Event Driven Architecture

Have you ever wondered what ReactPHP/NodeJs meant by "non blocking I/O"? Or why would being "event-driven" allow nginx to be more efficient than Apache?

If you find it easier to understand abstract concepts like these by implementing them, then you're in luck because in this talk we'll create a simple HTTP server, then develop an event loop and finally create a simple Promise class.

Transcript

1. Event Driven Architecture Understanding Event Loops and the point of async Loïc Faugeron http://constant.co @epiloic
2. Robert C. Martin - https://blog.8thlight.com/uncle-bob/2015/08/06/let-the-magic-die.html “If you’ve ever written a web server, then the magic is gone” @epiloic
3. 1. HTTP Server 2. Event Loop 3. Scheduling 4. Promise 5. Thread Pool
4. 1. A story of Input / Output Also known as “I/O”
5. What is “I/O”? Server / Client communication via sockets 5 @epiloic
6. Example: HTTP Server 6 @epiloic
7. Creating a socket 7 @epiloic
8. 8 @epiloic Caution! When the queue is full... Picture: Nick Webb (CC BY 2.0 - https://flic.kr/p/5AykUp)
9. Looping to infinite and beyond 9 @epiloic
10. Creating dedicated sockets for clients 10 @epiloic
11. 11 @epiloic Unqueueing To avoid... Picture: Nick Webb (CC BY 2.0 - https://flic.kr/p/5AykUp)
12. Waiting for data to be received… 12 @epiloic
13. I/O is slow Think about latency See https://gist.github.com/jboner/2841832#file-latency-txt
14. 14 @epiloic Meanwhile More queueing Picture: Nick Webb (CC BY 2.0 - https://flic.kr/p/5AykUp)
15. HTTP application 15 @epiloic
16. Waiting for data to be sent… 16 @epiloic
17. I/O is really slow And unreliable See https://gist.github.com/jboner/2841832#file-latency-txt
18. 18 @epiloic Meantime More queueing Picture: Nick Webb (CC BY 2.0 - https://flic.kr/p/5AykUp)
19. Saying goodbye to the client 19 @epiloic
20. Queue System Handles ~100 clients Picture: lorenz.markus97 (CC BY 2.0 - https://flic.kr/p/szWiqL)
21. Handling 10 000 clients? If only we could do something else while waiting... 21 @epiloic See the C10K problem: http://www.kegel.com/c10k.html by Dan Kegel
22. 2. Hang on! ready = poll(to_watch) Did you see what I did there?
23. Many implementations select, poll, epoll, kqueue, IOCP 23 @epiloic See epoll VS kqueue: http://www.eecs.berkeley.edu/~sangjin/2012/12/21/epoll-vs-kqueue.html by Sangjin Han
24. Example: HTTP Server 24 @epiloic
25. Collecting sockets to watch 25 @epiloic
26. Waiting for sockets to be ready 26 @epiloic
27. HTTP server socket is ready 27 @epiloic
28. Collecting more sockets to watch 28 @epiloic
29. HTTP client socket is ready 29 @epiloic
30. No longer watching closed sockets 30 @epiloic
31. Receiving events in a loop That’s an Event Loop! 31 @epiloic
32. Refactoring Event Loop 32 @epiloic
33. No distinctions between sockets 33 @epiloic
34. Injecting Event Loop in callbacks 34 @epiloic
35. Allows decoupled code Put Server / Client logic in callbacks 35 @epiloic
36. Event Loop usage 36 @epiloic
37. Adding server socket to Event Loop 37 @epiloic
38. Handling new client connections 38 @epiloic
39. Handling received data 39 @epiloic
40. Efficient Queue Using blocking time Picture: Sean McEntee (CC BY 2.0 - https://flic.kr/p/a7zKqg)
41. “Blocking, If it’s not solving all your problems, You simply aren’t using enough of it.” 41 @epiloic
42. Handling 0 clients? If only we could do something else while waiting... 42 @epiloic
43. 3. Wait a second! poll(to_watch, timeout) Did you see what I did there?
