127 lines
3.7 KiB
Groff
127 lines
3.7 KiB
Groff
.\"
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.\" Copyright (C) 2002 Chad David <davidc@acns.ab.ca>. 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 August 25, 2011
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.Dt SELRECORD 9
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.Os
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.Sh NAME
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.Nm seldrain ,
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.Nm selrecord ,
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.Nm selwakeup
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.Nd "record and wakeup select requests"
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.Sh SYNOPSIS
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.In sys/param.h
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.In sys/selinfo.h
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.Ft void
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.Fn seldrain "struct selinfo *sip"
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.Ft void
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.Fn selrecord "struct thread *td" "struct selinfo *sip"
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.Ft void
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.Fn selwakeup "struct selinfo *sip"
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.Sh DESCRIPTION
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.Fn seldrain ,
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.Fn selrecord
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and
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.Fn selwakeup
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are the three central functions used by
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.Xr select 2 ,
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.Xr poll 2
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and the objects that are being selected on.
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They handle the task of recording which threads are waiting on which objects
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and the waking of the proper threads when an event of interest occurs on an
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object.
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.Pp
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.Fn selrecord
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records that the calling thread is interested in events related to a given
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object.
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If another thread is already waiting on the object a collision will be flagged
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in
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.Fa sip
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which will be later dealt with by
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.Fn selwakeup .
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.Pp
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.Fn selrecord
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acquires and releases
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.Va sellock .
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.Pp
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.Fn selwakeup
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is called by the underlying object handling code in order to notify any waiting
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threads that an event of interest has occurred.
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If a collision has occurred,
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.Fn selwakeup
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will increment
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.Va nselcoll ,
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and broadcast on the global cv in order to wake all waiting threads so that
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they can handle it.
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If the thread waiting on the object is not currently sleeping or the wait
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channel is not
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.Va selwait ,
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.Fn selwakeup
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will clear the
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.Dv TDF_SELECT
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flag which should be noted by
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.Xr select 2
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and
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.Xr poll 2
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when they wake up.
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.Pp
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.Fn seldrain
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will flush the waiters queue on a specified object before its
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destruction.
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The object handling code must ensure that
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.Fa *sip
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cannot be used once
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.Fn seldrain
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has been called.
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.Pp
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The contents of
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.Fa *sip
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must be zeroed, such as by softc initialization, before any call to
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.Fn selrecord
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or
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.Fn selwakeup ,
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otherwise a panic may occur.
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.Fn selwakeup
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acquires and releases
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.Va sellock
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and may acquire and release
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.Va sched_lock .
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.Fn seldrain
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could usually be just a wrapper for
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.Fn selwakeup ,
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but consumers should not generally rely on this feature.
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.Sh SEE ALSO
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.Xr poll 2 ,
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.Xr select 2
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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 Chad David Aq Mt davidc@FreeBSD.org
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and
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.An Alfred Perlstein Aq Mt alfred@FreeBSD.org .
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