Improve child process termination on POSIX & Windows (#1078)
Co-authored-by: jingx8885 <jingxu8885@qq.com> Co-authored-by: Surya Prakash Susarla <susarla.surya.prakash.1998@gmail.com>
This commit is contained in:
Felix Weinberger
GitHub
parent
cf72565d9a
commit
e0336213e8
2 changed files with 552 additions and 15 deletions
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@ -1,3 +1,4 @@
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import logging
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import os
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import sys
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from contextlib import asynccontextmanager
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@ -6,17 +7,22 @@ from typing import Literal, TextIO
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import anyio
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import anyio.lowlevel
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from anyio.abc import Process
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from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
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from anyio.streams.text import TextReceiveStream
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from pydantic import BaseModel, Field
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import mcp.types as types
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from mcp.shared.message import SessionMessage
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from .win32 import (
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from mcp.os.posix.utilities import terminate_posix_process_tree
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from mcp.os.win32.utilities import (
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FallbackProcess,
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create_windows_process,
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get_windows_executable_command,
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terminate_windows_process_tree,
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)
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from mcp.shared.message import SessionMessage
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logger = logging.getLogger(__name__)
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# Environment variables to inherit by default
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DEFAULT_INHERITED_ENV_VARS = (
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@ -187,7 +193,7 @@ async def stdio_client(server: StdioServerParameters, errlog: TextIO = sys.stder
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await process.wait()
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except TimeoutError:
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# If process doesn't terminate in time, force kill it
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process.kill()
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await _terminate_process_tree(process)
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except ProcessLookupError:
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# Process already exited, which is fine
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pass
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@ -222,11 +228,38 @@ async def _create_platform_compatible_process(
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):
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"""
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Creates a subprocess in a platform-compatible way.
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Returns a process handle.
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Unix: Creates process in a new session/process group for killpg support
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Windows: Creates process in a Job Object for reliable child termination
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"""
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if sys.platform == "win32":
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process = await create_windows_process(command, args, env, errlog, cwd)
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else:
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process = await anyio.open_process([command, *args], env=env, stderr=errlog, cwd=cwd)
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process = await anyio.open_process(
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[command, *args],
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env=env,
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stderr=errlog,
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cwd=cwd,
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start_new_session=True,
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)
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return process
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async def _terminate_process_tree(process: Process | FallbackProcess, timeout_seconds: float = 2.0) -> None:
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"""
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Terminate a process and all its children using platform-specific methods.
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Unix: Uses os.killpg() for atomic process group termination
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Windows: Uses Job Objects via pywin32 for reliable child process cleanup
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Args:
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process: The process to terminate
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timeout_seconds: Timeout in seconds before force killing (default: 2.0)
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"""
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if sys.platform == "win32":
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await terminate_windows_process_tree(process, timeout_seconds)
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else:
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# FallbackProcess should only be used for Windows compatibility
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assert isinstance(process, Process)
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await terminate_posix_process_tree(process, timeout_seconds)
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@ -1,227 +0,0 @@
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"""
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Windows-specific functionality for stdio client operations.
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"""
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import shutil
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import subprocess
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import sys
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from pathlib import Path
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from typing import BinaryIO, TextIO, cast
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import anyio
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from anyio import to_thread
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from anyio.abc import Process
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from anyio.streams.file import FileReadStream, FileWriteStream
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from typing_extensions import deprecated
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def get_windows_executable_command(command: str) -> str:
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"""
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Get the correct executable command normalized for Windows.
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On Windows, commands might exist with specific extensions (.exe, .cmd, etc.)
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that need to be located for proper execution.
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Args:
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command: Base command (e.g., 'uvx', 'npx')
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Returns:
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str: Windows-appropriate command path
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"""
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try:
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# First check if command exists in PATH as-is
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if command_path := shutil.which(command):
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return command_path
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# Check for Windows-specific extensions
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for ext in [".cmd", ".bat", ".exe", ".ps1"]:
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ext_version = f"{command}{ext}"
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if ext_path := shutil.which(ext_version):
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return ext_path
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# For regular commands or if we couldn't find special versions
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return command
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except OSError:
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# Handle file system errors during path resolution
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# (permissions, broken symlinks, etc.)
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return command
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class FallbackProcess:
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"""
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A fallback process wrapper for Windows to handle async I/O
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when using subprocess.Popen, which provides sync-only FileIO objects.
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This wraps stdin and stdout into async-compatible
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streams (FileReadStream, FileWriteStream),
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so that MCP clients expecting async streams can work properly.
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"""
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def __init__(self, popen_obj: subprocess.Popen[bytes]):
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self.popen: subprocess.Popen[bytes] = popen_obj
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self.stdin_raw = popen_obj.stdin # type: ignore[assignment]
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self.stdout_raw = popen_obj.stdout # type: ignore[assignment]
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self.stderr = popen_obj.stderr # type: ignore[assignment]
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self.stdin = FileWriteStream(cast(BinaryIO, self.stdin_raw)) if self.stdin_raw else None
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self.stdout = FileReadStream(cast(BinaryIO, self.stdout_raw)) if self.stdout_raw else None
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async def __aenter__(self):
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"""Support async context manager entry."""
