Add lock on tee peer cleanup (#9446)

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libs/langchain/langchain/utils/aiter.py

@@ -107,6 +107,7 @@ async def tee_peer(
                             peer_buffer.append(item)
             yield buffer.popleft()
     finally:
+        async with lock:
             # this peer is done – remove its buffer
             for idx, peer_buffer in enumerate(peers):  # pragma: no branch
                 if peer_buffer is buffer:

libs/langchain/langchain/utils/iter.py

@@ -60,6 +60,7 @@ def tee_peer(
                             peer_buffer.append(item)
             yield buffer.popleft()
     finally:
+        with lock:
             # this peer is done – remove its buffer
             for idx, peer_buffer in enumerate(peers):  # pragma: no branch
                 if peer_buffer is buffer: