Revert "a different take"

This reverts commit 74d7b2a7d6.

common/lib/xmodule/xmodule/modulestore/__init__.py

@@ -23,7 +23,6 @@ from xblock.plugin import default_select
 from .exceptions import InvalidLocationError, InsufficientSpecificationError
 from xmodule.errortracker import make_error_tracker
 from xmodule.assetstore import AssetMetadata
-from xmodule.modulestore.django import NullSignalHandler
 from opaque_keys.edx.keys import CourseKey, UsageKey, AssetKey
 from opaque_keys.edx.locations import Location  # For import backwards compatibility
 from xblock.runtime import Mixologist
@@ -155,6 +154,17 @@ class ActiveBulkThread(threading.local):
         self.records = defaultdict(bulk_ops_record_type)
 
 
+class NullSignalHandler(object):
+    """
+    A null handler that does nothing
+    """
+    def send(self, *args, **kwargs):
+        """
+        No-op
+        """
+        pass
+
+
 class BulkOperationsMixin(object):
     """
     This implements the :meth:`bulk_operations` modulestore semantics which handles nested invocations
@@ -170,7 +180,23 @@ class BulkOperationsMixin(object):
     def __init__(self, *args, **kwargs):
         super(BulkOperationsMixin, self).__init__(*args, **kwargs)
         self._active_bulk_ops = ActiveBulkThread(self._bulk_ops_record_type)
-        self.signal_handler = NullSignalHandler()
+        self._signal_handler = None
+
+    @property
+    def signal_handler(self):
+        """
+        Return a signal handler, defaults to a null handler that does nothing.
+        """
+        if not self._signal_handler:
+            self._signal_handler = NullSignalHandler()
+        return self._signal_handler
+
+    @signal_handler.setter
+    def signal_handler(self, value):
+        """
+        Set the signal handler
+        """
+        self._signal_handler = value
 
     @contextmanager
     def bulk_operations(self, course_id, emit_signals=True):

common/lib/xmodule/xmodule/modulestore/django.py

@@ -110,17 +110,6 @@ class SignalHandler(object):
             log.info('Sent %s signal to %s with kwargs %s. Response was: %s', signal_name, receiver, kwargs, response)
 
 
-class NullSignalHandler(object):
-    """
-    A null handler that does nothing
-    """
-    def send(self, *args, **kwargs):
-        """
-        No-op
-        """
-        pass
-
-
 def load_function(path):
     """
     Load a function by name.

common/lib/xmodule/xmodule/modulestore/mongo/base.py

@@ -49,7 +49,6 @@ from xmodule.modulestore.edit_info import EditInfoRuntimeMixin
 from xmodule.modulestore.exceptions import ItemNotFoundError, DuplicateCourseError, ReferentialIntegrityError
 from xmodule.modulestore.inheritance import InheritanceMixin, inherit_metadata, InheritanceKeyValueStore
 from xmodule.modulestore.xml import CourseLocationManager
-from xmodule.modulestore.django import NullSignalHandler
 from xmodule.services import SettingsService
 
 log = logging.getLogger(__name__)
@@ -544,7 +543,7 @@ class MongoModuleStore(ModuleStoreDraftAndPublished, ModuleStoreWriteBase, Mongo
                  i18n_service=None,
                  fs_service=None,
                  user_service=None,
-                 signal_handler=NullSignalHandler(),
+                 signal_handler=None,
                  retry_wait_time=0.1,
                  **kwargs):
         """

common/lib/xmodule/xmodule/modulestore/split_mongo/split.py

@@ -85,7 +85,6 @@ from xmodule.error_module import ErrorDescriptor
 from collections import defaultdict
 from types import NoneType
 from xmodule.assetstore import AssetMetadata
-from xmodule.modulestore.django import NullSignalHandler
 
 
 log = logging.getLogger(__name__)
@@ -641,8 +640,7 @@ class SplitMongoModuleStore(SplitBulkWriteMixin, ModuleStoreWriteBase):
                  default_class=None,
                  error_tracker=null_error_tracker,
                  i18n_service=None, fs_service=None, user_service=None,
-                 services=None, signal_handler=NullSignalHandler(),
-                 **kwargs):
+                 services=None, signal_handler=None, **kwargs):
         """
         :param doc_store_config: must have a host, db, and collection entries. Other common entries: port, tz_aware.
         """