diff --git a/dddp/__init__.py b/dddp/__init__.py
index 7c3c404..db0f1c4 100644
--- a/dddp/__init__.py
+++ b/dddp/__init__.py
@@ -48,28 +48,27 @@ class ThreadLocal(local):
 
     _init_done = False
 
-    def __init__(self, **default_factories):
+    def __init__(self):
         """Create new thread storage instance."""
         if self._init_done:
             raise SystemError('__init__ called too many times')
         self._init_done = True
-        self._default_factories = default_factories
 
     def __getattr__(self, name):
         """Create missing attributes using default factories."""
         try:
-            factory = self._default_factories[name]
+            factory = THREAD_LOCAL_FACTORIES[name]
         except KeyError:
             raise AttributeError(name)
-        obj = factory()
-        setattr(self, name, obj)
-        return obj
+        return self.get(name, factory)
 
     def get(self, name, factory, *factory_args, **factory_kwargs):
         """Get attribute, creating if required using specified factory."""
-        if not hasattr(self, name):
+        update_thread_local = getattr(factory, 'update_thread_local', True)
+        if (not update_thread_local) or (not hasattr(self, name)):
             obj = factory(*factory_args, **factory_kwargs)
-            setattr(self, name, obj)
+            if update_thread_local:
+                setattr(self, name, obj)
             return obj
         return getattr(self, name)
 
@@ -99,11 +98,12 @@ def serializer_factory():
     return get_serializer('python')()
 
 
-THREAD_LOCAL = ThreadLocal(
-    alea_random=alea.Alea,
-    random_streams=RandomStreams,
-    serializer=serializer_factory,
-)
+THREAD_LOCAL_FACTORIES = {
+    'alea_random': alea.Alea,
+    'random_streams': RandomStreams,
+    'serializer': serializer_factory,
+}
+THREAD_LOCAL = ThreadLocal()
 METEOR_ID_CHARS = u'23456789ABCDEFGHJKLMNPQRSTWXYZabcdefghijkmnopqrstuvwxyz'