.\"	$OpenBSD: timeout.9,v 1.18 2002/02/15 02:02:50 art Exp $
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.\" Copyright (c) 2000 Artur Grabowski <art@openbsd.org>
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.Dd June 23, 1996
.Dt TIMEOUT 9
.Os
.Sh NAME
.Nm timeout_set ,
.Nm timeout_add ,
.Nm timeout_del ,
.Nm timeout_pending ,
.Nm timeout_initialized
.Nd execute a function after a specified period of time
.Sh SYNOPSIS
.Fd #include <sys/types.h>
.Fd #include <sys/timeout.h>
.Ft void
.Fn "timeout_set" "struct timeout *to" "void (*fn)(void *)" "void *arg"
.Ft void
.Fn "timeout_add" "struct timeout *to" "int ticks"
.Ft void
.Fn "timeout_del" "struct timeout *to"
.Ft int
.Fn "timeout_pending" "struct timeout *to"
.Ft int
.Fn "timeout_initialized" "struct timeout *to"
.Ft int
.Fn "timeout_triggered" "struct timeout *to"
.Sh DESCRIPTION
The
.Nm timeout
API provides a mechanism to execute a function at a given time.
The granularity of the time is limited by the granularity of the
.Xr hardclock 9
timer which executes
.Nm hz
times a second.
The function will be called at softclock interrupt level.
.Pp
It is the responsibility of the caller to provide these functions with
pre-allocated timeout structures.
All functions in this API may be used in interrupt context below
.Fn splclock .
.Pp
This API replaces the historic functions
.Fn timeout
and
.Fn untimeout .
.Pp
The function
.Fn timeout_set
prepares the timeout structure
.Fa to
to be used in future calls to
.Fn timeout_add
and
.Fn timeout_del .
The timeout will be prepared to call the function specified by the
.Fa fn
argument with a
.Fa void *
argument given in the
.Fa arg
argument.
Once initialized, the
.Fa to
structure can be used in repeatedly in
.Fn timeout_add
and
.Fn timeout_del
and does not need to be reinitialized unless you wish to
change the function called and/or the argument to it.
.Pp
The function
.Fn timeout_add
schedules the execution of the
.Fa to
timeout in at least
.Fa ticks Ns No /hz
seconds.
Negative values of
.Fa ticks
are illegal.
If the value is
.Sq 0
it will, in the current implementation, be treated as
.Sq 1 ,
but in the future it might cause an immediate timeout.
The timeout in the
.Fa to
argument must be already initialized by
.Fn timeout_set
and may not be used in calls to
.Fn timeout_set
until it has timed out or been removed with
.Fn timeout_del .
If the timeout in the
.Fa to
argument is already scheduled, the old execution time will be
replaced by the new one.
.Pp
The function
.Fn timeout_del
will cancel the timeout in the argument
.Fa to .
If the timeout has already executed or has never been added
the call will have no effect.
.Pp
The
.Fn timeout_pending
macro can be used to check if a timeout is scheduled to run.
.Pp
The
.Fn timeout_initialized
macro can be used to check if a timeout has been initialized.
.Pp
The
.Fn timeout_triggered
macro can be used to check if a timeout is running or has been run.
The 
.Fn timeout_add
and
.Fn timeout_del
functions clear the triggered state for that timeout.
.Sh CODE REFERENCES
These functions are implemented in the file
.Pa sys/kern/kern_timeout.c .
.Sh SEE ALSO
.Xr hz 9 ,
.Xr hzto 9 ,
.Xr sleep 9 ,
.Xr splclock 9 ,
.Xr tvtohz 9