Goroutines and channels — the Go concurrency model explained_

The select statement waits on multiple channel operations simultaneously, like a switch for channels. This is how you implement timeouts (select with time.After), cancellation (select with a done channel), and fan-in (merge multiple channels into one). Learn select early.

A goroutine is like a thread but much cheaper — the initial stack is a few kilobytes and grows as needed. You can launch thousands of goroutines without worrying about memory. The Go runtime multiplexes them onto OS threads automatically.

The Go mantra: do not communicate by sharing memory; share memory by communicating. Instead of a shared variable protected by a mutex, pass ownership of data through a channel. This eliminates whole classes of race conditions. The mutex is still there when you need it, but channels are the default.

The context package is how you propagate cancellation and deadlines through a goroutine tree. Every long-running function should accept a context.Context as its first parameter. When the context is cancelled, the function should stop and return. This is idiomatic Go.