Fix race condition causing PicklingError when there are several Zope threads

product/ERP5Type/dynamic/dynamic_module.py

 from types import ModuleType
 import sys
+import threading
 
 class DynamicModule(ModuleType):
   """This module may generate new objects at runtime."""
@@ -11,11 +12,16 @@ class DynamicModule(ModuleType):
   def __init__(self, name, factory, doc=None):
     super(DynamicModule, self).__init__(name, doc=doc)
     self._factory = factory
+    self._lock = threading.Lock()
 
   def __getattr__(self, name):
     if name[:2] == '__':
       raise AttributeError('%r module has no attribute %r'
                            % (self.__name__, name))
+    with self._lock:
+      try:
+        return super(DynamicModule, self).__getattribute__(name)
+      except AttributeError:
         obj = self._factory(name)
         # _factory can return an instance, a constant, or a class
         if isinstance(obj, type):
@@ -25,7 +31,6 @@ class DynamicModule(ModuleType):
           # if it's a module we want to set the name according to the
           # module it's being added to
           obj.__name__ = "%s.%s" % (self.__name__, name)
-
         setattr(self, name, obj)
         return obj