fix: Handle SIGTERM more gracefully in watchmedo

This fixes some misbehaviour where the child process could be orphaned
if watchmedo received multiple SIGTERMs causing the `stop()` call to be
interrupted. By raising a semantic exception after neutering the signal
handler, we give ourselves a better chance of killing the child.

src/watchdog/watchmedo.py

@@ -47,6 +47,13 @@
 CONFIG_KEY_PYTHON_PATH = 'python-path'
 
 
+class ShutdownWatchdog(Exception):
+    """
+    Semantic exception used to signal an external shutdown event.
+    """
+    pass
+
+
 def path_split(pathname_spec, separator=os.pathsep):
     """
     Splits a pathname specification separated by an OS-dependent separator.
@@ -531,10 +538,12 @@ def auto_restart(args):
     else:
         stop_signal = int(args.signal)
 
-    # Handle SIGTERM in the same manner as SIGINT so that
-    # this program has a chance to stop the child process.
+    # Handle SIGTERM by raising a semantic exception which will allow us to
+    # gracefully unwind and stop the observer
     def handle_sigterm(_signum, _frame):
-        raise KeyboardInterrupt()
+        # Neuter this handler immediately so we don't raise more than once
+        signal.signal(signal.SIGTERM, signal.SIG_DFL)
+        raise ShutdownWatchdog
 
     signal.signal(signal.SIGTERM, handle_sigterm)
 
@@ -550,8 +559,12 @@ def handle_sigterm(_signum, _frame):
                                kill_after=args.kill_after)
     handler.start()
     observer = Observer(timeout=args.timeout)
-    observe_with(observer, handler, args.directories, args.recursive)
-    handler.stop()
+    try:
+        observe_with(observer, handler, args.directories, args.recursive)
+    except ShutdownWatchdog:
+        pass
+    finally:
+        handler.stop()
 
 
 epilog = """Copyright 2011 Yesudeep Mangalapilly <yesudeep@gmail.com>.