Flow-Centric, Back-In-Time Debugging
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Flow-Centric, Back-In-Time Debugging Adrian Lienhard, Julien Fierz and Oscar Nierstrasz Software Composition Group University of Bern, Switzerland
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Transcript of Flow-Centric, Back-In-Time Debugging
Flow-Centric,Back-In-Time Debugging
Adrian Lienhard, Julien Fierz and Oscar Nierstrasz
Software Composition Group University of Bern, Switzerland
class Account {
Money balance;
void deposit(Money amount) {
this.balance += money;
}
...
}
Debugger call stack
....
....
....
....
..
NullPointerException >>
class Company {
void pay(Money money, Person person) {
person.account().deposit(money);
}
}
class Account {
Money balance;
void deposit(Money amount) {
this.balance += money;
}
...
}
where does the
account object
come from?
Debugger call stack
...
NullPointerException >>
class Company {
void pay(Money money, Person person) {
person.account().deposit(money);
}
}
class Account {
Money balance;
void deposit(Money amount) {
this.balance += money;
}
...
}
return
where does the
account object
come from?
Debugger call stack
...
NullPointerException >>
class Company {
void pay(Money money, Person person) {
person.account().deposit(money);
}
}
class Account {
Money balance;
void deposit(Money amount) {
this.balance += money;
}
...
}
returnfield read
where does the
account object
come from?
Debugger call stack
...
NullPointerException >>
class Company {
void pay(Money money, Person person) {
person.account().deposit(money);
}
}
class Person {
void createAccount(Bank bank) {
this.account = bank.openAccount();
}
}
class Account {
Money balance;
void deposit(Money amount) {
this.balance += money;
}
...
}
returnfield readfield writereturn
where does the
account object
come from?
Debugger call stack
...
class Company {
void pay(Money money, Person person) {
person.account().deposit(money);
}
}
class Bank {
Account openAccount() {
return new Account();
}
}
class Person {
void createAccount(Bank bank) {
this.account = bank.openAccount();
}
}
class Account {
Money balance;
void deposit(Money amount) {
this.balance += money;
}
...
}
returnfield readfield writereturnallocation
where does the
account object
come from?
Debugger call stack
...
In 50% of the cases the execution stack contains essentially no information about the bug’s cause.
[Liblit PLDI’05]
lost method executions
current call stack
With Back-in-time debuggers, we have all data we need at hand
complete execution history
With Back-in-time debuggers, we have all data we need at hand
⇒ programs slow down and run out of memory
Large amount of data:
With Back-in-time debuggers, we have all data we need at hand
⇒ programs slow down and run out of memory
Large amount of data:Popthier etal.
OOPSLA'07
Lienhard etal.
ECOOP'08
With Back-in-time debuggers, we have all data we need at hand
Large amount of data:
⇒ developer may not find the root cause⇒ programs slow down and run out of memory
?
Developer: “where did this object come from?”
Problem: how far back in time do we need to step?
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Flow-centric debugging
Object flow (red) mapped to execution trace
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Flow-centric debugging
Object flow (red) mapped to execution trace
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The Compass Debugger
Debugger frontend makes object flow accessible
Debugging VM tracks object flow
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1 8
2
4
6
5
3
7
9
Frontend
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Execution trace visualization
selected method
methodstart time
stackdepth
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Navigating Execution Traces
execution trace
call stack
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execution stack
method traceobject flow of aselected value
object flow list
Object flow
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short demo...
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Alias Objectvalue
1*
*0..1
Activation
context1
*
origin
0..1
caller
*
ASTNode
Alias
Activation
Dynamic model Static modelCompass Model
Compass Frontend
Object Flow VM
program
execution
recording
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Conclusion
http://scg.iam.unibe.ch/research/objectflowPrototype:
Flow-centric views improve the effectiveness of debugging
Conventional back-in-time debuggers adopt traditional stack-oriented views
Future work: concurrency bugs
