alarm, alarmd

alarm, alarmd

Request a Signal after a Real-Time Interval

Portability: POSIX.1 conforming, UNIX compatible

SYNOPSIS
DESCRIPTION
RETURN VALUE
CAUTION
PORTABILITY
EXAMPLE
SEE ALSO

SYNOPSIS

#include <lclib.h>

unsigned int alarm(unsigned int sec);
double alarmd(double sec);

The synopsis for the POSIX implementation is as follows:

#include <sys/types.h>
#include <unistd.h>

unsigned int alarm(unsigned int sec);

You may use either set of header files in your program.

DESCRIPTION

alarm and alarmd request that a SIGALRM signal be generated after the number of seconds specified by its argument. Any previous call to alarm or alarmd is canceled. If the argument to either of the alarm functions is 0, any previous alarm or alarmd request is canceled, but no SIGALRM signal is generated. An argument greater than a day (86400 seconds) is treated as a day.

The SIGALRM signal is asynchronous, so it is discovered only when a function is called or returns. For this reason, as well as because of competition from other users, the signal may take slightly longer than the specified amount of time to be generated.

alarmd performs the same actions as alarm but permits the amount of time to be specified with greater accuracy. The accuracy of timing depends on the operating system and CPU model.

RETURN VALUE

The alarm functions return the number of seconds remaining from any previous interval. ( alarm rounds up to an integer of seconds.) If no interval is currently active, 0 is returned.

CAUTION

Under VM/SP and VM/HPO CMS, you must use the CP command SET TIMER REAL for proper functioning of alarm and alarmd . If SET TIMER REAL is not in effect, a diagnostic message is produced and a SIGALRM signal is generated immediately.

If SIGALRM is handled by USS, alarmd is not available in releases of OS/390 prior to MVS 5.2.2..

PORTABILITY

alarmd is not portable.

EXAMPLE

This example counts the number of divisions you can do in 5 seconds:

#include <lclib.h>
#include <signal.h>
#include <setjmp.h>
#include <lcjmp.h>
#include <stdio.h>

void timeout(int signum);
jmp_buf jbuf;
volatile int i;
int jcode;

main()
{
      /* Establish SIGALRM handling.                    */
   onjmp(jbuf, jcode, done);
   signal(SIGALRM, &timeout);

      /* Perform calculations.                          */
   alarm(5);
   for (i = 1; ; i++) {
      i/=1;
      sigchk();
   }
   done:
       printf("%d divisions executed in 5 seconds.\n", i);
   return;

}

   /* SIGALRM handler gets out of loop.                 */
void timeout(int signum)
{
  longjmp(jbuf, 1);
}