@Override
  public boolean contains(Object o) {
    if (o == null) return false;
    lock.lock();
    try {
      return list.contains(o);
    } finally {
      lock.unlock();
    }
  }
Returns <pre>true</pre> if this deque contains the specified element.
More formally, returns <pre>true</pre> if and only if this deque contains
at least one element <pre>e</pre> such that <pre>o.equals(e)</pre>.

@param o object to be checked for containment in this deque
@return <pre>true</pre> if this deque contains the specified element
llap-server/src/java/org/apache/hadoop/hive/llap/daemon/impl/PriorityBlockingDeque.java