Optimizing Your App for Multitasking on iPad in iOS 9...Brittany Paine iOS SpringBoard Engineer Jon...

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#WWDC15

Optimizing Your App for Multitasking on iPad in iOS 9

Brittany Paine iOS SpringBoard EngineerJon Drummond iOS SpringBoard Engineer

App Frameworks

Session 212

Multitasking Sessions

Getting Started with Multitasking on iPad in iOS 9 Presidio Tuesday 4:30PM

Multitasking Essentials for Media-Based Apps on iPad in iOS 9 Pacific Heights Wednesday 2:30PM

Optimizing Your App for Multitasking in iOS Presidio Wednesday 3:30PM

Multitasking Sessions


Multitasking Essentials for Media-Based Apps on iPad in iOS 9 Pacific Heights Wednesday 2:30PM

Optimizing Your App for Multitasking in iOS Presidio Wednesday 3:30PMOptimizing Your App for Multitasking in iOS

CPU

1 frame

FreeSystem Primary App

Memory

FreeSystem Primary App Secondary App

Memory

System Secondary App PiP

Memory

Primary App


Memory

!!


Memory

What Is SpringBoard?

idle timer

app launching

event routing

application lifecycleproximity detection

orientation lock

external display management home screen

lock screen

control center

app switcher

voice control

phone calls

wallpaper

notification center

icons

folders

notificationsremote notifications

alarms

do not disturbsystem gestures

alerts


UIApplication


SpringBoard

SpringBoard

The original multitasking app

SpringBoard

The original multitasking appFaced the same multitasking challenges as you do now

SpringBoard

The original multitasking appFaced the same multitasking challenges as you do nowLearned a lot of lessons along the way

Optimizing Your AppThe easy stuff

Optimizing Your App

Fix memory leaks

The easy stuff

Optimizing Your App

Fix memory leaksFix retain cycles and unbounded memory growth

The easy stuff

Optimizing Your App

Fix memory leaksFix retain cycles and unbounded memory growthFix inefficient algorithms

The easy stuff

Great Performance Involves Tradeoffs

a

Memory

b

CPU

c

Disk Space I/O

e

GPU


a

Memory CPU

c

Disk Space I/O

e

GPU

b


a

Memory

b

CPU

c

Disk Space I/O

e

GPU

a

Memory

b

CPU I/O

Digging In

a

Memory

b

CPU I/O

Digging In

CPU and disk I/O are minimalwhile scrolling

Digging In

a

Memory

b

CPU I/O


Digging In

a

Memory

b

CPU I/O

All icons kept in memory


Digging In

a

Memory

b

CPU I/O

System reclaims memory by terminating processes

All icons kept in memory


Memory ManagementWorking set


The critical objects and resources you need right now


The critical objects and resources you need right now• Keep it small


The critical objects and resources you need right now• Keep it small• It might change based on context


The critical objects and resources you need right now• Keep it small• It might change based on context• Don’t let it grow unbounded

Working Set = Every Page

Working Set = 1 Page

a

Memory

b

CPU

Digging In

I/O

a

Memory

b

CPU

Digging In

I/O

CPU and disk I/O are highwhile scrolling

Digging In

a

Memory CPU I/O

b


Digging In

Memory CPU I/O

a b


Very few icons in memory

CPU ManagementMain thread

Main thread’s top priority is responding to user eventsDon’t do unnecessary work

CPU ManagementQuality of service

User Interactive* Is this work actively involved in updating the UI?

User Initiated Is this work required to continue user interaction?

Utility Is the user aware of the progress of this work?

Background Can this work be deferred to start at a better time?

