#include <unistd.h> 
#include <stdlib.h> 
#include <stdio.h>
#include <errno.h>
#include <signal.h>
#include <sys/time.h>
#include <sys/resource.h>

//
// Purpose:	Test interval virtual timer
// Usage:	fib -n 2000 >& /dev/null & ... & vtimer-basic	# w/ interference
//		vtimer-basic				# w/o interference
// Calls:	gettimeofday, getrusage, sigemptyset, sigaction, setitimer
// Ideas:
// o Virtual interval timer (ITIMER_VITUAL) accounts only for time used by process
// o Granularity is typically the granularity of the system clock (10 msec).
//	So, alarm is never triggered early but could be triggered late
// o If there is another CPU-intensive process running, our process will only
//	get 50% of the CPU.
// o Examples:
//   Example 1 (with interference)
//		clock	etime	utime	stime
//		1	2.088	1.010	0
//		2	4.128	2.010	0	DELTA etime = K x DELTA utime + overhead
//		3	6.168	3.010	0		where K = 2, the # of running
//		4	8.208	4.010	0		processes
//		5	10.248	5.010	0
//		6	12.288	6.010	0
//		7	14.328	7.010	0
//		8	16.368	8.010	0
//		9	18.408	9.010	0
//		10	20.448	10.010	0
//		11	22.488	11.010	0
// o Example 2 (without interference)
//		1	1.047	1.010	0
//		2	2.087	2.010	0	DELTA etime = DELTA utime + overhead
//		3	3.127	3.010	0
//		4	4.167	4.010	0
//		5	5.207	5.010	0
//		6	6.247	6.010	0
//		7	7.287	7.010	0
//		8	8.327	8.010	0
//		9	9.367	9.010	0
//		10	10.407	10.010	0
//		11	11.456	11.010	0
// History:
// o 8 Jan 2007	kenw: creation
//

int	ctick;			// clock ticks every 1 sec
struct timeval	ctm;		// current time
struct timeval	otm;		// original time
struct rusage	ru;

static void sighandler(int s) {
  int	oerrno;
  int	etime;		// elapsed time (msec)
  time_t utime, stime;	// user and system time usage

  oerrno = errno;

  ++ctick;
  gettimeofday(&ctm, 0);
  etime = 1000*(ctm.tv_sec - otm.tv_sec)
    				+ (ctm.tv_usec - otm.tv_usec)/1000;
  getrusage(RUSAGE_SELF, &ru);
  utime = 1000*ru.ru_utime.tv_sec + ru.ru_utime.tv_usec/1000;
  stime = 1000*ru.ru_stime.tv_sec + ru.ru_stime.tv_usec/1000;
  printf("%d\t%d.%03d\t%d.%03d\t%d\n", ctick, etime/1000, etime%1000,
					utime/1000, utime%1000, stime);

  errno = oerrno;
}

int main(void) {
  struct sigaction act;
  struct itimerval val;

  ctick = 0;

  act.sa_handler = sighandler;		// init SIGVTALRM handler
  act.sa_flags = 0;
  if (sigemptyset(&act.sa_mask) || sigaction(SIGVTALRM, &act, NULL)) {
    perror("Gurk!!! Failed to init SIGVTALRM handler");
    exit( 1 );
  }

  val.it_interval.tv_sec = 1;		// 1-sec interval
  val.it_interval.tv_usec = 0;
  val.it_value = val.it_interval;
  if (setitimer(ITIMER_VIRTUAL, &val, NULL) == -1) {
    perror("Gurk!!! Failed to init ITIMER_VIRTUAL"); 
    exit( 1 );
  }

  gettimeofday(&otm, 0);		// our epoch
  while ( 1 );
}