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.Dd $Mdocdate: August 1 2023 $
.Dt UALARM 3
.Os
.Sh NAME
.Nm ualarm
.Nd schedule high resolution SIGALRM delivery
.Sh SYNOPSIS
.In unistd.h
.Ft useconds_t
.Fn ualarm "useconds_t microseconds" "useconds_t interval"
.Sh DESCRIPTION
.Bf -symbolic
This is a simplified interface to
.Xr setitimer 2 .
.Ef
.Pp
The
.Fn ualarm
function schedules the
.Dv SIGALRM
signal for delivery to the calling process after at least the given number of
.Fa microseconds
have elapsed.
If
.Fa interval
is non-zero,
the
.Dv SIGALRM
signal is scheduled for redelivery to the calling process every
.Fa interval
microseconds thereafter.
.Pp
If an alarm is already pending,
an additional call to
.Fn ualarm
supersedes the prior call.
.Pp
If
.Fa microseconds
is zero,
any pending alarm is cancelled and the value of
.Fa interval
is ignored.
.Sh RETURN VALUES
The
.Fn ualarm
function returns the number of microseconds remaining until the next
alarm is scheduled for delivery,
or zero if no alarm is pending.
.Sh SEE ALSO
.Xr setitimer 2 ,
.Xr sigaction 2 ,
.Xr sigsuspend 2 ,
.Xr alarm 3 ,
.Xr signal 3 ,
.Xr sleep 3 ,
.Xr usleep 3
.Sh STANDARDS
The
.Fn ualarm
function conforms to
.St -xpg4.2 .
.Sh HISTORY
The
.Fn ualarm
function first appeared in
.Bx 4.3 .
.Sh CAVEATS
The
.Fn ualarm
function is implemented with the per-process
.Dv ITIMER_REAL
timer described in
.Xr setitimer 2 .
Use of both
.Fn ualarm
and
.Xr setitimer 2
in the same program may yield confusing behavior.