https://pawelurbanek.com/rails-thread-safety

Ensuring thread safety is critical if you want to develop a performant Rails app. Unfortunately, threading-related bugs are often sneaky and only manifest in highly concurrent production environments. In this blog post, we’ll discuss code examples that are not thread-safe. I’ll also describe a toolkit for debugging and discuss possible solutions. Developing an eye for spotting these errors before shipping to production can save you a lot of headaches.