UT

IN

UI

BG

* Main thread

Building Responsive and Efficient Apps with GCD Nob Hill Friday 10:00AM

Power, Performance, and Diagnostics: What’s New in GCD and XPC WWDC14

dispatch_queue_t iconQueue = dispatch_queue_create("IconGenerationQueue", DISPATCH_QUEUE_SERIAL);

for (IRIcon *icon in [iconPage icons]) { dispatch_async(iconQueue, ^{ [self _iconQueue_generateImageForIcon:icon]; }); }];

CPU ManagementQoS overrides

Lower priority queues can be temporarily boosted when a higher priority queue is waiting for itThe system needs a hint that you want a QoS override to occur

Strategy Overrides?

dispatch_sync()

dispatch_block_wait()

dispatch_group_wait()

dispatch_semaphore_wait()

QoS OverridesDispatch


Power, Performance, and Diagnostics: What’s New in GCD and XPC WWDC14

dispatch_sync(iconQueue, ^{ // ensure icon generation completes at caller QoS });

UIImage *image = [icon image];


2 3 4

e fa c - overlay bd - overlay

2 3 4

e f

Working Set = 3 Pages

c - overlayd - overlay

43 5


gc - overlayd - overlay

fe

43 5


gc - overlayd - overlay

e

h

4

e

2 3


c - overlay gd - overlay

h

42 3


c - overlay gd - overlay

s

FreeSystem IconReel


FreeSystem IconReel


FreeSystem IconReel


Secondary App

Managing Memory GrowthMemory warnings


Happens when• The system is under memory pressure• Your process is approaching its memory limit


Happens when• The system is under memory pressure• Your process is approaching its memory limit

What to do• Remove anything not in the working set

- Clear cached data- Release images- Release view controllers

Memory WarningsAPIs

In your UIApplicationDelegate and UIViewControllers-[UIApplicationDelegate applicationDidReceiveMemoryWarning:] -[UIViewController didReceiveMemoryWarning]

Anywhere in an application processUIApplicationDidReceiveMemoryWarningNotification

In libraries and extensionsDISPATCH_SOURCE_TYPE_MEMORYPRESSURE

Managing Memory GrowthNSCache

NSDictionary-likeIdeal for objects that can be regenerated on demand Trims under memory pressureTrims for application lifecycle changes

FreeSystem


Secondary AppIconReel

System


FreeSecondary AppIconReel

a

Recap

Memory CPU I/O

a

Recap

Memory CPU I/O

Working Set

a

Recap

NSCache{Adaptive

Memory CPU I/O

Working Set

Advanced Adaptive MemoryLeveraging the Virtual Memory System

Jon Drummond iOS SpringBoard Engineer

Primary AppSystem Secondary App

Primary AppSystem

Memory Warning

Secondary App

!!

System Primary App Secondary App

System Primary App PiPSecondary App

!

System Primary App Secondary App PiP

Secondary AppSystem Primary App PiP

Secondary AppSystem PiP

!!

System PiPSecondary App

“The world outside your process should be regarded as hostile and bent upon your destruction.”

Me, almost everyday

Advanced Adaptive Memory


Memory is the most constrained resource on iOS• No swap


Memory is the most constrained resource on iOS• No swap

System can require memory faster than it can be released• CPU contention during memory

warnings can slow or prevent apps from releasing it

Classification Description Reclaimable?

Dirty Memory in active use

Purgeable Otherwise-dirty memory designated as not in-use

Clean Read-only memorybacked by files on disk

Memory Classification


Clean or purgeable memory is reclaimable


Leeway

Leveraging the Virtual Memory SystemGoals

Minimize dirty memory usageMaximize purgeable and clean memory usage

iOS App Performance: Memory WWDC12

Minimizing Dirty Memory


Use less of it!


Use less of it!Classify otherwise dirty memory as purgeable• Can be automatically reclaimed when not in use• Best for “nice to have” data that can be recomputed

IconReelAdopting purgeable data

Working SetNSCache NSCache



In Use/Dirty



In Use/Dirty PurgeablePurgeable


!!

System

Reclaimable

Primary App Secondary App PiP

!!


Memory Warning!!

NSPurgeableData• beginContentAccess • endContentAccess • isContentDiscarded

APIPurgeable Data

- memory now considered dirty- memory now considered purgeable- has the memory been reclaimed?

