JavaScript Event Loop

1. JavaScript Event Loop • Not yo mama’s multithreaded approach. • slidesha.re/ZPC2nD

2. Who is Thomas Hunter? • Web developer for 8+ years • Dow, Ford, Quicken, Startup, Barracuda • Started development with PHP & MySQL • Became a Node.js fanboy • Writing a book on Backbone.js for Packt • @tlhunter | me@thomashunter.name

3. What does MultiThreaded mean? • Makes use of separate CPU Cores as “Threads” • Uses a single process within the Operating System • True concurrency • Can have Race Conditions (simultaneous memory use) • “Hard” to get it right • Ran out of Ghz, hardware adds more cores

4. JavaScript is SingleThreaded • Makes use of a single CPU core • CPU intensive work is never “concurrent” • Easier to pull off, as in less technical difficulties

5. Technical Implementation • Stack: • Functions to run and available variables • More added as code is run • Stuff guaranteed to run in order • Heap: • “Chaotic” listing of objects • Queue: • Gets added to stack when stack empty • setTimeout and setInterval added here Credit: Mozilla Developer Network http://mzl.la/Y5Dh2x

6. Example Code-run • console.log("Adding code to the queue"); • setTimeout(function() {// Added somewhere in Heap • console.log("Running next code from queue"); • }, 0); • function a(x) { // Added somewhere in Heap • console.log("a() frame added to stack"); • b(x); • console.log("a() frame removed from stack"); • } • function b(y) { // Added somewhere in Heap • console.log("b() frame added to stack"); • console.log("Value passed in is " + y); • console.log("b() frame removed from stack"); • } • console.log("Starting work for this stack"); • a(42); • console.log("Ending work for this stack"); Adding code to the queue Starting work for this stacka() frame added to stackb() frame added to stackValue passed in is 42b() frame removed from stacka() frame removed from stackEnding work for this stackRunning next code from queue

7. Your App is Mostly Asleep • Node.js: All I/O is non-blocking • E.g. it gets thrown into the Queue • Browser: Wait for a click to happen • PHP: Wait for a MySQL query to run • These show how slow I/O can be → L1-Cache 3 cyclesL2-Cache 14 cyclesRAM 250 cyclesDisk 41,000,000 Network 240,000,000

8. Sequential vs Parallel • Traditional web apps perform each I/O Sequentially • With an Event Loop, they can be run in Parallel • Since most time is wasted doing I/O, very inefficient

9. Non JS Event Loops • Event Loops can be implemented in other languages • However, JavaScript was built this way, feels “natural” • Examples: • Ruby: EventMachine • Python: Twisted & Tornado • PHP: ReactPHP

10. !JS Event Loop Examples EventMachine in Ruby Node.js • require 'eventmachine' • module Echo • def post_init • puts "Someone Connected" • end • def receive_data data • send_data "#{data}" • close_connection if data =~ /quit/if • end • end • EventMachine.run { • EventMachine.start_server "127.0.0.1", 8081, Echo • } var net = require('net'); var server = net.createServer(function (socket){ console.log('Someone Connected'); socket.pipe(socket); }); server.listen(1337,'127.0.0.1');

11. Event Loops are Awesome! • No race conditions • Typical web apps spend their time waiting on I/O • No funky syntax; it just works • Perform I/O operations “in parallel” easily • Stateful web applications are easy compared to PHP • Long run apps, don’t need web servers, shared data...

12. Event Loops aren’t Awesome! • CPU intensive work will block your process • You can offload work to different processes (Node.js) • It isn’t making use of those 8 cores you’ve got • You can use the Multi-node module though (Node.js) • Memory leaks are possible, not so with PHP • You can program better and prevent it though ;-)

13. Web Workers • You can use MultiThreaded JavaScript in your browser • IE10, Firefox 3.5, Chrome 4, Safari 4, Opera 10.6 • var worker = newWorker('task.js'); • Use Message Passing to share data • You share simple JSON data, not complex objects • Prevents deadlocks/race conditions because of this

14. Conclusion • Great for I/O bound applications (most web apps) • Horrible for CPU bound applications (do it in C ;) • Appears to be a single multi-threaded process • “Fakes” concurrency • thomashunter.name @tlhunter slidesha.re/ZPC2nD