The Global VM Lock (GVL), is an implementation detail of the Ruby VM. At a high-level, it prevents code across multiple threads from running in parallel. The GVL can have a big impact on the performance and responsiveness of any application that uses more than a single thread to do its work. I’ve recently presented on this topic at RubyKaigi 2023; live interactive examples, the video, and slides are available at https://ivoanjo.me/blog/2023/07/23/understanding-the-ruby-global-vm-lock-by-observing-it/ .