Rails 3 ActiveRecord .skip_callback thread safety

Question

Is this code thread safe?

MyModel.skip_callback(:save, :before, :my_callback)
my_model_instance.update_attributes(attributes)
MyModel.set_callback(:save, :before, :my_callback)

Can i safely use it to avoid retrigger the same callback recursively?

Here is an example

class Blog < ActiveRecord::Base

  after_save  :update_blog_theme, :if => :active_theme_id_changed?

  # ...

  private

  def update_blog_theme

    # Reuses a previously used BlogTheme or creates a new one
    blog_theme = BlogTheme.find_by_theme_id_and_blog_id(
                      self.active_theme_id, 
                      self.id)

    blog_theme ||= BlogTheme.create!( 
                     :theme_id => active_theme_id, 
                     :blog_id => self.id )

    Blog.skip_callback(:save, :after, :update_blog_theme)
    self.update_attributes!(:active_blog_theme_id => blog_theme.id) 
    Blog.set_callback(:save, :after, :update_blog_theme)

  end

end

Answer 1

skip_callback and set_callback are NOT thread safe. I was able to confirm this while trying to create some records within sidekiq (a threaded async job processor). As soon as I re-enable the callbacks, there is a race condition that results in callbacks being called. If I comment the callback re-activation code, there are no issues.

I have found a number of possible solutions to the issue including two gems:

• the 'sneaky-save' gem
• the 'skip_activerecord_callbacks' gem

The sneaky-save gem seems to be the most straight-forward and intention-revealing option here. The gem essentially bypasses the ActiveRecord persistence methods and executes straight sql.

It is also the only one that I can confidently say is thread-safe. It is also a very small and understandable gem. The downside is that it does not call validations. Thus you would need to call validations yourself.

Anand A. Bait put together a great rundown on a number options. I am skeptical that all five options are threadsafe. The two gems mentioned above are listed along with other possible options in Anand's post here: http://www.allerin.com/blog/save-an-object-skipping-callbacks-in-rails-3-application/