code: private void beginObject () {
  		if (DEBUG) {
  			if (depth == 0)
  				thread = Thread.currentThread();
  			else if (thread != Thread.currentThread())
  				throw new ConcurrentModificationException("Kryo must not be accessed concurrently by multiple threads.");
  		}
  		if (depth == maxDepth) throw new KryoException("Max depth exceeded: " + depth);
  		depth++;
  	}
docs: --- Utility ---