public final double sampleTotalCount(){
  long count=_totalCount.get();
  long lastCount=_lastTotalCount;
  _lastTotalCount=count;
  return count - lastCount;
}

public final double sampleTotalCount ( ) { long count = _totalCount . get ( ) ; long lastCount = _lastTotalCount ; _lastTotalCount = count ; return count - lastCount ; }
sample the total count
