@Override
  public E take() throws InterruptedException {
    DelayedElement<E> el = queue.take();
    return el == null ? null : el.element;
  }
A blocking queue implementation for adding a constant delay. Uses a DelayQueue as a backing store
@param <E> type of elements
hbase-server/src/test/java/org/apache/hadoop/hbase/util/ConstantDelayQueue.java