How to do an ajax callback after a Delayed Job has finished in Ruby on Rails?

I allow users on my site to rotate their photos. I accomplish this by an ajax call to a Delayed_Job process (via Heroku) that rotates the photo. After they press "rotate photo", I show a loading spinner. But my question is this: what is the best way for my page to know when the Delayed_Job is complete, so I can load the new photo?

Do I need to have a continuous ajax polling of my server to determine if the Delayed Job is complete? Or is 开发者_开发知识库there any way I can implement an ajax callback to my page that will notify my page when the Delayed Job has finished?

Thanks in advance.

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There's a bunch of ways to deal with this kind of thing. You could do ajax polling as you've mentioned, you could use the comet approach where you essentially leave a connection open until whatever it is on the server has completed, or you could even go all out and use web sockets (probably a bit overkill for this task though).

Without sockets, there's currently no way to have your server send a message to the client, without the client requesting it.

In any case, you should decide whether the need or want to background the task warrants all the extra work of dealing with the polling/comet/sockets. Rotating an image shouldn't take long at all. Depending on whether you can afford to lock up a server process, it'd be a lot simpler to just do the image manipulation in the foreground (not delayed_job). Then, when the ajax request to that action has completed, you know the task is completed.