4. node.js
• Server-side Javascript runtime
• Google V8
• CommonJS modules
• API for highly concurrent programming
• All I/O is non-blocking (asynchronous)
• Achieved using Event Loop
5. Two approaches to I/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);
});
});
});
16. Why threads are bad
• Hard to program
• Shared state and locks
17. Why threads are bad
• Hard to program
• Shared state and locks
• Deadlocks
18. Why threads are bad
• Hard to program
• Shared state and locks
• Deadlocks
• Giant locks decrease concurrency
19. Why threads are bad
• Hard to program
• Shared state and locks
• Deadlocks
• Giant locks decrease concurrency
• Fine-grained locks increase complexity
20. Why threads are bad
• Hard to program
• Shared state and locks
• Deadlocks
• Giant locks decrease concurrency
• Fine-grained locks increase complexity
• Race conditions
21. Why threads are bad
• Hard to program
• Shared state and locks
• Deadlocks
• Giant locks decrease concurrency
• Fine-grained locks increase complexity
• Race conditions
• Context switching costs
24. When threads are good
• Support Multi-core CPUs
• CPU-heavy work
25. When threads are good
• Support Multi-core CPUs
• CPU-heavy work
• Little or no shared state
26. When threads are good
• Support Multi-core CPUs
• CPU-heavy work
• Little or no shared state
• Threads count == CPU cores count
27. Event Loop
user perspective
• 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!");
});
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
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
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/');
54. sleep()
• It is a blocking call per definition
• Browser JS has no blocking functions
55. sleep()
• It is a 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 is a 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 is a 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 go next
• github.com/ry/node
• groups.google.com/group/nodejs
• howtonode.org
• dailyjs.org
• search twitter for node.js
• github.com/ncr/flickr_spy
