Announcements. Today s Topics

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1 Announcements We will discuss final project ideas on Monday Three guest presenters coming to class Lab 5 is due on Wednesday Nov 4 th 1 Extensible - CSE 436 Software Networking Engineering Platform Workshop 1 Today s Topics Memory Usage Blocks System warnings Concurrency Threads Opera;ons and queues Audio Midterm 2 Extensible - CSE 436 Software Networking Engineering Platform Workshop 2

2 Memory on the iphone StarDng points for performance Load lazily Don t leak Watch your autorelease footprint Reuse memory System memory warnings are a last resort Respond to warnings or be terminated 3 Extensible - CSE 436 Software Networking Engineering Platform Workshop 3 Loading Lazily Pervasive in Cocoa frameworks Do only as much work as is required Applica;on launch ;me! Think about where your code really belongs Use muldple NIBs for your user interface If you are not using Storyboard 4 Extensible - CSE 436 Software Networking Engineering Platform Workshop 4

3 Loading a Resource Too Early What if it s not needed undl much later? Or not at all? - (id)init { self = [super init]; if (self) { // Too early... myimage = [self readsomehugeimagefromdisk]; return self; 5 Extensible - CSE 436 Software Networking Engineering Platform Workshop 5 Loading a Resource Lazily Wait undl someone actually requests it, then create it - (UIImage *) myimage { if (myimage == nill) { myimage = [self readsomehugeimagefromdisk]; Ends up benefidng both memory and launch Dme Not always the right move, consider your specific situadon NoDce that the above implementadon is not thread- safe! 6 Extensible - CSE 436 Software Networking Engineering Platform Workshop 6

4 Autorelease and You Autorelease simplifies your code Worry less about the scope and life;me of objects When an autorelease pool pops, it calls release on each object An autorelease pool is created automadcally for each iteradon of your applicadon s run loop 7 Extensible - CSE 436 Software Networking Engineering Platform Workshop 7 So What s the Catch? What if many objects are autoreleased before the pool pops? Consider the maximum memory footprint of your applicadon 8 Extensible - CSE 436 Software Networking Engineering Platform Workshop 8

5 A Crowded Pool... 9 Extensible - CSE 436 Software Networking Engineering Platform Workshop 9 Reducing Your High- Water Mark When many objects will be autoreleased, create and release your own pool Usually not necessary, don t do this without thinking! Tools can help iden;fy cases where it s needed Loops are the classic case 10 Extensible - CSE 436 Software Networking Engineering Platform Workshop 10

6 Memory AllocaDon and Leaks 11 Extensible - CSE 436 Software Networking Engineering Platform Workshop 11 Demo 12 Extensible - CSE 436 Software Networking Engineering Platform Workshop 12

7 Autorelease in a Loop Remember that many methods return autoreleased objects for (int i = 0; i < somelargenumber; i++) { NSString *string =...; string = [string lowercasestring]; string = [string stringbyappendingstring:...]; NSLog(@ %@, string); 13 Extensible - CSE 436 Software Networking Engineering Platform Workshop 13 (Old Way) CreaDng an Autorelease Pool One opdon is to create and release for each iteradon for (int i = 0; i < somelargenumber; i++) { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; NSString *string =...; string = [string lowercasestring]; string = [string stringbyappendingstring:...]; NSLog(@ %@, string); [pool release]; 14 Extensible - CSE 436 Software Networking Engineering Platform Workshop 14

8 (New Way) CreaDng an Autorelease Pool One opdon is to create and release for each iteradon for (int i = 0; i < somelargenumber; i++) { NSString *string =...; string = [string lowercasestring]; string = [string stringbyappendingstring:...]; NSLog(@ %@, string); 15 Extensible - CSE 436 Software Networking Engineering Platform Workshop 15 Blocks A variable type that stores executable code Lets you create blocks of code to pass around like an object Example ^{ NSDate *date = [NSDate date]; NSLog(@ The date and Dme is %@,date); ; 16 Extensible - CSE 436 Software Networking Engineering Platform Workshop 16

