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0+ curated questions with the same answer shape every time: quick recap, deep dive, pitfalls, and follow-ups. Coverage includes .
Ruby concurrency questions are a litmus test for production experience. This module covers the MRI GVL (Global VM Lock) — what it prevents (true CPU parallelism for threads) and what it allows (IO-bound concurrency), Thread lifecycle and Thread.new, Mutex and synchronize for shared state, Queue and SizedQueue, Fiber as cooperative concurrency (not preemptive), Fiber vs Thread trade-offs, Ractor (Ruby 3) share-nothing model and message passing, the async gem event loop over Fibers, and Puma vs Unicorn concurrency models. Every answer names the failure mode — thread-safety bugs in shared mutable state, blocking the GVL in CPU-bound work, the cooperative-scheduling trap in Fiber.
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Numbers 1–0 follow the order we recommend — click any row to open the full answer, or use the sticky Next link at the bottom of each page to go Q1 → Q0.