Task #5708: Destruct Bus objects atexit, to guarantee destruction in python...

Task #5708: Destruct Bus objects atexit, to guarantee destruction in python 2.4 without placing requirements on using the code

LCS/MessageBus/src/msgbus.py

@@ -28,6 +28,7 @@ import os
 import signal
 import logging
 import lofar.messagebus.message as message
+import atexit
 
 # Candidate for a config file
 broker="127.0.0.1" 
@@ -43,6 +44,8 @@ class BusException(Exception):
 
 class Session:
     def __init__(self, broker):
+        self.closed = False
+
         logger.info("[Bus] Connecting to broker %s", broker)
         self.connection = qpid.messaging.Connection(broker)
         self.connection.reconnect = True
@@ -54,12 +57,30 @@ class Session:
         except qpid.messaging.MessagingError, m:
             raise BusException(m)
 
-    def __del__(self):
+        # NOTE: We cannuot use:
+        #  __del__: its broken (does not always get called, destruction order is unpredictable)
+        #  with:    not supported in python 2.4, does not work well on arrays of objects
+        #  weakref: dpes not guarantee to be called (depends on gc)
+        #
+        # Note that this atexit call will prevent self from being destructed until the end of the program,
+        # since a reference will be retained
+        atexit.register(self.close)
+
+    def close(self):
+        if self.closed:
+            return
+
+        self.closed = True
+
         # NOTE: session.close() freezes under certain error conditions,
         # f.e. opening a receiver on a non-existing queue.
         # This seems to happen whenever a Python exception was thrown
         # by the qpid wrapper.
         #
+        # This especially happens if we would put this code in __del__.
+        # Note that we cannot use __enter__ and __exit__ either due to
+        # ccu001/ccu099 still carrying python 2.4.
+        #
         # See https://issues.apache.org/jira/browse/QPID-6402
         #
         # We set a timeout to prevent freezing, which obviously leads
@@ -69,6 +90,13 @@ class Session:
         except qpid.messaging.exceptions.Timeout, t:
             logger.error("[Bus] Could not close connection: %s", t)
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, type, value, traceback):
+        self.close()
+        return False
+
     def address(self, queue, options):
         return "%s%s; {%s}" % (self._queue_prefix(), queue, options)