.\" $NetBSD: callout.9,v 1.4 2001/06/21 11:59:00 wiz Exp $ .\" .\" Copyright (c) 2000 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 March 21, 2000 .Dt CALLOUT 9 .Os .Sh NAME .Nm callout_init , .Nm callout_reset , .Nm callout_stop .Nd execute a function after a specified length of time .Sh SYNOPSIS .Fd #include .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_stop" "struct callout *c" .Ft int .Fn "callout_active" "struct callout *c" .Ft int .Fn "callout_pending" "struct callout *c" .Ft int .Fn "callout_expired" "struct callout *c" .Ft void .Fn "callout_deactivate" "struct callout *c" .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 starts (or resets) 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 . Note that if the timer associated with the callout handle is already running, it will be implicitly stopped before being reset. Once the timer is started, the callout handle is marked as .Em ACTIVE and .Em PENDING . Once the timer expires, .Em PENDING status is cleared. Expiration of the timer does not affect .Em ACTIVE status. .Pp The .Fn callout_stop function stops the timer associated the callout handle .Fa c . The .Em ACTIVE and .Em PENDING status for the callout handle is cleared. It is safe to call .Fn callout_stop on a callout handle that is not active, so long as it is initialized. .Pp The .Fn callout_active function tests the .Em ACTIVE status of the callout handle .Fa c . An .Em ACTIVE callout is one that has been started but not explicitly stopped. Testing .Em ACTIVE status is a way to determine if a callout has been started. Once the callout fires, the executed function may clear .Em ACTIVE status. See .Fn callout_deactivate below. .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 the opposite of .Fn callout_pending . That is to say that .Fn callout_expired returns true when the callout function has been called. .Pp The .Fn callout_deactivate function clears the .Em ACTIVE status of the callout handle .Fa c . Note that is only safe to call .Fn callout_deactivate if the callout function has already been executed, i.e. the callout is no longer .Em PENDING . \" .Sh SEE ALSO \" .Xr hz 9 .Sh HISTORY The .Nm callout facility is based on the work of Adam M. Costello and George Varghese, published in a technical report entitled .Dq Redesigning the BSD Callout and Timer Facilities , and Justin Gibbs's subsequent integration into .Fx . It was modified for .Nx by Jason R. Thorpe, who also added optional statistics gathering and an alternate sorting mode for the callwheel. .Pp The original work on the data structures used in this implementation was published by G. Varghese and A. Lauck 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.