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

2

3

4

5

6

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

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
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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

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

Dynamic Control Flow Analysis
11

Dynamic Control Flow Analysis
delete
upload
12

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

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

Dynamic Data Analysis
image:Image copy:Image
a1 a2
:File
name = 'cat.jpg'
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Dynamic Data Analysis
Reference Patterns Ownership Trees
[De Pauw, Sevitsky ECOOP’99] [Hill, Noble, Potter JVLC’02]
16

Dynamic Data Analysis
image:Image copy:Image
a1 a2
:File
name = 'cat.jpg'
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Dynamic Data Analysis
image:Image ? copy:Image
a1 a2
:File
name = 'cat.jpg'
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Dynamic Analysis
control flow data data flow
! ! ?
method reference reference
execution structure transfer
19

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

Thesis
Object references must be
captured and modeled explicitly.
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image:Image copy:Image
Runtime a1 a2
:File
Object Flow
Metamodel
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image:Image copy:Image
Runtime a1 a2
:File
Object Flow
Metamodel
Object
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image:Image copy:Image
Runtime a1 a2
:File
Object Flow
Metamodel
* 1
Alias Object
value
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image:Image copy:Image
Runtime a1 a2
:File
Object Flow
Metamodel
0..1 * 1
*
Alias Object
origin value
25

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

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

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

delete
upload
duplicate
Runtime
caller
0..1
Activation
Object Flow *
1 context
Metamodel
0..1 * * 1
*
Alias Object
origin value
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Object Flow
30

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

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

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

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

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

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

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

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

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

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

Inter-unit Flow View
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Chronological
propagation
42

Chronological
propagation
42

Chronological
propagation
42

Spanning flows
Parser (4)
43

Spanning flows
IRBuilder
44

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

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

Feature "Upload" Feature "Duplicate" Feature "Delete"
[Salah and Mancoridis ICSM'04]
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Feature "Upload" Feature "Duplicate" Feature "Delete"
image:
a1
:File
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Feature "Upload" Feature "Duplicate" Feature "Delete"
image: image: copy:
a1 a1 a2
:File :File
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Feature "Upload" Feature "Duplicate" Feature "Delete"
image: image: copy: image: copy:
a1 a1 a2 a1 a2
:File :File :File
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Feature "Upload" Feature "Duplicate" Feature "Delete"
0..1
* * 1
Activation Feature
1 context
* * 1
0..1 *
Alias Object
origin value
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delete
upload
duplicate
Feature "Upload" Feature "Duplicate" Feature "Delete"
0..1
* * 1
Activation Feature
1 context
* * 1
0..1 *
Alias Object
origin value
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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.
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Object Dependency Graph
of feature Receive Message
Open Join Channel
Connect Send Message
54

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

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

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

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

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

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

duplicate
61

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

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

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

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

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

Execution Trace Test Blueprint
68

Initial Study I
Let a developer use the tool:
12 tests in 2h
Execution Trace Test Blueprint
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Initial Study II
Rewrote assertions of 14 existing tests:
72 identical, 12 missed, 5 additional
Execution Trace Test Blueprint
70

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

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

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

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Specification of object flow tracking
by extending language semantics
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Example execution
Computer Dynamic
Source Code
(formal semantics) Analysis Data
f := new File
...
return f
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Example execution
Computer Dynamic
Source Code
(formal semantics) Analysis Data
f := new File allocation
...
return f
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Example execution
Computer Dynamic
Source Code
(formal semantics) Analysis Data
f := new File allocation
...
field-write
return f
78

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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