9 Assigning Blocks to Variables void (^now) (void) return type name parameters void (^now) (void) = ^{ NSDate *date = [NSDate date]; NSLog(@ The date and Dme is %@,date); ; now(); 17 Extensible - CSE 436 Software Networking Engineering Platform Workshop 17 Blocks Blocks are closures They close around variables in scope when the block is declared NSDate *date = [NSDate date]; void (^now)(void) = ^{ NSLog(@ The date and Dme is %@,date); ; now(); sleep(5); date = [NSDate date]; now(); 18 Extensible - CSE 436 Software Networking Engineering Platform Workshop 18

10 Demo 19 Extensible - CSE 436 Software Networking Engineering Platform Workshop 19 Object CreaDon Overhead Most of the Dme, creadng and deallocadng objects is not a significant hit to applicadon performance In a Dght loop, though, it can become a problem... for (int i = 0; i < somelargenumber; i++) { MyObject *object = [[MyObject alloc] initwithvalue:...]; [object dosomething]; [object release]; 20 Extensible - CSE 436 Software Networking Engineering Platform Workshop 20

11 Reusing Objects Update exisdng objects rather than creadng new ones Combine intuidon and evidence to decide if it s necessary MyObject *myobject = [[MyObject alloc] init]; for (int i = 0; i < somelargenumber; i++) { myobject.value =...; [myobject dosomething]; [myobject release]; Remember - [UITableView dequeuereusablecellwithidendfier] 21 Extensible - CSE 436 Software Networking Engineering Platform Workshop 21 Memory Warnings Coexist with system applicadons Memory warnings issued when memory runs out Respond to memory warnings or face dire consequences! 22 Extensible - CSE 436 Software Networking Engineering Platform Workshop 22

12 Responding to Memory Warnings Every view controller gets didreceivememorywarning By default, releases the view if it s not visible Release other expensive resources in your subclass - (void)didreceivememorywarning { // Always call super [super didreceivememorywarning]; // Release expensive resources [expensiveresource release]; expensiveresource = nil; 23 Extensible - CSE 436 Software Networking Engineering Platform Workshop 23 What Other Resources Do I Release? Images Sounds Cached data 24 Extensible - CSE 436 Software Networking Engineering Platform Workshop 24

13 Use SQLite for Large Data Sets Many data formats keep everything in memory SQLite can work with your data in chunks 25 Extensible - CSE 436 Software Networking Engineering Platform Workshop 25 Concurrency 26 Extensible - CSE 436 Software Networking Engineering Platform Workshop 26

14 Why Concurrency? With a single thread, long- running operadons may interfere with user interacdon MulDple threads allow you to load resources or perform computadons without locking up your endre applicadon 27 Extensible - CSE 436 Software Networking Engineering Platform Workshop 27 Threads on the iphone Based on the POSIX threading API /usr/include/pthread.h Higher- level wrappers in the FoundaDon framework 28 Extensible - CSE 436 Software Networking Engineering Platform Workshop 28

15 NSThread Basics Run loop automadcally instandated for each thread Each NSThread needs to create its own autorelease pool Convenience methods for messaging between threads 29 Extensible - CSE 436 Software Networking Engineering Platform Workshop 29 (Old way) Typical NSThread Use Case - (void)someacdon:(id)sender { // Fire up a new thread [NSThread detachnewthreadselector:@selector(dowork:) withtarget:self object:somedata]; - (void)dowork:(id)somedata { NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; [somedata dolotsofwork]; // Message back to the main thread [self performselectoronmainthread:@selector(alldone:) withobject:[somedata result] waitundldone:no]; [pool release]; 30 Extensible - CSE 436 Software Networking Engineering Platform Workshop 30

