AspectJ and AP

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AspectJ and AP

• Karl Lieberherr

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Two enhancements

• A new kind of static crosscutting
• declare traversal t strategy
• introduces a new traversal method that traverses
  objects of Source(strategy) according to the
  strategy
• A new kind of type patterns
• Define a set of types using a strategy apply
  strategy to class graph.
• ContainedIn(strategy)
• ReachableThrough(strategy)

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A new kind of static crosscutting

• declare traversal t strategy
• introduces a new traversal method that traverses
  objects of Source(strategy) according to the
  strategy
• this generalizes the AspectJ introduction Type
  TypePattern.Id(Formals)Body that defines a new
  method on all types in TypePattern. With the
  traversal introduction the body depends on the
  current type.

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Use of traversals

• The declared traversals can be invoked on objects
  o by giving a visitor object as argument o.t(v).
• This is similar to DemeterJ.

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Type patterns

• What is already in AspectJ
• A type pattern defines a collection of types.
• Type names are type patterns.
• A special type name picks out all types,
  including primitive types.
• Subtype pattern A denotes all subtypes of A.

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New kinds of type patterns Strategy type patterns

• define a set of types declaratively
• two kinds of strategy type patterns
• ContainedIn(D) selects the set of all types that
  are in the scope of strategy D.
• ReachableThrough(D) selects the set of all types
  t from which the target of D can be reached
  through the source of D and following D.

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Scope of a strategy

• The scope of a strategy modulo a class graph is
  the set of types whose instances may appear on
  traversal paths of objects of the class graph.

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Strategy type patterns

• Reachable(D) x there is a path in the class
  graph from x to a node in ContainedIn(D)
• ReachableThrough(D) xContainedIn(join(x to
  Source(D), D)) is not empty.

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Examples

• For security purposes we want to advise all calls
  of get methods of classes from Portfolio to
  Posting. Strategy type pattern
• ContainedIn(from Portfolio to Posting)

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Examples

• We want to advise all methods of types from which
  Money is reachable through Retirement
• ReachableThrough(from Retirement to Money)
• Reachable(Money) all types from which we can
  reach Money.

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Two kinds of traversal methods

• traversals with side effects
• return type void for around methods
• traversals without side effects
• non-void return type

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Traversal strategies

• D A,B join(D1,D2) merge(D1,D2)
• We can use them in three different graphs
  relevant to programming
• call trees
• class graphs
• object trees

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Interpretation of traversal strategies

• D A,B join(D1,D2) merge(D1,D2)
• Source(A,B) A
• Target(A,B) B
• Source(join(D1,D2) )Source(D1)
• Target(join(D1,D2) )Target(D2)
• Source(merge(D1,D2) )Source(D1)
• Target(merge(D1,D2) )Target(D1)

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Interpretation of traversal strategies

• D A,B join(D1,D2) merge(D1,D2)
• WF(A,B) true // well-formed
• WF(join(D1,D2) )WF(D1) WF(D2) Target(D1)
  Source(D2)
• WF(merge(D1,D2) ) WF(D1) WF(D2)
  Source(D1)Source(D2) Target(D1)Target(D2)

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Dynamic call tree

• nodes are operation calls labeled by operation
  name and arguments
• edges a operation calls another operation
• Path back contents of run-time stack

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Interpretation of traversal strategies

• D A,B join(D1,D2) merge(D1,D2)
• A and B are operation names
• A,B the set of B-nodes reachable from A-nodes
• join(D1,D2) the set of Target(D2)-nodes
  reachable from Source(D1)-nodes following D1 and
  then following D2.

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Interpretation of traversal strategies

• merge(D1,D2) the union of the set of
  Target(D1)-nodes reachable from Source(D1)-nodes
  following D1 and the set of Target(D2)-nodes
  reachable from Source(D2)-nodes following D2.

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Translation Rules

• t(D1)
• flow(A) B
• t(D1) t(D2)
• flow(t(D1)) t(D2)

• D1
• from A to B
• merge(D1,D2)
• join(D1,D2)

rules join Target(D1) Source(D2) merge
Source(D1) Source(D2) Target(D1) Target(D2)
Source, Target definitions Source(from A to B)
A Target(from A to B) B Source(join(D1,D2)
Source(D1) Target(join(D1,D2)
Target(D2) Source(merge(D1,D2))
Source(D1) Target(merge(D1,D2)) Target(D1)
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Correspondences

• t(D1)
• flow(A) B
• flow(A)
• flow(flow(A) B) C
• flow(flow(flow(A) B) C) E
• (flow(flow(A) B1) C) (flow(flow(A)
  B2) C)
• t(D1) t(D2)
• flow(t(D1)) t(D2)
• flow(flow(A) B) (flow(B) C)
• flow(flow(A) B) C

• D1
• from A to B
• from A to
• from A via B to C
• from A via B via C to E
• merge(from A via B1 to C,
  from A via B2 to C)
• merge(D1,D2)
• join(D1,D2)
• join (from A to B, from B to C)

subset(flow(B)) flow(B) subset(flow(B))
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Class graph

• D
• A,B
• join(D1,D2)
• merge(D1,D2)

• PathSet(D)
• Paths(A,B)
• PathSet(D1).PathSet(D2)
• PathSet(D1) PathSet(D2)

we are only interested in the set of
nodes touched by the path sets -gt subgraph of
class graph
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Object tree

• D
• A,B

• subgraph of O
• subgraph of O consisting of all paths from an
  A-node to a B-node, including prematurely
  terminated paths.

