242 lines
7.2 KiB
Groff
242 lines
7.2 KiB
Groff
.\" $NetBSD: callout.9,v 1.13 2003/10/27 16:52:01 thorpej Exp $
|
|
.\"
|
|
.\" Copyright (c) 2000, 2003 The NetBSD Foundation, Inc.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" This code is derived from software contributed to The NetBSD Foundation
|
|
.\" by Jason R. Thorpe.
|
|
.\"
|
|
.\" 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.
|
|
.\" 3. All advertising materials mentioning features or use of this software
|
|
.\" must display the following acknowledgement:
|
|
.\" This product includes software developed by the NetBSD
|
|
.\" Foundation, Inc. and its contributors.
|
|
.\" 4. Neither the name of The NetBSD Foundation nor the names of its
|
|
.\" contributors may be used to endorse or promote products derived
|
|
.\" from this software without specific prior written permission.
|
|
.\"
|
|
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
|
|
.\" ``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 FOUNDATION OR CONTRIBUTORS
|
|
.\" 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.
|
|
.\"
|
|
.Dd October 26, 2003
|
|
.Dt CALLOUT 9
|
|
.Os
|
|
.Sh NAME
|
|
.Nm callout_init ,
|
|
.Nm callout_reset ,
|
|
.Nm callout_schedule ,
|
|
.Nm callout_setfunc ,
|
|
.Nm callout_stop ,
|
|
.Nm callout_expired ,
|
|
.Nm callout_invoking ,
|
|
.Nm callout_ack ,
|
|
.Nm CALLOUT_INITIALIZER ,
|
|
.Nm CALLOUT_INITIALIZER_SETFUNC
|
|
.Nd execute a function after a specified length of time
|
|
.Sh SYNOPSIS
|
|
.In sys/callout.h
|
|
.Ft void
|
|
.Fn "callout_init" "struct callout *c"
|
|
.Ft void
|
|
.Fn "callout_reset" "struct callout *c" "int ticks" \
|
|
"void (*func)(void *)" "void *arg"
|
|
.Ft void
|
|
.Fn "callout_schedule" "struct callout *c" "int ticks"
|
|
.Ft void
|
|
.Fn "callout_setfunc" "struct callout *c" "void (*func)(void *)" "void *arg"
|
|
.Ft void
|
|
.Fn "callout_stop" "struct callout *c"
|
|
.Ft int
|
|
.Fn "callout_pending" "struct callout *c"
|
|
.Ft int
|
|
.Fn "callout_expired" "struct callout *c"
|
|
.Ft int
|
|
.Fn "callout_invoking" "struct callout *c"
|
|
.Ft void
|
|
.Fn "callout_ack" "struct callout *c"
|
|
.Fd CALLOUT_INITIALIZER
|
|
.Pp
|
|
.Fn CALLOUT_INITIALIZER_SETFUNC "func" "arg"
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm callout
|
|
facility provides a mechanism to execute a function at a given time.
|
|
The timer is based on the hardclock timer which ticks
|
|
.Dv hz
|
|
times per second.
|
|
The function is called at softclock interrupt level.
|
|
.Pp
|
|
Clients of the
|
|
.Nm callout
|
|
facility are responsible for providing pre-allocated
|
|
callout structures, or
|
|
.Dq handles .
|
|
The
|
|
.Nm callout
|
|
facility replaces the historic
|
|
.Bx
|
|
functions
|
|
.Fn timeout
|
|
and
|
|
.Fn untimeout .
|
|
.Pp
|
|
The
|
|
.Fn callout_init
|
|
function initializes the callout handle
|
|
.Fa c
|
|
for use.
|
|
If it is inconvenient to call
|
|
.Fn callout_init ,
|
|
statically-allocated callout handles may be initialized by assigning
|
|
the value
|
|
.Dv CALLOUT_INITIALIZER
|
|
to them.
|
|
.Pp
|
|
The
|
|
.Fn callout_reset
|
|
function resets and starts the timer associated with the callout handle
|
|
.Fa c .
|
|
When the timer expires after
|
|
.Fa ticks Ns No /hz
|
|
seconds, the function specified by
|
|
.Fa func
|
|
will be called with the argument
|
|
.Fa arg .
|
|
If the timer associated with the callout handle is already running,
|
|
the callout will simply be rescheduled to execute at the newly specified
|
|
time.
