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.\" Copyright (c) 1996 Joerg Wunsch
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.Dd April 13, 1996
.Os
.Dt TIMEOUT 9
.Sh NAME
.Nm timeout ,
.Nm untimeout
.Nd schedule timer events
.Sh SYNOPSIS
.Fd #include <sys/systm.h>
.Fd #include <sys/kernel.h>

.Ft typedef void \*(lptimeout_t\*(rp \*(lpvoid *\*(rp;

.Ft typedef timeout_t *timeout_func_t;

.Ft void
.Fn timeout "timeout_func_t func" "void *arg" "int ticks"
.Ft void
.Fn untimeout "timeout_func_t func" "void *arg"
.Sh DESCRIPTION
The
.Nm timeout
facility allows the execution of a function after a specified amount
of time.  The function
.Ar func
is being called with the opaque argument
.Ar arg
after
.Ar ticks
timer ticks have been elapsed.  It's often convenient to use the
external variable
.Dv hz
to compute the amount of
.Ar ticks
to wait.
.Pp
If the timeout event should be removed before the timer expires,
.Nm untimeout
must be called with the exact
.Ar func
and
.Ar arg
arguments as the corresponding call to
.Fn timeout .
.Pp
Unlike the functions of
.Xr sleep 9 ,
.Fn timeout
and
.Fn untimeout
can be called from within an interrupt context.
.Sh SEE ALSO
.Xr sleep 9
.Sh HISTORY
The
.Nm timeout
facility is very old.
.Sh BUGS
Since the timer queue is sorted and uses time differences rather than
absolute times, inserting and removing timer events can be costly if
it is done too frequently.
.Sh AUTHORS
This man page has been written by
.ie t J\(:org Wunsch.
.el Joerg Wunsch.