1 / 24

Extending the Field Access Pointcuts of AspectJ to Arrays

Extending the Field Access Pointcuts of AspectJ to Arrays. Kung Chen and Chin-Hung Chien* National Chengchi University Hon Hai Precision Industry Co., Ltd*. ICS 2006 – Taipei, December 2006. Agenda. Background: Aspect-Oriented Programming (AOP) in AspectJ Motivation

leena
Download Presentation

Extending the Field Access Pointcuts of AspectJ to Arrays

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Extending the Field Access Pointcuts of AspectJ to Arrays Kung Chen and Chin-Hung Chien* National Chengchi University Hon Hai Precision Industry Co., Ltd* ICS 2006 – Taipei, December 2006

  2. Agenda • Background: Aspect-Oriented Programming (AOP) in AspectJ • Motivation • Design Considerations • Specification of the New Pointcuts • Implementation • Conclusions

  3. Basic Mechanisms of AOP • Aspect • Pointcut • Advice • Weaving Implement Crosscutting concerns modularly advice Class Class pointcut pointcut pointcut aspect where weaving Do what

  4. Aspects in AspectJ aspect Name [extends a] { pointcut1; pointcut2; … advice1; advice2; … fields methods } Crosscutting points Actions to take in matched pointcuts Pointcut: selecting a collection of join points

  5. Method call join point: Join Points Model of AspectJ, 1 • Join point is a well-defined point in a program’s execution • Method call: publicvoid move(int dx, int dy) { setX(_x + dx); setY(_y + dy); }

  6. field set join point: field reference join point: Join Points Model of AspectJ, 2 • Our focus: Field reference and set join points: publicvoid setX(int newx) { x = newx; ..println(x); }

  7. Agenda • Background: Aspect-Oriented Programming (AOP) in AspectJ • Motivation • Design Considerations • Specification of the New Pointcuts • Implementation • Conclusions

  8. Example aspect GuardedX { static final int MAX_CHANGE = 100; before(int newval): set(static int T.x)&& args(newval) { if (Math.abs(newval - T.x) > MAX_CHANGE) throw new RuntimeException(); }} Field Access Join Points of AspectJ • Pointcut Designators • get(aFieldSignature) • set(aFieldSignature) • Join Points • field reference • field set

  9. Limitations in Using Field Access Pointcuts • What if the fields we are interested in are arrays? set(* *.ar) 01 public class FieldPointcuts {02 static int ar[];03 public static void main(04 String[] args) {05 ar = new int[] {100}; //set06 ar[0] = 200; //get 07 }08 } after() returning (int[] a) : get(* *.ar)

  10. What We Expect • Field access pointcuts can also be applied to array elements and further expose information on • the index values of the array element being set or retrieved, and • the value being set to or retrieved from the array element. ar[0] = 200;

  11. Related Work • Bruno Harbulot proposed the following arrayset pointcut designator: before(int i, Object s, Object[] a): arrayset() && args(i, s) && target(a) { System.out.println (" Arrayset: ["+i+"/"+(a.length-1)+"] = "+s) ; } • The idea is to treat array element set as a call to a “set(int index, object newValue)”

  12. Mismatch Match Mismatch Problems with Harbulot’s Work • Ambiguous matching of join points arrayset() && args(i, s) && target(a) actually two assignments to two 1-D arrays on the byte-code level ss[0][1] = “two join points”; actually three assignments to three 1-D arrays on the byte-code level arrayset() && args(i1,i2,s) && target(a) sss[0][1][2] = “two join points, too”;

  13. Agenda • Background: Aspect-Oriented Programming (AOP) in AspectJ • Motivation • Design Considerations • Specification of the New Pointcuts • Implementation • Conclusions

  14. How We Address This Problem • Fix the array target(s) of interest • only need to focus on arrays which are fields of some class • arrays local to a method are irrelevant • Include a specification of field signature in our array set/get pointcuts.

