SMT-based Debugging Support for ContextJ: Enhancing Context-Aware Software Development

1. COP 2011 CJAdviser:SMT-based Debugging Support forContextJ* • ShizukaUchio (Kyushu University, Japan) • NaoyasuUbayashi (Kyushu University, Japan) • Yasutaka Kamei (Kyushu University, Japan) • July 25, 2011

2. Overview-- Trace analysis with SMT-solver We can check a variety of object-context dependencies such as “Do two objects A and B exist in the Context X at the same time ? ” SMT Unit Test A B X Context Dependence Graph SMT: Satisfiability Modulo Theories

3. Outline • Motivation --Debugging issues in COP • CJAdviser: Trace analysis with SMT solver • Related work • Conclusion and Future work

4. Motivation

5. Motivation • Context-awareness plays an important role in developing adaptive software. • COP can treat context as a module and enables programmers to describe the context-aware behavior elegantly. • However, it becomes difficult to debug the programs due to the complexity of COP execution and the dependence between objects and contexts.

6. Example: ContextJ* Code Employer Person Address Layer Employment Layer Name: UchioShizuka; Address: Arae1 Name: UchioShizuka; Address: Arae1; [Employer] Name: Ubayashi; Address: Motooka Employer ubayashi = new Employer("Ubayashi", "Motooka"); Person uchio = new Person("UchioShizuka", "Arae1", ubayashi); with(Layers.Address).eval( new Block() { public void eval() { System.out.println(uchio); }}); with(Layers.Address, Layers.Employment).eval( newBlock() { public void eval() { System.out.println(uchio); }}); public class Employer implements IEmployer { layers.define(Layers.Address,newIEmployer() { public String toString() { return layers.next(this) + "; Address: " + address;}}); public class Person implements IPerson { layers.define(Layers.Address,newIPerson() { public String toString() { return layers.next(this) + "; Address: " + address;}}); layers.define(Layers.Employment,newIPerson() { public String toString() { return layers.next(this) + "; [Employer] " + employer;}});

7. Execution Trace • Q2: When uchio enters Address and Employment layers, the layered method toString (Address layer) is invoked after the layered method toString (Employment layer) is invoked. • Where is this order specified ? • Is the order defined by layers.define ? Q1: Address layer and Employment layer are instantiated just after Employer object is instantiated. Why ?

8. More concerns … • Is there a possibility of simultaneously activating two layers A and B ? • Is the layer A activated sometime ? • Do two objects X and Y exist in the layer A at the same time ?

9. CJAdviser:Trace analysis with SMT solver

10. Our approach SMT Unit Test Context Dependence Graph SMT: Satisfiability Modulo Theories

11. SMT (Satisfiability Modulo Theories) • SMT generalizes SAT (Boolean satisfiability) by adding equality reasoning, arithmetic, and other first-order theories. • Yices is an SMT solver that decides the satisfiability of formulas containing • uninterpreted function symbols with equality, • linear real and integer arithmetic, scalar types recursive datatypes, tuples, records, extensional arrays, fixed-size bit-vectors, • quantifiers • lambda expressions

12. CJLogger Context Object ContextJ* execution (period) Context Logging Object CXDG: Context dependence graph

13. Yices encoding -- CXDG Syntax is similar to Scheme : ; Type definitions (define-type obj (scalar Employer Person)) (define-type layer (scalar Address Employment)) (define-type with-period (subrange 1 2)) (define-type log-count (subrange 0 4)) (define-type obj-with-layer (tuple with-period obj layer)) (define-type logging (-> intobj-with-layer)) (define log::logging) : ; Log data (CXDG: Context dependence graph) (define test-run::logging (update (update (update (update (update (update log (0) (mk-tuple 1 Person Address)) (1) (mk-tuple 1 Employer Address)) (2) (mk-tuple 2 Person Address)) (3) (mk-tuple 2 Employer Address)) (4) (mk-tuple 2 Person Employment)))) Array

14. CJQuery DebugConcerns Context Object Query (period) Context SAT or UNSAT Object Yices

15. Case 1:Do a person and an employer exist in the Address layer at the same time ? (define i::log-count) (define j::log-count) (define t::with-period) (assert (and (/= ij) (= (test-run i) (mk-tuplet Person Address)) (= (test-run j) (mk-tuplet Employer Address)))) (check) SAT i = 2, j = 3, and t = 2

16. Case 2:Do a person and an employer exist in the same layer at the same time ? (define i::log-count) (define j::log-count) (define t::with-period) (define l::layer) (assert (and (/= ij) (= (test-run i) (mk-tuplet Person l)) (= (test-run j) (mk-tuplet Employer l)))) (check) SAT i = 2, j = 3, t = 2, and l=Address.

17. Case 3:Does a person exist in the Employment layer sometime? (define i::log-count) (define t::with-period) (assert (= (test-run i) (mk-tuplet Person Employment))) (check) SAT i = 4 and t = 2

18. Related work

19. Related work • Whyline [Ko, A. J. et al. ICSE2008] • allows programmers to ask “Why did” and “Why didn‘t” questions about the bugs. • provides answers of the bug causes. • DebugAdvisor [Ashok, B. et al. FSE2009] • allows programmers to express the context of the bugs and search through diverse data such as natural language text and core dumps.

20. Conclusion and Future work

21. Conclusion and Future work • We proposed CJAdviser, SMT-based Debugging Support for ContextJ*. • Future work • Support for Jcop • User Interface (cf. Whyline) • Scalability • Real case Studies

22. Thank you for your attention.