[aosd-discuss] Naive question About Cflow Point cut

[Michael Haupt]

Hi Eric,

Eric Bodden wrote:
> class A {
>     int field;
>  
>     void foo() {
>        this.field = someComplicatedCalculation(someEvaluation());
>     }
> ...
> }
>  
> As you will know, the call above *can* be matched by a set-pointcut
> on A.field. before(set(* A.field)) will execute before the set event
> (and before the call to someComplicatedCalculation(...)),

the invocation of the complex calculation is an entirely different join 
point and has nothing to do with the set join point that is matched by 
the set() PCD. After all, the actual *set* join point occurs *after* the 
complex calculation has returned.

> [...] cflow(set(* A.field))
> however, will match all the joinpoints in between, which in this case
> will be everything from the inner call to someEvaluation() untill the
> return of someComplicatedCalculation(...)).

If we assume that someComplicatedCalculation() is a method declared in 
A, a pointcut like this one:

call(* A.*(..)) && cflow(set(int A.field))

will match nothing. One might ask whether a combination like 
cflow(set(...)) makes sense at all.

There is some interesting behaviour if you attach some advice to the set 
join point that prints to System.out, and use a combination of this with 
a pointcut like the above. You will observe that cflow(set(...)) matches 
those join points that are introduced by advice attached to the set join 
point.

Example:

-----
before(): set(int A.field) {
   System.out.println("set");
}

before(): call(* *(..)) && cflow(set(int A.field)) {
   System.out.println("cflow match");
}
-----

This will eventually end up in a stack overflow because all calls to 
System.out.println() in the first advice will be matched by the second 
pointcut.

Best regards,

Michael Haupt

-- 
Dipl.-Ing. Michael Haupt            haupt at informatik.tu-darmstadt.de
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