/*-------------------------------------------------------------------*/
/* testalarmtimeout.c                                                */
/* The alarm system call to implement a timeout.                     */
/*-------------------------------------------------------------------*/

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <signal.h>
#include <unistd.h>

/*-------------------------------------------------------------------*/

static void mySignalHandler(int iSignal)

/* This function is intended to be a handler for signals of type
   SIGALRM.  Print a timeout message to stdout, and exit. */

{
   printf("\nSorry.  You took too long.\n");
   exit(EXIT_FAILURE);
}

/*-------------------------------------------------------------------*/

int main(int argc, char *argv[])

/* Illustrate using an alarm to cause a timeout. */

{
   int i;
   void (*pfRet)(int);
   sigset_t sSigSet;
   int iRet;

   /* Make sure that SIGALRM is not blocked. */
   sigemptyset(&sSigSet);
   sigaddset(&sSigSet, SIGALRM);
   iRet = sigprocmask(SIG_UNBLOCK, &sSigSet, NULL);
   assert(iRet == 0);

   pfRet = signal(SIGALRM, mySignalHandler);
   assert(pfRet != SIG_ERR);

   printf("Enter a number:  ");
   alarm(5);
   scanf("%d", &i);
   alarm(0);

   printf("You entered the number %d.\n", i);
   return 0;
}

/* Sample execution:

$ gcc217 testalarmtimeout.c -o testalarmtimeout
$ testalarmtimeout
Enter a number:  123
You entered the number 123.
$ testalarmtimeout
Enter a number:
Sorry.  You took too long.

*/