Server Side Event Driven Programming

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

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

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))

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

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

Asynchronous with threads/processes

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

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

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

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

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

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.

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

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

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

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) { }); }); });

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");

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

Node.js Workers Synchronous call Workers are blocked Call returns

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

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

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

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

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

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

Server Side Event Driven Programming

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