.\"	$OpenBSD: timeout.9,v 1.15 2001/07/17 02:32:51 krw 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.
.Pp
The old
.Fn timeout
and
.Fn untimeout
interface is implemented as wrappers around the new API, but it's
obsolete and will be removed in the future.
.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
.Sh BUGS
The
.Fn timeout_add
function executes in linear time depending on the number of pending timeouts.
It will also block all interrupts while inserting the timeout
to the timeout queue.
Thus it is not recommended to use a large number of timeouts in the system.