class_docstr: Flask Combo Retrieval server, which helps to aggregate different retrieval services
code: def run(self, url, port=None):
      threading.Thread(
          target=lambda: self.app.run(
              host=url, threaded=True, port=port
          )
      ).start()
  
imports: import pickle
  import threading
  from typing import List, Union
  import faiss
  import numpy
  import torch
  from flask import Flask, jsonify, request
  from flask_restful import Api, Resource
  from nemo.collections.common.tokenizers.tokenizer_spec import TokenizerSpec
  from nemo.collections.nlp.modules.common.megatron.retrieval_services.retrieval_service import DynamicFaissRetrievalService, FaissRetrievalService
  from nemo.collections.nlp.modules.common.megatron.retrieval_services.util import lock
label_desc: Use image node_id 2 for calling the ComboRetrievalServer obj's underlying member method code with example usage: obj.run(url, port) without return types