.Fn msleep ,
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this function accepts a spin mutex rather than a default mutex for its
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.Fa mtx
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parameter.
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It is also more limited in that it does not accept a
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.Fa priority
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parameter.
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Thus, it will not change the priority of a sleeping thread,
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and it does not support the
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.Dv PDROP
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and
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.Dv PCATCH
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flags.
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.Sh RETURN VALUES
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See above.
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.Sh SEE ALSO
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.Xr ps 1 ,
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.Xr malloc 9 ,
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.Xr mi_switch 9
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.Sh HISTORY
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The sleep/wakeup process synchronization mechanism is very old.
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It
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appeared in a very early version of
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.Ux .
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.Pp
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The
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.Fn tsleep
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function appeared in
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.Bx 4.4 .
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The
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.Fn msleep
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function appeared in
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.Fx 5.0 ,
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and the
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.Fn msleep_spin
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function appeared in
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.Fx 7.0 .
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.Pp
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The
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.Fn sleep
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function used to be the traditional form.
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It did not let you specify a timeout or a
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.Fa wmesg ,
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hence it was discontinued.
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.Sh AUTHORS
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.An -nosplit
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This manual page was written by
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.An J\(:org Wunsch Aq joerg@FreeBSD.org .
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