StreamableHTTP session manager shutting down

[LTaooo]

Initial Checks

• I confirm that I'm using the latest version of MCP Python SDK
• I confirm that I searched for my issue in https://github.com/modelcontextprotocol/python-sdk/issues before opening this issue

Description

When the MCP tool is being executed, it occasionally displays the message "StreamableHTTP session manager shutting down". Subsequently, when another request is made, an error occurs, specifically "Task group is not initialized. Make sure to use run()".

Example Code

Python & MCP Python SDK

python: 3.12
mcp: 1.10.1

[LTaooo]

Only the MCP has shut down; FastAPI has not.

[mehmetaltuntas]

Are you able to provide StreamableHTTPServerTransport setup where you get the initialise it all?

[LTaooo]

Are you able to provide StreamableHTTPServerTransport setup where you get the initialise it all?

# lifespan.py
@asynccontextmanager
async def lifespan(app: FastAPI):
    try:
        await _on_startup()
        if Config.get(MCPConfig).enable:
            mcp.register(app)
            async with mcp.mcp.session_manager.run():
                await _after_startup()
                yield
        else:
            await _after_startup()
            yield
    finally:
        await _on_shutdown()

# mcp.py
mcp = FastMCP(name=Config.get(AppConfig).app_name)
# noinspection PyProtectedMember
def register(app: FastAPI):
    config = Config.get(MCPConfig)
    app.mount(config.mount, mcp.streamable_http_app())
    config.init_tools()

[LTaooo]

Test Script

It's not 100% error-prone.

# Client
async def main():
    async with streamablehttp_client(
            "http://127.0.0.1:8000/mcp",
    ) as (
        read_stream,
        write_stream,
        _,
    ):
        async with ClientSession(read_stream, write_stream) as session:
            await session.initialize()
            tasks = []
            for i in range(10):
                task = asyncio.create_task(process_book(session, i))
                tasks.append(task)

            results = await asyncio.gather(*tasks)
            return results


async def process_book(session, i):
    tool_result = await session.call_tool(
        "create_book",
        {"name": f'book_{i}', 'author': f'author_{i}', "address": {"city": 'hello', "street": f'street_{i}'}},
        read_timeout_seconds=timedelta(seconds=600),
    )
    print(tool_result.content)
    return tool_result

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

# Server


@router.post('/create', summary='create a book', operation_id=OperationEnum.create_book.value.id)
    async def create(
        name: Annotated[str, Body(description='book name')],
        author: Annotated[str, Body(description='book author')],
        address: Annotated[BookAddress, Body(description='book address', embed=True)],
    ) -> CommonRes[BookGetRes]:
        """
        create a book
        """
        await asyncio.sleep(60 * 5)
        return Response.success()

[LTaooo]

