This document summarizes Adrian Lienhard's PhD defense on dynamic object flow analysis. The defense addressed tracking object references and aliasing at runtime to visualize object flows between classes and features. The thesis proposed explicitly modeling object references using an object flow metamodel to capture activation contexts, object origins, and value transfers. This allows visualizing low-level object dependencies to support tasks like feature location, impact analysis, and test blueprint generation.

1. Dynamic
Object Flow Analysis
PhD defense
Adrian Lienhard
Advisor: Oscar Nierstrasz

2. 2

3. 3

4. 4

5. 5

6. 6

7. image:Image copy:Image
a1 a2
:File
name = 'cat.jpg'
image := Image newFor: file. // creates a1
copy := image duplicate. // creates a2
7

8. image:Image copy:Image
a1 a2
:File
name = nil
image := Image newFor: file. // creates a1
copy := image duplicate. // creates a2
copy delete
// file.name := nil
8

9. image:Image copy:Image
a1 a2
:File
name = nil
image := Image newFor: file. // creates a1
copy := image duplicate. // creates a2
copy delete
// file.name := nil
image display
// file.name asUrl NullPointerException
9

10. image:Image copy:Image
a1 a2
:File
name = nil
image := aliasing is a problem because a1
Object Image newFor: file. // creates
copy := image duplicate. // creates a2
it introduces hidden dependencies.
copy delete
// file.name := nil
image display
// file.name asUrl NullPointerException
10

11. Dynamic Control Flow Analysis
11

12. Dynamic Control Flow Analysis
delete
upload
12

13. Dynamic Control Flow Analysis
delete
upload
Feature "Upload" Feature "Duplicate" Feature "Delete"
[Salah and Mancoridis ICSM'04]
13

14. Dynamic Control Flow Analysis
? delete
upload
Feature "Upload" Feature "Duplicate" Feature "Delete"
14

15. Dynamic Data Analysis
image:Image copy:Image
a1 a2
:File
name = 'cat.jpg'
15

16. Dynamic Data Analysis
Reference Patterns Ownership Trees
[De Pauw, Sevitsky ECOOP’99] [Hill, Noble, Potter JVLC’02]
16

17. Dynamic Data Analysis
image:Image copy:Image
a1 a2
:File
name = 'cat.jpg'
17

18. Dynamic Data Analysis
image:Image ? copy:Image
a1 a2
:File
name = 'cat.jpg'
18

19. Dynamic Analysis
control flow data data flow
! ! ?
method reference reference
execution structure transfer
19

20. Dynamic Analysis
control flow data data flow
! ! ?
method reference reference
execution structure transfer
20

21. Thesis
Object references must be
captured and modeled explicitly.
21

22. image:Image copy:Image
Runtime a1 a2
:File
Object Flow
Metamodel
22

23. image:Image copy:Image
Runtime a1 a2
:File
Object Flow
Metamodel
Object
23

24. image:Image copy:Image
Runtime a1 a2
:File
Object Flow
Metamodel
* 1
Alias Object
value
24

25. image:Image copy:Image
Runtime a1 a2
:File
Object Flow
Metamodel
0..1 * 1
*
Alias Object
origin value
25

26. Runtime
Object Flow
Metamodel
0..1 * * 1
*
Alias Object
origin value
26

27. Runtime
caller
0..1
Activation
Object Flow *
Metamodel
0..1 * 1
*
Alias Object
origin value
27

28. Runtime
caller
0..1
Activation
Object Flow *
1 context
Metamodel
0..1 * * 1
*
Alias Object
origin value
28

29. delete
upload
duplicate
Runtime
caller
0..1
Activation
Object Flow *
1 context
Metamodel
0..1 * * 1
*
Alias Object
origin value
29

30. Object Flow
30

31. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
31

32. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
32

33. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
33

34. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
34

35. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
35

36. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
36

37. Detecting flows between classes
Activation
1 context
0..1 * *
* 1
Alias Object
origin value
37

38. Detecting flows between classes
Method
1
*
Activation
1 context
0..1 * *
* 1
Alias Object
origin value
38

39. Detecting flows between classes
Class A Class
1
*
Method
Class B 1
*
Activation
1 context
Class C
0..1 * *
* 1
Alias Object
origin value
39

