1. AspectAda Aspect-Oriented Programming for Ada95
Computer Science & Software Engineering
AspectAda
Aspect-Oriented Programming for Ada95
WORLD CLASS – through people, technology and dedication
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2. Agenda Separation of Concerns + Crosscutting
Aspect-Oriented Programming (AOP) Model
Logging Example
AspectAda Prototype Architecture
Effect on SW Quality
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3. Separation of Concerns (SoC)
“Separation of Concerns (SoC)” (Parnas, Dijkstra):
realization of problem domain concepts into separate units of software.
Benefits of SoC
Better analysis and understanding of systems
Easy adaptability, maintainability and high degree of reusability.
Low Coupling/High Cohesion
SoC Fundamental to SW Development
Ada95 SoC
Packages, Subprograms,
Tagged Types, Protected Types, Tasks
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4. Crosscutting Concerns
Certain properties cannot be localized in single modular units, but their implementation cuts across the decomposition hierarchy of the system.
These properties are called crosscutting concerns, or aspects.
Concern (Requirement)
Functional
Non-functional
Design
Crosscutting Concern
A concern that is implemented in more than one location
security, logging, synchronization, fault tolerance, design by contract
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5. Initial Picture of Crosscutting
[Constantinides]
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6. CORBA Servant Implementation
procedure Do_Some(Self: in out Object; Data : in Data_t) is
begin
 Tracer.Enter(Self.TraceId, “Do_Some”);
 Mutex.Lock(Self.Lock);
....
-- Do business-logic
--(Also invoking methods across CORBA)
Fault_Tolerance.Log_State(Make_Stream(Data));
Mutex.Unlock(Self.Lock);
Tracer.Exit(Self.TraceId, “Do_Some”);
exception
when event : others =>
 Mutex.Unlock(Self.Lock);
 Error_Logger.Log_Error(event, “Unknown Exception in Do_Some”);
end Do_Some;
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7. Crosscutting identification
procedure Do_Some(Self: in out Object; Data : in Data_t) is
begin
 Tracer.Enter(Self.TraceId, “Do_Some”);
 Mutex.Lock(Self.Lock);
....
-- Do business-logic
--(Also invoking methods across CORBA)
Fault_Tolerance.Log_State(Make_Stream(Data));
Mutex.Unlock(Self.Lock);
Tracer.Exit(Self.TraceId, “Do_Some”);
exception
when event : others =>
 Mutex.Unlock(Self.Lock);
 Error_Logger.Log_Error(event, “Unknown Exception in Do_Some”);
end Do_Some;
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8. Symptoms of Crosscutting
Crosscutting imposes two symptoms on software development:
Code scattering: implementation of some concerns not well modularized but cuts across the decomposition hierarchy of the system.
Code tangling: a module may contain implementation elements (code) for various concerns.
Problems
Low cohesion
Strong coupling
Low reusability, adaptability
Difficult comprehensibility
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9. AOP Version Aspects Composition rules Tracer Mutex FT State
procedure Do_Some(Self: in out Object; Data : in Data_t) is
begin
-- Do business-logic
--(Also invoking methods across CORBA)
end Do_Some;
Aspects
Tracer
Mutex
FT State
Exception handling
Composition rules
Rules for inserting aspect behavior to components
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10. AOP Programming Model
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11. Aspect Oriented Programming
AOP Complementary to OOP as OOP was to procedural programming
Also applicable to procedural programming
Aspect Languages extends traditional programming languages
Abstractions for representing crosscutting concerns (Aspects)
Composition of Aspects and traditional modules (Weaving)
Improves modularity, adaptability, traceability
AspectJ – Dominant AOP language extension for Java
AspectAda – Our Proposal to extend Ada95
Influenced by AspectJ
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12. Joinpoint Well defined instant in the execution of a program
Subprogram execution
Finalization, Initialization, Adjust (Controlled Types)
Variable access (Object declarations)
Package body statement block
Named block statements
Named loop statements
Rendezvous/Entry points
procedure Do_Some(Self: in out M_Object; Data : in Data_t) is
...
begin
end Do_Some;
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13. Pointcuts Set of joinpoints (object declaration)
Pointcut expression (AspectJ Influenced)
Primitive pointcuts
Call
Execution
Get/Set of variables
Wildcard matching (*, ..)
