Subjective-C: Bringing Context to Mobile Platform Programming

Subjective-CBringing Context to Mobile Platform Programming

ICTEAM / UCLouvain / Belgium

Alfredo Cádiz Jean-Christophe Libbrecht

Julien Goffaux

Software Language Engineering

Sebastián GonzálezNicolás Cardozo

Kim Mens

3rd International Conference on

13 October 2010Thursday 21 October 2010




Julien Goffaux



Kim Mens


Sebastián González

Kim Mens





Julien Goffaux



Kim Mens


Sebastián González

Kim Mens


2

Research Context

Thursday 21 October 2010

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??

?

?

programming in isolation programming in contextProgramming Mindset Towards a Mindset Shift

3

Research Goal


class phone {

method receive ( call ) {

if ( phone.isOffHook( ) )play( phone.callWaitingSignal( ), 2 );

else if ( phone.environment( ).acoustics( ).isQuiet( ) )phone.vibrate( 5 );

else if ( phone.user( ).isUnavailable( ) )forwardCall( call, phone.forwardNumber( ) );

elseplay( phone.ringTone( ), 10 );

}

conditional statements

4

Contemporary Solution


class phone {






}


4



class phone {






}


4


·


class phone {






}


4


·


class phone {






}


4


∅

·


class phone {






}


Tangled

Fixed 4

Scattered


∅

·


class Phone{ attribute strategy; method receive ( call ) { strategy.receive ( call ); } }

special software architecturesContemporary Solution

5Thursday 21 October 2010

class UnavailableStrategy{ method receive ( call ) { ... } }

class QuietStrategy{ method receive ( call ) { ... } }

class OffHookStrategy{ method receive ( call ) { ... } }

class DefaultStrategy{ method receive ( call ) { ... } }


UnavailableStrategy

OffHookStrategy


5

QuietStrategyPhone

DefaultStrategy

·







UnavailableStrategy

OffHookStrategy


5

QuietStrategyPhone

DefaultStrategy

·







UnavailableStrategy

OffHookStrategy


5

QuietStrategyPhone

DefaultStrategy

Infrastructural burdenFixed adaptation points


Solution Language engineering approach

6



Prototypes

Multiple dispatch

PMD

6SmalltalkSelfCLOS



Prototypes

Multiple dispatch

PMD

Subjective Programming

6SmalltalkSelfCLOS


Context Management


Prototypes

Multiple dispatch

PMD


6SmalltalkSelfCLOS


Context Management


Prototypes

Multiple dispatch

Context-Oriented Programming

PMD


6SmalltalkSelfCLOS


Context Management

Solution

Ambience

Language engineering approach

Prototypes

Multiple dispatch


PMD

[DLS’07]


6SmalltalkSelfCLOS


Context Management

Solution

Ambience


Prototypes

Multiple dispatch


PMD

[DLS’07]


6SmalltalkSelfCLOS


Context Management

Solution

Ambience


Prototypes

Multiple dispatch


Open Classes

Single dispatch

PMD

[DLS’07]

Objective-C


6SmalltalkSelf CCLOS


Context Management

Solution

Ambience


Prototypes

Multiple dispatch


Open Classes

Single dispatch


PMD

[DLS’07]

Objective-C




Context ManagementContext Management

Solution

Ambience


Prototypes

Multiple dispatch


Open Classes

Single dispatch


PMD

[DLS’07]

Objective-C





Solution

Ambience


Prototypes

Multiple dispatch


Open Classes

Single dispatch


PMD

[DLS’07]


Objective-C





Solution

Ambience


Prototypes

Multiple dispatch


Subjective-C

Open Classes

Single dispatch


PMD

[DLS’07]


Objective-C





Solution

Ambience


Prototypes

Multiple dispatch


Subjective-C

Open Classes

Single dispatch


PMD

[DLS’07]


Objective-C




1 General mindset

2 Context definition

3 Context-specific behaviour

4 Context relations

5 Implementation

6 Efficiency

Subjective-C

7Thursday 21 October 2010

external

Context-Aware System Architecture

Subjective-C

context effectcontext

information

ActuatorsSensors

arbitratedcontext changes

World

Context Discovery

Context Management

Active Context

8

internal

Application Behaviour

1 Mindset1 Mindset 2 Context 3 Behaviour 4 Relations 5 Implementation 6 Efficiency


Low battery charge

High CPU load

Battery charge = 220 mAh

Computationally accessible information

Idle cycles = 11 MHz

action can be taken

Well-defined situation(Contexts)

Location = 51°26′N 5°29′E Eindhoven

no semantics

What is context?

