{"action":"created","issue":{"url":"https://api.github.com/repos/celery/celery/issues/4553","repository_url":"https://api.github.com/repos/celery/celery","labels_url":"https://api.github.com/repos/celery/celery/issues/4553/labels{/name}","comments_url":"https://api.github.com/repos/celery/celery/issues/4553/comments","events_url":"https://api.github.com/repos/celery/celery/issues/4553/events","html_url":"https://github.com/celery/celery/issues/4553","id":299105350,"node_id":"MDU6SXNzdWUyOTkxMDUzNTA=","number":4553,"title":"ImproperlyConfigured when using allow_join_result","user":{"login":"keaneokelley","id":2617725,"node_id":"MDQ6VXNlcjI2MTc3MjU=","avatar_url":"https://avatars2.githubusercontent.com/u/2617725?v=4","gravatar_id":"","url":"https://api.github.com/users/keaneokelley","html_url":"https://github.com/keaneokelley","followers_url":"https://api.github.com/users/keaneokelley/followers","following_url":"https://api.github.com/users/keaneokelley/following{/other_user}","gists_url":"https://api.github.com/users/keaneokelley/gists{/gist_id}","starred_url":"https://api.github.com/users/keaneokelley/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/keaneokelley/subscriptions","organizations_url":"https://api.github.com/users/keaneokelley/orgs","repos_url":"https://api.github.com/users/keaneokelley/repos","events_url":"https://api.github.com/users/keaneokelley/events{/privacy}","received_events_url":"https://api.github.com/users/keaneokelley/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":1,"created_at":"2018-02-21T19:52:27Z","updated_at":"2018-08-13T03:47:24Z","closed_at":null,"author_association":"NONE","body":"## Checklist\r\n\r\n- [x] I have included the output of ``celery -A proj report`` in the issue.\r\n```\r\nsoftware -> celery:4.1.0 (latentcall) kombu:4.1.0 py:3.6.4+\r\n            billiard:3.5.0.3 redis:2.10.6\r\nplatform -> system:Linux arch:64bit, ELF imp:CPython\r\nloader   -> celery.loaders.app.AppLoader\r\nsettings -> transport:redis results:redis:///\r\n\r\nbroker_url: 'redis://localhost:6379//'\r\nresult_backend: 'redis:///'\r\n```\r\n- [x] I have verified that the issue exists against the `master` branch of Celery.\r\n\r\n## Steps to reproduce\r\n```python\r\ng = group(mytask.s(t) for t in things).delay()\r\nwith allow_join_result():\r\n    g.get(on_message=callback, propagate=False)\r\n```\r\n## Expected behavior\r\nShould work as expected, as seen on: https://stackoverflow.com/a/45491380\r\n## Actual behavior\r\n```python\r\n[2018-02-21 13:31:29,930: ERROR/ForkPoolWorker-2] Task project.modules.discovery.scheduled_scan[47449b63-053e-4a56-9b30-91b2cfa88577] raised unexpected: ImproperlyConfigured('Backend does not support on_message c\r\nallback',)\r\nTraceback (most recent call last):\r\n  File \"/home/user/.envs/project/lib/python3.6/site-packages/celery/app/trace.py\", line 374, in trace_task\r\n    R = retval = fun(*args, **kwargs)\r\n  File \"/home/user/.envs/project/lib/python3.6/site-packages/celery/app/trace.py\", line 629, in __protected_call__\r\n    return self.run(*args, **kwargs)\r\n  File \"/home/user/dev/project/project/modules/discovery.py\", line 149, in scheduled_scan\r\n    NmapScan.run_scans()\r\n  File \"/home/user/dev/project/project/modules/discovery.py\", line 89, in run_scans\r\n    g.get(on_message=cls.push_update, propagate=False)\r\n  File \"/home/user/.envs/project/lib/python3.6/site-packages/celery/result.py\", line 635, in get\r\n    on_message=on_message,\r\n  File \"/home/user/.envs/project/lib/python3.6/site-packages/celery/result.py\", line 687, in join\r\n    'Backend does not support on_message callback')\r\ncelery.exceptions.ImproperlyConfigured: Backend does not support on_message callback\r\n```\r\nThis is caused because the call to `ResultSet.supports_native_join` returns None after the `IndexError`, as `result[0]` doesn't exist (yet?):\r\nhttps://github.com/celery/celery/blob/bc366c887f194a3ff1f99671d9742a525a066339/celery/result.py#L801\r\nThis seems like un-intended behavior? Note that it works fine without the `allow_join_result`, although that is needed in my case."},"comment":{"url":"https://api.github.com/repos/celery/celery/issues/comments/412401690","html_url":"https://github.com/celery/celery/issues/4553#issuecomment-412401690","issue_url":"https://api.github.com/repos/celery/celery/issues/4553","id":412401690,"node_id":"MDEyOklzc3VlQ29tbWVudDQxMjQwMTY5MA==","user":{"login":"auvipy","id":6212603,"node_id":"MDQ6VXNlcjYyMTI2MDM=","avatar_url":"https://avatars1.githubusercontent.com/u/6212603?v=4","gravatar_id":"","url":"https://api.github.com/users/auvipy","html_url":"https://github.com/auvipy","followers_url":"https://api.github.com/users/auvipy/followers","following_url":"https://api.github.com/users/auvipy/following{/other_user}","gists_url":"https://api.github.com/users/auvipy/gists{/gist_id}","starred_url":"https://api.github.com/users/auvipy/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/auvipy/subscriptions","organizations_url":"https://api.github.com/users/auvipy/orgs","repos_url":"https://api.github.com/users/auvipy/repos","events_url":"https://api.github.com/users/auvipy/events{/privacy}","received_events_url":"https://api.github.com/users/auvipy/received_events","type":"User","site_admin":false},"created_at":"2018-08-13T03:47:24Z","updated_at":"2018-08-13T03:47:24Z","author_association":"MEMBER","body":"can you suggest the improve error message?"}}
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