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Introduction to node.js
- 1. There’s no sleep() in Javascript Introduction to node.js twitter.com/jacek_becela github.com/ncr
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- 3. node.js • Server-side Javascriptruntime • Google V8 • CommonJS modules
- 4. node.js • Server-side Javascriptruntime • Google V8 • CommonJS modules • API for highly concurrent programming • All I/O is non-blocking (asynchronous) • Achieved using Event Loop
- 5. Two approaches toI/O // blocking I/O + threads var urls = db.query("select * from urls"); // wait urls.each(function (url) { var page = http.get(url); // wait save(page); // wait }); // non-blocking I/O + event loop db.query("select * from urls", function (urls) { urls.each(function (url) { http.get(url, function (page) { save(page); }); }); });
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- 7. I/O Costs • L1:3 cycles http://nodejs.org/jsconf.pdf
- 8. I/O Costs • L1:3 cycles • L2: 14 cycles http://nodejs.org/jsconf.pdf
- 9. I/O Costs • L1:3 cycles • L2: 14 cycles • RAM: 250 cycles http://nodejs.org/jsconf.pdf
- 10. I/O Costs • L1:3 cycles • L2: 14 cycles • RAM: 250 cycles • DISK: 41,000,000 cycles http://nodejs.org/jsconf.pdf
- 11. I/O Costs • L1:3 cycles • L2: 14 cycles • RAM: 250 cycles • DISK: 41,000,000 cycles • NETWORK: 240,000,000 cycles http://nodejs.org/jsconf.pdf
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- 15. Why threads arebad • Hard to program
- 16. Why threads arebad • Hard to program • Shared state and locks
- 17. Why threads arebad • Hard to program • Shared state and locks • Deadlocks
- 18. Why threads arebad • Hard to program • Shared state and locks • Deadlocks • Giant locks decrease concurrency
- 19. Why threads arebad • Hard to program • Shared state and locks • Deadlocks • Giant locks decrease concurrency • Fine-grained locks increase complexity
- 20. Why threads arebad • Hard to program • Shared state and locks • Deadlocks • Giant locks decrease concurrency • Fine-grained locks increase complexity • Race conditions
- 21. Why threads arebad • Hard to program • Shared state and locks • Deadlocks • Giant locks decrease concurrency • Fine-grained locks increase complexity • Race conditions • Context switching costs
- 22. When threads aregood
- 23. When threads aregood • Support Multi-core CPUs
- 24. When threads aregood • Support Multi-core CPUs • CPU-heavy work
- 25. When threads aregood • Support Multi-core CPUs • CPU-heavy work • Little or no shared state
- 26. When threads aregood • Support Multi-core CPUs • CPU-heavy work • Little or no shared state • Threads count == CPU cores count
- 27. Event Loop userperspective • You already use it everyday for I/O • You register callbacks for events • Your callback is eventually fired $("a").click(function () { console.log("clicked!"); }); $.ajax(..., function (...) { console.log("internets!"); });
- 28. Event Loop lifecycle
- 29. Event Loop life cycle • Initialize empty event loop (just an array)
- 30. Event Loop life cycle • Initialize empty event loop (just an array) • Read and “execute” code
- 31. Event Loop life cycle • Initialize empty event loop (just an array) • Read and “execute” code • Execute non-I/O code
- 32. Event Loop life cycle • Initialize empty event loop (just an array) • Read and “execute” code • Execute non-I/O code • Add every I/O call to the event loop
- 33. Event Loop life cycle • Initialize empty event loop (just an array) • Read and “execute” code • Execute non-I/O code • Add every I/O call to the event loop • End of source code reached
- 34. Event Loop life cycle • Initialize empty event loop (just an array) • Read and “execute” code • Execute non-I/O code • Add every I/O call to the event loop • End of source code reached • Event loop starts iterating
- 35. Event Loop life cycle • Initialize empty event loop (just an array) • Read and “execute” code • Execute non-I/O code • Add every I/O call to the event loop • End of source code reached • Event loop starts iterating • All this happens in a single thread
- 36. Event Loop lifecycle
- 37. Event Loop life cycle • Iterate over a list of events and callbacks
- 38. Event Loop life cycle • Iterate over a list of events and callbacks • Perform I/O using non-blocking kernel facilities: epoll, kqueue, /dev/poll, select
- 39. Event Loop life cycle • Iterate over a list of events and callbacks • Perform I/O using non-blocking kernel facilities: epoll, kqueue, /dev/poll, select • Event Loop goes to sleep
- 40. Event Loop life cycle • Iterate over a list of events and callbacks • Perform I/O using non-blocking kernel facilities: epoll, kqueue, /dev/poll, select • Event Loop goes to sleep • Kernel notifies the Event Loop
- 41. Event Loop life cycle • Iterate over a list of events and callbacks • Perform I/O using non-blocking kernel facilities: epoll, kqueue, /dev/poll, select • Event Loop goes to sleep • Kernel notifies the Event Loop • Event Loop executes and removes a callback
- 42. Event Loop life cycle • Iterate over a list of events and callbacks • Perform I/O using non-blocking kernel facilities: epoll, kqueue, /dev/poll, select • Event Loop goes to sleep • Kernel notifies the Event Loop • Event Loop executes and removes a callback • Program exits when Event Loop is empty
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- 44. Event Loop limitations •Callbacks have to return fast
- 45. Event Loop limitations •Callbacks have to return fast • No CPU-heavy stuff
- 46. Event Loop limitations •Callbacks have to return fast • No CPU-heavy stuff • What about multi-core CPUs
- 47. Event Loop limitations •Callbacks have to return fast • No CPU-heavy stuff • What about multi-core CPUs • Web Workers using separate processes
- 48. Event Loop limitations •Callbacks have to return fast • No CPU-heavy stuff • What about multi-core CPUs • Web Workers using separate processes • Can do CPU-heavy stuff
- 49. Event Loop limitations •Callbacks have to return fast • No CPU-heavy stuff • What about multi-core CPUs • Web Workers using separate processes • Can do CPU-heavy stuff • No shared memory - no locks
- 50. Event Loop limitations •Callbacks have to return fast • No CPU-heavy stuff • What about multi-core CPUs • Web Workers using separate processes • Can do CPU-heavy stuff • No shared memory - no locks • Communication using message passing
- 51. Hello World var sys= require('sys'), http = require('http'); http.createServer(function (req, res) { setTimeout(function () { res.sendHeader(200, {'Content-Type': 'text/plain'}); res.write('Hello World'); res.close(); }, 2000); }).listen(8000); sys.puts('Server running at http://127.0.0.1:8000/');
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- 53. sleep() • It isa blocking call per definition
- 54. sleep() • It isa blocking call per definition • Browser JS has no blocking functions
- 55. sleep() • It isa blocking call per definition • Browser JS has no blocking functions • Except synchronous AJAX which is supposed to be used in “unload” event
- 56. sleep() • It isa blocking call per definition • Browser JS has no blocking functions • Except synchronous AJAX which is supposed to be used in “unload” event • You can emulate sleep() using a “while” loop and checking wall clock but what’s the point...
- 57. sleep() • It isa blocking call per definition • Browser JS has no blocking functions • Except synchronous AJAX which is supposed to be used in “unload” event • You can emulate sleep() using a “while” loop and checking wall clock but what’s the point... • The real reason: JavaScript exceution and Event Loop live in a single thread
- 58. Where to gonext • github.com/ry/node • groups.google.com/group/nodejs • howtonode.org • dailyjs.org • search twitter for node.js • github.com/ncr/flickr_spy
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