This document discusses server-side event-driven programming using Node.js. It covers how Node.js uses an event loop and asynchronous non-blocking I/O to handle many connections concurrently with high performance. Common Node.js concepts are explained like first-class functions, callbacks, and event emitters. Node.js is compared to traditional threaded programming and shown to have advantages in scalability and efficiency. Example Node.js applications and APIs are provided.

1. Emerging Paradigms -
Server Side Event Driven
Programming
Kamal Hussain
http://www.linkedin.com/in/hussainkamal/

2. Agenda
● Linear Vs Nonlinear Code
● Concurrency through threads and events
● Event loop
● PHP and Javascript
● Node.js - closeup
● Important concepts

3. We are used to ..
val client = new HttpClient()
val method = new GetMethod("http:
//www.google.com")
val statusCode = client.executeMethod
(method)
println("Server responded with %d" .
format(statusCode))

4. Event driven approach
var callback = function(data) {
console.log("firing callback " +
data);
};
$.get('/endpoint', callback);
console.log('Did you see callback?');

5. Achieving scale and concurrency
● Multiple threads/processes
● Size the threadpool correctly
● Each thread is responsible for one task such
as serving a request
● Asynchronous programming

6. Asynchronous with
threads/processes

7. Asynchronous with events

8. Problems with Threads
● Hard to program
● Memory requirements are high
● Large overhead
● Context switching
● Priority inversion

9. Threads wait
udemy.com

10. Cost of IO
L1 Cache 3 Cycles
L2 Cache 14 Cycles
RAM 250 cycles
Disk 41 000 000 cycles
Network 240 000 000 cycles

12. Event Loop Architecture
courtsey: http://www.johanndutoit.net/

13. Writing synchronous Vs
Asynchronous
// Good: write files asynchronously
fs.writeFile('message.txt', 'Hello Node', function (err) {
console.log("It's saved and the server remains responsive!");
});
// BAD: write files synchronously
fs.writeFileSync('message.txt', 'Hello Node');
console.log("It's saved, but you just blocked ALL requests!");
This can cause performance drop from thousands of requests/seconds to a few
dozen/second.
http://engineering.linkedin.com/nodejs/blazing-fast-nodejs-10-performance-tips-
linkedin-mobile

14. Tale of two languages
● PHP was invented in 1994 by Rasmus
Lerdorfas as a replacement for CGI scripts
● PHP was a substitute for single-threaded C
programs
● Brendan Eich developed Javascript in 1995
for a completely different purpose. JS was
designed to run within Netscape Navigator
and was primarily designed to handle
events.
PHP -> eventless, Javascript -> eventful

15. Node.js
● Ryan Dahl invented Node.js in 2009 as a
continuation of Javascript heritage.
● Node.js is modeled after multi-task, multi-
page handling of a web server.

16. What's Node.js?
"Node.js is a server-side software system designed for
writing scalable Internet applications, notably web servers.
Programs are written on the server side in JavaScript,
using event-driven, asynchronous I/O to minimize overhead
and maximize scalability."
- from wikipedia

17. Node.js - asynchronous I/O
● First class functions
● Closures
● Event loop
● Callback counters
CPU intensive tasks are delegated to workers

18. PHP Way
$fp = fopen("fp.txt", 'w)
fwrite($fp, "hello world");
fclose($fp);

19. Node.js way
var fs = require('fs');
fs.open('fp.txt', 'w', 0666,
function(error, fp) {
fw.write(fp, 'helloworld', null,
'utf-8', function() {
fs.close(fp, function(error) {
});
});
});

20. Node.js simple example
var http = require('http');
http.createServer(function(req, res) {
res.writeHead(200, {'Content-Type' :
'text/plain'});
res.end("Hello Worldn");
}).listen(8000, "127.0.0.1");
console.log("Server running at http:
//127.0.0.1:8000");

21. Node.js Core APIs
Events
EventTransmitter
Event listener
Event emitter
Call back
Http
I/O

22. Node.js Workers
Synchronous call
Workers are blocked
Call returns

23. Workers Vs Events
Workers
1 event per connection
N workers per CPU
Events
N connections per CPU
1 process per CPU

24. Node.js Typical Applications
● Proxy
● API server
○ REST API calls
○ Simple transformations
See performance comparisons at:
http://www.slideshare.net/FabianFrankDe/nodejs-performance-case-study

25. Concepts to learn
First class functions
Lambdas - anonymous functions
Closures
Non-blocking IO

26. Deploying Node.js
http://www.slideshare.net/BenLin2/webconf-nodejsproductionarchitecture

27. Key takeaway
Learn Javascript and
functional programming.
Future is brighter :)

28. Reference
● Node - Up and Running by Tom Hughes-Croucher,
Mike Wilson - Oreilly
● Node.js for PHP Developers - Oreilly
● Javascript: The definitive guide - Oreilly
● LinkedIn, Netflix Blogs
● http://architects.dzone.com/articles/nodejs-php-
programmers-1-event
● https://www.udemy.com/lectures/understanding-the-
nodejs-event-loop-91298
● https://speakerdeck.com/guldenpt/before-start-coding-
in-node-dot-js