Trigger the reloading of a page after a background job

Question

I have a rails 4 application, that is doing a background calculus. So the user press a button and it launches a background job for the long calculus (using delay_job) and arrive on a waiting page. Despite the fact that the calculus is done asynchronously, I would like to find a way to warn the user and automatically reload it page once the calculus is finish.

I have looked at several solutions :

• Faye or private_pub => I can't afford to use another server for this very specific job
• ActionController::Live => I am not sure how to trigger the action once the job is finished
• Polling => best solution for the moment, but I expect to find something that is less greedy than polling

If you have any smart solution for this problem, or any advise for my limitation in the listed ideas.

Answer 1

I'll explain how this works for you

---

HTTP

When you send the request to Rails, your browser doesn't have any way to "listen" to what happens to anything other than a direct response. The HTTP request is "sent" & doesn't have any mechanism to wait until the asynchronous process is complete

Your job is to give your app a "listener" so that your front-end can receive updates as they are generated (out of scope of HTTP), hence the websocket or SSE stuff

We've set up what you're looking for before, using Pusher

---

"Live"

Achieving "live" functionality is what you need

This basically means keeping a request open "perpetually" to the server; listening to any of the "events" the server sends back. This is done with JS on the front-end, where the client will "subscribe" to a channel (typically a user-centric one), and will then have all the data sent to it

We used a third-party system called Pusher to achieve this recently:

#GemFile
gem "pusher", "~> 0.12.0"    

#app/controllers/message.rb
def send_message
    public_key = self.user.public_key
    Pusher['private-user-' + public_key].trigger('message_sent', {
        message: "Message Sent"
    })  
end

   #app/assets/javascripts/application.js
   pusher = new Pusher("***********",
     cluster: 'eu'
   )

   channel = pusher.subscribe("private-user-#{gon.user}")
   channel.bind "message_sent", (data) ->
    alert data.message

Hope this gives another option for you