Concurrency

What happens when two things run at once, and why order stops being obvious.

4 concepts · 170 minutes

• The Node.js RuntimeJavaScript outside the browser: modules, streams, and a single thread doing a lot of I/O.
• The Event LoopOne thread, a queue, and a rule about when it drains — the model that explains every 'why did this run last?'.
• Concurrency vs ParallelismDealing with many things at once vs doing many things at once — not the same, and the distinction matters.
• Race ConditionsTwo things interleaving in an order you never tested — the bug class that only shows up in production.