public void putAll(Collection<? extends E> c) {
    if (c == null) {
      throw new NullPointerException();
    }
    lock.writeLock().lock();
    try {
      delegate.addAll(c);
      if (!delegate.isEmpty()) {
        notEmpty.signal();
      }
    } finally {
      lock.writeLock().unlock();
    }
  }
Inserts the specified elements at the tail of the queue. Any elements already present in the
queue are ignored.
@param c the elements to add
hbase-server/src/main/java/org/apache/hadoop/hbase/master/normalizer/RegionNormalizerWorkQueue.java