Worker Pools

A worker pool is a long-lived, fixed-size set of goroutines that pull jobs off a shared channel, do the work, and push results onto another channel. It's the standard Go primitive for bounding concurrency on something expensive: a database, an external API, a CPU-heavy transform. Fan-out is the basic shape for a single batch; this lesson treats the pool as a reusable resource with its own lifecycle (start, drain, close), proper sizing rules, graceful shutdown, and error handling.