Features of AOP languages

1
Features of AOP languages

• AOP languages have the following main elements
• a join point model (JPM) wrt base PL
• a specification language for expressing sets of
  join points (JPS)
• a means of specifying behavior involving join
  points (BJP)
• encapsulated units combining JPS and BJP (CSB)
• method of attachment of units to base program (AU)

2
Features of AOP languages

• AOP languages have the following main elements
• a join point model (JPM) wrt base PL
• a specification language for expressing sets of
  join points (JPS)
• a means of specifying behavior involving join
  points (BJP)
• encapsulated units combining JPS and BJP (CSB)
• method of attachment of units to base program (AU)

JPS and BJP are sometimes overlapping. JPS might
already define an initial behavior plus a set of
join points in that behavior.
3
Comparing

• AspectJ
• DemeterJ
• DJ
• ATC
• AspectC
• Aspectual Collaborations
• D (COOL, RIDL)
• BETA
• RG

4
AspectJ

• from Xerox PARC

5
AspectJ JPM

• principled points of execution
• message sends (basically a method call), message
  receptions, method executions
• field references (get and set)
• exception throwing and handling
• constructor execution
• which context is available at each join point?

6
AspectJ JPS

• pointcut designators
• primitive calls(sig), receptions(sig),
  executions(sig), instanceof(type), within(type),
  cflow(pcd), getter(sig?), setter(sig?)
• operators , , !
• can name a pointcut and expose context
• pointcut foo (V v)pcd (using v)
• pointcut maybe abstract (declaration) and defined
  in a subaspect.

7
AspectJ BJP

• before, after, around a pointcut.
• can refer to thisJoinPoint
• explain join point object
• instance of JoinPoint class. Interface
  getSignature(), getActualParameters(),
• JoinPoint has eleven subclasses CallJoinPoint,
  ReceptionJoinPoint, ExecutionJoinPoint,
  ExceptionJoinPoint,
• in around (instead of) can say proceed()

8
AspectJ CSB

• an aspect contains a list of advice and point
  cut declarations and introductions and regular
  fields and methods.

9
Explaining aspect instance

• when you declare an aspect, you say either of
  eachJVM() or of eachobject(pcd)
• logging log stream put in aspect instance of
  each VM (one instance for whole program)
• dft mark field put it in aspect instance of each
  object (node object of the graph)

10
AspectJ AU

• ajc takes a list of files aspects and classes
  and weaves them together.

11
DemeterJ

• From Northeastern

12
DemeterJ JPM

• traversal method calls on Java object,
  constructor calls

13
DemeterJ JPS

• strategies
• define family of traversal programs to be
  enhanced
• approximation function mapping object graphs to
  subgraphs
• are enhanced by visitors
• sentences
• define family of Java objects executions of
  constructor calls
• are not further enhanced

14
DemeterJ BJP

• visitor classes
• before

15
DemeterJ CSB

• adaptive methods
• void f() to S (V1, V2)

16
DemeterJ AU

• make new .beh file, add to .prj file, demeterj

17
DJ

• Java library from Northeastern
• Present two views of DJ as an AOP system
• Two views
• object graphs as join points
• object graph slices as join points

18
DJ JPM

• object graph nodes and edges
• principled points traversal of nodes or edges
• fix a traversal algorithm

19
DJ JPS

• strategies
• define family of traversal programs to be
  enhanced
• approximation function mapping object graphs to
  subgraphs (object graph slices)

20
DJ BJP

• visitor classes
• before(A a), after(C c), cbefore_x(Object a,
  Object b), caround_x(Object a, Object b,
  Subtraverser st)
• each method applies to a different part of the
  point cut (strategy)

21
DJ CSB

• aspectual methods
• void f(ClassGraph cg)
• cg.traverse(this,
• from A to S,
• new Visitor() )