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Object tree

• D
• join(D1,D2)

• subgraph of O
• subgraph of O consisting of all paths following
  D1 and those reaching Target(D1) concatenated
  with all paths following D2.

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Object tree

• D
• merge(D1,D2)

• subgraph of O
• subgraph of O consisting of all paths following
  D1 or following D2.

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Purposes of strategies

• DJ
• Traversal
• strategy graph
• class graph
• object graph
• Purposes
• select og with sg
• extract node labels
• select cg with sg

• AspectJ
• General computation
• strategy call graph
• static call graph
• dynamic call graph
• Purposes
• select dcg with sycg
• extract node labels
• select scg with sycg

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Examples

• select subgraph from call of serviceRequest to
  doWork

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program without arguments

• With aspects we can avoid passing certain
  arguments.
• What kind of method arguments can we avoid this
  way?

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addition example with dynamic call graph

• compute cost of a service request from the call
  of service_request, whenever we arrive at a call
  of make_connection, add 5 whenever we arrive at
  a call of make_priority_connection that is not
  within a call of service_reservation, add 10
• merge(from service_request to make_connection,
  from service_request bypassing service_reservation
  to make_priority_connection)

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How to program in DemeterJ-style in AspectJ

• Compute total salaries paid be a company from
  Company.traverse to Salary.traverse
• assume traverse is from Company to
• my try
• aspect Sum
• int total 0 static public int
  getTotal()return total
• pointcut add(Salary s) target(s)
• call(void .traverseSum(..))
• before() add(Salary s) total s.getVal()
• // Company c new c.traverseSum()
  println(Sum.getTotal())

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How to program visitor in AspectJ

• aspect Sum issingleton // default exactly one
  instance
• aspect Sum
• int total 0 static public int
  getTotal()return total
• pointcut add(Salary s) target(s)
• call(void .traverseSum(..))
• before() add(Salary s) total s.getVal()
• // Company c new c.traverseSum()
  println(Sum.getTotal())
• // alternative Sum sumAspectObject
  Sum.aspectOf()
• // println(sumAspectObject.getTotal())
• // but getTotal may no longer be static???

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Visitors in AspectJ
class Cd_graph int countInhRels()
this.allInh(new UniversalVisitor()) return
0
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Visitors in AspectJ
aspect Count static int total pointcut
init() target(Cd_graph) call(int
countInhRels()) pointcut incrementing()
target(Vertex) call( allInh_Cd_graph_trv_b
ef(UniversalVisitor)) before()init()
total0 before()counting() total int
around() init() thisJoinPoint.proceed()
return total
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aspect TraversalAdvice static int total //
accumulation pointcut init() target(Source)
call(int adaptiveMethod()) pointcut
processing() target(Target) call(
where_Source_trv_bef(UniversalVisitor))
before()init() total0 before()processing()
total int around() init()
thisJoinPoint.proceed() return total
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How to program visitor in AspectJ

• aspect Sum issingleton // default exactly one
  instance
• aspect Sum
• int total public int getTotal()return total
• // for setting total to 0
• pointcut init() call Company.traverse()
• pointcut add(Salary s) target(s)
• call(void .traverseSum(..))
• before init() total 0
• before add(Salary s) total s.getVal()
• // Company c new c.traverseSum()
• // Sum sumAspectObject Sum.aspectOf()
• // println(sumAspectObject.getTotal())

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Simulate a DJ visitor

• want aspect Id percflow(call Company.traverseSum)
• but this is not reusable

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Typed collections as an aspect

• aspect that checks that all elements of a list
  belong to class fruit. Applies to a list with a
  specific name.
• better done through a JAXB approach.

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Our Body

• NervousSystem CentralNervousSystem
  PeripheralNervousSystem.
• CentralNervousSystem Brain SpinalCord.
• PeripheralNervousSystem SensoryDivision
  MotorDivision.
• MotorDivision SomaticNervousSystem
  AutonomicNervousSystem.

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Our Body

• SomaticNervousSystem voluntary action
• AutonomicNervousSystem involuntary action
  SympatheticNervousSystem ParasympatheticNervousSys
  tem.
• SympatheticNervousSystem fight or flight.
• ParasympatheticNervousSystem rest and digest.