Problems creating a milisecond timeout timer for threads

Hi!
I have a few threads (pthread) that are created at the same time and run simultaneously. Each of them should last for a given amount time and then finish. For example, if thread#1 should last for 5 seconds and thread#2 for 3 seconds, thread#2 should finish 2s before thread#1, but the total amount of time (for both) has to be around 5s.
If I use the time() function (time.h), it works but with a resolution of 1s. In order to have a resolution of 1 millisecond, I was using the clock() function but it works completely wrong depending of the number of threads.
I would appreciate ANY comments about a accurate millisecond timer to create a timeout (or virtual interruption) for threads.
Thanks.

hi,

/***********************************************************************
* Code listing from "Advanced Linux Programming," by CodeSourcery LLC  *
* Copyright (C) 2001 by New Riders Publishing                          *
* See COPYRIGHT for license information.                               *
***********************************************************************/

#include <signal.h>
#include <stdio.h>
#include <string.h>
#include <sys/time.h>

void timer_handler (int signum)
{
  static int count = 0;
  printf ("timer expired %d times\n", ++count);
}

int main ()
{
  struct sigaction sa;
  struct itimerval timer;

  /* Install timer_handler as the signal handler for SIGVTALRM.  */
  memset (&sa, 0, sizeof (sa));
  sa.sa_handler = &timer_handler;
  sigaction (SIGVTALRM, &sa, NULL);

  /* Configure the timer to expire after 250 msec...  */
  timer.it_value.tv_sec = 0;
  timer.it_value.tv_usec = 250000;
  /* ... and every 250 msec after that.  */
  timer.it_interval.tv_sec = 0;
  timer.it_interval.tv_usec = 250000;
  /* Start a virtual timer.  It counts down whenever this process is
     executing.  */
  setitimer (ITIMER_VIRTUAL, &timer, NULL);

  /* Do busy work.  */
  while (1);
}

hope that helps