FreeBSD-5.3/share/man/man9/selrecord.9

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.\" $FreeBSD: src/share/man/man9/selrecord.9,v 1.2 2002/05/30 13:29:17 ru Exp $
.\"
.Dd March 20, 2002
.Dt SELRECORD 9
.Os
.Sh NAME
.Nm selrecord ,
.Nm selwakeup
.Nd "record and wakeup select requests"
.Sh SYNOPSIS
.In sys/param.h
.In sys/selinfo.h
.Ft void
.Fn selrecord "struct thread *td" "struct selinfo *sip"
.Ft void
.Fn selwakeup "struct selinfo *sip"
.Sh DESCRIPTION
.Fn selrecord
and
.Fn selwakeup
are the two central functions used by
.Xr select 2 ,
.Xr poll 2
and the objects that are being selected on.
They handle the task of recording which threads are waiting on which objects
and the waking of the proper threads when an event of interest occurs on an
object.
.Pp
.Fn selrecord
records that the calling thread is interested in events related to a given
object.
If another thread is already waiting on the object a collision will be flagged
in
.Fa sip
which will be later dealt with by
.Fn selwakeup .
.Pp
.Fn selrecord
acquires and releases
.Va sellock .
.Pp
.Fn selwakeup
is called by the underlying object handling code in order to notify any waiting
threads that an event of interest has occurred.
If a collision has occurred,
.Fn selwakeup
will increment
.Va nselcoll ,
and broadcast on the global cv in order to wake all waiting threads so that
they can handle it.
If the thread waiting on the object is not currently sleeping or the wait
channel is not
.Va selwait ,
.Fn selwakeup
will clear the
.Dv TDF_SELECT
flag which should be noted by
.Xr select 2
and
.Xr poll 2
when they wake up.
.Pp
.Fn selwakeup
acquires and releases
.Va sellock
and may acquire and release
.Va sched_lock .
.Sh SEE ALSO
.Xr poll 2 ,
.Xr select 2
.Sh AUTHORS
.An -nosplit
This man page was written by
.An Chad David Aq davidc@FreeBSD.org
and
.An Alfred Perlstein Aq alfred@FreeBSD.org .