Initial idea

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

@@ -154,6 +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
@@ -169,7 +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 = None
+        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

@@ -26,7 +26,6 @@ from xmodule.contentstore.django import contentstore
 from xmodule.modulestore.draft_and_published import BranchSettingMixin
 from xmodule.modulestore.mixed import MixedModuleStore
 from xmodule.util.django import get_current_request_hostname
-from xmodule.util.null_handler import NullHandler
 import xblock.reference.plugins
 
 
@@ -130,7 +129,7 @@ def create_modulestore_instance(
         i18n_service=None,
         fs_service=None,
         user_service=None,
-        signal_handler=NullHandler(),
+        signal_handler=None,
 ):
     """
     This will return a new instance of a modulestore given an engine and options

common/lib/xmodule/xmodule/modulestore/mixed.py

@@ -16,7 +16,6 @@ from opaque_keys.edx.keys import CourseKey, AssetKey
 from opaque_keys.edx.locator import LibraryLocator
 from opaque_keys.edx.locations import SlashSeparatedCourseKey
 from xmodule.assetstore import AssetMetadata
-from xmodule.util.null_handler import NullHandler
 
 from . import ModuleStoreWriteBase
 from . import ModuleStoreEnum
@@ -109,7 +108,7 @@ class MixedModuleStore(ModuleStoreDraftAndPublished, ModuleStoreWriteBase):
             fs_service=None,
             user_service=None,
             create_modulestore_instance=None,
-            signal_handler=NullHandler(),
+            signal_handler=None,
             **kwargs
     ):
         """

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

@@ -50,7 +50,6 @@ from xmodule.modulestore.exceptions import ItemNotFoundError, DuplicateCourseErr
 from xmodule.modulestore.inheritance import InheritanceMixin, inherit_metadata, InheritanceKeyValueStore
 from xmodule.modulestore.xml import CourseLocationManager
 from xmodule.services import SettingsService
-from xmodule.util.null_handler import NullHandler
 
 log = logging.getLogger(__name__)
 
@@ -544,7 +543,7 @@ class MongoModuleStore(ModuleStoreDraftAndPublished, ModuleStoreWriteBase, Mongo
                  i18n_service=None,
                  fs_service=None,
                  user_service=None,
-                 signal_handler=NullHandler(),
+                 signal_handler=None,
                  retry_wait_time=0.1,
                  **kwargs):
         """

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

@@ -67,7 +67,6 @@ from bson.objectid import ObjectId
 from xblock.core import XBlock
 from xblock.fields import Scope, Reference, ReferenceList, ReferenceValueDict
 from xmodule.errortracker import null_error_tracker
-from xmodule.util.null_handler import NullHandler
 from opaque_keys.edx.locator import (
     BlockUsageLocator, DefinitionLocator, CourseLocator, LibraryLocator, VersionTree, LocalId,
 )
@@ -641,7 +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=NullHandler(), **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.
         """

common/lib/xmodule/xmodule/modulestore/tests/utils.py

@@ -6,7 +6,6 @@ from opaque_keys.edx.keys import UsageKey
 from unittest import TestCase
 from xblock.fields import XBlockMixin
 from xmodule.x_module import XModuleMixin
-from xmodule.util.null_handler import NullHandler
 from xmodule.modulestore import ModuleStoreEnum
 from xmodule.modulestore.draft_and_published import ModuleStoreDraftAndPublished
 from xmodule.modulestore.edit_info import EditInfoMixin
@@ -37,7 +36,7 @@ def create_modulestore_instance(
         i18n_service=None,
         fs_service=None,
         user_service=None,
-        signal_handler=NullHandler(),
+        signal_handler=None,
 ):
     """
     This will return a new instance of a modulestore given an engine and options

common/lib/xmodule/xmodule/modulestore/xml.py

@@ -26,7 +26,6 @@ from xmodule.x_module import (
 from xmodule.modulestore.xml_exporter import DEFAULT_CONTENT_FIELDS
 from xmodule.modulestore import ModuleStoreEnum, ModuleStoreReadBase, LIBRARY_ROOT, COURSE_ROOT
 from xmodule.tabs import CourseTabList
-from xmodule.util.null_handler import NullHandler
 from opaque_keys.edx.locations import SlashSeparatedCourseKey, Location
 from opaque_keys.edx.locator import CourseLocator, LibraryLocator
 
@@ -336,7 +335,7 @@ class XMLModuleStore(ModuleStoreReadBase):
     def __init__(
             self, data_dir, default_class=None, source_dirs=None, course_ids=None,
             load_error_modules=True, i18n_service=None, fs_service=None, user_service=None,
-            signal_handler=NullHandler(), target_course_id=None, **kwargs   # pylint: disable=unused-argument
+            signal_handler=None, target_course_id=None, **kwargs   # pylint: disable=unused-argument
     ):
         """
         Initialize an XMLModuleStore from data_dir