Composition using and, or, xor, not
When a pointcut is matched, an advice can be executed
My_PC : Pointcut :=
execution Some_Pk.Do_* (in out M_Object; ..) or
execution Some_Pk.Set_* (in out M_Object; ..);
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14. Advice Code module (as a subprogram) that attaches to a pointcut
Injects behavior at all joinpoints selected by that pointcut
Three types:
Before (code injected before the joinpoint)
After (code injected after the joinpoint)
Around (code injected around (in place of) code from joinpoint
advice Around(Mutex_A : in out Mutex_Aspect) is
begin
Mutex_A.Mutex.Lock;
Proceed;
Mutex_A.Mutex.Unlock;
when others =>
raise;
end Around;
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15. Aspect A modular unit of crosscutting behavior
Advice type (tagged)
Simple (Performance)
Detailed (Contextual information)
Advice(s) bound to pointcut(s) (Advice clause)
Like a package can have subprograms, types ...
Parameterized to bind to one or more pointcut(s)
generic
Mutex_P : Pointcut;
aspect Mutex_Aspects is
type Mutex_Aspect is new Simple_Aspect
with record
Mutex : Mutex_t;
end Mutex_Aspect;
advice Around.....
for Around’Advice use Mutex_P;
end Mutex_Aspects;
Generic
Aspect
Composition rules
Ada95
Modules
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16. Logging Example
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17. AOP Tracing Example: Aspect Spec
with AspectAda;
generic
Tracer_P : Pointcut;
aspect Tracer is
type Tracer_Aspect is
new Aspect_Ada.Detailed_Aspect with null record;
advice Before(Tracer : in Tracer_Aspect);
for Before’Pointcut use Tracer_P;
advice After(Tracer : in Tracer_Aspect);
for After’Pointcut use Tracer_P;
end Tracer;
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18. AOP Tracing Example: Aspect Body
with Ada.Text_IO; use Ada.Text_IO;
with Aspect_Ada; use Aspect_Ada;
aspect body Tracer is
advice Before(Tracer : in Tracer_Aspect) is begin
Put_Line(“==> “ & Image(Get_Join_Point(Tracer).all));
end Before;
advice After(Tracer : in Tracer_Aspect) is begin
Put_Line(“<==” & Image(Get_Join_Point(Tracer).all));
end After;
end Tracer;
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19. AOP Tracing Example: Composition Rules
with Tracer; use Tracer;
weaver CMS_Proto is
Gun_Control_All_PC : Pointcut := execution Gun*.*(..);
aspect Gun_Control_Logger is
new Tracer_Aspect(Tracer_P => Gun_All_PC);
end CMS_Proto;
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20. AspectAda Prototype Architecture
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21. AspectAda Architecture: Conceptual View
[Hofmeister Notation]
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22. Weaver Prototype: Modular View
ASIS Based (Ada95)
AdaGOOP (Aspects, Pointcuts)
Ada.Containers
Easy to adapt to Ada2005
Merging
Selection
ASIS
Aspect
Parser
Pointcut
JoinPointModel
Controller
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23. Effects on SW Quality
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24. Effects on SW Quality Cohesion Coupling Adaptability
One concern in Ada95 module
Crosscutting concerns modularized in aspects
Coupling
Minimal coupling modeled using pointcut expressions
Reversed dependency direction
Adaptability
Code comprehensibility
Tradeoff
Traceability
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25. Future Work Extended joinpoint model
Call, Set/Get
Named blocks, named loops
Export of context at Joinpoints (objects, arguments)
Extend GPS Plugin (GNAT Programming System)
Joinpoint model and Ada generics
Increased Aspect reusability
Design by contract support
Open for suggestions
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26. Conclusion Crosscutting concerns
Joinpoint model (joinpoints, pointcuts, advices, aspects)
Tracing using AspectAda
AspectAda Prototype Architecture
Effects on SW Quality
Future Work
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27. WORLD CLASS – through people, technology and dedication
End
WORLD CLASS – through people, technology and dedication
KONGSBERG April 23, 2019