Ruby Concurrency: What Actually Happens

Ruby's four concurrency primitives — processes, threads, fibers, and Ractors — each serve different workloads, and knowing when to use which matters. Fibers offer I/O concurrency with far less overhead than threads (20x faster creation, 10x faster switching), making them ideal for LLM streaming or HTTP-heavy jobs. Crucially, Ruby's fiber scheduler is colorless: existing Net::HTTP and pg code works unchanged, no async rewrites needed.