ActiveWaiter

A simple mechanism allowing your users to wait for the completion of your ActiveJob

Scenario

You have an export PDF feature that you've implemented directly in the controller action.

As data grows, your HTTP request takes longer and starts timing out. So you decide to move the PDF generating code into a background job.

def index
  respond_to do |format|
    format.html
    format.pdf {
      ExportPdfJob.perform_later(@things, current_user)
      redirect_to :back, notice: "We'll email your PDF when it's done!"
    }
  end
end

But how do you get that PDF into the hands of your users now? Email? Push notification? Manual reload?

You have no PDF ready for download (yet). Please reload.

Solution

Let ActiveWaiter enqueue that job instead and redirect to it's progress tracking page.

def index
  respond_to do |format|
    format.html
    format.pdf {
      uid = ActiveWaiter.enqueue(ExportPdfJob, @things, current_user)
      redirect_to active_waiter_path(uid)
    }
  end
end

# routes.rb
mount ActiveWaiter::Engine => "/active_waiter(/:id)"

When the job completes, the user will be redirected to the url returned by the job. However, if you want the user to be presented with a download link, add download: 1 params instead

redirect_to active_waiter_path(uid, download: 1)

And we need to add a bit of code into your ActiveJob class

• 1) add include ActiveWaiter::Job
• 2) return a url from your perform method to link to the result page (or file)

class ExportPdfJob < ActiveJob::Base
  queue_as :default

  # (1)
  include ActiveWaiter::Job

  def perform(things, current_user)
    count = things.count.to_f
    files = []
    things.each_with_index do |thing, index|
      files << generate_pdf(thing)

      # (a)
      update_active_waiter percentage: (100 * (index+1) / count)
    end

    # (2)
    upload(combine(files)).s3_url
  rescue Exception => e

    # (b)
    update_active_waiter error: e.to_s
  end
end

Optionally, you can also

• a) report progress while your job runs, using update_active_waiter(percentage:)
• b) report if there were any errors, using update_active_waiter(error:)

Configuration

By default, ActiveWaiter uses a simple Bootstrap layout. To use your application's layout, configure:

ActiveWaiter.configure do |config|
  config.layout = "layouts/application"
end

Next, prefix any routes used in your application's layout with main_app., e.g. main_app.sign_in_path.

This is required because ActiveWaiter is a Rails Engine mounted into your application, and it doesn't know about the routes declared within your application.