V10/man/man2/alarm.2

.TH ALARM 2
.CT 2 time_man
.SH NAME
alarm, nap, pause \(mi schedule timing delays
.SH SYNOPSIS
.nf
.B unsigned alarm(seconds)
.B unsigned seconds;
.PP
.B void nap(ticks)
.PP
.B void pause()
.fi
.SH DESCRIPTION
.I Alarm
causes signal
.BR SIGALRM ,
see
.IR signal (2),
to be sent to the invoking process
in the number of seconds given by the argument.
Unless caught or ignored, the signal terminates the process.
.PP
Alarm requests are not stacked;
successive calls reset the alarm clock.
If the argument is 0,
any alarm request is canceled.
Because the clock has a one second resolution,
the signal may occur up to one second early;
because of scheduling delays,
resumption of execution of when the signal is
caught may be delayed an arbitrary amount.
.PP
The return value is the amount of time
previously remaining in the alarm clock.
.PP
.I Nap
suspends execution of
the current process
for 
the specified number of clock ticks.
If
.I ticks
is negative,
it is taken to be zero;
if it is greater than two seconds,
it is taken to be two seconds.
.PP
.I Pause
only returns upon termination of a signal handler started during the
.IR pause .
It is used to give up control while waiting for
a signal,
usually from
.I kill
(see
.IR signal (2)),
.IR alarm (2),
or the terminal driver
.IR ttyld (4).
.SH "SEE ALSO"
.IR kill (1), 
.IR signal (2), 
.IR setjmp (3), 
.IR sleep (3)
.SH BUGS
If the argument to
.I alarm
is greater than 65535,
it is treated as 65535.
.br
If the alarm clock expires
during a call to
.IR alarm ,
the return value will be 0,
and the signal will be delivered
immediately after the system call returns.
If the routine calling
.I alarm
saves the return value
and later restores it,
it will disable any alarm
set by the signal handler.