docs: private BlockingQueue<V> retrieveSharedQueue(String key) {
  		BlockingQueue<V> queue = mediations.get(key);
  		if (queue == null) {
  			queue = new ArrayBlockingQueue<V>(1);
  			BlockingQueue<V> commonQueue = mediations.putIfAbsent(key, queue);
  			return commonQueue != null ? commonQueue : queue;
  		} else {
  			return queue;
  		}
  	}