Fixing “uninitialized constant” errors in rake tasks when using Rails threadsafe! mode

I ran into this problem where I was getting “uninitialized constant” errors when running rake tasks. These are tasks which had been working and I verified that the proper paths were set (eager_load_paths). When searching I saw information about config.threadsafe! being a problem so I disabled it and the problems vanished. However, I wanted to use config.threadsafe!, specifically for allow_concurrency. So, how to resolve this.

Why not just use allow_concurrency?

Well the other options set by threadsafe! are mostly to disable things which are buggy when using concurrency. So using allow_concurrency by itself seems likely to cause problems.

How about forcing the loading to happen?

You can call the following to force the loading of classes in a particular task:


However, I found this did not fix the tasks, possibly because of not running the before_eager_load hooks.

How about re-enabling dependency_loading?

The following code placed in config/environments/production.rb seemed to fix the problems:

config.dependency_loading = true if $rails_rake_task

But I have to wonder what is the point of even using threadsafe! in a rake task and whether this will introduce any bugs.

How about not call config.threadsafe! when running rake tasks?

This seems to be the best option. In the config/environments/production.rb file this line enables threadsafe! except when being called by a rake task:

config.threadsafe! unless $rails_rake_task

Note that this cannot be in application.rb because $rails_rake_task has not been set at that point and that this feature is broken on certain versions of Rails.

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