Rails 4: How to send mail in a separate thread? - ruby-on-rails

Question

I have an application that needs to occasionally send an email blast to the entire user base when an admin does something. This was working fine, but when there are a lot of users, the page for the admin will wait until all the mail is sent, which is undesirable.
To mitigate this, I tried sending email in a new thread:
t = Thread.new do
User.all.each do |user|
Mailer.email(user).deliver
end
end
at_exit{ t.join }
This worked fine, but then in my test suite, I can't test to ensure the email sending works:
# This test now fails with the new Thread above
test "admin action should send email blast" do
assert_difference("ActionMailer::Base.deliveries.count", User.count) do
post :action
end
end
So my questions are:
Is this method the best way to send email in a new Thread? Or is there a gem available that handles this kind of interaction?
How can I test that the emails are sent in my test suite if the sending is done in a new thread? Is there a way to check to wait for all threads to finish?

Answer 1

In rails 4.2 there's a special class that handles jobs called ActiveJob, active job allows you to queue long tasks for another process to handle them in the background, also you can queue tasks for a certain time, like for example "send this email tomorrow at 8 am".
For these queues to get handled you need to choose a backend to handle them, here's a list of backends that support ActiveJob
Each has it's pros and cons, sidekiq for example is a multithread handler, so it uses lower memory, while for example sucker punch uses the same thread as the main server, so it uses a lot less memory, suitable if you have a low memory server that can't handle a second ruby thread.
As for the testing part, rails guide already explains how to test your emails and test things like if emails has been queued or not, and test that the right template was rendered, and if it contains the right text.

Answer 2

I think you want to send mail asynchronously, For that you may use many gems like - delayed jobs, sidekiq etc. I would personally recommend to use sidekiq as its faster and used Redis in memory db behind the scene.
With Rails 4.2, Active jobs are introduced, so using it has advantage that you can switch from one queuing system to other without having any worry at any time and you can specify which queing machinery yiu want like
module YourApp
class Application < Rails::Application
# Be sure to have the adapter's gem in your Gemfile
# and follow the adapter's specific installation
# and deployment instructions.
config.active_job.queue_adapter = :sidekiq
end
end

Answer 3

I prefer using a queue based approach for async tasks. [Delayed job] (https://github.com/collectiveidea/delayed_job) is one option, but I prefer using [sidekiq] (http://sidekiq.org).
[Here] (http://blog.remarkablelabs.com/2013/01/using-sidekiq-to-send-emails-asynchronously) is an example of sending emails asynchronously using sidekiq.

Answer 4

Best way to send emails in separate threads is to use delayed jobs or similar gem.
https://github.com/collectiveidea/delayed_job
With delayed jobs gem, you can also send emails or do something else in different threads at scheduled time.
Another option is to use sidekiq, install sidekiq gem and add this line to application.rb file
config.active_job.queue_adapter = :sidekiq