这是我的代码，我试图从谷歌酒吧子阅读消息

func (p *PubSubSource) Read(_ context.Context, readRequest sourcesdk.ReadRequest, messageCh chan<- sourcesdk.Message) {
    if len(p.messages) > 0 {
        return
    }
    log.Println("Request timeout", readRequest.TimeOut())
    ctx, cancelFunc := context.WithTimeout(context.Background(), readRequest.TimeOut())
    defer cancelFunc()
    cctx, cancel := context.WithCancel(ctx)
    receiveMesg := make(chan *pubsub.Message)
    p.subscription.ReceiveSettings.MaxOutstandingMessages = int(readRequest.Count())
    go p.subscription.Receive(cctx, func(_ context.Context, msg *pubsub.Message) {
        fmt.Printf("Got message------------------: %s\n", string(msg.Data))
        receiveMesg <- msg

    })
    for {
        select {
        case <-ctx.Done():
            log.Println("Timeout done ------------************************")
            cancel()
            return

        case msg := <-receiveMesg:
            log.Println("Executing Loop--------")

            p.lock.Lock()
            messageCh <- sourcesdk.NewMessage(
                msg.Data,
                sourcesdk.NewOffset([]byte(msg.ID), "0"),
                msg.PublishTime,
            )
            p.messages[msg.ID] = msg
            p.lock.Unlock()

        default:
            continue

        }

    }
}

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问题是case <-ctx.Done()：never gets executed，why？.我想在超时结束时退出父函数，但ctx.Done()从未被调用，我这样做对吗？有更好的方法来实现它吗？