Cancellation belongs to the whole request tree.

A request may launch multiple goroutines and downstream calls. Go context carries cancellation, deadlines, and request-scoped values across those boundaries. Derived contexts form a tree: cancelling a parent tells its descendants to stop. Passing this context explicitly helps related work respond to the lifetime of the request.

The Go Blog · Jul 29, 2014

Why it matters

Helpful when a network timeout should also stop downstream calls and background computation tied to that request.

More context

Make the caller’s deadline available where blocking work happens. A context communicates cancellation; the receiving code still needs to observe it or call APIs that do. Avoid putting unrelated configuration into request-scoped values.

Keep in mind

Cancellation is cooperative. Passing a context does not forcibly terminate arbitrary code or reverse completed side effects.

Original read