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return self
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async def __aexit__(
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self,
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exc_type: BaseException | None,
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exc_val: BaseException | None,
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exc_tb: object | None,
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) -> None:
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"""Terminate and wait on process exit inside a thread."""
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self.popen.terminate()
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await to_thread.run_sync(self.popen.wait)
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# Close the file handles to prevent ResourceWarning
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if self.stdin:
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await self.stdin.aclose()
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if self.stdout:
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await self.stdout.aclose()
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if self.stdin_raw:
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self.stdin_raw.close()
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if self.stdout_raw:
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self.stdout_raw.close()
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if self.stderr:
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self.stderr.close()
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async def wait(self):
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"""Async wait for process completion."""
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return await to_thread.run_sync(self.popen.wait)
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def terminate(self):
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"""Terminate the subprocess immediately."""
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return self.popen.terminate()
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def kill(self) -> None:
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"""Kill the subprocess immediately (alias for terminate)."""
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self.terminate()
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# ------------------------
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# Updated function
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# ------------------------
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async def create_windows_process(
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command: str,
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args: list[str],
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env: dict[str, str] | None = None,
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errlog: TextIO | None = sys.stderr,
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cwd: Path | str | None = None,
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) -> Process | FallbackProcess:
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"""
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Creates a subprocess in a Windows-compatible way.
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Attempt to use anyio's open_process for async subprocess creation.
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In some cases this will throw NotImplementedError on Windows, e.g.
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when using the SelectorEventLoop which does not support async subprocesses.
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In that case, we fall back to using subprocess.Popen.
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Args:
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command (str): The executable to run
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args (list[str]): List of command line arguments
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env (dict[str, str] | None): Environment variables
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errlog (TextIO | None): Where to send stderr output (defaults to sys.stderr)
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cwd (Path | str | None): Working directory for the subprocess
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Returns:
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FallbackProcess: Async-compatible subprocess with stdin and stdout streams
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"""
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try:
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# First try using anyio with Windows-specific flags to hide console window
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process = await anyio.open_process(
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[command, *args],
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env=env,
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# Ensure we don't create console windows for each process
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creationflags=subprocess.CREATE_NO_WINDOW # type: ignore
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if hasattr(subprocess, "CREATE_NO_WINDOW")
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else 0,
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stderr=errlog,
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cwd=cwd,
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)
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return process
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except NotImplementedError:
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# Windows often doesn't support async subprocess creation, use fallback
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return await _create_windows_fallback_process(command, args, env, errlog, cwd)
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except Exception:
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# Try again without creation flags
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process = await anyio.open_process(
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[command, *args],
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env=env,
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stderr=errlog,
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cwd=cwd,
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)
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return process
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async def _create_windows_fallback_process(
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command: str,
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args: list[str],
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env: dict[str, str] | None = None,
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errlog: TextIO | None = sys.stderr,
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cwd: Path | str | None = None,
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) -> FallbackProcess:
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"""
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Create a subprocess using subprocess.Popen as a fallback when anyio fails.
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This function wraps the sync subprocess.Popen in an async-compatible interface.
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"""
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try:
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# Try launching with creationflags to avoid opening a new console window
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popen_obj = subprocess.Popen(
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[command, *args],
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stdin=subprocess.PIPE,
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stdout=subprocess.PIPE,
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stderr=errlog,
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env=env,
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cwd=cwd,
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bufsize=0, # Unbuffered output
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creationflags=getattr(subprocess, "CREATE_NO_WINDOW", 0),
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)
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return FallbackProcess(popen_obj)
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except Exception:
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# If creationflags failed, fallback without them
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popen_obj = subprocess.Popen(
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[command, *args],
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stdin=subprocess.PIPE,
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stdout=subprocess.PIPE,
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stderr=errlog,
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env=env,
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cwd=cwd,
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bufsize=0,
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)
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return FallbackProcess(popen_obj)
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@deprecated(
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"terminate_windows_process is deprecated and will be removed in a future version. "
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"Process termination is now handled internally by the stdio_client context manager."
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)
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async def terminate_windows_process(process: Process | FallbackProcess):
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"""
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Terminate a Windows process.
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Note: On Windows, terminating a process with process.terminate() doesn't
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always guarantee immediate process termination.
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So we give it 2s to exit, or we call process.kill()
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which sends a SIGKILL equivalent signal.
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Args:
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process: The process to terminate
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"""
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try:
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process.terminate()
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with anyio.fail_after(2.0):
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await process.wait()
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except TimeoutError:
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# Force kill if it doesn't terminate
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process.kill()
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