Warn when trying to use runworker with in memory layer

channels/asgi.py

@@ -75,6 +75,10 @@ class ChannelLayerWrapper(object):
     def __str__(self):
         return "%s (%s)" % (self.alias, name_that_thing(self.channel_layer))
 
+    def local_only(self):
+        # TODO: Can probably come up with a nicer check?
+        return "inmemory" in self.channel_layer.__class__.__module__
+
 
 def get_channel_layer(alias="default"):
     """

channels/management/commands/runworker.py

@@ -1,6 +1,6 @@
 from __future__ import unicode_literals
 
-from django.core.management import BaseCommand
+from django.core.management import BaseCommand, CommandError
 from channels import channel_layers, DEFAULT_CHANNEL_LAYER
 from channels.log import setup_logger
 from channels.worker import Worker
@@ -13,6 +13,12 @@ class Command(BaseCommand):
         self.verbosity = options.get("verbosity", 1)
         self.logger = setup_logger('django.channels', self.verbosity)
         self.channel_layer = channel_layers[DEFAULT_CHANNEL_LAYER]
+        # Check that handler isn't inmemory
+        if self.channel_layer.local_only():
+            raise CommandError(
+                "You cannot span multiple processes with the in-memory layer. " +
+                "Change your settings to use a cross-process channel layer."
+            )
         # Check a handler is registered for http reqs
         self.channel_layer.registry.check_default()
         # Launch a worker