How Open Source Powers Facebook on Android

The Facebook application on Android is a terrifically complicated beast, compiled from a large codebase developed by hundreds of software engineers. Despite this, a new alpha release that we’re pretty sure is solid is pushed three times a week. We’d not be able to go this fast, or scale our development team this effectively, without using large amounts of OSS.

In this talk, I’ll discuss the Open Source tools that help us build Facebook for Android, how we contribute technology to OSS, and how we do our best to be good citizens in the broader OSS world. I’ll do this by looking at the full life cycle of a release, going from how we organize our git repo, do code reviews in phabricator, through building using tools such as Buck, to how we’ve improved the quality of our releases using OSS testing tools such as Selendroid.

Transcript

1. How Open Source Powers Facebook on Android SIMON STEWART (@shs96c) Software Engineer, London
2. Facebook and OSS Over 200 repositories on GitHub 13k commits in the first 6 months of 2014 9.9M lines of code React, Shimmer, Pop, KVOController, HHVM, Hack, Presto, Warp, Haxl, and so many more…. ! Personal Story: Almost every line of code I’ve written at Facebook has been Open Sourced.
3. I’m here to talk about Android
4. The Things You May Already Know Facebook on Android is a native application Facebook on Android is worked on by 100s of engineers Facebook on Android is released every 4 weeks Facebook on mobile is used by 1 Billion Monthly Active Users
5. Building Facebook
6. AR AR AR AL AL AL AB GR AB GR AL AL AL Buck
7. Buck Smarts 1 Build rule knows all of the inputs that can affect its output 2 Changes to dx and proguard for faster compilation 3 Java ABI smarts 4 Android resource smarts 5 Daemon to watch file changes and kick off builds
8. Exopackage Exopackage is an optimization for building and installing development builds of Android apps.
9. Exopackage http://facebook.github.io/buck/article/exopackage.html Gradle Buck Speed Up Clean build 33 6 5.5 x Incremental build 17 1.7 10 x No-op build 6 0.2 30 x
10. Caching in Buck 3% 97% repeated build work unique build work
11. Android’s Evolution Gingerbread Larger displays, WebM support, better native code development Honeycomb New “Look and Feel”, Action and System bars introduced, hardware acceleration, multicore support, tweaks to SD Card access Ice Cream Sandwich UI refresh, more hardware acceleration JellyBean “Project Butter”, lock screen improvements, RTL languages now supported KitKat UI refresh, Chromium WebViews, API for messaging and storage “L” ART enabled by default, “Material Design”
13. Origami
15. Rebound public SpringExample() {
 ...
 springSystem = new SpringSystem();
 spring = springSystem
 .createSpring()
 .setSpringConfigConfig(DEFAULT_TRANSITION_SPRING)
 .addListener(transitionSpringListener);
 }
 public void toggleSpring() {
 double value = spring.getEndValue();
 spring.setEndValue(value == 0 ? 1 : 0);
 }
16. Rebound private class TransitionSpringListener extends SimpleSpringListener { 
 @Override
 public void onSpringUpdate(Spring spring) {
 // map the spring function to desired view properties
 float value = (float) spring.getValue();
 float scale = SpringUtil.mapValueFromRangeToRange(value, 0, 1, 0.75, 1);
 
 // update the views
 photoView.setScaleX(scale);
 photoView.setScaleY(scale);
 } 
 }
17. https://facebook.github.io/conceal/ https://flic.kr/p/29KvKK Conceal: Fast Cryptography
18. Source Control & Code Review Testing Releasing
19. Source Control ▪ A single tree ▪ Hundreds of thousands of files ▪ Millions of lines ▪ > 2 commits/day ▪ Original source control not scaling ▪ Moving to Mercurial ▪ Easy to extend
20. Mercurial Contributions ▪Contributed >1000 patches ▪Hosted the past 2 Mercurial sprints ▪Open Sourced ▪ hgwatchman ▪ remotefilelog
21. Watchman and Mercurial ▪Watchman quickly answers “Which files have changed?” status diff checkout commit hg hgwatchman
22. Large Repos Are Slow ▪Lots of commits a day ▪ Pulls are slow ▪ Checkouts are slow ▪Years of history ▪ Clones are slow ▪ Requires lots of disk space ▪Impacts developers and build infrastructure
23. remotefilelog to the Rescue! rebase (p75) pull (p90) clone hg remotefilelog
24. Phabricator
25. Phabricator: Image Macros
26. Source Control & Code Review Testing Releasing
27. Unit Integration End-to-end Manual Types of Tests
28. https://flic.kr/p/jaYTYe Unit Testing: JUnit and Robolectric
29. https://flic.kr/p/7TMfGf End to End: Selendroid
30. Build 
 Slave COMMANDS Build 
 Slave Build Master COMMANDS STATUS Repository • Subversion • Mercurial • Bazaar • Darcs • GIT • CVS CHANGES POLL Notifiers • Email • Web Status • IRC • Status Client Continuous Builds: Buildbot
31. Source Control & Code Review Testing Releasing
32. Android Release Process 4 weeks of development 4 weeks of development 3.5 weeks of stabilization RC Master Release branch
33. https://flic.kr/p/kAT3Ba “Manual” Testing: Dogfood, Alpha and Beta