Listing 2. init_timer, Setting the Timer Interrupt

/* fd_set variable required to use select() */
static fd_set set_of_pipes;
void init_timer (void (*vec)(), long interval)
{
  static int called = 0;
  struct sigaction sigspec;
  void sigusr1_handler(int);
  int p_timer[2];
  pid_t ppid, parent_id;
  parent_id = getpid();
  if (pipe(p_timer))
    perror("pipe");            
  reg_process(p_timer[0], vec);
  ppid = fork();
  switch (ppid) {
  case -1:
    perror("fork");
    break;
    
  case 0:                  /* child */
    while (1){ 
      usleep(interval);
     /* something is written through the pipe to
        identify who's requesting the int. */
      write(p_timer[1], ".", 1);
      kill(parent_id, SIGUSR1);
    } 
  default:              /* parent */
    if (! called) {
      sigspec.sa_handler=sigusr1_handler;
      sigemptyset(&sigspec.sa_mask);
      /* Don't reset vector when signal is
         received (might not be portable) */
      sigspec.sa_flags=SA_RESTART;
      sigaction(SIGUSR1, &sigspec, NULL);
      called = 1;
    }
  }
}