40. Detecting flows between classes
Class A Class
1
*
Method
Class B 1
*
Activation
1 context
Class C
0..1 * *
* 1
Alias Object
origin value
40

41. Inter-unit Flow View
41

42. Chronological
propagation
42

43. Chronological
propagation
42

44. Chronological
propagation
42

45. Spanning flows
Parser (4)
43

46. Spanning flows
IRBuilder
44

47. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
l.
ard eta
[ Lienh AN'09]
L
COM
Metamodel
Activation
Alias Object
origin
Object Tracking
45

48. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
46

49. Feature "Upload" Feature "Duplicate" Feature "Delete"
[Salah and Mancoridis ICSM'04]
47

50. Feature "Upload" Feature "Duplicate" Feature "Delete"
image:
a1
:File
48

51. Feature "Upload" Feature "Duplicate" Feature "Delete"
image: image: copy:
a1 a1 a2
:File :File
49

52. Feature "Upload" Feature "Duplicate" Feature "Delete"
image: image: copy: image: copy:
a1 a1 a2 a1 a2
:File :File :File
50

53. Feature "Upload" Feature "Duplicate" Feature "Delete"
0..1
* * 1
Activation Feature
1 context
* * 1
0..1 *
Alias Object
origin value
51

54. delete
upload
duplicate
Feature "Upload" Feature "Duplicate" Feature "Delete"
0..1
* * 1
Activation Feature
1 context
* * 1
0..1 *
Alias Object
origin value
52

55. IRC client dependencies
Open
Setup
Connect
MOTD
Join Channel
Send Message
Receive Message
New Console
Disconnect
0 5 10 15 20 25 30 35
Our approach Salah et al.
53

56. Object Dependency Graph
of feature Receive Message
Open Join Channel
Connect Send Message
54

57. Object Dependency Graph
of feature Receive Message
Open Join Channel
Connect Send Message
55

58. Object Dependency Graph
of feature Receive Message
Open Join Channel
Connect Send Message
56

59. Object Dependency Graph
of feature Receive Message
Open Join Channel
Connect Send Message
57

60. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
ta l.
ard e
Lienh 07
'
ICPC
Metamodel
Activation
Alias Object
origin
Object Tracking
58

61. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
59

62. Writing a Unit Test
1. Setup
2. Invoke
3. Assert
60

63. duplicate
61

64. duplicate
Test Blueprint Objects
:Image existing
:Image (target) :Image (return) :Image new
References
existing
:File new
62

65. duplicate
Test Blueprint Objects
:Image existing
:Image (target) :Image (return) :Image new
References
existing
:File new
1 file := File named: 'cat.jpg'.
2 image := Image new.
3 image file: file.
63

66. duplicate
Test Blueprint Objects
:Image existing
:Image (target) :Image (return) :Image new
References
existing
:File new
1 file := File named: 'cat.jpg'. 4 copy := image duplicate.
2 image := Image new.
3 image file: file.
64

67. duplicate
Test Blueprint Objects
:Image existing
:Image (target) :Image (return) :Image new
References
existing
:File new
1 file := File named: 'cat.jpg'. 4 copy := image duplicate.
2 image := Image new.
3 image file: file. 5 self assert: copy class = Image.
6 self assert: copy file == file
65

68. duplicate
caller
0..1
* Activation
context
target parameters
* 1 *
0..1 * 1
Alias Object
origin value
66

69. IRBuilder>>add: 2 FunctionScope>>lookupVar:
1
NonClosureScopeFixer>>acceptVarNode:
InstanceScope>>newMethodScope
4
3
ace Test Blueprint
67

70. Execution Trace Test Blueprint
68

71. Initial Study I
Let a developer use the tool:
12 tests in 2h
Execution Trace Test Blueprint
69

72. Initial Study II
Rewrote assertions of 14 existing tests:
72 identical, 12 missed, 5 additional
Execution Trace Test Blueprint
70

73. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
al.
a rd et
Lienh '08
R
CSM
Metamodel
Activation
Alias Object
origin
Object Tracking
71

74. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
72

75. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
73

76. 74

77. Specification of object flow tracking
by extending language semantics
75

78. Example execution
Computer Dynamic
Source Code
(formal semantics) Analysis Data
f := new File
...
return f
76

79. Example execution
Computer Dynamic
Source Code
(formal semantics) Analysis Data
f := new File allocation
...
return f
77

80. Example execution
Computer Dynamic
Source Code
(formal semantics) Analysis Data
f := new File allocation
...
field-write
return f
78

81. Example execution
Computer Dynamic
Source Code
(formal semantics) Analysis Data
f := new File allocation
...
field-write
return f
return
79

82. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
80

83. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking
81

84. Problem of conventional debuggers
In 50% of the cases the execution stack contains
essentially no information about the bug's cause.
[Liblit etal. PLDI'05]
82

85. Back-in-time debugging
Challenges
1. amount of data
2. execution overhead
83

86. Approaches
Omniscient Trace-oriented Trace-oriented
Debugger debugger (partial) debugger (full)
loss of old history loss of selected history complete history
overhead 100x overhead 10x overhead 100x
84

87. Approaches
Omniscient Trace-oriented Trace-oriented
Debugger
Our approach
debugger (partial) debugger (full)
low overhead
relevant history
loss of old history loss of history complete history
overhead 100x overhead 10x overhead 100x
85

88. Delete history when it
gets irrelevant
History of origins of objects
Previous field values of objects
Call stacks in which above appear
86

89. Before deletion
87

90. Before deletion
After deletion
88

91. Object Flow VM
regular objects alias
header header
header header
field_1 field_1 header
... value
field_2 field_2 ...
context
.... ....
field_n
pointer field_n
origin
predecessor
...
Typical model Object Flow VM
89

92. Capturing historical object state
t1 t2 t3
image := Image new image height: 17 image height: 42
90

93. Capturing historical object state
t1 t2 t3
image := Image new image height: 17 image height: 42
height
image: @t1 nil
91

94. Capturing historical object state
t1 t2 t3
image := Image new image height: 17 image height: 42
@t1 nil
predecessor
height
image: @t2 17
92

95. Capturing historical object state
t1 t2 t3
image := Image new image height: 17 image height: 42
@t1 nil
predecessor
@t2 17
predecessor
height
image: @t3 42
93

96. Capturing historical object state
t1 t2 t3
image := Image new image height: 17 image height: 42
@t1 nil
predecessor
@t2 17
predecessor
height
image: @t3 42
predecessor
0..1 0..1
Alias Object
origin
* 1
fields 94

97. Evaluation memory usage (1)
2.5e+09 1e+07
Number of aliases allocated (left Y-axis)
Number of aliases in memory (right Y-axis)
Number of objects in memory (right Y-axis)
2e+09 8e+06
1.5e+09 6e+06
1e+09 4e+06
5e+08 2e+06
0 0
0 200 400 600 800 1000
#classes
95

98. Evaluation memory usage (2)
7e+06 50
Number of aliases allocated
Number of aliases in memory
6e+06 Number of objects in memory
Ratio between aliases in 40
memory and allocated
5e+06
30
4e+06
%
3e+06
20
2e+06
10
1e+06
0 0
0 2 4 6 8 10 12 14 16 18
#samples
96

99. Evaluation memory usage (3)
1e+07
Number of aliases allocated
9e+06 Number of aliases in memory
Number of objects in memory
8e+06
7e+06
6e+06
5e+06
4e+06
3e+06
2e+06
1e+06
0
5 10 15 20 25
#requests
97

100. Evaluation run-time overhead
Overhead GC
Recording off 1.15 1.6%
Recording on 3.84 27.6%
Largest overhead: 6.9
98

101. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
al.
a rd et
Object Tracking Lienh P'08
O
ECO
99

102. Visualizing Feature Test
Object Flows Dependencies Blueprints
Runtime Monitoring in the VM
Metamodel
Activation
Alias Object
origin
Object Tracking