public BucketList<K,V> getSentinel(int index){
		int key = makeSentinelKey(index);
		boolean splice;
		while(true){
			Window window = find(head, key);
			Node pred = window.pred;
			Node curr = window.curr;
			if(curr.key == key){
				return new BucketList<K,V>(curr);
			} else{
				Node node = new Node(key);
				node.next.set(pred.next.getReference(), false);
				splice = pred.next.compareAndSet(curr, node, false, false);
				if(splice)
					return new BucketList<K,V>(node);
				else continue;
			}
		}
	}