The document discusses object-centric debugging which allows debugging operations at the level of individual objects. Object-centric breakpoints allow halting execution based on message sends or state access for a specific object. Object-centric behavior allows dynamically adding methods to a single object. The implementation uses techniques like reflectivity, proxies, and anonymous classes but currently lacks a clear model. Problems include needing to migrate objects and unstable tools. Part II previews a reverse object-centric debugger being developed collaboratively.

1. Object-Centric Debugging: a preview
Steven Costiou steven.costiou@inria.fr
RMoD
Inria Lille - Nord Europe
2019

2. 2

3. Part I
Object-Centric Debugging
3

4. Demo
4

5. What is object-centric debugging?
5

6. Object-centric debugging
• Debugging operations at the level of objects
• Only target objects are affected
• Examples:
• A breakpoint active for one object only
• A method available for one object only
6

7. Why object-centric debugging?
7

8. Why Object-centric debugging?
• Debugging one object among many:
• Collections (Hinkle, Jones, Johnson, 1993)
• Events
• Graphical objects
8

9. Object-Centric Features
(preview)
9

10. Object-centric breakpoints
• Break when a message is received
• haltOnCall => on every method call
• haltOnCall: #selector => for given selector only
• haltOnNextCall => on next method call
• haltOnceOnCall: #selector => only once for given selector
• haltOnCallWhen: condition => if condition is met
10

11. Object-centric breakpoints
• Break on state access
• haltOnWriteTo: #instVarName => when instVarName is written
• haltOnRead: #instVarName => when instVarName is read
• haltOnWrite => when any instance variable is written
• haltOnRead => when any instance variable is read
11

12. Object-centric behavior
• Object-centric methods
• compile: sourceCode => compiles and add new methods
• uses: aTrait => acquires behavior from Trait
• acquire: aCompiledMethod => acquire the method
12

13. Object-centric debugging,
how is it implemented?
13

14. Implementation
14
Object-centric
breakpoints
Object-centric
behavior

15. Implementation
15
Reflectivity
Proxies
Object-centric
breakpoints
Object-centric
behavior

16. Implementation
16
Reflectivity
Proxies
Talents
Object-centric
breakpoints
Object-centric
behavior

17. Implementation
17
Reflectivity
Proxies
Talents
Anonymous
Classes
Object-centric
breakpoints
Object-centric
behavior

18. Implementation
18
Reflectivity
Proxies
Talents
Anonymous
Classes
Object-centric
breakpoints
Object-centric
behavior
Object-centric
… ???

19. Implementation goal
19
Reflectivity Proxies Talents
Anonymous
Classes
Object-centric
breakpoints
Object-centric
behavior
Object-centric layer
Object-centric
…

20. Current problems
• Implementation is mixing up different techniques without any
clear interaction model
• Requires to migrate the object to an anonymous subclass
• Installation of object-centric instrumentation is not thread-safe
• Sometimes make tools unstable
• Obtaining objects to debug (but work has been done on that…)
20

21. Part II
Object-Centric Reverse Debugging
21

22. Demo
22

23. Reverse object-centric debugger
23

24. Reverse object-centric debugger
24

25. Reverse object-centric debugger
25

26. Reverse object-centric debugger
26

27. Reverse object-centric debugger
27

28. Reverse object-centric debugger
28

29. Reverse object-centric debugger
29

30. Reverse object-centric debugger
30

31. Reverse object-centric debugger
31

32. Reverse object-centric debugger
32

33. Reverse object-centric debugger
33
WIP

34. Reverse object-centric debugger
• AST interpreter - Carolina Hernandez Phillips
• Reverse-execution - Vincent Aranega, Steven Costiou
• Object-centric debugger - Steven Costiou
• Scriptable debugger - Thomas Dupriez
34
Who’s working on it?

35. Thanks! Questions?
35
Object-Centric
Reverse Debugging
Object-Centric
Debugging
• haltOnCall
• haltOnCall: #selector
• haltOnNextCall
• haltOnceOnCall: #selector
• haltOnCallWhen: condition
• haltOnWriteTo: #instVarName
• haltOnRead: #instVarName
• haltOnWrite
• haltOnRead
• compile: sourceCode
• uses: aTrait
• acquire: aCompiledMethod