Logs

INFO:     127.0.0.1:57464 - "POST /mcp/ HTTP/1.1" 200 OK
2025-07-09 09:56:48 | INFO     | logging:callHandlers:1762 - Processing request of type CallToolRequest
2025-07-09 09:56:48 | INFO     | logging:callHandlers:1762 - Processing request of type CallToolRequest
2025-07-09 09:56:48 | INFO     | logging:callHandlers:1762 - Processing request of type CallToolRequest
2025-07-09 09:56:48 | INFO     | logging:callHandlers:1762 - Processing request of type CallToolRequest
2025-07-09 10:00:32 | INFO     | logging:callHandlers:1762 - StreamableHTTP session manager shutting down
ERROR:      + Exception Group Traceback (most recent call last):
  |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\starlette\routing.py", line 692, in lifespan
  |     async with self.lifespan_context(app) as maybe_state:
  |                ^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "C:\Users\STGF\AppData\Roaming\uv\python\cpython-3.12.9-windows-x86_64-none\Lib\contextlib.py", line 231, in __aexit__
  |     await self.gen.athrow(value)
  |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\fastapi\routing.py", line 133, in merged_lifespan
  |     async with original_context(app) as maybe_original_state:
  |                ^^^^^^^^^^^^^^^^^^^^^
  |   File "C:\Users\STGF\AppData\Roaming\uv\python\cpython-3.12.9-windows-x86_64-none\Lib\contextlib.py", line 231, in __aexit__
  |     await self.gen.athrow(value)
  |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\fastapi\routing.py", line 133, in merged_lifespan
  |     async with original_context(app) as maybe_original_state:
  |                ^^^^^^^^^^^^^^^^^^^^^
  |   File "C:\Users\STGF\AppData\Roaming\uv\python\cpython-3.12.9-windows-x86_64-none\Lib\contextlib.py", line 231, in __aexit__
  |     await self.gen.athrow(value)
  |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\fastapi\routing.py", line 133, in merged_lifespan
  |     async with original_context(app) as maybe_original_state:
  |                ^^^^^^^^^^^^^^^^^^^^^
  |   File "C:\Users\STGF\AppData\Roaming\uv\python\cpython-3.12.9-windows-x86_64-none\Lib\contextlib.py", line 231, in __aexit__
  |     await self.gen.athrow(value)
  |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\fastapi\routing.py", line 133, in merged_lifespan
  |     async with original_context(app) as maybe_original_state:
  |                ^^^^^^^^^^^^^^^^^^^^^
  |   File "C:\Users\STGF\AppData\Roaming\uv\python\cpython-3.12.9-windows-x86_64-none\Lib\contextlib.py", line 231, in __aexit__
  |     await self.gen.athrow(value)
  |   File "D:\project\py\mr-tools-service\core\lifespan.py", line 22, in lifespan
  |     async with mcp.mcp.session_manager.run():
  |                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "C:\Users\STGF\AppData\Roaming\uv\python\cpython-3.12.9-windows-x86_64-none\Lib\contextlib.py", line 231, in __aexit__
  |     await self.gen.athrow(value)
  |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\server\streamable_http_manager.py", line 106, in run
  |     async with anyio.create_task_group() as tg:
  |                ^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 772, in __aexit__
  |     raise BaseExceptionGroup(
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Exception Group Traceback (most recent call last):
    |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\server\streamable_http_manager.py", line 235, in run_server
    |     async with http_transport.connect() as streams:
    |                ^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "C:\Users\STGF\AppData\Roaming\uv\python\cpython-3.12.9-windows-x86_64-none\Lib\contextlib.py", line 231, in __aexit__
    |     await self.gen.athrow(value)
    |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\server\streamable_http.py", line 846, in connect
    |     async with anyio.create_task_group() as tg:
    |                ^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 772, in __aexit__
    |     raise BaseExceptionGroup(
    | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
    +-+---------------- 1 ----------------
      | Exception Group Traceback (most recent call last):
      |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\server\streamable_http.py", line 919, in connect
      |     yield read_stream, write_stream
      |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\server\streamable_http_manager.py", line 238, in run_server
      |     await self.app.run(
      |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\server\lowlevel\server.py", line 500, in run
      |     async with AsyncExitStack() as stack:
      |                ^^^^^^^^^^^^^^^^
      |   File "C:\Users\STGF\AppData\Roaming\uv\python\cpython-3.12.9-windows-x86_64-none\Lib\contextlib.py", line 754, in __aexit__
      |     raise exc_details[1]
      |   File "C:\Users\STGF\AppData\Roaming\uv\python\cpython-3.12.9-windows-x86_64-none\Lib\contextlib.py", line 737, in __aexit__
      |     cb_suppress = await cb(*exc_details)
      |                   ^^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\shared\session.py", line 223, in __aexit__
      |     return await self._task_group.__aexit__(exc_type, exc_val, exc_tb)
      |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
      |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 772, in __aexit__
      |     raise BaseExceptionGroup(
      | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
      +-+---------------- 1 ----------------
        | Exception Group Traceback (most recent call last):
        |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\server\lowlevel\server.py", line 511, in run
        |     async with anyio.create_task_group() as tg:
        |                ^^^^^^^^^^^^^^^^^^^^^^^^^
        |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\anyio\_backends\_asyncio.py", line 772, in __aexit__
        |     raise BaseExceptionGroup(
        | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
        +-+---------------- 1 ----------------
          | Traceback (most recent call last):
          |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\server\lowlevel\server.py", line 539, in _handle_message
          |     await self._handle_request(
          |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\server\lowlevel\server.py", line 593, in _handle_request
          |     await message.respond(response)
          |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\shared\session.py", line 134, in respond
          |     await self._session._send_response(  # type: ignore[reportPrivateUsage]
          |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\mcp\shared\session.py", line 346, in _send_response
          |     await self._write_stream.send(session_message)
          |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\anyio\streams\memory.py", line 242, in send
          |     self.send_nowait(item)
          |   File "D:\project\py\mr-tools-service\.venv\Lib\site-packages\anyio\streams\memory.py", line 211, in send_nowait
          |     raise ClosedResourceError
          | anyio.ClosedResourceError
          +------------------------------------

[LTaooo]

#841

It has been fixed, and I tested it with no issues.