Improving App Launch Time

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Intro @the69geeks

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Exception Type: EXC_CRASH (SIGKILL) Exception Codes: 0x0000000000000000, 0x0000000000000000 Exception Note: EXC_CORPSE_NOTIFY Termination Reason: Namespace SPRINGBOARD, Code 0x8badf00d Termination Description: SPRINGBOARD, process-launch watchdog transgression: com.go-jek.xxxxx.develop exhausted real (wall clock) time allowance of 20.00 seconds | ProcessVisibility: Unknown | ProcessState: Running | WatchdogEvent: process-launch | WatchdogVisibility: Foreground | WatchdogCPUStatistics: ( | "Elapsed total CPU time (seconds): 27.590 (user 27.590, system 0.000), 69% CPU", | "Elapsed application CPU time (seconds): 0.128, 0% CPU" | ) Triggered by Thread: 0

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Improving iOS App Launch Time A discussion about how we approached this problem

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Agenda • What affects launch timing (Measure and Improve) • Why did we faced the issue • How we zeroed on the approach to fix (Pre-Main only) • How we fixed this problem • Key takeaway from the journey

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App Launch Times • Cold Launch • Warm Launch • Hot Launch

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What aﬀects launch timing • Pre-Main • Post-Main

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What aﬀects launch timing • Pre-Main • Measure using DYLD_PRINT_STATISTICS

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What aﬀects launch timing • Pre-Main • Measure using DYLD_PRINT_STATISTICS • dylib load time, rebase/binding, objc setup, Static Initializers

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What aﬀects launch timing • Pre-Main • Measure using DYLD_PRINT_STATISTICS • dylib load time, rebase/binding, objc setup, Static Initializers across code • Post-Main • Measure using Instruments

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What aﬀects launch timing • iOS version, because DYLD version ships with OS

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What aﬀects launch timing • iOS version, because DYLD version ships with OS • Battery Level (Power Saver mode)

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What aﬀects launch timing • iOS version, because DYLD version ships with OS • Battery Level (Power Saver mode) • Hardware Capacity

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What aﬀects launch timing • iOS version, because DYLD version ships with OS • Battery Level (Power Saver mode) • Hardware Capacity • Binary Size

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Post-Main • Time Spent In: • app(Will)DidFinishedLaunching methods • loadView/viewWill(Did)Appear/draw methods

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App(Will)DidFinishedLaunching • Singleton initializations (Facebook, Firebase etc?) •

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App(Will)DidFinishedLaunching • Singleton initializations (Facebook, Firebase etc?) • DB connection / Core Data/ Model Layer Initialization •

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App(Will)DidFinishedLaunching • Singleton initializations (Facebook, Firebase etc?) • DB connection / Core Data/ Model Layer Initialization • User Location?

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App(Will)DidFinishedLaunching • Singleton initializations (Facebook, Firebase etc?) • DB connection / Core Data/ Model Layer Initialization • User Location? • Analytics? •

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App(Will)DidFinishedLaunching • Singleton initializations (Facebook, Firebase etc?) • DB connection / Core Data/ Model Layer Initialization • User Location? • Analytics? • Setup Key Window • … many more

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ViewRendering (RootVC) • Setup Navigation Container (e.g. TabBarVC)

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ViewRendering (RootVC) • Setup Navigation Container (e.g. TabBarVC) • Prepare Datasource/ViewModel/VIPER stack •

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ViewRendering (RootVC) • Setup Navigation Container (e.g. TabBarVC) • Prepare Datasource/ViewModel/VIPER stack • Time require to layout any Complex View

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ViewRendering (RootVC) • Setup Navigation Container (e.g. TabBarVC) • Prepare Datasource/ViewModel/VIPER stack • Time require to setup View (complex layout) • Any other work done in ViewDid(Will)Load (Auth, StateRestoration etc)

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Post-Main Use os_signpost for taking accurate measures of a method which is contributing to launch time. Ex: ViewDidLoad of RootViewController

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Post-Main Use os_signpost for taking accurate measures of a method which is contributing to launch time. Ex: ViewDidLoad of RootViewController

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POI Details

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Post-Main Measurement Demo

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Skipped Post-Main • Overall gains < 10% • Eﬀorts >>

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Focused on Pre-Main

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~19 seconds Before Optimization (iPhone6s 12.3.1)

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~7.5 Seconds After Optimization (iPhone6s 12.3.1)

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Pre-Main Time exec() to main() Better Guide: https://developer.apple.com/videos/play/wwdc2016/406

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Dyld: The WorkHorse • Load dylibs • Fix Ups • Objc Setup • Initializer

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Dyld: The WorkHorse • Load dylibs • Kernel loads Dyld

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Dyld: The WorkHorse • Load dylibs • Kernel loads Dyld • Dyld loads dylibs

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Dyld: The WorkHorse • Load dylibs • Fix Ups • Bind all dylibs together

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Dyld: The WorkHorse • Fix Ups • Rebase • Adjust pointers inside image

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Dyld: The WorkHorse • Rebase • Adjust pointers inside image • Slid = actual_address - preferred_address

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Dyld: The WorkHorse • Bindings • Adjust pointers outside image • Find symbol and malloc

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Dyld: The WorkHorse • Load dylibs • Fix Ups • Objc Setup

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Dyld: The WorkHorse • Load dylibs • Fix ups • Objc Setup • Initializer

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DYLD_PRINT_STATISTICS Total pre-main time: 249.96 milliseconds (100.0%) dylib loading time: 191.67 milliseconds (76.6%) rebase/binding time: 15.74 milliseconds (6.2%) ObjC setup time: 9.54 milliseconds (3.8%) initializer time: 33.00 milliseconds (13.2%) slowest intializers : libSystem.B.dylib : 2.49 milliseconds (0.9%) libBacktraceRecording.dylib : 5.08 milliseconds (2.0%) libMainThreadChecker.dylib : 14.41 milliseconds (5.7%) libViewDebuggerSupport.dylib : 7.90 milliseconds (3.1%)

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Why did we faced this issue?

