Go Channel读写陷入无限循环

问题描述：

First of all, I want to make Long Polling notification system. To be more specific, I will make http request, and response will be returned only if map channel is true.

This is the code block I used:

var MessageNotification = make(map[string]chan bool, 10)

func GetNotification(id int, timestamp int) notification {
    <-MessageNotification["1"]

    var chat_services []*models.Chat_service
    o := orm.NewOrm()

    _, err := o.QueryTable("chat_service").Filter("Sender__id", id).RelatedSel().All(&chat_services)

    if err != nil {
        return notification{Status: false}
    }
    return notification{Status: true, MessageList: chat_services}
}

func SetNotification(id int) {
    MessageNotification[strconv.Itoa(id)] <- true
}

This is controller block :

func (c *ChatController) Notification() {

data := chat.GetNotification(1,0)

c.Data["json"] = data
c.ServeJSON()

  }


func (c *ChatController) Websocket(){


    chat.SetNotification(1)

    c.Data["json"] = "test"
    c.ServeJSON();

}

function names and variable created for test.

No error occurred. Thanks for your help.

答

You're not creating your channel.

var MessageNotification = make(map[string]chan bool, 10)

This line makes a map with capacity 10, but you're not creating the actual channels in the map. As a result, `SetNotification["1"] is a nil channel, and sends and receives on nil channels block indefinitely.

You need to put in

MessageNotification["1"] = make(chan bool)

You can include a size if desired (and I have a hunch your "10" in the map make was supposed to be the buffering for that channel). This can even be done conditionally:

func GetNotification(id int, timestamp int) notification {
    if _, ok := MessageNotification["1"]; !ok { // if map does not contain that key
        MessageNotification["1"] = make(chan bool, 10)
    }

    <-MessageNotification["1"]
    // ...
}

func SetNotification(id int) {
    if _, ok := MessageNotification[strconv.Itoa(id)]; !ok { // if map does not contain that key
        MessageNotification[strconv.Itoa(id)] = make(chan bool, 10)
    }

    MessageNotification[strconv.Itoa(id)] <- true
}

This way the first location that tries to access the channel adds it to the map and properly makes the channel, so sends and receives on it will actually function.

Go Channel读写陷入无限循环

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