🐛 MCP Server tool loading yeilds warning/error about an ignore async generator

[wudstrand]

Description

When connecting to multiple MCP servers I am getting an error RuntimeError: async generator ignored GeneratorExit. I can replicate with the example provided in your documetation

Full Error

Exception ignored in: <async_generator object HTTP11ConnectionByteStream.__aiter__ at 0x112c68640>
Traceback (most recent call last):
  File "/Users/willudstrand/python/ai-assistant/clients/.venv/lib/python3.12/site-packages/httpcore/_async/connection_pool.py", line 404, in __aiter__
    yield part
RuntimeError: async generator ignored GeneratorExit
Exception ignored in: <coroutine object HTTP11ConnectionByteStream.aclose at 0x112d7dfc0>
Traceback (most recent call last):
  File "/Users/willudstrand/python/ai-assistant/clients/.venv/lib/python3.12/site-packages/httpcore/_async/http11.py", line 348, in aclose
    await self._connection._response_closed()
  File "/Users/willudstrand/python/ai-assistant/clients/.venv/lib/python3.12/site-packages/httpcore/_async/http11.py", line 239, in _response_closed
    async with self._state_lock:
  File "/Users/willudstrand/python/ai-assistant/clients/.venv/lib/python3.12/site-packages/httpcore/_synchronization.py", line 77, in __aenter__
    await self._anyio_lock.acquire()
  File "/Users/willudstrand/python/ai-assistant/clients/.venv/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 1799, in acquire
    await AsyncIOBackend.cancel_shielded_checkpoint()
  File "/Users/willudstrand/python/ai-assistant/clients/.venv/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 2349, in cancel_shielded_checkpoint
    with CancelScope(shield=True):
  File "/Users/willudstrand/python/ai-assistant/clients/.venv/lib/python3.12/site-packages/anyio/_backends/_asyncio.py", line 457, in __exit__
    raise RuntimeError(
RuntimeError: Attempted to exit cancel scope in a different task than it was entered in
Exception ignored in: <async_generator object HTTP11ConnectionByteStream.__aiter__ at 0x112d96740>
Traceback (most recent call last):
  File "/Users/willudstrand/python/ai-assistant/clients/.venv/lib/python3.12/site-packages/httpcore/_async/connection_pool.py", line 404, in __aiter__
    yield part
RuntimeError: async generator ignored GeneratorExit

Steps to replicate

1. Run a simple mcp server locally on port 8000
2. Setup a uv environment with the requirements below
3. Run the script provided

Requirements

langchain-mcp-adapters==0.1.9
asyncio==3.4.3
mcp==1.9.2

Script

import asyncio

from langchain_mcp_adapters.client import MultiServerMCPClient


async def main():
    client = MultiServerMCPClient(
        {
            "mcp_server": {
                "url": "http://localhost:8000/mcp/",
                "transport": "streamable_http",
            }
        }
    )

    tools = await client.get_tools()
    print("here")

if __name__ == "__main__":
    asyncio.run(main())

[nitin302]

@eyurtsev any update please?

[thormtl]

Any updates to this one? :)

[pi-crust]

@eyurtsev
I'm encountering this issue when using MultiServerMCPClient with streamable_http within Chainlit.
any updates on this so far?

[mous222]

@wudstrand @pi-crust I faced a similar issue in a similar context (not LangChain, but AnyIO context).

You can use this workaround until an official fix from the MCP team is merged.

I just submitted this PR to MCP SDK with the fix - waiting for team validation (in case no extra side-effects).

The gist provides drop-in replacement classes that resolve the async generator cleanup issue.

Let me know if it works on your side!

[mous222]

[UPDATE] My PR was merged, I thing just an upgrade of the mcp lib should fix it