22
DJ AU

• add methods to classes

23
DJ Second view Doug

• Doug Orleans

24
DJ JPM

• object graph slices nodes and edges
• fix a traversal algorithm

25
DJ JPS

• strategies
• define family of traversal programs to be
  enhanced
• approximation function mapping object graphs to
  subgraphs (object graph slices)
• in addition visitor methods are pointcut
  designators
• pointcut designators are encoded in signatures of
  visitor methods

26
DJ BJP

• visitor classes
• each visitor method is advice on the point cut
  specified by the method signature

27
DJ CSB

• a visitor class is a package of advice
• when you use a visitor in a traversal of an ogs
  (in traverse) then each pointcut is intersected
  with the traversal pointcut, namely
  cflow(traverse). (can also use within)

28
DJ AU

• to attach an aspect you call traverse with an
  aspect (visitor).
• traverse expression attaches the aspect to an
  object graph slice.

29
AspectC

• From the University of BC

30
AspectC JPM

• function calls, variable references
• data available args to function calls

31
AspectC JPS

• point cut designators
• call (foo( c )) all calls of function foo with
  one argument
• cflow( any point cut designator) whatever comes
  afterwards on the stack
• varref(name)
• combine with , and !

32
AspectC BJP

• before, after, around

33
AspectC CSB

• are hardwired together when advice is given, you
  need to give point cut

34
AspectC AU

• concatenated to the source

35
ATC

• From Doug Orleans at Northeastern

36
ATC JPMAspects in Tiny CLOS

• generic function receptions, method executions
• use MOP to implement aspects
• what data is exported see join point object

37
ATC JPS !

• point cut designators
• predicate on aspect instance and join point
  object
• explain join point object
• instance of ltjoin-pointgt class. Interface slots
  generic (generic function being called), args
  (actual parameters), stack (stack of join points
  in current control flow)
• ltjoin-pointgt has two subclasses
  ltreception-join-pointgt and ltexecution-join-pointgt
• ltexecution-join-pointgt has additional slot
  method (being executed)
• (all the traversal methods in the cflow of the
  first traversal call)

38
ATC BJP

• before, after, around take aspect instance and
  join point object as argument.
• around has third arg continuation
• generic function ...

39
ATC CSB

• advice has a pointcut generic function (like an
  abstract pointcut in AspectJ). Methods of generic
  function are specified separately.
• an aspect contains a list of advice (no point cut
  declaration)
• an aspect is an instance of ltaspectgt

40
Explaining aspect instance

• class ltaspectgt has two subclasses
  ltaspect-of-each-vmgt ltaspect-of-each-object gt
• logging log stream put in aspect instance of
  each VM (one instance for whole program)
• dft mark field put it in aspect instance of each
  object (node object of the graph)

41
ATC AU !

• ltaspectizablegt mixin has slot aspects holds
  list of attached aspects
• ltaspectizable-genericgt is a subclass of both
  ltgenericgt and ltaspectizablegt (ltgenericgt is the
  class of all generic functions)
• add-aspect! , remove-aspect!
• all generic functions in base program are
  aspectizable (non-obliviousness ok)

42
Aspectual Collabs

• From NU

43

• join point model allows for parameterization
  join point patterns and their instances.

44
Aspectual Collaborations JPM

• principled points of execution ?
• abstract join points that are mapped by the
  adapter to concrete ones
• execution of methods modified by collaboration
• enhance the class graph open classes add more
  members to existing classes
• which context is available at each join point?

45
Aspectual Collaborations JPM

• syntactic methods and fields, not points of
  execution
• Replacement allows us to capture execution
• Two kinds of method capture
• tradeoff between access to arguments/result vs.
  generality

46
Aspectual Collaborations JPS

• sets of join points collaboration adapter (in
  the adapters we express the cross cutting)
• collaboration roles only have the flavor of an
  abstract pointcut.
• adapter specifies links between methods and
  fields
• requirements can be exported unfulfilled.
• future version globbing with guard operators

47
Aspectual Collaborations BJP

• before, after, around for methods
• can refer to actual parameters
• in replace (around (instead of)) can say
  expected()
• Depending on which join point model can
  access/modify aguments or cannot.

