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Fix process termination in stdio client #496

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Fix process termination in stdio client #496

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5ffc436
Fix process termination in stdio client
ashrobertsdragon Apr 12, 2025
a1641fd
Fix WIndows Poractor loop teardown ValueError (#391) and infinite han…
ashrobertsdragon May 1, 2025
3482857
Merge branch 'main' into windows-process
ashrobertsdragon May 1, 2025
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18 changes: 8 additions & 10 deletions src/mcp/client/stdio/__init__.py
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Original file line number Diff line number Diff line change
Expand Up @@ -6,17 +6,16 @@

import anyio
import anyio.lowlevel
from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
from anyio.streams.memory import (
MemoryObjectReceiveStream,
MemoryObjectSendStream,
)
from anyio.streams.text import TextReceiveStream
from pydantic import BaseModel, Field

import mcp.types as types

from .win32 import (
create_windows_process,
get_windows_executable_command,
terminate_windows_process,
)
from .win32 import create_windows_process, get_windows_executable_command

# Environment variables to inherit by default
DEFAULT_INHERITED_ENV_VARS = (
Expand Down Expand Up @@ -173,10 +172,9 @@ async def stdin_writer():
yield read_stream, write_stream
finally:
# Clean up process to prevent any dangling orphaned processes
if sys.platform == "win32":
await terminate_windows_process(process)
else:
process.terminate()
tg.cancel_scope.cancel()
process.terminate()
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This won't work if the process doesn't react to SIGTERM. We need a timeout and a fallback on SIGKILL.
Please test it with https://github.com/modelcontextprotocol/servers/blob/main/src/everything/index.ts#L13 (windows & unix)

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Ref: #555

await process.wait()


def _get_executable_command(command: str) -> str:
Expand Down
22 changes: 0 additions & 22 deletions src/mcp/client/stdio/win32.py
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Original file line number Diff line number Diff line change
Expand Up @@ -9,7 +9,6 @@
from typing import TextIO

import anyio
from anyio.abc import Process


def get_windows_executable_command(command: str) -> str:
Expand Down Expand Up @@ -86,24 +85,3 @@ async def create_windows_process(
[command, *args], env=env, stderr=errlog, cwd=cwd
)
return process


async def terminate_windows_process(process: Process):
"""
Terminate a Windows process.

Note: On Windows, terminating a process with process.terminate() doesn't
always guarantee immediate process termination.
So we give it 2s to exit, or we call process.kill()
which sends a SIGKILL equivalent signal.

Args:
process: The process to terminate
"""
try:
process.terminate()
with anyio.fail_after(2.0):
await process.wait()
except TimeoutError:
# Force kill if it doesn't terminate
process.kill()