1. Objective C/C++
Работа с памятью без
использования Instruments

2. Memory and resource management
LOCAL OBJECTS

3. C
• System language
• Portable assembler

4. C
• Memory management - C example
static bool check_memory()
{
! Something * a = (Something *)malloc( sizeof(Something) );
! if( !a )
! ! return false;
! do_something(a);
! if( some_condition(a) )
! {
! ! free(a);
! ! return true;
! }
! // Lots of code
! free(a);
! return false;
}

5. C
• Resource management - C example
static bool check_file(const char * name)
{
! FILE * fs = fopen(name, "rb");
! if( !fs )
! ! return false;
! int first = fgetc(fs);
! if( first == 32 )
! {
! ! fclose(fs);
! ! return true;
! }
! // Lots of code
! fclose(fs);
! return false;
}

6. C
• Resource management - C example
static bool check_file(const char * name)
{
! FILE * fs = fopen(name, "rb");
! if( !fs )
! ! return false;
! int first = fgetc(fs);
! if( first == 32 )
! {
! ! fclose(fs);
! ! return true;
! }
! // Lots of code
! fclose(fs);
! return false;
}

7. Java
• Memory management example
static public boolean check_memory()
{
Something a = new Something();
a.do_something();
if( a.some_condition() )
return true;
// Lots of code
return false;
}

8. Java
• Resource management example
static public boolean check_file(String name) throws Exception
{
FileInputStream fs = new FileInputStream(name);
int first = fs.read();
if( first == 32 )
return true;
// Lots of code
return false;
}

9. Java
• Resource management example
static public boolean check_file(String name) throws Exception
{
FileInputStream fs = new FileInputStream(name);
int first = fs.read();
if( first == 32 )
return true;
// Lots of code
return false;
}
static public void delete_if_bad(String name) throws Exception
{
if( !check_file(name) )
new java.io.File(name).delete();
}

10. Java
• Resource management - with finally
static public boolean check_file2(String name) throws Exception
{
FileInputStream fs = null;
try
{
fs = new FileInputStream(name);
int first = fs.read();
if( first == 32 )
return true;
// Lots of code
return false;
}
finally{
if( fs != null )
fs.close();
}
}

11. Java
• Resource management - with catch
static public boolean check_file3(String name) throws Exception
{
FileInputStream fs = null;
try
{
fs = new FileInputStream(name);
int first = fs.read();
if( first == 32 )
return true;
// Lots of code
}
catch(Exception e)
{}
try {
if( fs != null )
fs.close();
}
catch(Exception e)
{}
return false;
}

12. C#
• Memory management example
static public bool check_memory()
{
Something a = new Something();
a.do_something();
if( a.some_condition() )
return true;
// Lots of code
return false;
}

13. C#
• Resource management example
static public bool check_file(String name)
{
using( FileInputStream fs = new FileInputStream(name) )
{
int first = fs.read();
if( first == 32 )
return true;
// Lots of code
}
return false;
}

14. C++
• System language
• Life without garbage collector?
• Unique semantic!

15. C++
• Memory management - what C
developer thinks?
• If I know C I already know C++!
static bool check_memory()
{
! Something * a = new Something;
! if( !a )
! ! return false;
! a->do_something();
! if( a->some_condition() )
! {
! ! delete a;
! ! return true;
! }
! // Lots of code
! delete a;
! return false;
}

16. C++
• Memory management - what C
developer thinks?
• If I know C I already know C++!
static bool check_memory()
{
! Something * a = (Something *)malloc( sizeof(Something) );
! if( !a )
! ! return false;
! do_something(a);
! if( some_condition(a) )
! {
! ! free(a);
! ! return true;
! }
! // Lots of code
! free(a);
! return false;
}

17. C++
• Are there exceptions in C++?
• Are they good or evil? Good!
• If I do not use them?
• You are allowed not to throw
• But good C++ design always uses
exceptions, so you better be prepared

18. C++
• Memory management example
static bool check_memory()
{
! std::auto_ptr<Something> a( new Something );
! a->do_something();
! if( a->some_condition() )
! ! return true;
! // Lots of code
! return false;
}

19. C++
• Resource management example
static bool check_file(const std::string & name)
{
! liba::FileInputStream fs(name);
! int first = fs.read();
! if( first == 32 )
! ! return true;
! // Lots of code
! return false;
}

20. C++
• Resource management example
static bool check_file(const std::string & name)
{
! std::auto_ptr<liba::FileInputStream> fs( liba::create_fis(name) );
! int first = fs->read();
! if( first == 32 )
! ! return true;
! // Lots of code
! return false;
}

21. C++
• Delete is for implementing libraries!
{
std::auto_ptr<Something> a( new Something(...) );
if( ... )
return;
}
• No difference between memory and
other resource types