NSCache

CPU I/O

Working Set

Memory

{Adaptive

IconReelSystem resources

NSCache

Purgeable

CPU I/O

Working Set

Memory

{Adaptive


IconReelData characteristics


Absolutely essential


Absolutely essentialExpensive to generate


Absolutely essentialExpensive to generateCan be pre-computed


Absolutely essentialExpensive to generateCan be pre-computedStatic once generated


Absolutely essentialExpensive to generateCan be pre-computedStatic once generatedPerfect candidate for caching to a file!

Working Set


NSCache

CPU I/OMemory

Purgeable

Working Set


NSCache

CPU I/OMemory Disk Space

Purgeable

Working Set



NSCache

Purgeable


Working Set


NSCache

Purgeable

Maximizing Clean Memory


Memory backed by a file on disk is considered clean• Data in such a file can be “memory mapped”



Memory and file contents must match exactly• Ideal for read-only data



Memory and file contents must match exactly• Ideal for read-only data

Data in memory is evicted and reloaded on your behalf• Allows for random access

Memory Mapped Data

Data in Memory

Memory Mapped Data

Data in Memory

File on Disk

Memory Mapped Data

Memory Mapped Data

File on Disk

Memory Mapped Data

IconReel

Memory Mapped Image Data

IconReel

IconReel



NSCache/Purgeable

Working Set



Working Set

APIMemory Mapped Data

typedef NS_OPTIONS(NSUInteger, NSDataReadingOptions) { NSDataReadingMappedIfSafe, NSDataReadingMappedAlways, … };

@interface NSData (NSDataCreation)

- (nullable instancetype)initWithContentsOfFile:(NSString *)path options:(NSDataReadingOptions)readOptionsMask error:(NSError **)errorPtr;

@end

CaveatsLeveraging the Virtual Memory System

VM Addressable Space0x00000000 0xFFE00000


Not appropriate for small chunks of data



Not appropriate for small chunks of dataVirtual Memory misuse• Fragmentation• Exhaustion



Not appropriate for small chunks of dataVirtual Memory misuse• Fragmentation• Exhaustion

Abusing the VM system can result in process termination


Summary

Summary

Use Instruments to identify and fix bugs

Summary

Use Instruments to identify and fix bugsPrioritize your work appropriately and don’t block the main thread

Summary

Use Instruments to identify and fix bugsPrioritize your work appropriately and don’t block the main threadIdentify and manage your working set

Summary

Use Instruments to identify and fix bugsPrioritize your work appropriately and don’t block the main threadIdentify and manage your working setUse caches and respond tomemory warnings

Summary

Use Instruments to identify and fix bugsPrioritize your work appropriately and don’t block the main threadIdentify and manage your working setUse caches and respond tomemory warningsLeverage the virtual memory system to increase reclaimable memory

Summary

Use Instruments to identify and fix bugsPrioritize your work appropriately and don’t block the main threadIdentify and manage your working setUse caches and respond tomemory warningsLeverage the virtual memory system to increase reclaimable memoryGreat performance requires tradeoffs

“It is not the strongest or the most intelligent who survive, but those who can best manage change.”

Charles Darwin (apocryphal)

More Information

DocumentationAdopting MultitaskingEnhancements on iPadPerformance OverviewInstruments User Guidehttp://developer.apple.com/iOS

Technical SupportApple Developer Forumshttp://developer.apple.com/forums

Developer Technical Supporthttp://developer.apple.com/support/technical

General InquiriesCurt Rothert, App Frameworks [email protected]

Related Sessions


Multitasking Essentials for Media-Based Apps oniPad in iOS 9 Pacific Heights Wednesday 2:30PM

Performance on iOS and watchOS Presidio Friday 11:00AM


Labs

Cocoa Touch and Multitasking Lab Frameworks Lab B Wednesday 9:00AM

Power and Performance Lab Frameworks Lab C Friday 12:00PM

Optimizing Your App for Multitasking on iPad in iOS 9...Brittany Paine iOS SpringBoard Engineer Jon...

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