🚑 Check for a replaced PID file in join

This patch works around an issue described in
#7 by also comparing the stat of
PID files. Otherwise it misses cases when PID file
gets recreated faster that the check loop hits
another existence check.

magicbus/plugins/opsys.py

@@ -265,8 +265,16 @@ def wait(self, timeout=None, poll_interval=0.1):
 
     def join(self, timeout=None, poll_interval=0.1):
         """Return when the PID file does not exist, or the timeout expires."""
+        try:
+            initial_stat = os.stat(self.pidfile)
+        except OSError:  # file does not exist
+            return
+
         starttime = time.time()
         while timeout is None or time.time() - starttime <= timeout:
-            if not os.path.exists(self.pidfile):
-                return
+            try:
+                if initial_stat != os.stat(self.pidfile):
+                    return  # file has been changed/replaced
+            except OSError:
+                return  # file does not exist
             time.sleep(poll_interval)

magicbus/test/test_signals.py

@@ -57,6 +57,7 @@ def test_SIGHUP_daemonized(self):
         kill(pid, SIGHUP)
 
         # Give the server some time to restart
+        pidfile.join()
         time.sleep(1)
         for _ in range(6):
             new_pid = pidfile.wait(5)