HP-UX Reference (11i v3 07/02) - 2 System Calls (vol 5)

alarm(2) alarm(2)

NAME

alarm - set a process’s alarm clock

SYNOPSIS

#include <unistd.h>

unsigned int alarm(unsigned int sec);

DESCRIPTION

alarm() instructs the alarm clock of the calling process to send the signal

SIGALRM to the calling pro-

cess after the number of real-time seconds speciﬁed by sec have elapsed; see signal(5). Speciﬁc implemen-

tations might place limitations on the maximum supported alarm time. The constant

MAX_ALARM deﬁned

speciﬁes the implementation-speciﬁc maximum. Whenever sec is greater that this

maximum, it is silently rounded down to it. On all implementations,

MAX_ALARM is guaranteed to be at

least 31 days (in seconds).

Alarm requests are not stacked; successive calls reset the alarm clock of the calling process.

If sec is 0, any previously made alarm request is canceled.

Alarms are not inherited by a child process across a

fork(), but are inherited across an

exec().

On systems that support the

getitimer() and setitimer() system calls, the timer mechanism

used by alarm() is the same as that used by ITIMER_REAL . Thus successive calls to alarm()

getitimer() , and setitimer() set and return the state of a single timer. In addition, alarm()

sets the timer interval to zero.

RETURN VALUE

alarm() returns the amount of time previously remaining in the alarm clock of the calling process.

WARNINGS

In some implementations, error bounds for alarm are −1, +0 seconds (for the posting of the alarm, not the

restart of the process). Thus a delay of 1 second can return immediately. The

setitimer() routine can

be used to create a more precise delay.