use an other status that PENDING for queries which does not work

[yves-renier]

When asking for the status of an incorrect task is currently returning the status 'PENDING'.
for example: https://test-graphai.epfl.ch/translation/translate/status/wrong-status
That makes the handling of errors very difficult as if the task is outdated I will be waiting for the task to complete for ever.
It would be much easier for me if the 'PENDING' state is reserved for valid tasks and an other status is used in case of errors.

[RamtinYazdanian]

This is a celery feature, apparently as an optimization. The status of a task is only updated by the task itself, and there is no on-the-fly access to the queue. The task id that celery returns is the future id of the last task (as you can see when you actually get results, where the name of the task is something like video_6.something_callback, which is my naming convention for final tasks), and as a result, the task id doesn't exist anywhere unless the chain of tasks actually gets to the last task. This is why errors somewhere in the middle of the chain result in the task_id permanently giving you a PENDING status, because the task with that id is never created in the first place. When it's the last task itself that fails, you do get a detailed status, but that's quite rare as the last task is always a database callback.

The Flower interface (which, on both servers, is on http://localhost:5555) allows for the monitoring of tasks, and that's how I debug right now: knowing what endpoint you were trying to use, I find the last task in that chain with a FAILED state and look at the error message. Unfortunately this means that it's currently very difficult to do this programmatically. In order to make tasks fail more transparently, I'll have to do a refactor of all the tasks in order to catch all exceptions and explicitly set the status of the final task to FAILED wherever any step of the chain fails. For now, we should continue as we have, and I'll later do a big refactor and improve error handling.