How Can I Use Run Manager to Stream Response on RetrievalQA?

Question

I'm working with the langchain library and transformers to build a language model application. I want to integrate a CallbackManagerForLLMRun to stream responses in my RetrievalQA chain. Below is the code I have so far, including my custom LLAMA class, which uses the /home/llama/LLM/llama/CACHE-Llama-3-8B-chat-merged model from transformers.

from transformers import AutoModelForCausalLM, AutoTokenizer
from abc import ABC
from langchain.llms.base import LLM
from typing import Any, List, Mapping, Optional
from langchain.callbacks.manager import CallbackManagerForLLMRun
device = "cuda" # the device to load the model onto

model = AutoModelForCausalLM.from_pretrained(
    "/home/llama/LLM/llama/CACHE-Llama-3-8B-chat-merged",
    torch_dtype="auto",
    device_map="auto"
)
tokenizer = AutoTokenizer.from_pretrained("/home/llama/LLM/llama/CACHE-Llama-3-8B-chat-merged")

class LLAMA(LLM, ABC):
     max_token: int = 10000
     temperature: float = 0.01
     top_p = 0.9
     history_len: int = 3

     def __init__(self):
         super().__init__()

     @property
     def _llm_type(self) -> str:
         return "LLAMA3"

     @property
     def _history_len(self) -> int:
         return self.history_len

     def set_history_len(self, history_len: int = 10) -> None:
         self.history_len = history_len

     def _call(
         self,
         prompt: str,
         stop: Optional[List[str]] = None,
         run_manager: Optional[CallbackManagerForLLMRun] = None,
     ) -> str:
         messages = [
             {"role": "system", "content": "You are a helpful assistant."},
             {"role": "user", "content": prompt}
         ]
         text = tokenizer.apply_chat_template(
             messages,
             tokenize=False,
             add_generation_prompt=True
         )
         model_inputs = tokenizer([text], return_tensors="pt").to(device)
         generated_ids = model.generate(
             model_inputs.input_ids,
             max_new_tokens=512
         )
         generated_ids = [
             output_ids[len(input_ids):] for input_ids, output_ids in zip(model_inputs.input_ids, generated_ids)
         ]

         response = tokenizer.batch_decode(generated_ids, skip_special_tokens=True)[0]
         return response

     @property
     def _identifying_params(self) -> Mapping[str, Any]:
         """Get the identifying parameters."""
         return {"max_token": self.max_token,
                 "temperature": self.temperature,
                 "top_p": self.top_p,
                 "history_len": self.history_len}
                 
 llm = LLAMA()
    embeddings = HuggingFaceEmbeddings(model_name=embedding_model_dict[EMBEDDING_MODEL],model_kwargs={'device': EMBEDDING_DEVICE})

    docs = load_file(filepath)

    docsearch = FAISSWrapper.from_documents(docs, embeddings)

    prompt = PromptTemplate(
        template=PROMPT_TEMPLATE, input_variables=["context_str", "question"]
    )

    chain_type_kwargs = {"prompt": prompt, "document_variable_name": "context_str"}
    qa = RetrievalQA.from_chain_type(
        llm=llm,
        chain_type=CHAIN_TYPE,
        retriever=docsearch.as_retriever(search_kwargs={"k": VECTOR_SEARCH_TOP_K}),
        chain_type_kwargs=chain_type_kwargs)

    query = "Give me a short introduction to large language model."
    print(qa.run(query))