Clean deletion of a Version

[humitos]

When a Version is deleted, we are triggering clear_artifacts and symlink_project but the later is triggered before the object deletion; so, I think if the task is ran before it's effectively deleted the symlink won't be properly synced:

https://github.com/rtfd/readthedocs.org/blob/5472906a067adc60f42556108993255393408410/readthedocs/builds/models.py#L181-L187

To fix this we could chain some Celery task in this order:

1. trigger clear_artifacts
2. delete the Version object
3. trigger symlink_projects

Take into account that the first and last have to be executed in a broadcast call but the second one should be executed just once since it affects the database.

This method Version.delete is not used in the codebase at all, so I'm not sure if this is a priority. I found that all the Versions are activated/deactivated but not deleted.

Ref: #3649 (comment)

[agjohnson]

We can use Celery task chaining to accomplish this probably.

[stsewd]

This method Version.delete is not used in the codebase at all, so I'm not sure if this is a priority. I found that all the Versions are activated/deactivated but not deleted.

Actually, we delete the versions when syncing the versions

https://github.com/rtfd/readthedocs.org/blob/4fbe0afde6bd0fc9fc14baee79dd361d68f714cb/readthedocs/restapi/utils.py#L134-L154

https://github.com/rtfd/readthedocs.org/blob/4fbe0afde6bd0fc9fc14baee79dd361d68f714cb/readthedocs/restapi/views/model_views.py#L196-L196

I'm not sure about chaining the tasks. What I understand, is that we access to the versions from the symlink_project task, which is in a race condition with the deletion of the current version.

So at least that clear_artifacts is in a race condition with symlink_projects, we can just change the call order and that would be enough.

[agjohnson]

which is in a race condition with the deletion of the current version.

What would the race condition here be? If we remove a version and try to symlink, does the symlink stay?

[stsewd]

symlink_project access to all versions and a version is being deleted at the same time. So, probably the symlink would stay