Merge branch 'main' into main

Author: SoldierSacha

pyproject.toml

@@ -32,6 +32,7 @@ dependencies = [
     "pydantic-settings>=2.5.2",
     "uvicorn>=0.23.1; sys_platform != 'emscripten'",
     "jsonschema>=4.20.0",
+    "pywin32>=310; sys_platform == 'win32'",
 ]
 
 [project.optional-dependencies]
@@ -125,4 +126,6 @@ filterwarnings = [
     "ignore::DeprecationWarning:websockets",
     "ignore:websockets.server.WebSocketServerProtocol is deprecated:DeprecationWarning",
     "ignore:Returning str or bytes.*:DeprecationWarning:mcp.server.lowlevel",
+    # pywin32 internal deprecation warning
+    "ignore:getargs.*The 'u' format is deprecated:DeprecationWarning"
 ]

src/mcp/client/stdio/__init__.py

@@ -1,3 +1,4 @@
+import logging
 import os
 import sys
 from contextlib import asynccontextmanager
@@ -6,18 +7,22 @@
 
 import anyio
 import anyio.lowlevel
+from anyio.abc import Process
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from anyio.streams.text import TextReceiveStream
 from pydantic import BaseModel, Field
 
 import mcp.types as types
-from mcp.shared.message import SessionMessage
-
-from .win32 import (
+from mcp.os.posix.utilities import terminate_posix_process_tree
+from mcp.os.win32.utilities import (
+    FallbackProcess,
     create_windows_process,
     get_windows_executable_command,
-    terminate_windows_process,
+    terminate_windows_process_tree,
 )
+from mcp.shared.message import SessionMessage
+
+logger = logging.getLogger(__name__)
 
 # Environment variables to inherit by default
 DEFAULT_INHERITED_ENV_VARS = (
@@ -38,6 +43,9 @@
     else ["HOME", "LOGNAME", "PATH", "SHELL", "TERM", "USER"]
 )
 
+# Timeout for process termination before falling back to force kill
+PROCESS_TERMINATION_TIMEOUT = 2.0
+
 
 def get_default_environment() -> dict[str, str]:
     """
@@ -180,10 +188,12 @@ async def stdin_writer():
         finally:
             # Clean up process to prevent any dangling orphaned processes
             try:
-                if sys.platform == "win32":
-                    await terminate_windows_process(process)
-                else:
-                    process.terminate()
+                process.terminate()
+                with anyio.fail_after(PROCESS_TERMINATION_TIMEOUT):
+                    await process.wait()
+            except TimeoutError:
+                # If process doesn't terminate in time, force kill it
+                await _terminate_process_tree(process)
             except ProcessLookupError:
                 # Process already exited, which is fine
                 pass
@@ -218,11 +228,38 @@ async def _create_platform_compatible_process(
 ):
     """
     Creates a subprocess in a platform-compatible way.
-    Returns a process handle.
+
+    Unix: Creates process in a new session/process group for killpg support
+    Windows: Creates process in a Job Object for reliable child termination
     """
     if sys.platform == "win32":
         process = await create_windows_process(command, args, env, errlog, cwd)
     else:
-        process = await anyio.open_process([command, *args], env=env, stderr=errlog, cwd=cwd)
+        process = await anyio.open_process(
+            [command, *args],
+            env=env,
+            stderr=errlog,
+            cwd=cwd,
+            start_new_session=True,
+        )
 
     return process
+
+
+async def _terminate_process_tree(process: Process | FallbackProcess, timeout_seconds: float = 2.0) -> None:
+    """
+    Terminate a process and all its children using platform-specific methods.
+
+    Unix: Uses os.killpg() for atomic process group termination
+    Windows: Uses Job Objects via pywin32 for reliable child process cleanup
+
+    Args:
+        process: The process to terminate
+        timeout_seconds: Timeout in seconds before force killing (default: 2.0)
+    """
+    if sys.platform == "win32":
+        await terminate_windows_process_tree(process, timeout_seconds)
+    else:
+        # FallbackProcess should only be used for Windows compatibility
+        assert isinstance(process, Process)
+        await terminate_posix_process_tree(process, timeout_seconds)

src/mcp/client/stdio/win32.py

@@ -0,0 +1 @@
+"""Platform-specific utilities for MCP."""

src/mcp/os/__init__.py

@@ -0,0 +1 @@
+"""POSIX-specific utilities for MCP."""

src/mcp/os/posix/__init__.py

@@ -0,0 +1,60 @@
+"""
+POSIX-specific functionality for stdio client operations.
+"""
+
+import logging
+import os
+import signal
+
+import anyio
+from anyio.abc import Process
+
+logger = logging.getLogger(__name__)
+
+
+async def terminate_posix_process_tree(process: Process, timeout_seconds: float = 2.0) -> None:
+    """
+    Terminate a process and all its children on POSIX systems.
+
+    Uses os.killpg() for atomic process group termination.
+
+    Args:
+        process: The process to terminate
+        timeout_seconds: Timeout in seconds before force killing (default: 2.0)
+    """
+    pid = getattr(process, "pid", None) or getattr(getattr(process, "popen", None), "pid", None)
+    if not pid:
+        # No PID means there's no process to terminate - it either never started,
+        # already exited, or we have an invalid process object
+        return
+
+    try:
+        pgid = os.getpgid(pid)
+        os.killpg(pgid, signal.SIGTERM)
+
+        with anyio.move_on_after(timeout_seconds):
+            while True:
+                try:
+                    # Check if process group still exists (signal 0 = check only)
+                    os.killpg(pgid, 0)
+                    await anyio.sleep(0.1)
+                except ProcessLookupError:
+                    return
+
+        try:
+            os.killpg(pgid, signal.SIGKILL)
+        except ProcessLookupError:
+            pass
+
+    except (ProcessLookupError, PermissionError, OSError) as e:
+        logger.warning(f"Process group termination failed for PID {pid}: {e}, falling back to simple terminate")
+        try:
+            process.terminate()
+            with anyio.fail_after(timeout_seconds):
+                await process.wait()
+        except Exception as term_error:
+            logger.warning(f"Process termination failed for PID {pid}: {term_error}, attempting force kill")
+            try:
+                process.kill()
+            except Exception as kill_error:
+                logger.error(f"Failed to kill process {pid}: {kill_error}")

src/mcp/os/posix/utilities.py

@@ -0,0 +1 @@
+"""Windows-specific utilities for MCP."""