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fix: Async callback for langchain (#353)
* fix: Async callback for langchain Signed-off-by: Frost Ming <me@frostming.com>
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,87 @@ | ||
from __future__ import annotations | ||
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import asyncio | ||
from typing import Any, AsyncIterator | ||
from uuid import UUID | ||
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from langchain.callbacks.base import AsyncCallbackHandler | ||
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class AsyncIteratorCallbackHandler(AsyncCallbackHandler): | ||
"""Callback handler that returns an async iterator.""" | ||
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@property | ||
def always_verbose(self) -> bool: | ||
return True | ||
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def __init__(self) -> None: | ||
self.queue = asyncio.Queue() | ||
self.done = asyncio.Event() | ||
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async def on_chain_start( | ||
self, | ||
serialized: dict[str, Any], | ||
inputs: dict[str, Any], | ||
*, | ||
run_id: UUID, | ||
parent_run_id: UUID | None = None, | ||
tags: list[str] | None = None, | ||
metadata: dict[str, Any] | None = None, | ||
**kwargs: Any, | ||
) -> None: | ||
self.done.clear() | ||
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async def on_llm_new_token(self, token: str, **kwargs: Any) -> None: | ||
if token is not None and token != "": | ||
print(token, end="") | ||
self.queue.put_nowait(token) | ||
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async def on_chain_end( | ||
self, | ||
outputs: dict[str, Any], | ||
*, | ||
run_id: UUID, | ||
parent_run_id: UUID | None = None, | ||
tags: list[str] | None = None, | ||
**kwargs: Any, | ||
) -> None: | ||
self.done.set() | ||
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async def on_chain_error( | ||
self, | ||
error: BaseException, | ||
*, | ||
run_id: UUID, | ||
parent_run_id: UUID | None = None, | ||
tags: list[str] | None = None, | ||
**kwargs: Any, | ||
) -> None: | ||
self.done.set() | ||
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async def aiter(self) -> AsyncIterator[str]: | ||
while not self.queue.empty() or not self.done.is_set(): | ||
# Wait for the next token in the queue, | ||
# but stop waiting if the done event is set | ||
done, other = await asyncio.wait( | ||
[ | ||
# NOTE: If you add other tasks here, update the code below, | ||
# which assumes each set has exactly one task each | ||
asyncio.ensure_future(self.queue.get()), | ||
asyncio.ensure_future(self.done.wait()), | ||
], | ||
return_when=asyncio.FIRST_COMPLETED, | ||
) | ||
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# Cancel the other task | ||
if other: | ||
other.pop().cancel() | ||
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# Extract the value of the first completed task | ||
token_or_done = done.pop().result() | ||
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# If the extracted value is the boolean True, the done event was set | ||
if token_or_done is True: | ||
break | ||
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# Otherwise, the extracted value is a token, which we yield | ||
yield token_or_done |
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