Why does Rails console create so many Ruby processes?

Question

I experimented with a Rake task with Cron. I started with no Ruby processes, then the Cron job started and spawned one process. The highlighted process below is what is run by Cron, which is expected:

I wanted to check if any records were being written to the database. I ran rails c to enter the Rails console, and noticed that suddenly four other ruby processes showed up in my process list as above. Why would this happen? I think that running the console should create one other process and not four.

After quitting the console, I am left with three Ruby processes including the Rake task that is running.

I am using Rails 4.2.

It's not that I find this to be problematic, but I am curious why there would need to be more than one process for a REPL and then two leftover processes after the REPL is closed.

Answer 1

This is because of spring which has shipped with rails by default for a little while now.

You might notice that the second time you run rails c is a lot faster than the first time. This is because the first time you run a springified script your app is loaded as normal and then forks to run what you requested. The second time around this loader script can just fork a second time, so you get a much faster startup. This possible because of these extra processes you have noticed.

You can see them by running

spring status

And you can kill them by running

spring stop