Subjective-C: Bringing Context to Mobile Platform Programming

3rd International Conference on
Software Language Engineering

Subjective-C
Bringing Context to Mobile Platform Programming

ICTEAM / UCLouvain / Belgium

Sebastián González Alfredo Cádiz
Nicolás Cardozo Jean-Christophe Libbrecht
Kim Mens Julien Goffaux

13 October 2010
Thursday 21 October 2010

3rd International Conference on
Software Language Engineering

Subjective-C
Bringing Context to Mobile Platform Programming

ICTEAM / UCLouvain / Belgium

Sebastián González
Sebastián González Alfredo Cádiz
Nicolás Cardozo Jean-Christophe Libbrecht
Kim Mens
Kim Mens Julien Goffaux

13 October 2010

Research Context

2

Research Goal
Programming Mindset Towards a Mindset Shift
programming in isolation programming in context

?
?
?

?
?
?

3

Contemporary Solution
conditional statements
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( ) );
else
play( phone.ringTone( ), 10 );
}

4

class phone {
phone.vibrate( 5 ); ·
else
play( phone.ringTone( ), 10 );
}

4

class phone {
else
play( phone.ringTone( ), 10 ); ∅
}

4

class phone {
else
play( phone.ringTone( ), 10 ); ∅
}

Tangled
Scattered
Fixed 4

special software architectures

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

5


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

class QuietStrategy
class Phone { method receive ( call ) { ... } } ·
method receive ( call ) class OffHookStrategy
{ strategy.receive ( call ); } } { method receive ( call ) { ... } }

class UnavailableStrategy

5


class DefaultStrategy

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

class UnavailableStrategy

Infrastructural burden
Fixed adaptation points
5

Solution Language engineering approach

6


Multiple dispatch
Prototypes

PMD
CLOS
Self Smalltalk 6


Subjective Programming
Multiple dispatch
Prototypes

PMD
CLOS
Self Smalltalk 6


Context Management
Multiple dispatch
Prototypes

PMD
CLOS
Self Smalltalk 6


Context-Oriented Programming
Context Management
Multiple dispatch
Prototypes

PMD
CLOS
Self Smalltalk 6


Ambience [DLS’07]

Context Management
Multiple dispatch
Prototypes

PMD
CLOS
Self Smalltalk 6


Ambience [DLS’07]

Context Management
Multiple dispatch Single dispatch
Prototypes Open Classes

PMD Objective-C
CLOS C
Self Smalltalk 6


Ambience [DLS’07]

Context Management
Subjective Programming Subjective Programming

PMD Objective-C
CLOS C
Self Smalltalk 6


Ambience [DLS’07]

Context Management Context Management

PMD Objective-C
CLOS C
Self Smalltalk 6


Ambience [DLS’07]


PMD Objective-C
CLOS C
Self Smalltalk 6


Ambience [DLS’07] Subjective-C

PMD Objective-C
CLOS C
Self Smalltalk 6

Subjective-C
1 General mindset
2 Context definition
3 Context-specific behaviour
4 Context relations
5 Implementation
6 Efficiency
7

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

Context-Aware System Architecture

World
Sensors Actuators
Subjective-C
Context Application
Discovery Behaviour
external internal context
effect
context
information arbitrated
context
Context changes Active
Management Context
8


What is context?
Computationally Well-deﬁned situation
accessible information (Contexts)
Z axis = 0.03 Landscape orientation
Battery charge = 220 mAh Low battery charge
Idle cycles = 11 MHz High CPU load
Location = 51°26′N 5°29′E Eindhoven

no semantics action can be taken

situations can be reiﬁed
9


Case Study

10


Case Study
UILabel class
drawTextInRect:
Draws the receiver’s text in the speciﬁed rectangle.
- (void)drawTextInRect:(CGRect)rect
Parameters
rect
The rectangle in which to draw the text.
Discussion
You 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.
Availability
Available in iOS 2.0 and later.
Declared In
UILabel.h
11


Subjective-C: Look & Feel

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

12


Open classes
@implementation UILabel (color) Objective-C
#context Landscape
}
@end

12


Open classes
COP #context Landscape
Subjective-C
}
@end

12


Open classes
COP #context Landscape
Subjective-C
}
@end

✓ Adaptation of any existing component
✓ No access to original source code needed
✓ Adaptations can be cleanly modularised
12


Context Relations
Strong Inclusion Eindhoven Netherlands

Weak Inclusion Museum Quiet

Requirement HDVideo BatteryHigh

Exclusion Landscape Portrait

13


Programmatic Context Deﬁnition
// Create contexts
Context* 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];
...

