It seems like you're indentation is off. Can you switch to use 2 spaces as the indentation unit throughout? 😄

It would look like this:

module ActiveSupport
  class FileEventedUpdateChecker
    attr_reader :listener

    # The rest of your code...
  end
end

Remember to strip whitespace at the end of every line too (and empty lines should have no spaces) 😄

Could you please remove this indentation?

Yes I missed this one. I will remove that,

IMO this comment needs to be more descriptive as to why / how performance will be improved - especially because in some environments (Windows, for instance) the "fast" version requires an additional gem.