/*--------------------------------------------------------------------*/
/* testalarm.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 message to stdout, and reset the alarm. */

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

   /* Reset the alarm. */
   alarm(2);
}

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

/* Demonstrate the alarm() function.  As usual, argc is the
   command-line argument count, and argv contains the command-line
   arguments.  The function never returns. */

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

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

   /* Set a 2 second alarm.  After 2 seconds of real time, send a
   SIGALRM signal to this process. */
   alarm(2);

   /* Enter an infinite loop. */
   printf("Entering an infinite loop\n");
   fflush(stdout);
   for (;;)
      sleep(1);

   /* Will not reach this point. */
}

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

/* Sample execution:

$ gcc217 testalarm.c -o testalarm

$ testalarm
Entering an infinite loop
In myHandler
In myHandler
In myHandler
In myHandler
^C

*/