1. Inheritance Anomalies
Synchronization of concurrent objects and inheritance.
Key paper: [Matsuoka93] Analysis of Inheritance Anomalies in OOPL.
“When coding a base class (…) the code related to concurrency control cannot be effectively inherited and/or refined in a subclass without non-trivial redefinitions of the methods implementation.” [C. Lopes PhD]
Laura Benitez
COM3362 Winter'02

2. Separation of core and synchronization behaviors (1)
Synchronization constraint:
In a certain state an object can accept only certain methods to maintain its internal integrity.
Bounded-Buffer object:
Get(): if buffer not empty.
Put(): if buffer not full.
Laura Benitez
COM3362 Winter'02

3. Separation of core and synchronization behaviors (2)
Synchronization code:
Portion of code where the synchronization behavior is controlled.
It must always be consistent with the synchronization constraint.
Laura Benitez
COM3362 Winter'02

4. When are Inheritance Anomalies found?
Partition of acceptable states (Get2())
History-only sensitiveness of acceptable states (Gget(), DoubleClick() )
Modification of acceptable states. (Lock)
Laura Benitez
COM3362 Winter'02

5. How does AOP helps? AO program OO program Core behavior
Synchronization
behavior
Other concern-
related behavior
Laura Benitez
COM3362 Winter'02

6. Double click No inheritance anomalies! History-only related behavior
Mouse
MouseWDc
2-button
3-button
Wheel
LeftClick();
RightClick();
LeftPress();
LeftRelease();
WheelClick();
WheelRollUp();
WheelRollDown();
MiddleClick();
Mouse
MouseWDc
2-button
3-button
Wheel
LeftClick();
RightClick();
LeftPress();
LeftRelease();
WheelClick();
WheelRollUp();
WheelRollDown();
MiddleClick();
Laura Benitez
COM3362 Winter'02

7. Double clicks (1) Laura Benitez COM3362 Winter'02 aspect DoubleClick {
  private String MouseWDc.prevOp;
private String MouseWDc.get_prevOp() { return prevOp; }
private void MouseWDc.set_prevOp(String op) {prevOp=op;}
// very specific pointcuts allow us keeping the advice simple
pointcut pc(MouseWDc m): (call(* *(..))) && (!call(* get*(..))) && (!call(* set*(..))) && target(m) && !within(DoubleClick);
pointcut pcTB(TwoButton m): call(* *Click(..)) && target(m);
pointcut pcWM(WheelMouse m): (call(* LeftClick(..)) || call(* WheelClick(..))) && target(m);
after(MouseWDc m): pc(m) { // common behavior for doubleclicks
String curr_op = thisJoinPoint.getSignature().toShortString();
if(m.get_prevOp()!=null && m.get_prevOp().equals(curr_op)) {
if (curr_op.indexOf("LeftClick")!=-1) System.out.println("Double LeftClick detected");
} else {
if ((curr_op.indexOf("LeftClick")==-1) && (curr_op.indexOf("RightClick")==-1) && (curr_op.indexOf("WheelClick")==-1)) {
m.set_prevOp(curr_op); }
Laura Benitez
COM3362 Winter'02

8. Double clicks (2) } // end of aspect Laura Benitez COM3362 Winter'02
after (TwoButton m): pcTB(m) { // exclusive behavior for TwoButton Mice
String curr_op = thisJoinPoint.getSignature().toShortString();
if(m.get_prevOp()!=null && m.get_prevOp().equals(curr_op)) {
if (curr_op.indexOf("RightClick")!=-1) System.out.println("Double RightClick detected");
} else {
m.set_prevOp(curr_op); }
after (WheelMouse m): pcWM(m) { // exclusive behavior for Wheel Mice
if (curr_op.indexOf("WheelClick")!=-1) System.out.println("Double WheelClick detected");
} // end of aspect
Laura Benitez
COM3362 Winter'02

9. Advantages of using AOP
No code tangling caused by synchronization concerns
No inheritance anomalies associated with concurrency !
Higher level of reusability.
Laura Benitez
COM3362 Winter'02

10. Solutions found DJ Visitor to solve the Mouse problem. Using AspectJ:
Very specific pointcuts => simpler advice.
General pointcuts => more elaborated advice
Abstract aspects =>higher degree of reusability
Too many abstraction levels make code difficult to follow.
Open classes => incremental approach
Laura Benitez
COM3362 Winter'02

11. Comments
Solutions are very dependent on the parser for the simulation language.
Use AOP design has hardly been used instead of OOP design.
Laura Benitez
COM3362 Winter'02

12. Summary of best solutions
Building from scratch:
Use of AOP design and open classes
Using AspectJ:
Use abstract aspects for reusability
Use fine grained definition of pointcuts
Laura Benitez
COM3362 Winter'02