public void enqueue(){
  long current_time=System.nanoTime();
  long previous=Math.max(next,current_time - historySize);
  next=previous + delay;
  avail=Math.max(next,current_time);
  throttlers.add(this);
}

public void enqueue ( ) { long current_time = System . nanoTime ( ) ; long previous = Math . max ( next , current_time - historySize ) ; next = previous + delay ; avail = Math . max ( next , current_time ) ; throttlers . add ( this ) ; }
this throttler has elements pending but is not enqueued , so enqueue it
