ALARM

ALARM

NAME

alarm - set an alarm clock for delivery of a signal

SYNOPSIS

1. include <unistd.h>

unsigned int alarm(unsigned int seconds);

DESCRIPTION

alarm arranges for a SIGALRM signal to be delivered to the process in seconds seconds.

If seconds is zero, no new alarm is scheduled.

In any event any previously set alarm is cancelled.

If you want to wait for a time without using sleep(3) or alarm(2), then you might want to try select(2) with all the fdset's set to 0. select(2) also lets you pause for a subsecond delay.

Since a SIGALRM will interrupt a running syscall it's common to use alarm(2) to timeout syscalls that may take some time, for example connect(2).

RETURN VALUE

alarm returns the number of seconds remaining until any previously scheduled alarm was due to be delivered, or zero if there was no previously scheduled alarm.

NOTES

alarm(2) and setitimer(2) share the same timer; calls to one will interfere with use of the other.

sleep(3) may be implemented using SIGALRM; mixing calls to alarm(2) and sleep(3) is a bad idea.

Scheduling delays can, as ever, cause the execution of the process to be delayed by an arbitrary amount of time.

CONFORMING TO

SVr4, SVID, POSIX, X/OPEN, BSD 4.3

SEE ALSO

setitimer(2), signal(2), sigaction(2), gettimeofday(2), select(2), pause(2), sleep(3), select(2)