fix: avoid race conditions when removing multiple instance groups at …

…once

awx/api/generics.py

@@ -51,6 +51,8 @@
 from awx.api.metadata import SublistAttachDetatchMetadata, Metadata
 from awx.conf import settings_registry
 
+from django.db.transaction import get_connection
+
 __all__ = [
  'APIView',
  'GenericAPIView',
@@ -743,7 +745,16 @@ def unattach_by_id(self, request, sub_id):
  if parent_key:
  sub.delete()
  else:
- relationship.remove(sub)
+ with transaction.atomic():
+ cursor = get_connection().cursor()
+ # lock the table to prevent any race conditions at the database level
+ # a transaction will automatically release the lock once committed (or rolled back) and
+ # other transactions will automatically wait for the lock to be released
+ cursor.execute(f'LOCK TABLE {relationship.through._meta.db_table} IN SHARE ROW EXCLUSIVE MODE')
+ try:
+ relationship.remove(sub)
+ finally:
+ cursor.close()
 
  return Response(status=status.HTTP_204_NO_CONTENT)