Goroutines and channels — the Go concurrency model explained_

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.

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.

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.

A channel is a typed, goroutine-safe queue. Send with ch <- value, receive with value := <-ch. Channels can be buffered (non-blocking up to capacity) or unbuffered (sender blocks until receiver is ready). They are the idiomatic way to share data between goroutines.