48
Aspectual Collaborations CSB

• collaborations and adapters
• Each adapter is processed to generate a new
  collaboration. Collaborations can encapsulate
  some behavior and export other.

49
AC instances

• Complicated sharing model
• ?

50
Aspectual Collaborations AU

• ac-compiler (non existent) takes a list of files
  classes and collaborations and adapters and
  weaves them together.
• Weaving is incremental. Compilation is external
  to weaving.
• Process is finished when no more requirements
  remain.

51
Using AspectJ to implement collaborations/adapters

• AspectJ can only express the adapted
  collaborations ? It has abstract pointcuts.
• AspectJ supports interfaces with full methods and
  multiple inheritance

52
Goal

• Input classes, collaborations, adapters
• Output AspectJ code

53
D

• From Northeastern, continued at Xerox PARC

54
D

• From Cristas thesis and implemented in DemeterJ
• COOL
• RIDL
• concern specific aspect language

55
COOL JPM

• principled points of execution
• method calls
• which context is available at each join point?
  Can look at objects, but not modify them.

56
COOL JPS

• sets of join points exclusion sets
• exclusion sets do more than defining a set of
  join points initial behavior of coodination
• enhanced by method managers

57
COOL BJP

• method managers

58
COOL CSB

• coordinators

59
COOL AU

• demeterj takes coordinators (in .cool files) and
  .cd .beh and .ridl files and weaves them together.

60
RIDL JPM

• principled points of execution
• method calls and object graphs of parameters and
  return types
• which context is available at each join point?
  Parameters and return values are processed
  according to transfer specs.

61
RIDL JPS

• sets of join points for parameters and return
  types transfer specifications in portals specify
  them. Only initial behavior is of interest
  selecting an object graph slice. Portals list the
  methods

62
RIDL BJP

• transfer specifications modify behavior of
  methods. transfer specs are themselves aspects.
  Two layers. Similar to AP.

63
RIDL CSB

• portals

64
RIDL AU

• demeterj takes portals (in .ridl files) and .cd
  .beh and .cool files and weaves them together.

65
BETA

• from the Beta community (Aarhus, etc.)
• The BETA fragment system syntax directed program
  modularization (1983 paper)

66
BETA JPM

• join points
• slots designated positions in the source code
• class Leg
• ltltSLOT leg attributesgtgt
• -can weave new declarations into the join point
• which context is available at each join point?
  refer to what is in scope of slot.

67
BETA JPS

• pointcut designators
• have to explicitly write a set of slots into the
  base code or the fragments
• one slot name one pointcut

68
BETA BJP?

• This code goes into this slot.

69
BETA CSB

• Fragment binding process binding of fragments to
  slots
• fragment groups (named collection of fragments
  contributing to the implementation of an aspect)
• fragment group attributes (origin, include,
  body) references from one group to another
• origin required (except for basic fragment
  group) origin chain reached by traversal.

70
Fragment Graph
f1
f2
s1
71
BETA CSB

• a fragment group contains a list of slots
  embedded in code

72
BETA AU

• Through fragment system organization. Use of
  include include dingbats and Color.
• static

73
BETA

• need to define the slots where code can be
  inserted. No predefined join points.
• Good at composition of fragments. Fragments may
  have their own slots.
• Base program is not oblivious about aspects. But
  could have predefined join points.

74
BETA

• A fragment group is a modular unit of cross
  cutting implementation. It is an aspect.

75
RG

• memoization aspect
• compiler related aspects, operate on join points
  (message sends in the static call graph)
• fusion aspect
• memory management aspect
• modify behavior of compiler fancy pragma
• transformation almost not AOP
• could not be done in AspectJ ?