在 socket.io 中每秒发射一次不起作用

Question

I have a node.js server, on which a socket.io is supposed to emit something every second. But at the client side, the clients get the data more than every 30 seconds. Anybody has any idea why this is happening and what's the solution?

var redis = require("redis"),
    client = redis.createClient();    
const nsp_page=io.of('/myPage');

nsp_page.on('connection', function(socket){
    (function update_index() {
            client.get('boxIndex', function (err, data) {
                socket.emit('boxIndex',data);
            });
        setTimeout(update_index,1000);
    })();
});

Thanks

Answer 1

But at the client side, the clients get the data more than every 30 seconds. Anybody has any idea why this is happening and what's the solution?

Because your code sends the data every second. This line of code:

setTimeout(update_index,1000);

Causes it to call udpate_index() every second, not every 30 seconds. If you want it to update every 30 seconds, you would change that to this:

setTimeout(update_index, 30 * 1000);

---

But, note that the way your code works is very inefficient because you're calling the exact same client.get() for every single connected client. That's really inefficient. It would make more sense to call client.get() once and then broadcast that data to every connected client:

const redis = require("redis");
const client = redis.createClient();    
const nsp_page = io.of('/myPage');

setInterval(() => {
    client.get('boxIndex', function (err, data) {
        if (err) {
            console.log("boxIndex not found", err);
        } else {
            // send to all connected clients
            nsp_page.emit('boxIndex', data);
        }
    });
}, 30 * 1000)

When you have lots of connected clients, this will do only one query of your redis database every 30 seconds and use that result for all clients instead of calling redis separately for every single connected client.