Minimal reproducible test case for triggering: RuntimeError: You cannot use AsyncToSync in the same thread as an async event loop - just await the async function directly. when queuing multiple tasks in celery that call django channels group_send using async_to_sync. Steps to reproduce:

• Run docker-compose up -d to bring up django, celery, and other requirements
• Run docker-compose logs -f worker to watch celery logs
• In a separate tab run docker-compose exec python src/manage.py shell and then following in the shell:

  from celery_channels_test.celery import sync_send
  sync_send.delay()
  # verify task succeeded normally in celery logs
  for i in range(10):
      sync_send.delay()
  # note `RuntimeError` in celery logs
  

Now try using a task that doesn't use channels group_send, and note that there is no error thrown because an event loop is never detected:

• Run docker-compose up -d to bring up django, celery, and other requirements
• Run docker-compose logs -f worker to watch celery logs
• In a separate tab run docker-compose exec python src/manage.py shell and then following in the shell:

  from celery_channels_test.celery import detect_event_loop
  detect_event_loop.delay()
  # verify task succeeded normally in celery logs
  for i in range(10):
      sync_send.delay()
  # note lack of a ValueError that would be thrown if the event loop is running