16 (New way) Typical NSThread Use Case - (void)someacdon:(id)sender { // Fire up a new thread [NSThread detachnewthreadselector:@selector(dowork:) withtarget:self object:somedata]; - (void)dowork:(id)somedata { [somedata dolotsofwork]; // Message back to the main thread [self performselectoronmainthread:@selector(alldone:) withobject:[somedata result] waitundldone:no]; 31 Extensible - CSE 436 Software Networking Engineering Platform Workshop 31 UIKit and Threads Unless otherwise noted, UIKit classes are not threadsafe What does it mean to be thread safe? Objects must be created and messaged from the main thread 32 Extensible - CSE 436 Software Networking Engineering Platform Workshop 32

17 Demo: Threads and Xcode 33 Extensible - CSE 436 Software Networking Engineering Platform Workshop 33 Locks Protect cridcal secdons of code, mediate access to shared data NSLock and subclasses - (void)init{ mylock = [[NSLock alloc] init]; - (void)somemethod { [mylock lock]; // We only want one thread execudng this code at once [mylock unlock] 34 Extensible - CSE 436 Software Networking Engineering Platform Workshop 34

18 CondiDons NSCondiDon is useful for producer/consumer model Wait is equivalent to: unlock, sleep undl signalled, lock 35 Extensible - CSE 436 Software Networking Engineering Platform Workshop 35 The Danger of Locks Very difficult to get locking right! All it takes is one client poorly behaved client Accessing shared data outside of a lock Deadlocks Priority inversion 36 Extensible - CSE 436 Software Networking Engineering Platform Workshop 36

19 Threading Piqalls Subtle, nondeterminisdc bugs may be introduced Code may become more difficult to maintain In the worst case, more threads can mean slower code 37 Extensible - CSE 436 Software Networking Engineering Platform Workshop 37 AlternaDves to Threading Asynchronous (nonblocking) funcdons Specify target/ac;on or delegate for callback NSURLConnec;on has synchronous and asynchronous variants Timers One- shot or recurring Specify a callback method Managed by the run loop Higher level constructs like operadons 38 Extensible - CSE 436 Software Networking Engineering Platform Workshop 38

20 NSOperaDon Abstract superclass Manages thread creadon and lifecycle Encapsulate a unit of work in an object Specify priorides and dependencies 39 Extensible - CSE 436 Software Networking Engineering Platform Workshop 39 NSOperaDonQueue OperaDons are typically scheduled by adding to a queue Choose a maximum number of concurrent operadons Queue run operadons based on priority and dependencies 40 Extensible - CSE 436 Software Networking Engineering Platform Workshop 40

21 More on Concurrent Programming Grand Central Dispatch (GCD) Threading Programming Guide hsps://developer.apple.com/iphone/library/ documentadon/cocoa/conceptual/ MulDthreading 41 Extensible - CSE 436 Software Networking Engineering Platform Workshop 41 Blocks with Grand Central Dispatch (GCD) Blocks are closures They close around variables in scope when the block is declared NSDate *date = [NSDate date]; void (^now)(void) = ^{ sleep(5); NSDate *date = [NSDate date]; NSLog(@ The date and Dme is %@,date); ; //now(); dispatch_async(dispatch_get_main_queue(),now); NSLog (@ The original date is %@,date); 42 Extensible - CSE 436 Software Networking Engineering Platform Workshop 42

22 Audio 43 Extensible - CSE 436 Software Networking Engineering Platform Workshop 43 Uses for Audio Sound effects buuon clicks alert sounds short sounds accompanying user ac;ons Arbitrary length sounds (music, podcasts, spoken content) Streamed content from web services Recording audio 44 Extensible - CSE 436 Software Networking Engineering Platform Workshop 44

