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33 lines
1.1 KiB
Python
33 lines
1.1 KiB
Python
# Copyright (c) Meta Platforms, Inc. and affiliates.
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# All rights reserved.
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#
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# This source code is licensed under the terms described in the LICENSE file in
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# the root directory of this source tree.
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from contextvars import ContextVar
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from typing import AsyncGenerator, List, TypeVar
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T = TypeVar("T")
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def preserve_contexts_async_generator(
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gen: AsyncGenerator[T, None], context_vars: List[ContextVar]
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) -> AsyncGenerator[T, None]:
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"""
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Wraps an async generator to preserve context variables across iterations.
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This is needed because we start a new asyncio event loop for each streaming request,
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and we need to preserve the context across the event loop boundary.
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"""
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async def wrapper() -> AsyncGenerator[T, None]:
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while True:
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try:
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item = await gen.__anext__()
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context_values = {context_var.name: context_var.get() for context_var in context_vars}
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yield item
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for context_var in context_vars:
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_ = context_var.set(context_values[context_var.name])
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except StopAsyncIteration:
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break
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return wrapper()
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