使用Go中的select发送到频道有什么好处？

Question

In the example directory of Gorilla websocket there is a file called hub.go.

https://github.com/gorilla/websocket/blob/master/examples/chat/hub.go

Here you can find a method on the type hub that does this.

func (h *hub) run() {
    for {
        select {
        case c := <-h.register:
            h.connections[c] = true
        case c := <-h.unregister:
            if _, ok := h.connections[c]; ok {
                delete(h.connections, c)
                close(c.send)
            }
        case m := <-h.broadcast:
            for c := range h.connections {
                select {
                case c.send <- m:
                default:
                    close(c.send)
                    delete(h.connections, c)
                }
            }
        }
    }
}

Why does it not just send to the c.send channel straight up in the last case like this?

case m := <-h.broadcast:
    for c := range h.connections {
        c.send <- m
    }

Answer 1

It's method of guaranted nonblocking send to channel. In case of c.send chan can't accept new messages now, a default branch will be executed. Without select{} block sending to unbuffered or fully filled buffered channel can be blocked.