Comet Overview
Brian Moschel
Jupiter IT

Overview
Why Comet How It Showcase
Jabbify Demo
Comet? Overview Works

Why Comet?
• Web 2.0 Trends
1. Time Spent on a Page

Why Comet?
• Web 2.0 Trends
2. Half life of a Page’s Content

Why Comet?
• Demand for Comet is growing
• Desktop apps moving to the web
• Chat
• Real time updates
• Don’t like to reload
• Ajax:2003::Comet:2009

Uses
• Multi user collaboration apps
– Wiki
– Presentation
• Communication
– Chat
• Preventing stale data
– Stock ticker
– Social web updates
• Others?

Polling vs. Comet
Polling
Server
Are we Are we Are we
No No No
There yet? There yet? There yet?
Client
Comet Long Polling
Server
Wait for data
Wait for data
Client

How Comet Works: Client Side
• Long Poll
– How?
• XHR, JSONP, or any transport, with connection held open
– Pro
• It works cross browser
– Con
• More overhead
• Forever Frame
– How?
• Iframe
• Multipart XHR
– Pro
• Less overhead, quicker responses
– Con
• Lack of error handling, not cross browser

Client Side Issues
• Cross Browser
– Duh
• 2 Connection Limit
– Use wildcard DNS
– Xxx.mywebsite.com -> mywebsite.com
• Synchronous request s (for JSONP)
– Long poll has to close to allow other requests to
process

How Comet Works: Server Side
• Simultaneous connections
– Traditional servers can’t scale
– A thread shared multiple connections
• Wake up when you’re ready to send data

How Comet Works: Server Side
• Python
– Orbited
– Cometd
• Java
– Jetty
• Erlang
– ErlyComet
• .NET
– Lightstreamer
• Service
– Jabbify

Server Side Issues
• Scaling
– Every user = 1 connection
• Complexity
– Threading
– Learning Curve

What is Jabbify?
• Comet, simplified
• No server
• No setup
• JavaScript API and GET requests

Why Jabbify?
Simple to use
Scale easily
Rapid setup

Simple to use
synchronized (_continuations) {
for(Iterator<Map.Entry <String, ArrayList<Continuation>>> iter =
_continuations.entrySet().iterator(); iter.hasNext();){
Map.Entry<String, ArrayList<Continuation>> entry = iter.next();
ArrayList<Continuation> continuations = entry.getValue();
for(Continuation c : continuations){
c.resume();
}
}
_continuations.clear();
}
vs
Jabbify.connect({name: this.username}, this.continue_to('after_connect'))
after_connect: function(){
Jabbify.send('vote','submit', {result: this.result})
}

Scale easily
• Scaling comet >> Scaling traditional web
applications
• Resource intensive
• Jabbify is built to scale as usage grows

Rapid Setup
<New id=\"cf\" class=\"org.mortbay.jetty.plus.naming.Resource\">
<Arg>jms/connectionFactory</Arg>
<Arg>
<New class=\"org.apache.activemq.ActiveMQConnectionFactory\">
<Arg>failover:(tcp://localhost:61616)?initialReconnectDelay=20&amp;maxReconnectDe
lay=900</Arg>
</New>
</Arg>
</New>
vs
<script language=\"javascript\" type=\"text/javascript\" src=\"jabbify.js\"></script>

Comet is complex
• Client
– Transports (JSONP, Window.name, Flash, XHR, iframe)
• Server
– Special server
– Setup time
– Learning curve
• Scaling
– Resource consumption
– Threading issues

Jabbify is simple
• Client to Client Comet
– JavaScript API
• Jabbify.send(“message”,”create”,{message: “hi there”});
• Server to Client Comet
– GET requests
• https://jabbify.com/message_push?key=123&type=message...

How It Works

Demo

Take Home Points
Comet is coming
Jabbify = easy Comet

Showcase
• Jabbify Simple Chat Client
• Keyboard Demo
• Chat.unwrongest.com