9

Z axis = 0.03 Landscape orientation

situations can be reified

2 Context1 Mindset 2 Context 3 Behaviour 4 Relations 5 Implementation 6 Efficiency


http://toolserver.org/~geohack/geohack.php?pagename=Eindhoven_University_of_Technology&params=51_26_53_N_5_29_23_E_region:NL_type:edu

http://toolserver.org/~geohack/geohack.php?pagename=Eindhoven_University_of_Technology&params=51_26_53_N_5_29_23_E_region:NL_type:edu

10

1 Mindset 2 Context 3 Behaviour 4 Relations 5 Implementation 6 Efficiency

Case Study3 Behaviour



UILabel classdrawTextInRect:Draws the receiver’s text in the specified rectangle.- (void)drawTextInRect:(CGRect)rectParametersrect

The rectangle in which to draw the text.DiscussionYou should not call this method directly. This method should only be overridden by subclasses that want to modify the default drawing behavior for the label’s text.AvailabilityAvailable in iOS 2.0 and later.Declared InUILabel.h

Case Study

11

3 Behaviour



UILabel classdrawTextInRect:Draws the receiver’s text in the specified rectangle.- (void)drawTextInRect:(CGRect)rectParametersrect

The rectangle in which to draw the text.DiscussionYou should not call this method directly. This method should only be overridden by subclasses that want to modify the default drawing behavior for the label’s text.AvailabilityAvailable in iOS 2.0 and later.Declared InUILabel.h

Case Study

11

3 Behaviour


Subjective-C: Look & Feel

@implementation UILabel (color)#context Landscape- (void)drawTextInRect:(CGRect)rect { self.textColor = [UIColor greenColor]; [superContext drawTextInRect:rect];}@end

12

1 Mindset 2 Context 3 Behaviour 4 Relations 5 Implementation 6 Efficiency3 Behaviour




Open classesObjective-C

12





Open classesObjective-CCOP

Subjective-C

12





Open classesObjective-CCOP

Subjective-C

✓ Adaptation of any existing component✓ No access to original source code needed✓ Adaptations can be cleanly modularised

12



Context Relations

HDVideo BatteryHighRequirement

Museum Quiet

Eindhoven NetherlandsStrong Inclusion

Weak Inclusion

Landscape PortraitExclusion

13

1 Mindset 2 Context 3 Behaviour 4 Relations 5 Implementation 6 Efficiency4 Relations


// Create contextsContext* Room = [[Context alloc] initWithName:@"Room"];Context* Bedroom = [[Context alloc] initWithName:@"Bedroom"];Context* Day = [[Context alloc] initWithName:@"Day"];Context* Night = [[Context alloc] initWithName:@"Night"];...

// Register contexts[CONTEXT addContext:Room];[CONTEXT addContext:Bedroom];[CONTEXT addContext:Day];[CONTEXT addContext:Night];...

// Establish context relations[Day addExclusionRelationWith:Night];[Bedroom addHardInclusionRelationWith:Room];...

Programmatic Context Definition

14






Context Declaration Language

14

Relations:

Day >< NightSun >< Rain

Livingroom -> TVLivingroom -> WindowLivingroom -> LuminosityLivingroom -> TemperatureKitchen -> LuminosityBedroom -> TemperatureBedroom -> LuminosityBedroom -> WindowBathroom -> TemperatureBathroom -> Luminosity

Bathroom => RoomKitchen => RoomLivingroom => RoomBedroom => Room

TV =< ElectricityLuminosity =< ElectricityWindow =< Sun

Contexts:

RoomLivingroomKitchenBedroomBathroomDayNight

TVWindowTemperatureLuminosity

SunRainElectricity






Context Declaration Language

14



// Register context-specific methods[MANAGER addMethod:@selector(Context_Bedroom_getActiveRoom) forClass:[DomoticsServerViewController class] forContextNames:[[NSSet alloc] initWithObjects:@"Bedroom" ,nil] withDefautSel:@selector(getActiveRoom) withPriority:0];...




14


#context Bedroom-(Context*) getActiveRoom{! return [CONTEXT getContext:@"Bedroom"];}

Other Generated Code


// Register context-specific methods[MANAGER addMethod:@selector(Context_Bedroom_getActiveRoom) forClass:[DomoticsServerViewController class] forContextNames:[[NSSet alloc] initWithObjects:@"Bedroom" ,nil] withDefautSel:@selector(getActiveRoom) withPriority:0];...




