2. Aspect Instantiation Models (AIMs)
• What is an aspect?
– Crosscutting behavior + crosscutting state
• What is an AIM?
– 6 keyword in AspectJ: issingleton, pertarget, perthis,
percflow, percflowbelow, pertypewithin.
– Added incrementally to AspectJ
– More AIMs in other AOP languages
• There is a need for custom AIMs
– Challenge: decouple the definition of AIMs from the
evolution of the language
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3. Contribution of this Work
• Pluggable Aspect Instantiation Models
– Make AIMs pluggable!
❶ Language extension
– We introduce a new keyword: ‘perscope’
• Replaces the exiting 6 keywords
• Eliminates need for new keywords (hopefully)
❷ Interface for defining AIMs
– Third parties can design and implement new AIMs
❸ Library of AIM Implementations
– Fully implemented in ajc
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4. Outline
• Introduction
• Requirements
• Example
• Pluggable Mechanism
• Conclusion
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5. Motivation: “caching and auditing”
• Industrial Case Study
– Web application development with AspectJ
– Need for ‘persession’ and ‘perconversation’ AIMs
Cache
Cache
Cache Cache
Cache
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6. Current Solution
• Wait for a new release of AspectJ
– May take awhile…
• Modify the current ajc compiler
– Sisyphean, complex task
• Manage the state manually
– Tangled and scattered code
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7. Desired Solution
1. Pluggable 5.
Extensible AIM Flexible
Mechanism
2.
Declarative 4.
3. Efficient
Expressive
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8. Requirement 1: Extensible
• New AIMs can be introduced
– Perthread Perthread
– Persession
• Pre-defined AIMs can be refined
Per Recent
– Perthread that was started in the last hour
Thread
• Generic AIMs can be offered by
– Third-party providers
– AspectJ developers
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9. Requirement 2: Declarative
• Easy to use
– Like AspectJ
• AIMs implementation may vary
independently of their use
– Unlike AspectJ
AspectJ
public aspect MyAspect
perthis(myPointcut()){
}
perscope
public aspect MyAspect
perscope(Perthis, myPointcut()){
}
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10. Requirement 2: Declarative
• Easy to use
– Like AspectJ
• AIMs implementation may vary
independently of their use
– Unlike AspectJ
New keyword Class implements AIM
perscope
public aspect MyAspect
perscope(Perthis, myPointcut()){
}
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11. Requirement 3: Expressive
• Practical
– Realistically complex AIMs can be defined
– E.g., perconversation
• AspectJ compatible
– Can implement all 6 AspectJ AIMs
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12. Requirement 4: Efficient
• Weaving
– Implemented by bytecode weaving
• Runtime performance
– Generate the same bytecode as AspectJ
for the 6 AspectJ AIMs
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13. Requirement 5: Flexible
• Static AIM implementation
– Same woven performance as AspectJ
• Dynamic AIM implementation
– Encourages experimenting with AIMs
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14. Outline
• Introduction
• Requirements
• Example
• Pluggable Mechanism
• Evaluation
• Conclusion
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15. Example: Global Caching
Aspect
public aspect GlobalCaching AspectJ and perscope
extends SimpleCaching {
}
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16. Example: Perclient Caching
Aspect Aspect Aspect
Aspect
AspectJ
public aspect PerClientCaching extends SimpleCaching
perthis (cachedOperation(Object)) {
}
perscope
public aspect PerClientCaching extends SimpleCaching
perscope(Perthis, cachedOperation(Object)) {
}
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17. Example: Perconversation Caching
Aspect
Aspect
Aspect Aspect
public aspect PerConversationCaching
extends SimpleCaching perscope
perscope(Perconversation,
cachedOperation(Object)){
}
AspectJ
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18. Outline
• Introduction
• Requirements
• Example
• Pluggable Mechanism
– Dynamic
– Static
• Evaluation
• Conclusion
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19. Dynamic Implementation
• Implement the DynamicPerscope interface
• Specify how the aspect instance should be
bound, retrieved, and queried
public interface DynamicPerscope {
void bindAspect(Object aspekt, Object object);
Object aspectOf(Class<?> aspectType, Object
object);
boolean hasAspect(Class<?> aspectType, Object
object);
}
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20. DynamicPerscope: usage
public aspect PerThreadCaching extends SimpleCaching
perscope(Perthread, cachedOperation(Object)) {
}
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21. DynamicPerscope: implementation
public class Perthread implements DynamicPerscope {
private static ThreadLocal<Object> theAspect =
new ThreadLocal<Object>();
public void bindAspect(Object aspekt, Object o) {
if (theAspect.get() == null) {
theAspect.set(aspekt);
}
}
public Object aspectOf(Class<?> aspectType, Object o) {
return theAspect.get();
}
public boolean hasAspect(Class<?> aspectType, Object o){
return theAspect.get() != null;
}
}
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22. Static Implementation
• Bytecode manipulation
– Harder to implement
– Capable of producing efficient code
• StaticPerscope interface
– Hard-wired weaving code replaced with calls to the
StaticPerscope interface
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23. DynamicPerscope vs. StaticPerscope
• DynamicPerscope
– Regular Java code
– Intended for regular infrastructure programmers
• StaticPerscope
– More complex
– More efficient
– Intended for advanced infrastructure programmers
Note: these trade-offs are transparent to the
end user of AIM
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24. Outline
• Introduction
• Requirements
• Example
• Pluggable Mechanism
• Evaluation
• Conclusion
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25. Evaluation
• Implementing AspectJ built-in AIMs
– Caching example
– Law of Demeter (AspectBench compiler distribution)
• Implementing Non-AspectJ AIMs
– AspectS cflow advice activations
– JAsCo perthread AIM
– persession and perconversation
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26. Threats to Validity
• Implemented only for the ajc compiler
– Language feature
• AspectJ AIMs were tested on two examples
– Same bytecode is generated
• AIMs that cannot be implemented using
perscope
– Always true
AspectJ Other AOP
Languages
perscope Custom
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27. Outline
• Introduction
• Requirements
• Example
• Pluggable Mechanism
• Evaluation
• Conclusion
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28. Related Work
• Perscope vs. JAsCo
– IAspectFactory is used at runtime for aspect instantiation
– With perscope two choices: DynamicPerscope or
StaticPerscope
• Perscope vs. Caesar
– In Caesar aspect instantiated explicitly
– With perscope – implicitly according to aspect declaration
as in AspectJ
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29. Conclusion
• With perscope AIMs are pluggable
• New keyword ‘perscope’ is introduced
• Usage of AIMs is declarative
– As in AspectJ
• AIMs may be provided by third-parties
– Different than AspectJ
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30. Thank You!
• Questions?
• Contact information:
Software Engineering Research Lab
Open University of Israel
Email:
• lorenz@openu.ac.il
• victortr75@gmail.com
URL:
• http://aop.cslab.openu.ac.il/research/perscope/
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