44. Schedulers One off, periodic, idle, etc... 44 @epiloic
45. Example: One off Scheduler 45 @epiloic
46. Adding timer callbacks 46 @epiloic
47. Checking if any timers are due 47 @epiloic
48. Calling due timers’ callbacks 48 @epiloic
49. Removing one off timers afterwards 49 @epiloic
50. Scheduled Event Loop 50 @epiloic
51. Setting a smart timeout 51 @epiloic
52. Ticking the clock 52 @epiloic
53. Efficient Queue Using waiting time Picture: fdecomite (CC BY 2.0 - https://flic.kr/p/BW7Hh)
54. “Waiting, If it’s not solving all your problems, You simply aren’t using enough of it.” 54 @epiloic
55. Nesting more callbacks? If only we could make async code feel more sync... 55 @epiloic
56. 4. Async what you did there... No more puns, I promise
57. Futures and promises Async functions return a value, register callbacks via this value 57 @epiloic
58. Example: Deferrer / Promise 58 @epiloic
59. Injecting Deferrer’s setter in Promise 59 @epiloic
60. Passing callback to Promise... 60 @epiloic
61. … Which sets it in the Deferrer 61 @epiloic
62. Resolving the Deferrer, calls callbacks 62 @epiloic
63. Chaining calls To make it feel sync Picture: Mark Skipper (CC BY 2.0 - https://flic.kr/p/4FQ8DU)
64. “Callback, If it’s not solving all your problems, You simply aren’t using enough of it.” 64 @epiloic
65. Usage example? If only we could have a usage example... 65 @epiloic
66. 5. Filesystem U/O More U/O (Uh Oh) than I/O
67. Slowest I/O? Filesystem See https://gist.github.com/jboner/2841832#file-latency-txt
68. Poor non-blocking support Cannot be used with poll() 68 @epiloic See asynchronous disk I/O: http://blog.libtorrent.org/2012/10/asynchronous-disk-io/ by Arvid Norberg
69. Solution? Use the force a Thread Pool 69 @epiloic
70. Non Blocking Filesystem 70 @epiloic
71. Deferring FS call to Thread Pool 71 @epiloic
72. Calling callbacks, once thread is done 72 @epiloic
73. Blocking I/O Wrapped, in Threads Picture: Jamie (CC BY 2.0 - https://flic.kr/p/9Av7cj)
74. “Threading, If it’s not solving all your problems, You simply aren’t using enough of it.” 74 @epiloic
75. “Threading, If it’s not solving all your problems, You simply aren’t using enough of it.” 75 @epiloic NOT! Limits are good
76. 76 @epiloic Infinite pool Error cause: Filesystem limit Picture: Nick Webb (CC BY 2.0 - https://flic.kr/p/5AykUp)
77. 77 @epiloic Infinite limit Error cause: HDD/SSD burned Picture: Nick Webb (CC BY 2.0 - https://flic.kr/p/5AykUp)
78. True story Usually pool of 4 threads 78 @epiloic See ReactPHP filesystem - a word of caution: https://blog.wyrihaximus.net/2015/03/reactphp-filesystem/#a-word-of-caution by Cees-Jan Kiewiet
79. ConclusI/On
80. Making use of waiting time, to handle more clients 80 @epiloic Non blocking Idle Sync Feeling Blocking Event Loop Scheduling Promise Thread Pool
81. 81 @epiloic Used by... nginx See how it outperforms Apache: https://www.nginx.com/blog/nginx-vs-apache-our-view/ Picture: Thijs Feryn (https://speakerdeck.com/thijsferyn/varnish-or-nginx-symfony-live)
82. 82 @epiloic Used by... Libuv (Node.js) Node.js is a trademark of Joyent, Inc. and is used with its permission. We are not endorsed by or affiliated with Joyent. See an Introduction to libuv: https://nikhilm.github.io/uvbook/introduction.html by Nikhil Marathe
83. 83 @epiloic Used by… You?
84. Thank you 84 @epiloic Transcript of this presentation, in a blog article: https://gnugat.github.io/2016/04/27/event-driven-architecture.html