An Untyped Calculus of AspectOriented Programs

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An Untyped Calculus of Aspect-Oriented Programs

• Radha Jagadeesan
• Alan Jeffrey
• James Riely
• DEPAUL UNIVERSITY, CHICAGO

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Aspect Oriented Programming

• AOSD. Systematic methodology to address
  cross-cutting concerns
• A standard example logging
• AOP. Language support to localize cross
  cutting code
• This talk. About AOP languages

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Specification via translation

• Weaving describe operational semantics of a AOP
  language via compilation to the underlying
  paradigm.
• Aspect Java ! Java
• Aspect Scheme ! Scheme
• Aspect ML ! ML
• Aspect C ! C

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AOP languages and OO languages Folklore

• Execution in OO languages is an instance of
  execution in AOP languages
• Translation from OO programs P
• to AOP program Pasp
• P1 ! P2 , P1asp ! P2asp

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AOP languages and OO languages Folklore

• Execution in OO languages is an instance of
  execution in AOP languages
• Aspects interfere with OO principles

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Aspects interfere with OO programming
D1, D2 are distinguishable.
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Aspects as first class entities?

• Source semantics is non-trivial.
• Aspects OO redundancy
• Aspects interfere with OO principles

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Rest of the talk
Overview of results A sketch of the technical
development
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A calculus of AO programs

• Identify a core set of orthogonal primitives
• Only AROUND advice
• No method bodies
• Only call/execution pointcuts
• Direct description of the operational semantics
  of aspect based programs

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So what?

• Dynamic arrival of new advice permitted.

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Specification of weaving
No reductions are lost
No new reductions
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Limitations

• Limited vocabulary of pointcuts.
• Only call/execution join points
• Reflection, cflow not included
• Global specification of advice order

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Rest of this talk A sketch of the main ideas

• An overview of call vs. execution
• The aspect calculus
• Weaving

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An Advised Method call
u.foo()
oC
a
proceed()
o.foo(u)
uD
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An Advised Method call
u.foo()
oC
a
proceed()
o.foo(u)
uD
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Call advice

• Executed in the controlling context of the caller

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An Advised Method call
u.foo()
oC
a
proceed()
o.foo(u)
uD
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Execution advice

• Executed in the controlling context of the callee

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Rest of this talk

• An overview of call vs.. execution
• The aspect calculus
• Weaving

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The Aspect Calculus

• Class declarations
• Pointcuts
• Advice

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The Aspect Calculus Classes
Class list of method names Methods have no code
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The Aspect Calculus Pointcuts
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The Aspect Calculus Advice
Given fixed global ordering on advice names
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Reduction rules context
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Reduction rules fetching advice
Keep track of controlling object p Call
advice determined by static type. Execution
advice determined by dynamic type
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Reduction rules call advice
Controlling context of caller p Substitutions
for this, target proceed,
parameters
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Reduction rules execution advice
Controlling context of callee o Substitutions
for this, target proceed,
parameters
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Encoding Class Based Language 1
Create an exec advice for each method body
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Encoding Class Based Language 2
Name cbl_d_m precedes name cbl_c_m in ordering
on advice names
proceed
cbl_c_m
cbl_d_m
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Rest of this talk

• An overview of call vs. execution
• The aspect calculus
• Weaving

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Weaving
Programs that dynamically load advice affecting
existing classes cannot be woven statically.
For static advice, weaving algorithm is (by
now) standard. Novelty is specification of
weaving.
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Weaving Basic idea

• View as a kind of macro-expansion.
• To weave

Weave recursively
and associate result to the body of method m
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Weaving

• Alas. This doesnt necessarily terminate.
• However, postpone macro-expansion to runtime by
  freezing inside method bodies.
• Formalized in paper.

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A subtlety in correctness proof
Weaving of intermediate configurations requires
knowledge of controlling object
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Rest of this talk

• An overview of call vs. execution
• The aspect calculus
• Weaving
• Summary

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This talk A calculus of AOP programs

• Identify a core set of orthogonal primitives
• Direct description of the execution of programs
  in an aspect language.

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Moving along

• Scale Larger variety of pointcuts.
• Accurate treatment of advice order.
• Source level typing