Yes done() can be used as many times as you want.

here is an example:

package main

import (
        "context"
        "time"
)
func f(ctx context.Context) {
	for i:=0;i<10;i++{
		select {
		case <- ctx.Done():
			println("canceled")
		default:
			println(".")

		}

		time.Sleep(1*time.Second)
	}
	println("f exit")
}

func main() {

        ctx, cancel := context.WithCancel(context.Background())
        go f(ctx)
        time.Sleep(3*time.Second)
        println("call ctx cancel()")
        cancel()
        time.Sleep(10*time.Second)
        println("exit")
}

results:

go run cancel.go
.
.
.
call ctx cancel()
canceled
canceled
canceled
canceled
canceled
canceled
canceled
f exit
exit

See “canceled” got returned constantly after context was canceled.