Learning about kqueue

November 11, 2020

I’m trying to fix a bug in the rb-kqueue gem which occasionally crashes the ruby interpreter when I’m running a file-watching server while working on this site.

The bug seems to be in the rb-kqueue gem, which is a thin wrapper around *BSD’s kqueue API, which is an interface for subscribing to notifications when a file changes, similar to Linux’s inotify.

To understand what’s wrong with rb-kqueue, I’m going to start by learning how to make the most basic thing that does what rb-kqueue does. To start, forget ruby, and makd something simple in c.

Here’s how to get started with kqueue:

$ man kqueue

…and scroll down to the “EXAMPLES” section. Copy paste the example code into a c file, compile it, and run it. It will watch the file specified as an argument and print a message when the watched file changes.

Then read the manual page and modify the code to learn more.