ArrrrCamp 2014- Unicorn Unix Magic Tricks

By, Thorsten Ball
A couple of years ago, when I set out to really understand Unix from a developer's perspective, I found one invaluable resource for my Unix studies: the source code of the Unicorn web server. When I first encountered Unicorn, it seemed like magic to me: just by sending different signals to the server I could control important runtime settings. Unicorn allows me to scale the number of worker processes simply by sending a signal. Reloading configuration files and reopening log files is possible by sending signals. It even allows me to hot reload code once deployed. Again, all I need to do is send it a signal. But how does it do all that? Magic? This talk answers exactly this question.

We'll take a look at small snippets of the Unicorn source code and see that it isn't magic, but plain old Unix: forking, signal handling, pipes (even self-pipes), pre-spawning, master-worker architecture, file descriptor handling, system calls, the classic socket/bind/listen/accept sequence, Unix sockets, PID files and a lot more. There is even `eval`, but I'll keep quiet about that, I promise.

Unicorn is full of Unix. By studying its code we do not only learn how one of the most important pieces of Ruby infrastructure works, but also how Unix systems work. The talk will provide you with a foundation for programming in the Unix environment and show you how to leverage the powers of Unix.

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