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Caching: An Optimization Aspect. Class Diagram for Base. Back Item Target Container Source Caching Container C. contains. Item +name : String +check() : int. 0..*. Container +capacity : int +check() : int +addItem(Item it):void. Simple +weight : int +check() : int. Background.

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class diagram for base
Class Diagram for Base

Back

Item Target

Container Source

Caching

Container C

contains

Item

+name : String

+check() : int

0..*

Container

+capacity : int

+check() : int

+addItem(Item it):void

Simple

+weight : int

+check() : int

background
Background
  • Container/Simple both inherit from Item && Container contains vector of Item.
  • Cache the value of the sum for each container and the number of violations.
  • If the same container is checked again and there has been no change, we can reuse the cached values
caching aspect
Caching Aspect
  • Interface C (view it as a role)
    • Can have one of its methods cached
    • Requires a method allInvalidated:
      • Returns all objects whose caches would be invalidated by a modification to the current object
      • AspectJ interfaces can provide member implementations and fields: field cachedValue And method clearCache(){…}
        • Very useful! Define popular behaviors.
reusable
Reusable
  • Use abstract pointcuts to represent the methods to be cached (cachedmeth) and the methods to invalidate caches (invalidate).
  • Advice for those pointcuts.
object
Object
  • Object around(..) : cachedmeth …
  • Object cachedValue
back aspect
Back Aspect
  • Want to maintain an invariant.
  • Intercept calls that can affect the invariant.
old viewgraphs
Old viewgraphs
  • Alternative solution
hashtable method
HashTable method
  • Hashtable cache=new Hashtable();
  • pointcut changed(Container c):target(c) &&

call(* Container.addItem(..));

  • before(Container c):changed(c){ if(cache.containsKey(c)){

Container contain=c.getContainer();

cache.remove(c); //invalidate

while(contain!=null) { cache.remove(contain); contain=contain.getContainer();

slide10
pointcut getvalue(Item i):target(i) &&

call(* *.check(..));

  • int around(Item i):getvalue(i){ if(cache.containsKey(i))

return ((Integer)cache.get(i)).intValue(); int v=thisJoinPoint.proceed(i); cache.put(i,new Integer(v));

return v;

introductions
Introductions
  • private int Container.violations = 0;
  • private int Container.total = 0;
  • private boolean

Container.cacheIsValid = false;

slide12
pointcut getTotal(Container c):

call (int check(..)) && target(c);

  • int around (Container c): getTotal(c){

if(c.cacheIsValid){

System.out.println(c.name + " using cached value for total: " + c.total);

if(c.violations > 0){

System.out.println(c.name + " had " + c.violations + " violations");

return c.total; }

else return proceed(c);

slide13
after(Container c) returning (int tot): getTotal(c){

c.total = tot;

c.violations = c.total - c.capacity;

c.cacheIsValid = true;}

adding a new item
Adding a new item:
  • pointcut newItem(Container c, Item i): call(void setContainer(..)) &&

target(i) && args(c);

  • after(Container c, Item i): newItem(c, i){

c.setValid(false); }

  • public void Container.setValid(boolean isValid){ cacheIsValid = isValid;

if(getContainer() != null){

getContainer().setValid(isValid);

what was learned
What was learned?
  • The Hashtable allows us to better encapsulate the Caching aspect, leaving us with more elegant code that doesn’t pollute the name-space of Container
  • It seems cleaner for each Container to keep track of its total weight. This will also probably shorten the run-time.
part 1b d improving modularity and reusability
Part 1b/d: Improving modularity and reusability
  • If we don’t cache, we don’t need the back pointers in our containers. So make it an aspect!
  • Improve reusability through use of abstract aspects.
back pointer based on introductions
Back pointer: based on introductions
  • private Container Item.container;
  • public void Item.setContainer(Container c){

container = c;}

  • public Container Item.getContainer(){

return container;}

setting the bp
Setting the BP
  • pointcut addingItem(Container c, Item i): call (void addItem(..)) &&

target(c) && args(i);

  • after(Container c, Item i): addingItem(c, i){

i.setContainer(c);

}

abstract caching aspect
Abstract Caching Aspect
  • There is a Parent/Child relationship which can be useful in creating abstract aspects.
  • interface Parent extends Child{

void addItem(Child c);

  • abstract aspect Cashing{

abstract pointcut invalidate(Parent p);

abstract pointcut cashing(Parent p);

slide20

Such that we can implement interesting functionality based

  • only on knowledge that a Parent/Child relationship exists.
  • after(Parent p): invalidate(p){
  • while(p != null){
  • beforeInvalidate(p);
  • p.cashedValue = -1;
  • p = ((Child)p).getParent();
  • }
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