You've probably heard people around you talking mutexes, race conditions, or the GIL. Do you wonder what the heck they're talking about?
This book is a gentle introduction to these concepts and will give you the knowledge you need to become your teams resident concurrency expert. This book will help you get the story straight when it comes to multi-threaded concurrency in Ruby.
This was good--I really didn't understand threading at all before but now I have a better sense of the kinds of concurrency problems you might have and the reasonable steps you'd want to take to protect against those cases. I didn't play with the examples enough myself to really feel like I could sit down and code it out, but I'd go back to this for a refresher if I'm in that situation.
Perfect book to understand MultiThreading programming in Ruby. It basically clarifies a lot of misconceptions myths that many people have made false assumptions or incredible claims about the GIL which is a misunderstood part of MRI.