1. developers
Prashant Sridharan and Bear Douglas
github/coolasspuppy
github/beardouglas
@coolasspuppy
@beardigsit
Building Facebook’s Native Apps
Tuesday, May 7, 13

2. Agenda
▪ “Over the wall”: some history
▪ Product Teams and the Core Team
▪ Scheduling and Stabilizing Releases
▪ How We Develop
▪ Eating the Dogfood: Builds
▪ A Culture of Unit Testing
▪ Future of iOS at Facebook
Tuesday, May 7, 13

3. History
Tuesday, May 7, 13

4. Facebook for Mobile
▪ Web deeply engrained in Facebook’s DNA
▪ Use HTML5/Javascript within “wrapper” native app
▪ Developed our own framework for advanced integration
(image uploads, photo browsers, mixing native/web elements)
Tuesday, May 7, 13

5. HTML as an app platform
▪ What does it bring us?
One CodebaseInstant Updates A/B Testing
Tuesday, May 7, 13

6. HTML as an app platform
▪ Frequent performance problems
▪ No coherent multithreading strategy in web apps
▪ DOM manipulations and layout can spin out of control, lots of hacks
▪ Difficult memory management (<img>)
▪ Debugging and getting stack traces are extremely difficult
▪ Limited animations and effects
Tuesday, May 7, 13

7. A few good engineers
▪ Facebook for iOS 5.0 began as an experiment
▪ Could we achieve better results with native code?
▪ High barrier: rewrite all of Facebook’s mobile UI!
▪ Couldn’t disrupt company
▪ Move this to a war room!
Tuesday, May 7, 13

8. Winding Road
▪ Lots of changes along the way:
▪ Led to a rethink about how our APIs fetch data
▪ Experimented with advanced rendering to make feed smooth
▪ Sprinkle in some design changes
▪ Plenty of wrangling with Core Data and Core Animation
▪ Shipped internally starting in mid-2012
▪ Reaction: we liked it…
Tuesday, May 7, 13

9. Reaction
▪ Press loved it
▪ More importantly…
▪ Perceived Speed way up
▪ User Ratings way up
▪ 2x Speed increase!
Tuesday, May 7, 13

10. Team
Tuesday, May 7, 13

11. Scaling it Up
▪ We got it out the door, but…
▪ A few iOS engineers in a room won’t cut it
▪ Making Facebook a “mobile first” company
Tuesday, May 7, 13

12. Wake-up Call
▪ News Feed team invented phenomenal new story type
▪ … but they weren’t thinking about 5.0
▪ … and we didn’t know about News Feed developments
▪ Mad dash to port the story type to native code before 5.0
▪ Not an experience we wanted to repeat!
▪ Lots of cooperation required to keep abreast of product developments:
news feed, timeline, comments, photos, pages, places, events, …
Tuesday, May 7, 13

13. Prioritization and resources
▪ Every product wanted their features in the new native app
▪ Overwhelmed by prioritizing so many requests
▪ iOS Team still had very limited resources
Tuesday, May 7, 13

14. A multi-app ecosystem
Tuesday, May 7, 13

15. The Team Sandwich
Release Team: Release & Stabilization ProcessRelease Team: Release & Stabilization ProcessRelease Team: Release & Stabilization ProcessRelease Team: Release & Stabilization ProcessRelease Team: Release & Stabilization Process
Photos Feed Search Places Messages
Core Team: Shared LibrariesCore Team: Shared LibrariesCore Team: Shared Libraries
Tuesday, May 7, 13

16. Core Team: support and assist
▪ Build core, shared libraries
▪ Infrastructure and integration
▪ Keep the app fast and clean
Tuesday, May 7, 13

17. Product Cycle
Tuesday, May 7, 13

18. Timing Releases
▪ Simple model: Release X will have features A, B, C
▪ Next release at mercy of the slowest product team
▪ No choice but to wait until it’s “done”
▪ This slowed us down, and we want to move fast
Tuesday, May 7, 13

19. Fixed Release Cycle
▪ Ship an update every x weeks
▪ … no matter what
At Facebook we target a release every
4 weeks (approximately)
Tuesday, May 7, 13

20. Building features with an “off switch”
▪ Every feature must be built with a way to
turn it off
▪ If a feature destabilizes the build or isn’t
complete, turn it off and try again next
time
▪ #defines – or runtime switches
(preferred)
Tuesday, May 7, 13

21. Road to a new “Like Bar”
Tuesday, May 7, 13

22. Development
Tuesday, May 7, 13

23. Process
▪ Engineers make changes locally
▪ Submit changes for review
▪ Changes are automatically checked for build and unit test failures
▪ Team members review & suggest changes
▪ Once approved, submit to master
Tuesday, May 7, 13