22. Objective-C
• Memory management - what C
developer thinks?
• If I know C I already know Objective-C!
-(bool)check_memory
{
! Something * a = [[Something alloc] init];
! if( !a )
! ! return false;
! [a do_something];
! if( [a some_condition] )
! {
! ! [a release];
! ! return true;
! }
! // Lots of code
! [a release];
! return false;
}

23. Objective-C
• Memory management - what C
developer thinks?
• If I know C I already know Objective-C!
static bool check_memory()
{
! Something * a = (Something *)malloc( sizeof(Something) );
! if( !a )
! ! return false;
! do_something(a);
! if( some_condition(a) )
! {
! ! free(a);
! ! return true;
! }
! // Lots of code
! free(a);
! return false;
}

24. Objective-C
• Are there exceptions in Objective-C?
• Are they good or evil? Absolutely good!
-(void)parse_object:(NSDictionary *)dic {
! // Lots of code
! int val = [[[dic objectForKey:@"users"] objectAtIndex:0] intValue];
! // Lots of code
}
-(void)parse_object:(NSDictionary *)dic {
! // Lots of code
! NSArray * arr = [dic objectForKey:@"users"];
! if( ![arr isKindOfClass:[NSArray class]] )
! ! return; // But we must tell about error...
! NSNumber * num = [arr objectAtIndex:0];
! if( ![num isKindOfClass:[NSNumber class]] )
! ! return; // But we must tell about error...
! int val = [num intValue];
! // Lots of code
}

25. Objective-C
• Memory management example
-(bool)check_memory
{
! Something * a = [[[Something alloc] init] autorelease];
! [a do_something];
! if( [a some_condition] )
! ! return true;
! // Lots of code
! return false;
}

26. Objective-C
• Memory management example
-(bool)check_memory
{
! Something * a = [[[Something alloc] init] autorelease];
! [a do_something];
! if( [a some_condition] )
! ! return true;
! // Lots of code
! return false;
}
• Afraid of autorelease?
• Just start using it!
• It is widely used in Cocoa

27. Memory and resource management
LONG-LIVED OBJECTS

28. Approaches
Garbage collector Ownership graph

29. Approaches
• It takes lots of CPU time to untangle this!

30. Approaches
• You must prove the graph is acyclic!

31. Approaches
• What is more scary than memory leak?

32. Approaches
• What is more scary than memory leak?
• Dangling pointer!

33. Objective-C
• Retaining
@interface Something : NSObject {
! Anything * a;
}
@end
@implementation Something
-(void)do_something {
! Anything * new_a = [[[Anything alloc] init] autorelease];
! [a release]; // [a autorelease];
! a = [new_a retain];
}
-(void)dealloc {
! [a release];
! [super dealloc];
}
@end

34. Objective-C
• Retaining
@interface Something : NSObject {
! Anything * a;
}
@property(nonatomic, retain) Anything * a;
@end
@implementation Something
@synthesize a;
-(void)do_something {
! Anything * new_a = [[[Anything alloc] init] autorelease];
! self.a = new_a;
}
-(void)dealloc {
! self.a = 0;
! [super dealloc];
}
@end

35. Objective-C
• Subtle differences
! self.a = new_a; // Call property
! self->a = new_a; // Use variable
! a = new_a; // ???

36. Objective-C
• Subtle differences
@interface Something : NSObject {
! Anything * a_zlo_hren;
}
@property(nonatomic, retain) Anything * a;
@end
@implementation Something
@synthesize a = a_zlo_hren;
-(void)do_something {
! Anything * new_a = [[[Anything alloc] init] autorelease];
! self.a = new_a; // Call property
! self->a = new_a; // Use variable
! a = new_a; // ???
}

37. Objective-C
• 4 lines to free the memory? Too much.
Anything * a_zlo_hren;
@property(nonatomic, retain) Anything * a;
@synthesize a = a_zlo_hren;
! self.a = 0; // In dealloc

38. Objective-C++
• Objective C is also C++
@interface Something : NSObject {
! NSPtr<Anything> a;
}
@end
@implementation Something
-(void)do_something {
! Anything * new_a = [[[Anything alloc] init] autorelease];
! a = new_a;
}
@end
• 4 lines go down to 1, good!

39. Objective-C++
• Retain cycles
@interface Something : NSObject {
! Anything * a;
}
@property(nonatomic, retain) Anything * a;
@end
@interface Anything : NSObject {
! Something * s;
}
@property(nonatomic, retain) Something * s;
@end

40. Objective-C++
• Retain cycles
@interface Something : NSObject {
! Anything * a;
}
@property(nonatomic, retain) Anything * a;
@end
@interface Anything : NSObject {
! Something * s;
}
@property(nonatomic, retain) Something * s;
@end

41. Objective-C++
• Retain cycles
@interface Something : NSObject {
! Anything * a;
}
@property(nonatomic, retain) Anything * a;
@end
@interface Anything : NSObject {
! Something * s;
}
@end

42. Retain cycles
• Can compiler find them?
• Can runtime find them?
• Can tools find them?
• Is there a simple approach to avoid
them?

