Cancellation and bounded concurrent work

The idea

A context carries a cancellation signal and optionally a deadline through a call chain. Cancellation is cooperative: work stops only when the code or a called operation observes the signal. A worker can select between sending a result and receiving from ctx.Done, preventing an abandoned receiver from trapping it forever. Always define how callers learn whether work completed or was canceled.

Cancellation does not wait for every goroutine to exit. Use an explicit completion mechanism when shared resources must remain available until workers finish. Channel ownership also matters: the sender side should coordinate closing after all sends are finished. Receiving from a closed channel remains valid and reports completion through the second receive result; sending to a closed channel panics. Avoid tests that assume one scheduler ordering when several outcomes are permitted.

package main
import ("fmt"; "context")
func main(){ ctx,cancel:=context.WithCancel(context.Background()); cancel(); <-ctx.Done(); fmt.Println(ctx.Err()==context.Canceled); ch:=make(chan int,1); ch<-7; close(ch); v,ok:=<-ch; fmt.Println(v,ok); _,ok=<-ch; fmt.Println(ok) }

true
7 true
false

Cancellation closes the Done channel. A closed buffered channel still yields queued data before receives report that no values remain.