Realtime Web

pfleidi aka "der mit dem ..."

Realtime Web?

Well ... soft realtime

Hipster technology?

Nah. Fun stuff!

For teh lulz!

Instant updates!

Without having to reload websites!

Connecting users!

• Collaboration
• Chat
• Games
• Business (Monitoring)
• ...

Examples

• Google Docs
• Gmail
• Facebook Chat
• Etherpad
• WebGL Quake2 clone

Another example:
This presentation

http://roothausen.de:8080/

Join the party ...

Demo chat

Client side

Example: Realtime chat

Ajax polling

function ajaxCall() {
  $.get('/newmessages', function onComplete(response) {
    addNewMessagesToChat(response);
    // polling
    setTimeout(ajaxCall, 1000);
  }, 'json');
}
  

Comet

function cometCall() {
  // get new messages from server
  $.get('/newmessages', function (response) {
      // instantly make new call
      cometCall();
      addNewMessagesToChat(response);
    }, 'json');
};
  

Suboptimal ....

"But ... XHR works!"

Yes, but

• High latency
• Unidirectional communication
• Same-origin policy
• Overhead

Meh ... ;(

HTML5 to the rescue!

HTML5 WebSockets

• HTML5 draft
• Tunneled trough HTTP
• Event driven JS API
• Needs support on the server side

WebSockets API

var connection = new WebSocket(
      'ws://socket.host.tld/chat'
    );

connection.onmessage = function (message) {
  addNewMessagesToChat(message.data);
};

$('#sendbutton').click(function () {
    var text = $('#chatInput').val();
    connection.send("message: " + text);
});
  

Unified API?

What about graceful degradation?

Socket.io

var socket = new io.Socket(hostname, {
    port: port
});
socket.connect();

socket.on('message', function (message) {
  addNewMessageToChat(message);
});
  

Server side

Paradigm shift

• Good bye request/response paradigm
• Long living TCP connections
• Stateful interaction

Load pattern

High I/O and low CPU consumption

How do we scale?

Handling concurrency

• Event Loop
• Actor Model
• (Coroutines)
• (Threads/Processes)

[..] a folk definition of insanity is to do the same thing over and over again and to expect the results to be different. By this definition, we in fact require that programmers of multithreaded systems be insane.

-- The Problem with Threads, Edward A. Lee, UC Berkeley, 2006

Parallelism is not concurrency

The better solutions to this problem are lightweight and provide only high concurrency

Use the right tool

Frameworks

• Node.js (JS)
• Lift (Scala)
• Netty (Java/JVM)
• em-websocket (Ruby)
• SocketTornad.IO (Python)
• go-socket.io (Go)
• misultin (Erlang)

Opportunities

• Synchronisation
• New collaboration software
• Next generation of web based games
• Uniform Client/Server Models (MVC)

Questions?

Thank you!

Twitter

Github

My thesis