14


Other Generated Code


@implementation LowpassFilter

-(void)addAcceleration:(UIAcceleration*)accel{! double alpha = filterConstant;!! if(adaptive)! ! alpha = ... // big formula to calculate the alpha level!! x = accel.x * alpha + x * (1.0 - alpha);! y = accel.y * alpha + y * (1.0 - alpha);! z = accel.z * alpha + z * (1.0 - alpha);}

-(NSString*)name{! return adaptive ? @"Adaptive Lowpass Filter" : @"Lowpass Filter";}

...

15


Application Contexts


16



#context LowPassFilter-(void)addAcceleration:(UIAcceleration*)accel{! double alpha = [self getAlpha:accel];!! x = accel.x * alpha + x * (1.0 - alpha);! y = accel.y * alpha + y * (1.0 - alpha);! z = accel.z * alpha + z * (1.0 - alpha);}

#context !Adaptive-(double) getAlpha:(UIAcceleration*)accel{! return filterConstant;}

#context LowPassFilter Adaptive-(double) getAlpha:(UIAcceleration*)accel {! return // big formula to calculate the alpha level;}



16



#context LowPassFilter-(void)addAcceleration:(UIAcceleration*)accel{! double alpha = [self getAlpha:accel];!! x = accel.x * alpha + x * (1.0 - alpha);! y = accel.y * alpha + y * (1.0 - alpha);! z = accel.z * alpha + z * (1.0 - alpha);}

#context !Adaptive-(double) getAlpha:(UIAcceleration*)accel{! return filterConstant;}

#context LowPassFilter Adaptive-(double) getAlpha:(UIAcceleration*)accel {! return // big formula to calculate the alpha level;}

Relations:

LowPassFilter >< HighPassFilter LowPassFilter => FilterHighPassFilter => Filter

Contexts:

AdaptivePausedLowPassFilterHighPassFilterFilter



Implementation

17

dynamic method pre-dispatch

UILabel@property NSString *text@property UIFont *font...- (void)Portrait_drawTextInRect:(CGRect)rect- (void)Landscape_drawTextInRect:(CGRect)rect- (void)Default_drawTextInRect:(CGRect)rect- (void)drawTextInRect:(CGRect)rect

1 Mindset 2 Context 3 Behaviour 4 Relations 5 Implementation 6 Efficiency5 Implementation

Default impl

Landscape impl

Portrait impl


http://developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSString_Class/Reference/NSString.html#//apple_ref/doc/c_ref/NSString


http://developer.apple.com/library/ios/documentation/uikit/reference/UIFont_Class/Reference/Reference.html#//apple_ref/doc/c_ref/UIFont


Implementation

17




Default impl

Landscape impl

Portrait implvtable






Implementation

17




Default impl

Landscape impl

Portrait impl






Implementation

17




Default impl

Landscape impl

Portrait impl






Implementation

17



[CONTEXT activateContextWithName: @"Landscape"];


Default impl

Landscape impl

Portrait impl






Implementation

17





Default impl

Landscape impl

Portrait impl






Implementation

17




[CONTEXT deactivateContextWithName: @"Landscape"];


Default impl

Landscape impl

Portrait impl






Implementation

17






Default impl

Landscape impl

Portrait impl






Implementation

17



‣ no additional cost for method invocations‣ cost incurred at context switching time




Default impl

Landscape impl

Portrait impl






-(void) test:(int) mode {

if (mode == 1) result = 1;

...

else if (mode == N) result = N;

else result = 0;}

Objective-C

#context C1-(void) test{ result = 1; }

...

#context CN-(void) test{ result = N; }

-(void) test{ result = 0; }

Subjective-C

18

conditional statementscontext-specific methods

What is more efficient?1 Mindset 2 Context 3 Behaviour 4 Relations 5 Implementation 6 Efficiency6 Efficiency



...

#context CK-(void) test{ result = K; }

...



Subjective-Cfor (int i = 0; i < 1000; i++) {

// switch context if (i % 2) [CONTEXT activateContextWithName:@"CK"]; else [CONTEXT deactivateContextWithName:@"CK"];

// call test method repeatedly for (int j = 0; j < M; j++) [self test];}

19

Benchmark Setup1 Mindset 2 Context 3 Behaviour 4 Relations 5 Implementation 6 Efficiency6 Efficiency



...

#context CK-(void) test{ result = K; }

...