23 How to do it? Could be complex: Poten;ally mul;ple simultaneous sources Numerous possible outputs Dynamic events, oven out of user s control Different priori;es for seemingly similar ac;ons The OS manages the sound system You can ask for behavior, but the OS has control 45 Extensible - CSE 436 Software Networking Engineering Platform Workshop 45 CoreAudio High level, easy to use System Sound API - short sounds AVAudioPlayer class - ObjC, simple API Lower level, takes more effort but much more control Audio Toolbox - recording and playback, streaming, full control Audio Units - processing audio OpenAL - 3D posi;onal sound Which one you use depends on what you re trying to do Many of you are fine with System Sounds and AVAudioPlayer 46 Extensible - CSE 436 Software Networking Engineering Platform Workshop 46

24 Playing Short Sounds short means less than 5 seconds Very simple API, but has restricdons No looping No volume control Immediate playback Limited set of formats Linear PCM or IMA4.caf,.aif or.wav file 47 Extensible - CSE 436 Software Networking Engineering Platform Workshop 47 Playing Short Sounds Two step process Register the sound, get a sound ID in return Play the sound Op;onally can get callback when sound finishes playing NSURL *fileurl =... // url to a file SystemSoundID myid; // First register the sound AudioServicesCreateSystemSoundID ((CFURLRef)fileURL, &myid); // Then you can play the sound AudioServicesPlaySystemSound (myid); 48 Extensible - CSE 436 Software Networking Engineering Platform Workshop 48

25 Playing Short Sounds Clean up Dispose of sound ID when you re done Or if you get a memory warning SystemSoundID myid; // dispose of the previously registered sound AudioServicesDisposeSystemSoundID (myid); 49 Extensible - CSE 436 Software Networking Engineering Platform Workshop 49 ConverDng Sounds Command line udlity to convert sounds /usr/bin/afconvert Supports wide variety of input and output formats See man page for details Easily convert sounds to System Sounds formats /usr/bin/afconvert - f aiff - d BEI16 input.mp3 output.aif 50 Extensible - CSE 436 Software Networking Engineering Platform Workshop 50

26 Play longer sounds (> 5 seconds) AVAudioPlayer Locally stored files or in- memory (no network streaming) Can loop, seek, play, pause Provides metering Play muldple sounds simultaneously Cocoa- style API Ini;alize with file URL or data Allows for delegate Supports many more formats Everything the AudioFile API supports 51 Extensible - CSE 436 Software Networking Engineering Platform Workshop 51 Create from file URL or data AVAudioPlayer Simple methods for stardng/stopping AVAudioPlayer *player; NSString *path = [[NSBundle mainbundle] pathforresource...]; NSURL *url = [NSURL fileurlwithpath:path]; player = [[AVAudioPlayer alloc] initwithcontentsofurl:url]; if (!player.playing) { [player play]; else { [player pause]; 52 Extensible - CSE 436 Software Networking Engineering Platform Workshop 52

27 AVAudioPlayerDelegate Told when playback finishes Informed of audio decode errors Given hooks for handling interrupdons Incoming phone calls 53 Extensible - CSE 436 Software Networking Engineering Platform Workshop 53 OpenAL High level, cross- plaqorm API for 3D audio mixing Great for games Mimics OpenGL conven;ons Models audio in 3D space Buffers: Container for Audio Sources: 3D point emi`ng Audio Listener: Posi;on where Sources are heard More InformaDon: hsp:// 54 Extensible - CSE 436 Software Networking Engineering Platform Workshop 54

28 Playing Video Uses for Video: Provide cut- scene anima;on in a game Stream content from web sites Play local movies Play videos from applicadon bundle or remote URL Always full screen Configurable scaling modes Op;onal controls Supports:.mov,.mp4,.m4v,.3gp 55 Extensible - CSE 436 Software Networking Engineering Platform Workshop 55 Audio Demo 56 Extensible - CSE 436 Software Networking Engineering Platform Workshop 56

29 Midterm 57 Extensible - CSE 436 Software Networking Engineering Platform Workshop 57 Midterm Midterm Grades Average = 88% Median = 89% 58 Extensible - CSE 436 Software Networking Engineering Platform Workshop 58