code: def killall(self, wait = None):
          
          self.queue.close()
          self.count_lock.acquire()
          self.kill(self.shared['workers'])
          self.count_lock.release()
          self.tasks.close()
          self.terminate()
          self.kill_event.wait(wait)
docs: Kill all active workers.
          @wait: Seconds to wait until last worker ends.
                 If None it waits forever.