Server: Robust shutdown on stdio detach (signals, stdin/parent monitor, forced exit) (#363)

* Server: robust shutdown on stdio detach (signals, stdin/parent monitor, forced exit)\nTests: move telemetry tests to tests/ and convert to asserts

* Server: simplify _force_exit to os._exit; guard exit timers to avoid duplicates; fix Windows ValueError in parent monitor; tests: add autouse cwd fixture for telemetry to locate pyproject.toml

* Server: add DEBUG logs for transient stdin checks and monitor thread errors

* Mirror shutdown improvements: signal handlers, stdin/parent monitor, guarded exit timers, and os._exit force-exit in UnityMcpServer~ entry points

Author: dsarno

MCPForUnity/UnityMcpServer~/src/server.py

@@ -4,6 +4,9 @@
 from logging.handlers import RotatingFileHandler
 import os
 from contextlib import asynccontextmanager
+import signal
+import sys
+import threading
 from typing import AsyncIterator, Dict, Any
 from config import config
 from tools import register_all_tools
@@ -64,6 +67,10 @@
 # Global connection state
 _unity_connection: UnityConnection = None
 
+# Global shutdown coordination
+_shutdown_flag = threading.Event()
+_exit_timer_scheduled = threading.Event()
+
 
 @asynccontextmanager
 async def server_lifespan(server: FastMCP) -> AsyncIterator[Dict[str, Any]]:
@@ -186,9 +193,98 @@ def _emit_startup():
 register_all_resources(mcp)
 
 
+def _force_exit(code: int = 0):
+    """Force process exit, bypassing any background threads that might linger."""
+    os._exit(code)
+
+
+def _signal_handler(signum, frame):
+    logger.info(f"Received signal {signum}, initiating shutdown...")
+    _shutdown_flag.set()
+    if not _exit_timer_scheduled.is_set():
+        _exit_timer_scheduled.set()
+        threading.Timer(1.0, _force_exit, args=(0,)).start()
+
+
+def _monitor_stdin():
+    """Background thread to detect stdio detach (stdin EOF) or parent exit."""
+    try:
+        parent_pid = os.getppid() if hasattr(os, "getppid") else None
+        while not _shutdown_flag.is_set():
+            if _shutdown_flag.wait(0.5):
+                break
+
+            if parent_pid is not None:
+                try:
+                    os.kill(parent_pid, 0)
+                except ValueError:
+                    # Signal 0 unsupported on this platform (e.g., Windows); disable parent probing
+                    parent_pid = None
+                except (ProcessLookupError, OSError):
+                    logger.info(f"Parent process {parent_pid} no longer exists; shutting down")
+                    break
+
+            try:
+                if sys.stdin.closed:
+                    logger.info("stdin.closed is True; client disconnected")
+                    break
+                fd = sys.stdin.fileno()
+                if fd < 0:
+                    logger.info("stdin fd invalid; client disconnected")
+                    break
+            except (ValueError, OSError, AttributeError):
+                # Closed pipe or unavailable stdin
+                break
+            except Exception:
+                # Ignore transient errors
+                logger.debug("Transient error checking stdin", exc_info=True)
+
+        if not _shutdown_flag.is_set():
+            logger.info("Client disconnected (stdin or parent), initiating shutdown...")
+            _shutdown_flag.set()
+            if not _exit_timer_scheduled.is_set():
+                _exit_timer_scheduled.set()
+                threading.Timer(0.5, _force_exit, args=(0,)).start()
+    except Exception:
+        # Never let monitor thread crash the process
+        logger.debug("Monitor thread error", exc_info=True)
+
+
 def main():
     """Entry point for uvx and console scripts."""
-    mcp.run(transport='stdio')
+    try:
+        signal.signal(signal.SIGTERM, _signal_handler)
+        signal.signal(signal.SIGINT, _signal_handler)
+        if hasattr(signal, "SIGPIPE"):
+            signal.signal(signal.SIGPIPE, signal.SIG_IGN)
+        if hasattr(signal, "SIGBREAK"):
+            signal.signal(signal.SIGBREAK, _signal_handler)
+    except Exception:
+        # Signals can fail in some environments
+        pass
+
+    t = threading.Thread(target=_monitor_stdin, daemon=True)
+    t.start()
+
+    try:
+        mcp.run(transport='stdio')
+        logger.info("FastMCP run() returned (stdin EOF or disconnect)")
+    except (KeyboardInterrupt, SystemExit):
+        logger.info("Server interrupted; shutting down")
+        _shutdown_flag.set()
+    except BrokenPipeError:
+        logger.info("Broken pipe; shutting down")
+        _shutdown_flag.set()
+    except Exception as e:
+        logger.error(f"Server error: {e}", exc_info=True)
+        _shutdown_flag.set()
+        _force_exit(1)
+    finally:
+        _shutdown_flag.set()
+        logger.info("Server main loop exited")
+        if not _exit_timer_scheduled.is_set():
+            _exit_timer_scheduled.set()
+            threading.Timer(0.5, _force_exit, args=(0,)).start()
 
