[433] Check to make sure msqg isnt already running.

Check to ensure there is no existing daemon running before removing
the socket endpoint. Fail to start if one is. Added a new test to
check this behaviour.

src/bin/msgq/msgq.py.in

@@ -74,6 +74,8 @@ SPECFILE_LOCATION = SPECFILE_PATH + "/msgq.spec"
 
 class MsgQReceiveError(Exception): pass
 
+class MsgQRunningError(Exception): pass
+
 class MsgQCloseOnReceive(Exception):
     """Exception raised when reading data from a socket results in 'shutdown'.
 
@@ -268,11 +270,28 @@ class MsgQ:
         """Set up the listener socket.  Internal function."""
         logger.debug(TRACE_BASIC, MSGQ_LISTENER_SETUP, self.socket_file)
 
-        self.listen_socket = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
-
         if os.path.exists(self.socket_file):
+            # Rather than just blindly removing the socket file, attempt to
+            # connect to the existing socket to see if there is an existing
+            # msgq running. Only if that fails do we remove the file and
+            # attempt to create a new socket.
+            self._existing = True
+            try:
+                self._session = isc.cc.Session(self.socket_file)
+            except isc.cc.session.SessionError:
+                self._existing = False
+
+            self._session.close()
+            self._session = None
+
+            if self._existing:
+                logger.fatal(MSGQ_ALREADY_RUNNING)
+                raise MsgQRunningError("Message Queue daemon already running")
+
             os.remove(self.socket_file)
+
         try:
+            self.listen_socket = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
             self.listen_socket.bind(self.socket_file)
             self.listen_socket.listen(1024)
         except Exception as e:

src/bin/msgq/msgq_messages.mes

@@ -19,6 +19,10 @@
 # <topsrcdir>/tools/reorder_message_file.py to make sure the
 # messages are in the correct order.
 
+% MSGQ_ALREADY_RUNNING Another copy of the message queue daemon is already running.
+Only a single instance of the message queue daemon should ever be run at one
+time. This instance will now terminate.
+
 % MSGQ_CFGMGR_SUBSCRIBED The config manager subscribed to message queue
 This is a debug message. The message queue has little bit of special handling
 for the configuration manager. This special handling is happening now.

src/bin/msgq/tests/msgq_run_test.py

@@ -328,6 +328,14 @@ class MsgqRunTest(unittest.TestCase):
             'group': 'notifications/cc_members'
         }]}, msg)
 
+    def test_multiple_invocations(self):
+        """
+        Check to make sure that an attempt to start a second copy of the MsgQ
+        daemon fails.
+        """
+        self.__retcode = subprocess.call([MSGQ_PATH, '-s', SOCKET_PATH])
+        self.assertNotEqual(self.__retcode, 0)
+
 if __name__ == '__main__':
     isc.log.init("msgq-tests")
     isc.log.resetUnitTestRootLogger()