Fix process termination in stdio client

pyproject.toml

@@ -30,6 +30,7 @@ dependencies = [
     "python-multipart>=0.0.9",
     "sse-starlette>=1.6.1",
     "pydantic-settings>=2.5.2",
+    "psutil>=7.0.0",
     "uvicorn>=0.23.1; sys_platform != 'emscripten'",
 ]
 

src/mcp/client/stdio/__init__.py

@@ -1,12 +1,17 @@
 import os
 import sys
-from contextlib import asynccontextmanager
+from contextlib import asynccontextmanager, suppress
 from pathlib import Path
 from typing import Literal, TextIO
 
 import anyio
 import anyio.lowlevel
-from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
+import psutil
+from anyio.abc import Process
+from anyio.streams.memory import (
+    MemoryObjectReceiveStream,
+    MemoryObjectSendStream,
+)
 from anyio.streams.text import TextReceiveStream
 from pydantic import BaseModel, Field
 
@@ -173,10 +178,7 @@ 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()
+            await _terminate_process(process)
 
 
 def _get_executable_command(command: str) -> str:
@@ -214,3 +216,28 @@ async def _create_platform_compatible_process(
         )
 
     return process
+
+
+async def _terminate_process(process: Process):
+    """
+    Terminate the process and its children.
+
+    Note: On Windows, `process.terminate()` calls the Win32 `TerminateProcess` API,
+    which only terminates the specified process. Any child
+    processes remain running, which can lead to unclosed resources and may cause the
+    parent process to hang during shutdown. This function uses `psutil` to recursively
+    terminate the full process tree, ensuring a cleaner and more reliable shutdown.
+
+    Args:
+        process: The AnyIO process to terminate
+    """
+    with suppress(psutil.NoSuchProcess):
+        proc = psutil.Process(process.pid)
+        children = proc.children(recursive=True)
+        for child in children:
+            child.kill()
+    with suppress(ProcessLookupError):
+        if sys.platform == "win32":
+            await terminate_windows_process(process)
+        else:
+            process.terminate()