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Pluggable Aspect Instantiation Models
Victor Trakhtenberg
The Open University of Israel
Joint Work With
David H. Lorenz
The Open University of Israel
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
The Open University of Israel
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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Outline
• Introduction
• Requirements
• Example
• Pluggable Mechanism
• Conclusion
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Motivation: “caching and auditing”
• Industrial Case Study– Web application development with AspectJ
– Need for ‘persession’ and ‘perconversation’ AIMs
Cache
CacheCache Cache
Cache
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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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Desired Solution
2. Declarative
3. Expressive
1. Extensible
5. Flexible
4. Efficient
Pluggable AIM
Mechanism
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Requirement 1: Extensible
• New AIMs can be introduced– Perthread
– Persession
• Pre-defined AIMs can be refined– Perthread that was started in the last hour
• Generic AIMs can be offered by – Third-party providers
– AspectJ developers
Perthread
Per RecentThread
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Requirement 2: Declarative
• Easy to use– Like AspectJ
• AIMs implementation may vary independently of their use– Unlike AspectJ
public aspect MyAspect
perthis(myPointcut()){
}
public aspect MyAspect
perscope(Perthis, myPointcut()){
}
AspectJ
perscope
The Open University of Israel
Requirement 2: Declarative
• Easy to use– Like AspectJ
• AIMs implementation may vary independently of their use– Unlike AspectJ
public aspect MyAspect
perscope(Perthis, myPointcut()){
}
perscope
New keyword Class implements AIM
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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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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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Requirement 5: Flexible
• Static AIM implementation– Same woven performance as AspectJ
• Dynamic AIM implementation– Encourages experimenting with AIMs
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Outline
• Introduction
• Requirements
• Example
• Pluggable Mechanism
• Evaluation
• Conclusion
The Open University of Israel
Example: Global Caching
public aspect GlobalCaching
extends SimpleCaching {
}
Aspect
AspectJ and perscope
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Example: Perclient Caching
public aspect PerClientCaching extends SimpleCaching
perthis (cachedOperation(Object)) {
}
Aspect
Aspect
Aspect Aspect
AspectJ
public aspect PerClientCaching extends SimpleCaching
perscope(Perthis, cachedOperation(Object)) {
}
perscope
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Example: Perconversation Caching
public aspect PerConversationCaching
extends SimpleCaching
perscope(Perconversation,
cachedOperation(Object)){
}
Aspect
Aspect Aspect
Aspect
perscope
AspectJ
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Outline
• Introduction
• Requirements
• Example
• Pluggable Mechanism– Dynamic
– Static
• Evaluation
• Conclusion
The Open University of Israel
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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DynamicPerscope: usage
public aspect PerThreadCaching extends SimpleCaching
perscope(Perthread, cachedOperation(Object)) {
}
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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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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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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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Outline
• Introduction
• Requirements
• Example
• Pluggable Mechanism
• Evaluation
• Conclusion
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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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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
Other AOP Languages
Custom
AspectJ
perscope
The Open University of Israel
Outline
• Introduction
• Requirements
• Example
• Pluggable Mechanism
• Evaluation
• Conclusion
The Open University of Israel
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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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
The Open University of Israel
Thank You!
• Questions?
• Contact information:Software Engineering Research Lab
Open University of Israel
Email:
URL:
• http://aop.cslab.openu.ac.il/research/perscope/
