Discovering Faults in Idiom- Based Exception Handling. Magiel Bruntink, Arie van Deursen & Tom Tourwé

Transcription

1 Discovering Faults in Idiom- Based Exception Handling Magiel Bruntink, Arie van Deursen & Tom Tourwé

2 Implementing crosscutting concerns by means of idioms is fault prone 1. what are crosscutting concerns? 2. what are idioms, which idioms do we study and why are they fault prone? 3. how can we detect the faults?

3 Implementing crosscutting concerns by means of idioms is fault prone 1. what are crosscutting concerns? 2. what are idioms, which idioms do we study and why are they fault prone? 3. how can we detect the faults?

4 Separation of concerns Any given problem involves different kinds of concerns, which should be identified and separated to cope with complexity and to achieve the required engineering quality factors, such as adaptability, maintainability, extendibility and reusability E.W. Dijkstra, A Discipline of Programming, 1976.

5 Tyranny of the dominant decomposition No matter how (well) a software system is decomposed into modular units, some functionality will always crosscut that decomposition a program can be modularised in only one way at a time not all concerns align with that modularisation P. Tarr et al, N degrees of separation: multidimensional separation of concerns, 1999.

6 Crosscutting concerns are concerns that cut across the dominant decomposition of the software and lead to scattering, i.e. same (similar) functionality implemented in different modular units tangling, i.e. one modular unit implementing many different concerns

7 Implementing crosscutting concerns by means of idioms is fault prone 1. what are crosscutting concerns? 2. what are idioms, which idioms do we study and why are they fault prone? 3. how can we detect the faults?

8 Idioms are a prescribed way of implementing functionality... coding conventions design patterns cookbooks etc... and are often used to implement crosscutting concerns in the absence of aspects

9 Idiom-Based Exception Handling void f(int a, int *b) { g(a); h(b); LOG(CCXA_error, r);

10 Idiom-Based Exception Handling LOG(CCXA_error, r); error variable

11 Idiom-Based Exception Handling catch error returned LOG(CCXA_error, r);

12 Idiom-Based Exception Handling LOG(CCXA_error, r); if not OK, link to a new error and state context info

13 Idiom-Based Exception Handling only continue if OK LOG(CCXA_error, r);

14 Idiom-Based Exception Handling LOG(CCXA_error, r); return error

15 Idiom-based EH is fault prone because it is inherently complex... informally described and documented... not enforced by automatic tools... hard(er) to test

16 Implementing crosscutting concerns by means of idioms is fault prone 1. what are crosscutting concerns? 2. what are idioms, which idioms do we study and why are they fault prone? 3. how can we detect the faults?

17 Detecting faults In every function look for a variable that is used to hold exceptions... identify a possible way of executing that function that leads to undesired situations 1. What are error variables? 2. What are ways of executing a function? 3. What are undesired situations?

18 1. Error variable identification An error variable is a variable that has type int and is initialised to OK is only assigned to constants and/or results of function calls can only be used in comparisons, returns or LOG calls

19 1. Error variable identification An error variable is a variable that has type int and is initialised to OK is only assigned to constants and/or results of function calls can only be used in comparisons, returns or LOG calls

20 1. Error variable identification An error variable is a variable that has type int and is initialised to OK is only assigned to constants and/or results of function calls can only be used in comparisons, returns or LOG calls

21 2. Path identification G. A. Kildall. A unified approach to global program optimization

22 2. Path identification G. A. Kildall. A unified approach to global program optimization

23 3. Detecting undesired situations SMELL = State Machine for Exception Linking & Logging entry Track the value of the error variable by accept assignedok assignedconstant assignedunknown assignednot-ok reject writing the exception handling idiom as a DFA evaluating the DFA along all possible executions of a function D. Engler et al. Checking System Rules Using System-Specific, Programmer-Written Compiler Extensions

24 3. Detecting undesired situations entry accept assignedok assignedconstant assignedunknown assignednot-ok reject

25 3. Detecting undesired situations entry accept assignedok assignedconstant assignedunknown assignednot-ok reject

26 3. Detecting undesired situations entry accept assignedok assignedconstant assignedunknown assignednot-ok reject

27 3. Detecting undesired situations entry accept assignedok assignedconstant assignedunknown assignednot-ok reject

28 3. Detecting undesired situations entry accept assignedok assignedconstant assignedunknown assignednot-ok reject

29 3. Detecting undesired situations entry accept assignedok assignedconstant assignedunknown assignednot-ok reject

30 3. Detecting undesired situations entry accept assignedok assignedconstant assignedunknown assignednot-ok reject

31 3. Detecting undesired situations entry accept assignedok assignedconstant assignedunknown assignednot-ok reject

32 3. Detecting undesired situations entry accept assignedok assignedconstant assignedunknown assignednot-ok reject

33 3. Detecting undesired situations entry accept assignedok assignedconstant assignedunknown assignednot-ok reject

34 Experimental results Reported deviations False positives unintended deviations kloc CC CC CC CC CC CC Total

35 Experimental results Reported deviations False positives unintended deviations kloc CC CC CC CC CC CC Total unintended deviations/kloc

36 Experimental results Reported deviations False positives unintended deviations kloc CC CC CC CC CC CC Total < 25% false positives

37 Implementing crosscutting concerns by means of idioms is fault prone 1. We described the exception handling idiom precisely by means of a state machine 2. We implemented a static checker that verifies the correct use of the idiom 3. We showed experimental results of running the tool on ASMLs code base

38 Outlook Study alternatives/improvements to the idiom, and define (automated) migration path Generalise findings toward other idioms Generalise findings toward other software

39 Outlook Study alternatives/improvements to the idiom, and define (automated) migration path Generalise findings toward other idioms Generalise findings toward other software Interested in helping us?