14


Context Declaration Language
Contexts: Relations:
// Create contexts
Context* Bedroom = [[Context alloc] initWithName:@"Bedroom"]; >< Night
Room Day
Context* Livingroom
Day = [[Context alloc] initWithName:@"Day"]; Sun >< Rain
Context* Kitchen
Night = [[Context alloc] initWithName:@"Night"];
... Bedroom Livingroom -> TV
Bathroom Livingroom -> Window
// Register contexts Day Livingroom -> Luminosity
[CONTEXT addContext:Bedroom]; Night Livingroom -> Temperature
[CONTEXT addContext:Day]; Kitchen -> Luminosity
[CONTEXT addContext:Night]; TV Bedroom -> Temperature
... Window Bedroom -> Luminosity
Temperature Bedroom -> Window
// Establish context relations Luminosity Bathroom -> Temperature
[Bedroom addHardInclusionRelationWith:Room]; Bathroom -> Luminosity
... Sun
Rain Bathroom => Room
Electricity Kitchen => Room
Livingroom => Room
Bedroom => Room

TV =< Electricity
Luminosity =< Electricity
Window =< Sun 14


Context Declaration Language
// Create contexts
...

...

...

14


Other Generated Code
// Create contexts
...

...

// Establish context relations #context Bedroom
[Day addExclusionRelationWith:Night]; -(Context*) getActiveRoom{
! return [CONTEXT getContext:@"Bedroom"];
...
}

// 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
// Create contexts
...

...

...

// 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


Application Contexts
@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



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


Contexts:

#context LowPassFilter
Adaptive
Paused
{
LowPassFilter
! double alpha = [self getAlpha:accel];
HighPassFilter
!
! x = accel.x * alpha + x * (1.0 - alpha); Filter
! y = accel.y * alpha + y * (1.0 - alpha); Relations:
}
LowPassFilter >< HighPassFilter
LowPassFilter => Filter
#context !Adaptive
HighPassFilter => Filter
-(double) getAlpha:(UIAcceleration*)accel{
! return filterConstant;
}

#context LowPassFilter Adaptive
-(double) getAlpha:(UIAcceleration*)accel {
! return // big formula to calculate the alpha level;
}
16


Implementation
dynamic method pre-dispatch

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

17


Implementation

UILabel
... vtable
Portrait impl

17


Implementation

UILabel
...
Portrait impl

[CONTEXT activateContextWithName: @"Landscape"];

17


Implementation

UILabel
...
Portrait impl

[CONTEXT deactivateContextWithName: @"Landscape"];

17


Implementation

UILabel
...
Portrait impl

[CONTEXT deactivateContextWithName: @"Landscape"];

‣ no additional cost for method invocations
‣ cost incurred at context switching time 17


What is more efﬁcient?
Subjective-C Objective-C
context-speciﬁc methods conditional statements
#context C1 -(void) test:(int) mode {
-(void) test
{ result = 1; } if (mode == 1)
result = 1;
...
...
#context CN
-(void) test else if (mode == N)
{ result = N; } result = N;

-(void) test else
{ result = 0; } result = 0;
}
18


Benchmark Setup
Subjective-C
#context C1
-(void) test for (int i = 0; i < 1000; i++) {
{ result = 1; }
// switch context
... if (i % 2)
[CONTEXT activateContextWithName:@"CK"];
#context CK else
-(void) test [CONTEXT deactivateContextWithName:@"CK"];
{ result = K; }
// call test method repeatedly
... for (int j = 0; j < M; j++)
[self test];
#context CN }
-(void) test
{ result = N; }

-(void) test
{ result = 0; }
19


Benchmark Setup
Subjective-C
#context C1
-(void) test for (int i = 0; i < 1000; i++) {
{ result = 1; }
// switch context
... if (i % 2)
[CONTEXT activateContextWithName:@"CK"];
#context CK else
-(void) test [CONTEXT deactivateContextWithName:@"CK"];
{ result = K; }
... for (int j = 0; j < M; j++)
[self test];
#context CN }
-(void) test
{ result = N; }
N: number of variations
-(void) test K: selected branch
{ result = 0; }
M: method calls per mode switch 19


Benchmark Setup
Objective-C
-(void) test:(int) mode {
for (int i = 0; i < 1000; i++) {
if (mode == 1)
result = 1; // toggle operation mode
if (i % 2)
... mode = K;
else
if (mode == K) mode = 0;
result = K;
... for (int j = 0; j < M; j++)
[self test: mode];
else if (mode == N) }
result = N;

else
N: number of variations
result = 0; K: selected branch
}
M: method calls per mode switch 20

e case of 1 Mindset 2 Context 3 Behaviour 4 Relations 5 Implementation 6 Efﬁciency
Fig. 6.

N K M∗ N: number of variations
5 1 8230
10 1 4708 K: selected branch
50
5
1
5
3405
4521 M: method calls per context switch
10 10 2653
50 50 1148 105
ting point M ∗ between Subjective-C and Objective-C.
Subjective-C
104 Objective-C
parent in Fig. 6 because of the logarithmic scale.
103
milliseconds

M∗
102

101

100

10−1
100 101 102 103 104 105
method calls per context switch (M)

Fig. 6. Performance comparison using logarithmic scale (N = 50, K = 50).
iPhone 3GS, iOS 4.0 21


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)
Time for questions!
➡ Ensure behaviour consistency
http://ambience.info.ucl.ac.be

Subjective-C: Bringing Context to Mobile Platform Programming

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