NAME
alarm —
schedule SIGALRM delivery
SYNOPSIS
#include
<unistd.h>
unsigned int
alarm(unsigned
int seconds);
DESCRIPTION
The
alarm()
function schedules the SIGALRM signal for delivery
to the calling process after the given number of
seconds have elapsed.
If an alarm is already pending, another call to
alarm()
will supersede the prior call.
If seconds is zero, any pending alarm is cancelled.
RETURN VALUES
alarm() returns the number of seconds
remaining until the pending alarm would have expired. If the alarm has
already expired, the alarm was cancelled, or no alarm was ever scheduled,
alarm() returns zero.
SEE ALSO
setitimer(2), sigaction(2), sigsuspend(2), signal(3), sleep(3), ualarm(3)
STANDARDS
The alarm() function conforms to
IEEE Std 1003.1-2008 (“POSIX.1”).
HISTORY
An alarm() system call first appeared
outside of Bell Labs in the “50 changes” tape for
Version 6 AT&T UNIX. It was first
officially released with PWB/UNIX 1.0. For 4.1cBSD,
it was reimplemented as a wrapper around the
setitimer(2) system call.
CAVEATS
The alarm() function is implemented with
the per-process ITIMER_REAL timer described in
setitimer(2). Use of both alarm() and
setitimer(2) in the same program may yield confusing behavior.