Swift at Scale

SWIFT AT SCALE
WAR STORIES FROM
KAMILAH TAYLOR, SENIOR SOFTWARE ENGINEER, LINKEDIN
#SwiftSummit 2016 @kamilah

I SINCERELY PROMISE TO
KEEP MY SWIFT 3 MIGRATION
COMPLAINTS TO A MINIMUM.
@kamilah
SO THIS TALK... #SwiftSummit

REALLY I PROMISE EVEN THOUGH THIS IS HOW I DREAM OF XCODE NOW
@kamilah #SwiftSummit

SWIFT AT LINKEDIN
WHAT I MEAN WHEN I SAY AT SCALE
▸ In January 2015, we started the
complete rewrite of our ﬂagship
app in Swift, as part of project
Voyager
▸ It's not just one app, it's a growing
family of apps
▸ It's not just a family of apps, it's a
growing set of libraries, internally
and open sourced
▸ ~100 iOS devs, ~40 on ﬂagship

SWIFT AT LINKEDIN
THE WORKFLOW
▸ Weekly release cycles
▸ Large unit and integration test suites
▸ First version of Swift embraced - the betas (https://
engineering.linkedin.com/ios/our-swift-experience-
slideshare)
▸ Number of Swift ﬁles in our ﬂagship app - over 4500

HOW DO WE HAVE
IT ALL?
SPOILER ALERT: WE DON'T.
THIS IS HARD. HERE ARE
SOME STORIES.

THE COMPILER
STORIES
<- THIS NEVER STOPS
BEING TRUE

THE COMPILE TIME STORIES
DEVELOPER HAPPINESS + PRODUCTIVITY
▸ Compile times very very very long for large codebase (~25
min for a cold build on 15” rMBP)
▸ This has improved with each Xcode version
▸ Three workarounds
▸ code structure
▸ hardware
▸ objective-c (yes, really)

THE COMPILE TIME STORIES
THE SOLUTION FOR VOYAGER
▸ Mac Pros for everyone! (12 cores gave us a 2x speed boost over the top
of the line MBP)
▸ Switched generated models to ObjC (to reduce the number of Swift ﬁles)
▸ Code structure
▸ Dropped iOS 7 support
▸ Modularized using Cocoapod's devpods
▸ This broke debug symbols
▸ Converted devpods into dynamic frameworks

@kamilah
THE XCODE PROJECT FILE
FIELD NOTE NUMBER 12:
SOMETIMES YOU MAY NEED
DARK MAGIC TO EDIT THE
PROJECT FILE
#SwiftSummit

THE XCODE PROJECT FILE
DARK MAGIC IS NOT AN EXAGGERATION

THAT SEGFAULT 11 THOUGH
http://classicprogrammerpaintings.com/post/142796894989/c-
developers-aiding-a-comrade-facing-segfault

THAT SEGFAULT 11 THOUGH
SOMETIMES THE XCODE COMPILER JUST CRASHES
▸ The problem (on LinkedIn Learning): Our builds started to
ﬂakily fail because of a compiler crash once we added a
full test suite, as we geared up for our launch
▸ Even locally, the compiler would occasionally crash with a
segfault 11
▸ The solution: Back to manipulating the xcode project
settings, a skill I don't remember needing in the objective-
c days

THE BUILD ALWAYS NEEDS WORK
FAILED TO AUTHORIZE RIGHTS (0X1) WITH STATUS: -60007
▸ The problem: Our builds started to ﬂakily fail because of a
compiler crash (Xcode 7.3) - for everyone's app
▸ Really bad side effect - missing when an actual bad
commit went in while the trunk is red
▸ The solution: Our tools team found a work around by
splitting the test build (done in xcodebuild) and running
tests, now via xctool
▸ Funny follow up: had to revert this patch for Swift 3

THE SWIFT
MIGRATION STORIES
<- IF ONLY THIS WERE
NOT SO APT

SWIFT BETA - SWIFT 2
THE EARLY DAYS OF MIGRATING
▸ Pre Swift 2
▸ This mostly affected Slideshare, our ﬁrst Swift app
▸ No migrator tool so all manual

SWIFT BETA - SWIFT 2
THE EARLY DAYS OF MIGRATING
▸ Swift 2 migration
▸ Needed Xcode 7 for the improved build times
▸ 2 months before launch
▸ Migration tool crashed on large codebase (okay for
smaller apps at LinkedIn)
▸ (What we thought was) Lengthy, manual migration to
new Swift version for Voyager

BEYOND SWIFT 2
AND THEN 2016 CAME...WITH SWIFT 2.3 AND SWIFT 3

SWIFT 2 - SWIFT 2.3
IT WAS ONLY KIND OF A PAIN FREE MIGRATION
▸ Swift 2.3
▸ Again, we needed to upgrade to Xcode 8
▸ Actually quite painful for Voyager
▸ 14 Swift libraries, 4500 Swift ﬁles in Voyager
▸ For LinkedIn Learning, actually not so bad
▸ Took me about 1 week since libraries had already
been migrated and migrator "worked"

THAT INITIAL ERROR COUNT OF
666 WAS THE FIRST SIGN.
@kamilah
MIGRATING TO SWIFT 3 #SwiftSummit

SWIFT 3
QUITE POSSIBLY THE WORST DEVELOPER EXPERIENCE
▸ The migrator tool, pretty much useless
▸ Saving grace: http://swift.ayaka.me/posts/2016/6/17/
running-the-swift-30-migrator-on-a-standalone-swift-ﬁle
▸ Had a script that ran this for an entire directory
▸ The battle had only begun
▸ Massive effort to upgrade all the swift libraries from the
infra and voyager team

SWIFT 3 MIGRATION
QUITE THE COORDINATED EFFORT

THE SWIFT 3 MIGRATION
THESE ARE ACTUAL COMMIT MESSAGES FROM THE VOYAGER TEAM

SWIFT 3
QUITE POSSIBLY THE WORST DEVELOPER EXPERIENCE
▸ Voyager
▸ Froze the trunk for nearly two weeks
▸ LinkedIn Learning
▸ Still ongoing, even on our much smaller codebase (~800
Swift ﬁles) the migrator crashed

THE SWIFT 3 MIGRATION
OKAY A FEW MORE COMMIT MESSAGES

SO HOW DO WE DO SWIFT
AT SCALE AT LINKEDIN?

ALMOST DONE...
SO HOW HAVE WE DONE SWIFT AT SCALE AT LINKEDIN?
▸ Early adoption -> hard earned learnings both from our
developers and tools team
▸ Communicate communicate communicate
▸ Frequent knowledge sharing across the company
▸ Internal iOS meetups
▸ Many slack channels, including a dedicated one for swift 3
▸ Open sourced a swift style guide

ALMOST DONE...
SO HOW HAVE WE DONE SWIFT AT SCALE AT LINKEDIN?
▸ Constant experimentation on how to improve our build
and compile times
▸ Shout out to our tools team who are always trying to
improve the process, test new versions of Xcode

NOW I'M DONE
LEARNINGS
▸ This won't come for free
▸ Invest in your tools and infra teams
▸ Swift does require more developer time for maintenance,
though less time for training and actual coding
▸ Be ready with much patience and all the humor

SO LONG AND THANKS
FOR ALL THE SWIFT FUN

Swift at Scale

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