43. Retain cycles
• Can compiler find them?
Yes, soon (experimental languages).
• Can runtime find them?
• Can tools find them?
• Is there a simple approach to avoid
them?

44. Retain cycles
• Can compiler find them?
Yes, soon (experimental languages).
• Can runtime find them?
Yes, Garbage Collector.
• Can tools find them?
• Is there a simple approach to avoid
them?

45. Retain cycles
• Can compiler find them?
Yes, soon (experimental languages).
• Can runtime find them?
Yes, Garbage Collector.
• Can tools find them?
Yes, if included in test cases.
• Is there a simple approach to avoid
them?

46. Retain cycles
• Can compiler find them?
Yes, soon (experimental languages).
• Can runtime find them?
Yes, Garbage Collector.
• Can tools find them?
Yes, if included in test cases.
• Is there a simple approach to avoid
them?
Yes, analyze architecture.

47. Objective-C
• Containers always retain
@interface Something : NSObject {
! NSMutableArray * a;
}
@property(nonatomic, retain) NSMutableArray * a;
@end
-(void)do_something {
! Anything * new_a = [[[Anything alloc] init] autorelease];
! Anything * new_a2 = [[[Anything alloc] init] autorelease];
! [a addObject:new_a];
! [a addObject:new_a2];
}

48. Objective-C
• If we do not want to retain?
@interface Something : NSObject {
! NSMutableArray * a;
}
@property(nonatomic, retain) NSMutableArray * a;
@end
-(void)do_something {
! Anything * new_a = [[[Anything alloc] init] autorelease];
! Anything * new_a2 = [[[Anything alloc] init] autorelease];
! [a addObject:[NSValue valueWithNonretainedObject:new_a]];
! [a addObject:[NSValue valueWithNonretainedObject:new_a2]];
}
-(void)use_something {
! Anything * aa = [[a objectAtIndex:0] nonretainedObjectValue];
}

49. Objective-C
• What if we retain by accident?
@interface Something : NSObject {
! NSMutableArray * a;
}
@property(nonatomic, retain) NSMutableArray * a;
@end
-(void)do_something {
! Anything * new_a = [[[Anything alloc] init] autorelease];
! Anything * new_a2 = [[[Anything alloc] init] autorelease];
! [a addObject:new_a]; // Someone forgot
! [a addObject:new_a2]; // Someone forgot
}

50. Objective-C
• Containers are untyped
@interface Something : NSObject {
! NSMutableArray * a; // Of Anything
}
@property(nonatomic, retain) NSMutableArray * a; // Of Anything
@end
-(void)do_something {
! Anything * new_a = [[[Anything alloc] init] autorelease];
! Anything * new_a2 = [[[Anything alloc] init] autorelease];
! [a addObject:new_a];
! [a addObject:new_a2];
}

51. Objective-C
• Untyped containers are hard to prove
@interface Something : NSObject {
! NSMutableArray * a; // Of Anything
}
@property(nonatomic, retain) NSMutableArray * a; // Of Anything
@end
-(void)do_something {
! Anything * new_a = [[[Anything alloc] init] autorelease];
! NSString * str = @"Hi";
! [a addObject:new_a];
! [a addObject:str];
}

52. Objective-C++
• We can use great STL containers
@interface Something : NSObject {
! std::vector<Anything *> a;
}
@end
-(void)do_something {
! Anything * new_a = [[[Anything alloc] init] autorelease];
! NSString * str = @"Hi";
! a.push_back( new_a );
! a.push_back( str );
}

53. Objective-C++
• Retain strategy is independent
@interface Something : NSObject {
! std::vector< NSPtr<Anything> > a;
}
@end
-(void)do_something {
! Anything * new_a = [[[Anything alloc] init] autorelease];
! NSString * str = @"Hi";
! a.push_back( new_a );
! a.push_back( str );
}

54. Objective-C++
• Integration is almost flawless!
• Apple teams actually use C++ and STL
@interface Something : NSObject {
! std::vector< id<UIActionSheetDelegate> > a;
}
@end
-(void)do_something {
! std::for_each(a.begin(), a.end(), ^(id<UIActionSheetDelegate> x) {
! ! [x actionSheetCancel:nil];
! });
}

55. Success
• alloc-init-autorelease idiom
• NSPtr or @property(retain) to manage
retain/release
• Use text editor to eliminate all retain,
release
• Architecture with no cycles
• Typed containers (STL), so the compiler
can actually prove most of your
architecture

56. What we forgot?
• Active objects (timers, http requests)
• Parallel execution (NSOperation)

57. What we forgot?
• Active objects (timers, http requests)
• Parallel execution (NSOperation)
Do not worry!
This is also easy!

58. Q&A
Q&A
Grigory Buteyko
hrissan@mail.ru
www.dataart.com