PHP Socket Server vs node.js: Web Chat

Question

I want to program a HTTP WebChat using long-held HTTP requests (Comet), ajax and websockets (depending on the browser used). Userdatabase is in mysql. Chat is written in PHP except maybe the chat stream itself which could also be written in javascript (node.js):

I don't want to start a php process per user as there is no good way to send the chat messages between these php childs. So I thought about writing an own socket server in either PHP or node.js which should be able to handle more then 1000 connections (chat users). As a purely web developer (php) I'm not much familiar with sockets as I usually let web server care about connections. The chat messages won't be saved on disk nor in mysql but in RAM as an array or object for best speed.

As far as I know there is no way to handle multiple connections at the same time in a single php process (socket server), however you can accept a great amount of socket connections and process them successive in a loop (read and write; incoming message -> write to all socket connections). The problem is that there will most-likely be a lag with ~1000 users and mysql operations could slow the whole thing down which will then affect all users.

My question is: Can node.js handle a socket server with better performance? Node.js is event-based but I'm not sure if it can process multiple events at the same time (wouldn't that need multi-threading?) or if there is just an event queue. With an event queue it would be just like php: process user after user.

I could also spawn a php process per chat room (much less users) but afaik there are singlethreaded IRC servers which are also capable to handle thousands of users. (written in c++ or whatever) so maybe it's also possible in php.

I would prefer PHP over Node.js because then the project would be php-only and not a mixture of programming languages. However if Node can process connections simultaneously I'd probably choose it.

Answer 1

JavaScript, or in this case V8 which is the engine that Node is using, is by design single threaded. So yes there's just an event queue.

But in the end, that's not a problem, something's always gonna happen first, unless you're using multiple processors, and even then, you will most likely only have one network card... one router... you get the idea. Also, using 1000+ threads... not a good idea, scales badly, and you will find yourself in a concurrency HELL.

1000 chat users, that will be no problem at all for Node.js.

I can give you a pretty basic idea how you would set it up, this plain vanilla chat thingy works over telnet, it has.. no features, but it works:

var net = require('net'); // require the net module

var users = []; // keep track of the users

// setup a new tcp socket server
net.createServer(function(socket) { // provide a callback in case a new connection gets
                                    // established, socket is the socket object

    // keep track of this users names, via use of closures
    var name = '';

    // ask the new user for a name
    socket.write('Enter a Name(max 12 chars): ');

    // register a callback on the socket for the case of incoming data
    socket.on('data', function(buffer) { // buffer is a Buffer object containing the data
        if (name !== '') {  // in case this user has a name...

            // send out his message to all the other users...
            for(var i = 0; i < users.length; i++) {
                if (users[i] !== socket) { // ...but himself
                    users[i].write(name + ': '
                                   + buffer.toString('ascii').trim()
                                   + '\r\n');
                }
            }

        // otherwise take the data and use that as a name
        } else {
            name = buffer.toString('ascii').substring(0, 12).trim().replace(/\s/g, '_');
            socket.write('> You have joined as ' + name + '\r\n');

            // push this socket to the user list
            users.push(socket);
            for(var i = 0; i < users.length; i++) {
                if (users[i] !== socket) {
                    users[i].write('> ' + name + ' has joined' + '\r\n');
                }
            }
        }
    });

    // another callback for removing the user aka socket from the list
    socket.on('end', function() {
        users.splice(users.indexOf(socket), 1);
    });

// bind the server to port 8000
}).listen(8000);

There's no magic involved in here (besides the use of a closures), you don't have to do with raw socket programming and you won't have any concurrency problems. And you learn some of the latest hotness ;)

I recommend that you watch some of the talks that are listed on our Node.js tag wiki, to get a better grasp of how Node.js works.