  15. Requirements • Assignments to a multi-dimensional array can take several forms. • Our arrayset field set pointcut must be flexible enough to select all of them, either individually or as a group. 01 class Watch { 02 String [][][] sss= new [2][2][2];03 String [][] ss= {{“x”,”y”},{“w”,”z”}}; 04 String [] s= {“abc”, “def”};05 sss[0] = ss;06 sss[0][1] = s;07 sss[0][1][1] = “change”;08 ss [0] = s;09 ss[0][1] = “Me too”;10 s[0] = ss[1][1];… }

  16. Agenda • Background: Aspect-Oriented Programming (AOP) in AspectJ • Motivation • Design Considerations • Specification of the New Pointcuts • Implementation • Conclusions

  17. arrayset(* Watch.*) arrayget(* Watch.*) New Field Access Pointcuts • Conservative extension of the standard field pointcuts: • arrayset(aFieldSignature) • arrayget(aFieldSignature) • Orthogonal to other AspectJ pointcuts • target(), within() and withincode() • All array field set join points are treated as having a variable arguments: • the sequence of index values • the value the field is being set to

  18. Context Exposure, 1 • Using the args() pointcut aspect Monitor { before(int ix1, int ix2, int newVal): arrayset(* Watch.*) &&args(ix1, ix2, newVal) { //advice if (newVal > B.bounds[ix1, ix2]) { ArraySetSignature sig = (ArraySetSignature)tjp.getSignature(); String field = sig.getFieldType() + sig.getName(); throws new RuntimeException("Bad change"+ field) }} 01 class Watch { 02 String [][][] sss= new [2][2][2];03 String [][] ss= {{“x”,”y”},{“w”,”z”}}; 04 String [] s= {“abc”, “def”};05 sss[0] = ss;06 sss[0][1] = s;07 sss[0][1][1] = “change”;08 ss [0] = s;09 ss[0][1] = “Me too”;10 s[0] = ss[1][1];… } • Selective matching – assignments in Line 6 and 9 are captured.

  19. Context Exposure, 2 • Can also use the method thisJoinPoint.getArgs() void around() : arrayset( * data.*.* ) { try { ArraySetSignature sig = (ArraySetSignature)tjp.getSignature();Object[] args = tjp.getArgs(); Integer rhsValue = (Integer)args[args.length-1]; if (rhsValue.intValue() > MAX) { Log.add("Warning: " + sig.getName()); for (int i=0; i<args.length-1; i++) { Log.add("["+ args[i] +"]"); Log.add(" exceeds MAX"); } proceed(); } catch(IndexOutOfBoundException e) {} } • Provides great flexibility.

  20. Agenda • Background: Aspect-Oriented Programming (AOP) in AspectJ • Motivation • Design Considerations • Specification of the New Pointcuts • Implementation • Conclusions

  21. Implementation Using the AspectBench Compiler(abc) for AspectJ • We follow the standard steps outlined by the abc team to develop this extension. • But the following steps are non-trivial: • Identification of join point shadow • Extension of the pointcut matcher of abc

  22. FSM Based Shadow Matcher class C { … Object a[][][] = new Object[2][2][2]; …a[0][1][2] = new String("foo"); … } #1: $r2 = r0.<C:java.lang.Object[][][]a>#2: $r3 = $r2[0]#3: $r4 = $r3[1]#4: $r5 = new java.lang.String#5: specialinvoke $r5.<java.lang.String: void <init>(java.lang.String)>("foo")#6: $r4[2] = $r5 Cond. #1: instanceOf(getRhs(ca), ArrayFieldRef) Cond. #2: instanceOf(getRhs(ca), ArrayRef) && equalBase(getRhs(ca), ima) && instanceOf (getLhs(ca), Local) Cond. #3: instanceOf(getLhs(ca), ArrayRef) && equalBase(getLhs(ca), ima) Cond. #4: !hasNext()

  23. Conclusions • The field access pointcuts of AspectJ can be extended to expose index-value context for array fields. • A FSM-based implementation is presented using the abc compiler for AspectJ. • You are welcome to download it and try it yourself.

  24. Q & A

More Related