/* itimerV.c
 *
 * Neal Nelson  2009.11.04
 *
 * Set the virtual interval timer to 0.1 and then repeatedly accumulate its
 * value * from the sighandler handler on each 0.1 sec interrupt for a count
 * of 10. Display the accumulation at each interrupt.
 *
 * Doesn't work for some reason. No interrupts happen. Maybe because I'm
 * not accumulating any virtual time! Give some real work to do!
 *
 *
 */

#include <stdio.h>
#include <unistd.h>     /* for pause() */
#include <stdlib.h>
#include <sys/time.h>
#include <time.h>
#include <signal.h>

/* Prototypes must occur before sig handlers are referenced */
static void itimer_handler(int);
unsigned long fib(unsigned int n);

/* Initialize the virtual time accumulator */
static long virt_count = 0;

main()
{ int i;
  struct itimerval virt;

  /* Register the itimer_handler to catch SIGALRM, SIGVTALRM, SIGPROF */

  if (signal(SIGVTALRM, itimer_handler) == SIG_ERR)
    printf("Parent: Unable to create handler for SIGVTALRM\n");

  /* Initialize the virt itimer to one tenth of a second */
  virt.it_interval.tv_sec = 0;
  virt.it_interval.tv_usec = 99999;
  virt.it_value.tv_sec = 0;
  virt.it_value.tv_usec = 99999;


  setitimer(ITIMER_VIRTUAL, &virt, NULL);
  for (i = 0; i < 10; i++) pause();        /* catch 10 interrupts */
  printf("Done.\n");
}


static void itimer_handler(int signo)
{
  switch(signo)
  { printf("%d\n",signo);
    case SIGVTALRM:
      virt_count++;
      printf("Parent: received SIGVTALRM signal, virt_count: %ld\n",virt_count);
      break;
    default: break; /* should never get here */
  }
  return; 
}