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Document the current organization and helper functions used to implement

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the sleep queues used by msleep/wakeup and friends.

Submitted by:	sheldonh
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jhb 2001-01-23 19:24:35 +00:00
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.\" Copyright (c) 2000 John H. Baldwin <jhb@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE DEVELOPERS BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd Nov 3, 2000
.Dt SLEEPQUEUE 9
.Os
.Sh NAME
.Nm endtsleep ,
.Nm sleepinit ,
.Nm unsleep
.Nd manage the queues of sleeping processes
.Sh SYNOPSIS
.Fd #include <sys/param.h>
.Fd #include <sys/proc.h>
.Ft void
.Fn endtsleep "void *arg"
.Ft void
.Fn sleepinit "void"
.Ft void
.Fn unsleep "struct proc *p"
.Sh DESCRIPTION
The sleep queues used by
.Xr msleep 9
and friends are stored in a hash array.
The address of the wait channel is used to generate an index into the array.
Each entry in the array is a queue of processes that are sleeping on wait
channels that hash to that index.
.Xr msleep 9
places processes into their appropriate queues directly.
To handle timeouts, the
.Fn endtsleep
function is registered as a
.Xr timeout 9 .
When the process is woken by either
.Fn wakeup
or
.Fn wakeup_one ,
the timeout is revoked via
.Xr untimeout 9 .
If the process is not awakened soon enough, then
.Fn endtsleep
is called with
.Fa arg
pointing to the
.Li struct proc
of the process that timed out.
.Fn endtsleep
undoes the sleep and makes the process runnable if it is in the
.Dv SSLEEP
state.
The sleep queues and the hash array are protected internally by the
.Va sched_lock
mutex.
.Pp
.Fn unsleep
simply removes the process
.Fa p
from its sleep queue.
.Pp
.Fn sleepinit
is called during system startup and initializes the scheduler quantum
.Pq Va sched_quantum
and the sleep queues.
.Sh SEE ALSO
.Xr msleep 9 ,
.Xr runqueue 9 ,
.Xr scheduler 9