24. Source Control: Git
▪ Distributed development
▪ Designed for speed
▪ Open source
▪ Optimized for non-linear development
▪ Allows local branching
Tuesday, May 7, 13

25. Phabricator
Text
Tuesday, May 7, 13

26. Arcanist
▪ The command line counterpart to Phabricator
▪ arc lint
▪ Checks for common errors:
▪ Null pointers
▪ Syntax errors and style guideline violations
▪ Using APIs unavailable in all supported Android versions
▪ arc land
▪ Pushes code into the tree
Tuesday, May 7, 13

27. Buildbot
Tuesday, May 7, 13

28. Builds
Tuesday, May 7, 13

29. Downloading builds
▪ Deployed to entire company
▪ Signed with Enterprise Distribution profile
▪ Daily builds posted to internal web site
▪ Installed directly on device
▪ Use different Bundle IDs for different builds
Tuesday, May 7, 13

30. Tuesday, May 7, 13

31. Rage Shake
▪ Take out your stress on the device
▪ Captures:
▪ Screen shot (with annotations!)
▪ Network logs
▪ Last crash log
▪ Last x-seconds of logging
▪ Dumps the view hierarchy
▪ Automatically files a bug and sends it to Facebook
Tuesday, May 7, 13

32. Branching
▪ Two concurrent branches:
▪ Master
▪ Engineers make progress on future features
▪ All changes checked in here first
▪ …including bug fixes for Releases
▪ Release
▪ Once verified in Master…
▪ …“Release team” pulls them into Release branch
Tuesday, May 7, 13

33. Testing
Tuesday, May 7, 13

34. Testing is important to Facebook
▪ Not in Facebook’s culture:
▪ SDEs “in Test”
▪ Large QA departments
▪ Definitely in Facebook culture:
▪ High quality, reliable user experience
▪ We believe in developer-authored unit tests
Tuesday, May 7, 13

35. http://github.com/facebook/xctool
xctool
Tuesday, May 7, 13

36. Unit Testing on iOS
▪ Some built-in Xcode support:
▪ OCMock & SenTestingKit
▪ Uses dynamic nature of Objective-C
▪ Easy to set-up, and well documented
▪ BUT
▪ Many iOS engineers unfamiliar with testing
▪ Frameworks are immature
▪ Incomplete support in xcodebuild
▪ Doesn’t understand “Test” action in your Schemes
▪ Can’t run tests that require Simulator
Tuesday, May 7, 13

37. xctool
▪ Replacement for ‘xcodebuild’
▪ Runs Simulator tests
▪ Structured output
▪ Phabricator support built-in
▪ Customizable to other build systems
Tuesday, May 7, 13

38. Tuesday, May 7, 13

39. Tuesday, May 7, 13

40. http://github.com/facebook/buck
Buck
Tuesday, May 7, 13

41. We needed a better tool
▪ Minimal overhead in creating a module
▪ Keep boilerplate out of the codebase
▪ IDE friendly
▪ Faster clean builds
▪ Faster incremental builds
▪ Support ad-hoc build steps
Tuesday, May 7, 13

42. Buck: an Android build system
▪ build rule procedure for producing output files from input files
▪ build file file (named BUCK) where build rules are declared
▪ build target string identifier for a build rule
Tuesday, May 7, 13

43. Build Target
//java/com/facebook/share:ui
Root of the repository
Directory where the build file can be found
Name of the build rule
Tuesday, May 7, 13

44. Build Rule
android_library(
name = 'ui',
srcs = glob(['**/*.java']),
deps = [
'//android_res/com/facebook/share:res',
'//java/com/facebook/base:base',
'//third-party/java/guava:guava',
],
visibility = [ 'PUBLIC' ],
)
Tuesday, May 7, 13

45. Build File: Rules and Macros
Tuesday, May 7, 13

46. Dependency Graph
AR AR
AR
AL
AL AL
AL AL
AL
AB
GR
AB
GR
Tuesday, May 7, 13

47. Dependency Graph
AR AR
AR
AL
AL AL
AL AL
AL
AB
GR
AB
GR
Tuesday, May 7, 13

48. How does IntelliJ feel about all of this?
buck project FTW!
Tuesday, May 7, 13

49. Focus on Speed
▪ Parallel builds
▪ Unit tests take 4 minutes instead of 20 by using 8 threads
▪ Incremental
▪ Only rebuild what is necessary
Tuesday, May 7, 13

50. Migration: August 2012
Ant
Buck
3m40s
1m30s
Tuesday, May 7, 13

51. http://github.com/facebook/xctool
Now open source:
xctool and Buck
http://github.com/facebook/buck
Tuesday, May 7, 13

52. Future of Mobile @ Facebook
Tuesday, May 7, 13