Make database channel layer use transactions to stop dupes

channels/database_layer.py

@@ -6,7 +6,8 @@ import string
 import time
 
 from django.apps.registry import Apps
-from django.db import DEFAULT_DB_ALIAS, connections, models
+from django.db import DEFAULT_DB_ALIAS, connections, models, transaction
+from django.db.utils import OperationalError
 from django.utils import six
 from django.utils.functional import cached_property
 from django.utils.timezone import now
@@ -56,15 +57,20 @@ class DatabaseChannelLayer(object):
         self._clean_expired()
         # Get a message from one of our channels
         while True:
-            message = self.channel_model.objects.filter(channel__in=channels).order_by("id").first()
-            if message:
-                self.channel_model.objects.filter(pk=message.pk).delete()
-                return message.channel, self.deserialize(message.content)
+            try:
+                with transaction.atomic():
+                    message = self.channel_model.objects.filter(channel__in=channels).order_by("id").first()
+                    if message:
+                        self.channel_model.objects.filter(pk=message.pk).delete()
+                        return message.channel, self.deserialize(message.content)
+            except OperationalError:
+                # The database is probably trying to prevent a deadlock
+                time.sleep(0.1)
+                continue
+            if block:
+                time.sleep(1)
             else:
-                if block:
-                    time.sleep(1)
-                else:
-                    return None, None
+                return None, None
 
     def new_channel(self, pattern):
         assert isinstance(pattern, six.text_type)