How Open Source Powers Facebook on Android SIMON STEWART (@shs96c) Software Engineer, London 

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. 

I’m here to talk about Android 

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 

Building Facebook 

AR AR AR AL AL AL AB GR AB GR AL AL AL Buck 

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 

Exopackage Exopackage is an optimization for building and installing development builds of Android apps. 

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 

Caching in Buck 3% 97% repeated build work unique build work 

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” 

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Origami 

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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);
 } 

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);
 } 
 } 

https://facebook.github.io/conceal/ https://flic.kr/p/29KvKK Conceal: Fast Cryptography 

Source Control & Code Review Testing Releasing 

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 

Mercurial Contributions ▪Contributed >1000 patches ▪Hosted the past 2 Mercurial sprints ▪Open Sourced ▪ hgwatchman ▪ remotefilelog 

Watchman and Mercurial ▪Watchman quickly answers “Which files have changed?” status diff checkout commit hg hgwatchman 

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 

remotefilelog to the Rescue! rebase (p75) pull (p90) clone hg remotefilelog 

Phabricator 

Phabricator: Image Macros 

Source Control & Code Review Testing Releasing 

Unit Integration End-to-end Manual Types of Tests 

https://flic.kr/p/jaYTYe Unit Testing: JUnit and Robolectric 

https://flic.kr/p/7TMfGf End to End: Selendroid 

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 

Source Control & Code Review Testing Releasing 

Android Release Process 4 weeks of development 4 weeks of development 3.5 weeks of stabilization RC Master Release branch 

https://flic.kr/p/kAT3Ba “Manual” Testing: Dogfood, Alpha and Beta 

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