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Efficient Model Checking of Data Races with Automatically-extracted Distance- based Fitness Functions João Paulo, Elton Alves, Marcelo Damorim, Fernando.

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Presentation on theme: "Efficient Model Checking of Data Races with Automatically-extracted Distance- based Fitness Functions João Paulo, Elton Alves, Marcelo Damorim, Fernando."— Presentation transcript:

1 Efficient Model Checking of Data Races with Automatically-extracted Distance- based Fitness Functions João Paulo, Elton Alves, Marcelo Damorim, Fernando Castor

2 Agenda Concurrent Programing Race Model Checking JPF Reade-Writers set – Algorithm Guiding Model Checking

3 Por que multi-núcleo? Antigamente, apenas aumentar o número de transistores era suficiente para aumento de desempenho Juntamente com o aumentos de cache E aumento da frequência de clock Hoje em dia, não é mais o caso Número de transistores continua crescendo Mas a frequência de clock está estagnada Consumo de energia e aquecimento são os fatores limitantes

4 Fonte:

5 Por que multi-núcleo (cont.)? Novas abordagens tornaram-se necessárias Solução encontrada: paralelismo Diversos núcleos em uma mesma pastilha Memória única Reaproveitamento de outros componentes Localidade propicia melhor desempenho Alternativa: diversos processadores Supercomputadores usam essa abordagem Mais cara

6 “The biggest sea change in software development since the OO revolution is knocking at the door, and its name is Concurrency”. Herb Sutter

7 Concurrent Programming Is too hard! – Error prone It’s difficult to debug and find errors Most programmers thinks that know how to do it, but they don’t NonDeterminism, Deadlocks, Data Races…

8 Race Condition public class Ref { int i; void inc() { int t = i + 1; i = t; } public static void main(String args[]){ final Ref ref = new Ref(); new Thread(new Runnable(){ public void run(){ ref.inc(); } }).start(); new Thread(new Runnable(){ public void run(){ ref.inc(); } }).start(); assert ref.i == 2; } A race condition occurs if two threads access a shared variable at the same time without synchronization at least one of those accesses is a write

9 public class Ref { int i; void inc() { synchronized (this) { int t = i + 1; i = t; } public static void main(String args[]) { final Ref ref = new Ref(); new Thread(new Runnable() { public void run() { ref.inc(); } }).start(); new Thread(new Runnable() { public void run() { ref.inc(); } }).start(); assert ref.i == 2; } Field Guarded by Lock Lock acquired before the thread enter in block Ensure race freedom Guarantees the mutual exclusion

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13 Model Checking

14 Program Model Checking It performs model checking directly into the code Rigorous method that exhaustively explores all possible SUT behaviors Is it a test?

15 Model Checking Fonte:

16 Java PathFinder(JPF) An explicit state software model checker – Focus is on finding bugs in Java programs – Developed by NASA since 1999 – Turned Open Source in 2005 State Explosion problem

17 State Explosion # thread#Atomic Section Scheduling

18 How JPF Works Backtracking State Matching Partial Order Reduction Listener

19 How do Detect Races?

20 How do we Detect Potencial Races? Using a customized JPF listener For each PUTFIELD or GETFIELD – Get Object Reference Get the accessed Field – Get Current Thread » Get Current Instruction Get the set of Acquireds Locks

21 How do we Detect Potencial Races?[2] So, we have a report like this:

22 How do we Detect Potencial Races?[3] which can be simplified for this

23 How good is our solution?

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26 Our Research Idea Guide Model Checking Attempt to Avoid State explosion Uses heuristics to classifies a given a state – Interesting State has value 0 – Boring State has value Integer.Max Uses distance based fitness function

27 Our work-in-progress Find a heuristic function to guide the Model Checking Evaluate the function This is harder than we thought 

28 Our work-in-progress[2] CallTrace cg; /* computed on-the-fly */ AccessPair[] goals; /* computed on-the-fly */ MethodInfo driver; /* test driver */ int eval(State jpfState) { ThreadInfo[] tis = jpfState.threadInfos(); TraceInfo ti = cg.getTrace(); for(int i=0; i

29 If we are not so good to do it… The research goal could moves to compare the ‘potencial data race’ finded with other approaches 

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