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Code Metric • 12000+ Types (Class, Struct, Enum…)

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Code Metric • 12000+ Types (Class, Struct, Enum…) • > 8000 Swift ﬁles, ~1000 ObjC ﬁles (Pods)

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Code Metric • 12000+ Types (Class, Struct, Enum…) • > 8000 Swift ﬁles, ~1000 ObjC ﬁles (Pods) • >80 Dynamic Libraries (and growing)

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Development Silos • Team Structure: independent development

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Development Silos • Team Structure: independent development • Abstract Target in Podﬁle to make it magical

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target 'Vendor' do dynamic_frameworks internal_dynamic_frameworks special_dynamic_frameworks inherit! :search_paths target 'Framework1' do inherit! :search_paths end target 'Framework2' do inherit! :search_paths end end target 'DemoApp' do static_frameworks host_only_static_libs dynamic_frameworks internal_dynamic_frameworks special_dynamic_frameworks end

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Development Silos • Team Structure: independent development • Abstract Target in Podﬁle to make it magical • Complex Inter Target dependancies

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Development Silos • Team Structure: independent development • Abstract Target in Podﬁle to make it magical • Complex Inter Target dependancies • Messed up Build Settings per product

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Finding a solution • IDEAL: • Reduce internal (by merging) and external (building inhouse) framework count

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Finding a solution • IDEAL: • Reduce internal (by merging) and external (building inhouse) framework count • Make dependancies as Static Frameworks and link that with Product

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Finding a solution • IDEAL: • Reduce internal (by merging) and external (building inhouse) framework count • Make dependancies as Static Frameworks and link that with Product • Create create an Umbrella Framework from all Dependancies (Dynamic Framework) •

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Fixing the problem • Find out dependancies in diﬀerent targets

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Fixing the problem • Find out dependancies in diﬀerent targets • Create a Lite app version to compare app launch time

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Fixing the problem • Find out dependancies in diﬀerent targets • Create a Lite app version to compare app launch time • Prepare a checklist during the process of migration

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Fixing the problem • Find out dependancies in diﬀerent targets • Create a Lite app version to compare app launch time • Prepare a checklist during the process of migration • Automate whatever we can from Checklist

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Problems Faced • Splitting Framework into Static Libs and Resource Bundle (DEMO) • Custom script to copy all resource bundles to app

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Problems Faced • CocoaPods + New Build System issues Build system information error: Multiple commands produce '/Users/Ben/Library/ Developer/Xcode/DerivedData/myApp- awbgyiqiegnrtdayecemnuyfqnbc/Build/Products/Debug- iphonesimulator/myApp.app': 1) Target 'myApp' has create directory command with output '/Users/Ben/Library/Developer/Xcode/DerivedData/myApp- awbgyiqiegnrtdayecemnuyfqnbc/Build/Products/Debug- iphonesimulator/myApp.app' 2) That command depends on command in Target 'myApp': script phase “[CP] Copy Pods Resources”

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Problems Faced • Implicit dependancies not working; so as the Parallel builds • That needs updating all target’s linker ﬂags

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Problems Faced • As Implicit Dependancies were oﬀ, we need to add all imports explicitly • A script to automate inserting some must have imports

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Problems Faced • IntentDeﬁnition was not getting compiled correctly (autogen classes were not generated) • Copied the generated ﬁles manually

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Problems Faced • R.Swift was not working with Static Libs + Resource Bundle model • Run the r.swift script from resource bundle and add generated ﬁles to library • Later replaced R.swift with inhouse code

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Problems Faced • Change in Framework name affected DLS components in IB files (ModuleName for a class) • XIB files using component from another framework, and now the name of framework is changed

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Problems Faced • Archive failed couple of times: • One header for static library was in copied in sources • ResourceBundle executable was not code signed (Demo the plist)

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Problems Faced • A few Crashes due to wrong scheme selected for archive (for some products)

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DEMO

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Open Issues • Required to Drop Support for Armv7 ld: section __bundle (address=0x06748000, size=735061037) would make the output executable exceed available address range for architecture armv7 • A bit longer build times even after switching to New Build System • Pods still add copy resources step in static lib • Incremental builds are not building Delta changes only

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Takeaways • Performance is equally important as a feature

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Takeaways • Performance is equally important as a feature • Should be a Continuous Process (Don’t wait till blast)

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Takeaways • Performance is equally important as a feature • Should be a Continuous Process (Don’t wait till blast) • Measure what matters (part of CI?) • Using XCUITest

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Takeaways • Performance is equally important as a feature • Should be a Continuous Process (Don’t wait till blast) • Measure what matters (part of CI?) • Using XCUITest • Automate things which developer won’t be touching • Deployment target, swift version, optimization level etc

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Thank You • https://developer.apple.com/videos/play/wwdc2016/406/ • https://useyourloaf.com/blog/slow-app-startup-times/ • https://github.com/leavez/cocoapods-static-swift-framework • https://blog.automatic.com/how-we-cut-our-ios-apps- launch-time-in-half-with-this-one-cool-trick-7aca2011e2ea • https://medium.com/@kolyuchiy/a-record-breaking-story-of- boosting-the-launch-time-of-mail-rus-email-app-for- ios-59a266dd288a