/*--------------------------------------------------------------------*/
/* testalarmtimeout.c                                                 */
/* Author: Bob Dondero                                                */
/*--------------------------------------------------------------------*/

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <unistd.h>
#include <sys/types.h>   /* Required for splint. */

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

/* The name of the executable binary file. */

static const char *pcPgmName;

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

/* This function is intended to be a handler for signals of type
   SIGALRM. Write a timeout message to stdout, and exit. iSignal is
   number of the signal that caused this handler to execute. */

static void myHandler(int iSignal)
{
   char *pcMessage;
   ssize_t lByteCount;
   
   /* Really shouldn't call printf() here. See Bryant & O'Hallaron
      page 766. So call write() instead. */
   pcMessage = "\nSorry. You took too long.\n";
   lByteCount = write(1, pcMessage, strlen(pcMessage));
   if (lByteCount == -1) {perror(pcPgmName); exit(EXIT_FAILURE); }
   
   exit(EXIT_FAILURE);
}

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

/* Demonstrate using an alarm to cause a timeout. As usual, argc is
   the command-line argument count, and argv contains the command-line
   arguments. Return 0. */

int main(int argc, char *argv[])
{
   int i;
   void (*pfRet)(int);
   sigset_t sSigSet;
   int iRet;

   enum {ALARM_DURATION_SECONDS = 5};

   pcPgmName = argv[0];
   
   /* Make sure that SIGALRM signals are not blocked. */
   iRet = sigemptyset(&sSigSet);
   if (iRet == -1) {perror(argv[0]); exit(EXIT_FAILURE); }   
   iRet = sigaddset(&sSigSet, SIGALRM);
   if (iRet == -1) {perror(argv[0]); exit(EXIT_FAILURE); }   
   iRet = sigprocmask(SIG_UNBLOCK, &sSigSet, NULL);
   if (iRet == -1) {perror(argv[0]); exit(EXIT_FAILURE); }

   /* Install myHandler as the handler for SIGALRM signals. */
   pfRet = signal(SIGALRM, myHandler);
   if (pfRet == SIG_ERR) {perror(argv[0]); exit(EXIT_FAILURE); }

   printf("Enter a number: ");
   fflush(stdout);
   alarm(ALARM_DURATION_SECONDS);
   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.

*/