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Title: fix: avoid stdio cleanup BrokenResourceError race by lavish0000 · Pull Request #2219 · modelcontextprotocol/python-sdk · GitHub

Open Graph Title: fix: avoid stdio cleanup BrokenResourceError race by lavish0000 · Pull Request #2219 · modelcontextprotocol/python-sdk

X Title: fix: avoid stdio cleanup BrokenResourceError race by lavish0000 · Pull Request #2219 · modelcontextprotocol/python-sdk

Description: Summary cancel the stdio client task group before closing its memory streams during shutdown move memory stream teardown until after the task group has exited add a regression test that exits while stdout_reader is blocked on a zero-buffer send Problem stdio_client() starts background tasks that read process stdout and forward messages into a zero-buffer memory stream. If the caller exits the context without consuming read_stream, stdout_reader can block on read_stream_writer.send(...). Before this change, the cleanup path closed read_stream_writer while stdout_reader was still running inside the task group. That raises anyio.BrokenResourceError and surfaces as an ExceptionGroup during context exit. Fix The cleanup sequence now cancels the task group before any of the memory streams it owns are closed. The stream handles are closed only after the task group has exited, so stdout_reader and stdin_writer are no longer racing against stream teardown. Validation reproduced the failure locally on current main with a minimal stdio server that writes one JSON-RPC message and then idles uv run pytest tests/client/test_stdio.py uv run ruff check src/mcp/client/stdio.py tests/client/test_stdio.py uv run ruff format --check src/mcp/client/stdio.py tests/client/test_stdio.py uv run pyright src/mcp/client/stdio.py tests/client/test_stdio.py

Open Graph Description: Summary cancel the stdio client task group before closing its memory streams during shutdown move memory stream teardown until after the task group has exited add a regression test that exits whil...

X Description: Summary cancel the stdio client task group before closing its memory streams during shutdown move memory stream teardown until after the task group has exited add a regression test that exits whil...

Opengraph URL: https://github.com/modelcontextprotocol/python-sdk/pull/2219

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5593617 fix: avoid stdio cleanup BrokenResourceError race lavish0000 Mar 5, 2026 https://github.com/modelcontextprotocol/python-sdk/pull/2219/commits/55936172ee0ab9b09c3c5749d0099b1004499847
00920b5 fix: handle broken stdio streams during cleanup lavish0000 Mar 5, 2026 https://github.com/modelcontextprotocol/python-sdk/pull/2219/commits/00920b55818850cbbca7857b8c2684ad3c5f026a
54a9790 chore: retrigger CI after cancelled workflow lavish0000 Mar 6, 2026 https://github.com/modelcontextprotocol/python-sdk/pull/2219/commits/54a97908cabb91033956545258eb83e1f2333d08
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