Clear Connection.transaction_manager on close. Fixes #114

CHANGES.rst

@@ -8,6 +8,11 @@
 - Call _p_resolveConflict() even if a conflicting change doesn't change the
   state. This reverts to the behaviour of 3.10.3 and older.
 
+- Closing a Connection now reverts its ``transaction_manager`` to
+  None. This helps prevent errors and release resources when the
+  ``transaction_manager`` was the (default) thread-local manager. See
+  `issue 114 <https://github.com/zopefoundation/ZODB/issues/114>`_.
+
 4.4.3 (2016-08-04)
 ==================
 

src/ZODB/Connection.py

@@ -307,7 +307,9 @@ class Connection(ExportImport, object):
 
         self._debug_info = ()
 
-        if self.opened:
+        if self.opened and self.transaction_manager is not None:
+            # transaction_manager could be None if one of the __onCloseCallbacks
+            # closed the DB already, .e.g, ZODB.connection() does this.
             self.transaction_manager.unregisterSynch(self)
 
         if self._mvcc_storage:
@@ -333,6 +335,9 @@ class Connection(ExportImport, object):
         if am is not None:
             am.closedConnection(self)
 
+        # Drop transaction manager to release resources and help prevent errors
+        self.transaction_manager = None
+
     def db(self):
         """Returns a handle to the database this connection belongs to."""
         return self._db
@@ -1119,6 +1124,7 @@ class Connection(ExportImport, object):
                     c._storage.release()
             c._storage = c._normal_storage = None
             c._cache = PickleCache(self, 0, 0)
+            c.transaction_manager = None
 
     ##########################################################################
     # Python protocol

src/ZODB/DB.py

@@ -628,7 +628,8 @@ class DB(object):
 
         @self._connectionMap
         def _(c):
-            c.transaction_manager.abort()
+            if c.transaction_manager is not None:
+                c.transaction_manager.abort()
             c.afterCompletion = c.newTransaction = c.close = noop
             c._release_resources()