@Override
    public long getDelay(TimeUnit unit) {
      return unit.convert(end - EnvironmentEdgeManager.currentTime(), TimeUnit.MILLISECONDS);
    }
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