dynamic analysis and visualizing of data structures in java programs presented by sokhom pheng...

Dynamic Analysis and Visualizing of Data

Structures in Java Programs

Presented by Sokhom Pheng(Supervisor: Clark Verbrugge)

McGill UniversityFebruary 9th 2005

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Outline

Motivation Brief overview of *J Requirements for data structure (DS)

analysis Some algorithms for analysis Issues Future works

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Motivation

Visual understanding of data structure in java programs

Help understand code without looking at source code

Dynamic analysis

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Brief Overview of *J

Developed by Bruno Dufour in the sable lab

Java Application *J Analyzer

Data Structure Analyzer

*J Agent(JVMPI)

trace file

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Why isn’t *J enough for DS Analysis? JVMPI doesn’t provide all info

Missing references of objects Missing info on actual values for primitive

Important for accessing arrays Does not track objects

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Requirements for Data Structures Analysis Need to simulate the whole program

execution Keep track of the JVM stacks

Follow JVM design (VM Spec) Invocation stack for each thread Stack frame for each method

Execution stack to contain operand objects

Keep track of actual values (even of primitives) for array indices

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Represent Data Structures in Memory Object, method and class has unique ID and

entity (originally implemented in *J) ObjectEntity: ID, name, type, size, … MethodEntity: signature, name, class entity, … ClassEntity: name, number of methods/interfaces,

… Recreate objects and their references to each

other by executing bytecodes found in the trace Eg. putfield obj1 obj2

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Algorithm for DS Analysis

Goal: identifying data structures Started with identifying “tree”, “dag” and

“cycle” detected by DFS

tree dag cycle

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Algorithm for DS Analysis (con’d) Other way to identify DS

Combinatorial topology Shape represented by set of equations

Reference Shape Graph (RSG)1

Node represent memory location having similar reference patterns

1 A new Dependence Test Based on Shape Analysis for Pointer-Based Codes, Navarro, Corbera, Asenjo, Tineo, Plata, Zapata, LCPC 2004

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RSG Example

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Advantage over Static Analysispublic class BinaryTree { ...

public static void main(String[] args) {...tree.left = tree.right;tree.right = new Node(...);

... } ...}

class Node { ... }

Static Analysis

tree

dagdagdag

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Advantage over Static Analysis (con’d)From JOlden benchmark: BiSort

After 62 modifications

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Advantage over Static Analysis (con’d)From JOlden benchmark: BiSort

After 63 modifications

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Data Gathering Issues

Start up code JVMPI doesn’t start with JVM

Lack of array indices Primitive values from I/O

Native methods

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Potential Solutions

Look only at application code Ignore arrays for now

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Analysis Problems

Multiple entry points

tree dag

cycle

obj1 obj2

obj3

obj5

obj4

obj6

Sol’n: Look at all entry points individually

obj7

obj8

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Analysis Problems (con’d)

Garbage objects Induce multiple entry points Dead nodes not trivially distinguished from live

ones

obj1 obj2

obj3 obj4

Garbage Node

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Sol’n for Garbage Problem

Root set Exclude garbage objects not yet deleted by

garbage collector

Static fields, live variables and live methods parameters

obj2

obj1 obj1

obj2

obj1

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Example of Entry Points

public class Foo { static bar = new Bar();

public static void main(String[] args) {Foo foo = new Foo();foo.foo1(new Bar());...

}

public void foo1(Bar b) {Foo f = new Foo();...

}}class Bar { ... }

Root set

{bar}

{bar, foo}

{bar, foo}

{bar, foo, b, f}

{bar}

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DS Configuration Options

Self loop Why do they exist? Effect: makes everything cyclic

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DS Configuration Options (con’d) Doubly-connected DS

Effect: makes everything cyclic Not every edge is doubly-connected

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Gathering Other Useful Info

Encode “age” of modification How a DS evolves over time

Amount of garbage being carried “Drag” effect

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Drag Effect

From JOlden benchmark: Barnes-Hut

After 58 modifications

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Legend / Encoding

≤ 1000 byte codes

≤ 100 byte codes

≤ 10 byte codes

≤ 10000 byte codes

≤ 100000 byte codes

≤ 1000000 byte codes

> 1000000 byte codes

Age of node

New node

Cycle

DAG

Tree

obj1 Garbage

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Example

From JOlden benchmark: Barnes-Hut

After 13 modifications

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Garbage Option

Option to show garbage objects or not

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Representing Entry Points

Different shapes and colours for entry point depending on type of DS

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Drawing Tool

Dot / Graphviz Generates snapshots

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Drawing Issue

Drawing of one graph has no relation to drawing of the next Dot try to be optimal Jumps all over the place

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Drawing Issue Example

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Possible Solutions

Tom Sawyer Software (currently investigating) Incremental drawing

Hack into Dot’s source code Add “inter-frames” between snapshots

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Small Complete Example

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Future Works

Deal with arrays and unknown info Draw approximate graph

Handle start up code / native methods Investigate other drawing tools Add other analyses

RSG from LCPC paper Topological approach (set of equations)

Calculate “drags” for garbage objects Analyze more and more complex programs

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Thank You!