polling with delayed_job

Question

I have a process which takes generally a few seconds to complete so I\'m trying to use delayed_job to handle it asynchronously. The job itself works fine, my question is ho

Answer 1

The delayed_jobs table in your application is intended to provide the status of running and queued jobs only. It isn't a persistent table, and really should be as small as possible for performance reasons. Thats why the jobs are deleted immediately after completion.

Instead you should add field to your Available model that signifies that the job is done. Since I'm usually interested in how long the job takes to process, I add start_time and end_time fields. Then my dosomething method would look something like this:

def self.dosomething(model_id)

 model = Model.find(model_id)

  begin
    model.start!

    # do some long work ...

    rescue Exception => e
      # ...
    ensure
      model.finish!
  end
end

The start! and finish! methods just record the current time and save the model. Then I would have a completed? method that your AJAX can poll to see if the job is finished.

def completed?
  return true if start_time and end_time
  return false
end

There are many ways to do this but I find this method simple and works well for me.