|
|
Once the timer is started, the callout handle is marked as
|
|
.Em PENDING .
|
|
Once the timer expires,
|
|
the handle is marked as
|
|
.Em EXPIRED
|
|
and
|
|
.Em INVOKING ,
|
|
and the
|
|
.Em PENDING
|
|
status is cleared.
|
|
.Pp
|
|
The
|
|
.Fn callout_setfunc
|
|
function sets the function and argument of the callout handle
|
|
.Fa c
|
|
to
|
|
.Fa func
|
|
and
|
|
.Fa arg
|
|
respectively.
|
|
The callout handle must already be initialized.
|
|
If a callout will always be used with the same function and argument,
|
|
then
|
|
.Fn callout_setfunc
|
|
used in conjunction with
|
|
.Fn callout_schedule
|
|
is slightly more efficient than using
|
|
.Fn callout_reset .
|
|
If it is inconvenient to call
|
|
.Fn callout_setfunc ,
|
|
statically-allocated callout handles may be initialized by assigning
|
|
the value
|
|
.Dv CALLOUT_INITIALIZER_SETFUNC
|
|
to them, passing the function and argument to the initializer.
|
|
.Pp
|
|
The
|
|
.Fn callout_stop
|
|
function stops the timer associated the callout handle
|
|
.Fa c .
|
|
The
|
|
.Em PENDING
|
|
and
|
|
.Em EXPIRED
|
|
status for the callout handle is cleared.
|
|
It is safe to call
|
|
.Fn callout_stop
|
|
on a callout handle that is not pending, so long as it is initialized.
|
|
.Pp
|
|
The
|
|
.Fn callout_pending
|
|
function tests the
|
|
.Em PENDING
|
|
status of the callout handle
|
|
.Fa c .
|
|
A
|
|
.Em PENDING
|
|
callout is one that has been started and whose function has not yet
|
|
been called.
|
|
Note that it is possible for a callout's timer to have expired without
|
|
its function being called if interrupt level has not dropped low enough
|
|
to let softclock interrupts through.
|
|
Note that it is only safe to test
|
|
.Em PENDING
|
|
status when at softclock interrupt level or higher.
|
|
.Pp
|
|
The
|
|
.Fn callout_expired
|
|
function tests to see if the callout's timer has expired and its
|
|
function called.
|
|
.Pp
|
|
The
|
|
.Fn callout_invoking
|
|
function tests the
|
|
.Em INVOKING
|
|
status of the callout handle
|
|
.Fa c .
|
|
This flag is set just before a callout's function is being called.
|
|
Since the priority level is lowered prior to invocation of the
|
|
callout function, other pending higher-priority code may run before
|
|
the callout function is allowed to run.
|
|
This may create a race condition if this higher-priority code
|
|
deallocates storage containing one or more callout structures whose
|
|
callout functions are about to be run.
|
|
In such cases, one technique to prevent references to deallocated
|
|
storage would be to test whether any callout functions are in the
|
|
.Em INVOKING
|
|
state using
|
|
.Fn callout_invoking ,
|
|
and if so, to mark the data structure and defer storage
|
|
deallocation until the callout function is allowed to run.
|
|
For this handshake protocol to work, the callout function will
|
|
have to use the
|
|
.Fn callout_ack
|
|
function to clear this flag.
|
|
.Pp
|
|
The
|
|
.Fn callout_ack
|
|
function clears the
|
|
.Em INVOKING
|
|
state in the callout handle
|
|
.Fa c .
|
|
This is used in situations where it is necessary to protect against
|
|
the race condition described under
|
|
.Fn callout_invoking .
|
|
.Sh SEE ALSO
|
|
.Xr hz 9
|
|
.Sh HISTORY
|
|
The
|
|
.Nm callout
|
|
facility was implemented by Artur Grabowski and Thomas Nordin, based
|
|
on the work of G. Varghese and A. Lauck, described in the paper
|
|
Hashed and Hierarchical Timing Wheels: Data Structures for the
|
|
Efficient Implementation of a Timer Facility
|
|
in the Proceedings of the 11th ACM Annual Symposium on Operating System
|
|
Principles, Austin, Texas, November 1987.
|
|
It was adapted to the
|
|
.Nx
|
|
kernel by Jason R. Thorpe.
|