Subjective-Cfor (int i = 0; i < 1000; i++) {

// switch context if (i % 2) [CONTEXT activateContextWithName:@"CK"]; else [CONTEXT deactivateContextWithName:@"CK"];

// call test method repeatedly for (int j = 0; j < M; j++) [self test];}

19

Benchmark Setup

N: number of variationsK: selected branchM: method calls per mode switch

1 Mindset 2 Context 3 Behaviour 4 Relations 5 Implementation 6 Efficiency6 Efficiency



if (mode == 1) result = 1;

...

if (mode == K) result = K;

...

else if (mode == N) result = N;

else result = 0;}

Objective-Cfor (int i = 0; i < 1000; i++) {

// toggle operation mode if (i % 2) mode = K; else mode = 0;

// call test method repeatedly for (int j = 0; j < M; j++) [self test: mode];}

20

Benchmark Setup

N: number of variationsK: selected branchM: method calls per mode switch



10−1

100

101

102

103

104

105

100 101 102 103 104 105

milliseconds

method calls per context switch (M)

M∗

Subjective-C

Objective-C

Fig. 6. Performance comparison using logarithmic scale (N = 50, K = 50).

From the benchmarks we can conclude that the efficiency of Subjective-C

is highly dependent on its usage. Most benefits are obtained for contexts that

are not switched too often with respect to the rate of usage of affected methods.

For many common cases this condition will hold: context switches will usually be

sparse enough in time with respect to affected method calls. In particular, in each

of the three case studies described in Section 5, the Subjective-C implementation

did not give raise to apparent performance penalties.

Note that although gained efficiency for some use cases is a desirable side

effect of using Subjective-C, the more important benefits remain in the realm

of software engineering: improved modularisation, reusability, extensibility, and

dynamic adaptability.

7 Discussion, Limitations and Future Work

Even though Subjective-C is usable for application development on mobile de-

vices as suggested in Section 5, it still has rough edges we need to iron out. This

section describes the most salient ones, starting with the more technical and

going over to the more conceptual.

Super-Context Translation A caveat of the implementation presented in

Section 4.3 is the impossibility to retrieve the return value from a superContextmessage. Our current solution consists in having a different syntax when the

return value is needed, which complements the definition of the superContextconstruct given in Section 2.4:

[superContext selector] => variable;[superContext keyword: argument ...] => variable;


if (mode == 1)

result = 1;

else if (mode == 2)

result = 2;

...

else if (mode == N)

result = N;

else

result = 0;

}

-(void) test {

result = 0;

}

#context C1

-(void) test {

result = 1;

}

...

#context CN

-(void) test {

result = N;

}

Snippet 11. Dummy test methods in Objective-C (left) and Subjective-C (right) with

N + 1 behavioural variants. The choice of the variant depends on the application’s

current operating mode and the application’s current execution context, respectively.

for (int i = 0; i < 1000; i++) {

if (i % 2)

[CONTEXT activateContextWithName:@"CK"]; // mode = K;

else

[CONTEXT deactivateContextWithName:@"CK"]; // mode = 0;

for (int j = 0; j < M; j++)

[self test];

}

Snippet 12. Code to measure the relative cost of context changes with respect to

context-dependent method invocation in Subjective-C; the Objective-C counterpart is

analogous and is therefore just suggested as comments.

calls per context switch. Beyond this point, Subjective-C is more efficient than

Objective-C; the execution time in both approaches will tend to grow linearly,

although Objective-C will have a considerably higher slope due to conditional

statement execution,7 besides the cost of method invocation which is incurred in

both approaches. Table 4 summarises the intersection points for various values

of N and K, including the case of Fig. 6.

N K M∗

5 1 8230

10 1 4708

50 1 3405

5 5 4521

10 10 2653

50 50 1148

Table 4. Efficiency meeting point M∗between Subjective-C and Objective-C.

7This difference is not apparent in Fig. 6 because of the logarithmic scale.

21

N: number of variationsK: selected branchM: method calls per context switch

iPhone 3GS, iOS 4.0



Subjective-C✓ Context-oriented programming for a C-flavoured language✓ Runs on mobile phones✓ Run-time behaviour adaptation of any component (incl. 3rd party)✓ Permits clean modularisation of adaptations✓ Maximises adaptation points while avoiding architectural burden✓ Context interdependency system✓ Context declaration language✓ Can be more efficient than dynamic dispatch➡ Thread-local adaptations➡ Improving efficiency➡ Usability (IDE integration)➡ Ensure behaviour consistency



Subjective-C✓ Context-oriented programming for a C-flavoured language✓ Runs on mobile phones✓ Run-time behaviour adaptation of any component (incl. 3rd party)✓ Permits clean modularisation of adaptations✓ Maximises adaptation points while avoiding architectural burden✓ Context interdependency system✓ Context declaration language✓ Can be more efficient than dynamic dispatch➡ Thread-local adaptations➡ Improving efficiency➡ Usability (IDE integration)➡ Ensure behaviour consistency

http://ambience.info.ucl.ac.be


Time for questions!




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