Spawn Background Processes in Rails

Scott Persinger had a blog post about how to do background processing in rails. I have often wanted to have a simple way to do this (usually when sending out emails to users). So I decided to make a plugin out of Scott's idea. The plugin is called spawn and you can download it here (unzip it in your vendor/plugins directory).

Usage of the plugin is very simple. Just surround the code you want to run in the background within a 'spawn' block like this:

  spawn do
    logger.info("I feel sleepy...")
    sleep 11
    logger.info("Time to wake up!")
  end

If you run that in a controller you should find that your page is rendered well before the last log message is written out. That's all there is to it.

You might want to be aware of what's going on when you run a spawn block. Because ActiveRecord::Base only keeps single connections open to the database, spawn will open a new connection in a forked child process. This seems to work pretty well in my application. The overhead of forking is low compared to starting a new rails process and you have access to all of the current variables.

Let me know if you try this out and how it goes for you.

Update 2007/10/16
The latest version of the spawn plugin can now do forking or threading. It is now controlled at rubyforge so read more here.

Update 2008/12/28
The latest version of the spawn plugin now works with Rails 2.2.2. Get it at github using "./script/plugin install git://github.com/tra/spawn.git".