 
 # Run the server

Server/server.py

@@ -4,6 +4,9 @@
 from logging.handlers import RotatingFileHandler
 import os
 from contextlib import asynccontextmanager
+import sys
+import signal
+import threading
 from typing import AsyncIterator, Dict, Any
 from config import config
 from tools import register_all_tools
@@ -64,6 +67,10 @@
 # Global connection state
 _unity_connection: UnityConnection = None
 
+# Global shutdown coordination
+_shutdown_flag = threading.Event()
+_exit_timer_scheduled = threading.Event()
+
 
 @asynccontextmanager
 async def server_lifespan(server: FastMCP) -> AsyncIterator[Dict[str, Any]]:
@@ -186,9 +193,98 @@ def _emit_startup():
 register_all_resources(mcp)
 
 
+def _force_exit(code: int = 0):
+    """Force process exit, bypassing any background threads that might linger."""
+    os._exit(code)
+
+
+def _signal_handler(signum, frame):
+    logger.info(f"Received signal {signum}, initiating shutdown...")
+    _shutdown_flag.set()
+    if not _exit_timer_scheduled.is_set():
+        _exit_timer_scheduled.set()
+        threading.Timer(1.0, _force_exit, args=(0,)).start()
+
+
+def _monitor_stdin():
+    """Background thread to detect stdio detach (stdin EOF) or parent exit."""
+    try:
+        parent_pid = os.getppid() if hasattr(os, "getppid") else None
+        while not _shutdown_flag.is_set():
+            if _shutdown_flag.wait(0.5):
+                break
+
+            if parent_pid is not None:
+                try:
+                    os.kill(parent_pid, 0)
+                except ValueError:
+                    # Signal 0 unsupported on this platform (e.g., Windows); disable parent probing
+                    parent_pid = None
+                except (ProcessLookupError, OSError):
+                    logger.info(f"Parent process {parent_pid} no longer exists; shutting down")
+                    break
+
+            try:
+                if sys.stdin.closed:
+                    logger.info("stdin.closed is True; client disconnected")
+                    break
+                fd = sys.stdin.fileno()
+                if fd < 0:
+                    logger.info("stdin fd invalid; client disconnected")
+                    break
+            except (ValueError, OSError, AttributeError):
+                # Closed pipe or unavailable stdin
+                break
+            except Exception:
+                # Ignore transient errors
+                logger.debug("Transient error checking stdin", exc_info=True)
+
+        if not _shutdown_flag.is_set():
+            logger.info("Client disconnected (stdin or parent), initiating shutdown...")
+            _shutdown_flag.set()
+            if not _exit_timer_scheduled.is_set():
+                _exit_timer_scheduled.set()
+                threading.Timer(0.5, _force_exit, args=(0,)).start()
+    except Exception:
+        # Never let monitor thread crash the process
+        logger.debug("Monitor thread error", exc_info=True)
+
+
 def main():
     """Entry point for uvx and console scripts."""
-    mcp.run(transport='stdio')
+    try:
+        signal.signal(signal.SIGTERM, _signal_handler)
+        signal.signal(signal.SIGINT, _signal_handler)
+        if hasattr(signal, "SIGPIPE"):
+            signal.signal(signal.SIGPIPE, signal.SIG_IGN)
+        if hasattr(signal, "SIGBREAK"):
+            signal.signal(signal.SIGBREAK, _signal_handler)
+    except Exception:
+        # Signals can fail in some environments
+        pass
+
+    t = threading.Thread(target=_monitor_stdin, daemon=True)
+    t.start()
+
+    try:
+        mcp.run(transport='stdio')
+        logger.info("FastMCP run() returned (stdin EOF or disconnect)")
+    except (KeyboardInterrupt, SystemExit):
+        logger.info("Server interrupted; shutting down")
+        _shutdown_flag.set()
+    except BrokenPipeError:
+        logger.info("Broken pipe; shutting down")
+        _shutdown_flag.set()
+    except Exception as e:
+        logger.error(f"Server error: {e}", exc_info=True)
+        _shutdown_flag.set()
+        _force_exit(1)
+    finally:
+        _shutdown_flag.set()
+        logger.info("Server main loop exited")
+        if not _exit_timer_scheduled.is_set():
+            _exit_timer_scheduled.set()
+            threading.Timer(0.5, _force_exit, args=(0,)).start()
 
 
 # Run the server