Wednesday, March 22, 2023

Re: Django Channels 2 Group_send to channel layer causes runtime error: "got Future attached to a different loop"

how did you test it ? did you use a specific cmd to excute ?

Le vendredi 16 février 2018 à 22:08:55 UTC+1, Luke Hebert a écrit :
Trying to call the "alert_receive" consumer method

import json
from channels.consumer import SyncConsumer
from channels.exceptions import StopConsumer
from asgiref.sync import async_to_sync
from channels.layers import get_channel_layer

class ClientAlertPtrConsumer(SyncConsumer):
def websocket_connect(self, event):
(self.channel_layer.group_add)("AlertReceivers", self.channel_name)
"type": "websocket.accept",
def websocket_receive(self, event):
= json.dumps("received")
(self.channel_layer.group_send)("AlertReceivers", {"type":"alert.receive"})
def websocket_disconnect(self, event):
(self.channel_layer.group_discard)("AlertReceivers", self.channel_name)
raise StopConsumer

def alert_receive(self, event):                 # Get a message on the alert.receive type
= json.dumps("Group send working")
"type":"websocket.send",                # then send a message out on websocket protocol to whatever the 'self' channel is.

from outside this consumer class using the approach in documentation like this

from asgiref.sync import async_to_sync
from channels.layers import get_channel_layer
channel_layer = get_channel_layer()

(channel_layer.group_send)("AlertReceivers", {'type':"alert.receive"})

and getting the following traceback having to do with the concurrent.futures module:

Traceback (most recent call last):
  File "/usr/lib/python3.5/", line 91, in runcode
    exec(code, self.locals)
  File "<console>", line 1, in <module>
  File "/usr/local/lib/python3.5/dist-packages/asgiref/", line 49, in __call__
    return call_result.result()
  File "/usr/lib/python3.5/concurrent/futures/", line 398, in result
    return self.__get_result()
  File "/usr/lib/python3.5/concurrent/futures/", line 357, in __get_result
    raise self._exception
  File "/usr/local/lib/python3.5/dist-packages/asgiref/", line 63, in main_wrap
    result = await self.awaitable(*args, **kwargs)
  File "/usr/local/lib/python3.5/dist-packages/channels_redis/", line 313, in group_send
    pool = await self.connection(self.consistent_hash(group))
  File "/usr/local/lib/python3.5/dist-packages/channels_redis/", line 377, in connection
    self.pools[index] = await aioredis.create_redis_pool(**self.hosts[index])
  File "/usr/local/lib/python3.5/dist-packages/aioredis/commands/", line 197, in create_redis_pool
  File "/usr/local/lib/python3.5/dist-packages/aioredis/", line 59, in create_pool
    await pool.wait_closed()
  File "/usr/local/lib/python3.5/dist-packages/aioredis/", line 177, in wait_closed
    await asyncio.shield(self._close_waiter, loop=self._loop)
  File "/usr/lib/python3.5/asyncio/", line 361, in __iter__
    yield self  # This tells Task to wait for completion.
RuntimeError: Task <Task pending coro=<AsyncToSync.main_wrap() running at /usr/local/lib/python3.5/dist-packages/asgiref/> cb=[_run_until_complete_cb() at /usr/lib/python3.5/asyncio/]> got Future <Future pending> attached to a different loop

Note that the 
async_to_sync(channel_layer.group_send)("AlertReceivers", {'type':"alert.receive"})

within the websocket_receive method of the consumer class works well, sending the event out onto redis-based channel layers and then sending json encoded "Group send working" WS message to client. 

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