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Spin Model Checker

Samaneh NavabpourElectrical and Computer Engineering DepartmentUniversity of WaterlooSE-464Summer 2011

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Common Design Flaws

Deadlock Livelock, Starvation Under-specification Over-specification Violation of Constraints Etc. Most of the errors caused by these flaws

can be detected by model checking.

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Model Checking and Spin

Model Checking: Is an automated technique that, given a finite

model of a system and a logical property, systematically checks whether this property holds for that model.

Spin is a well known classical model checker. Aims towards concurrent systems Only checks functional properties Does not model real-time, but is capable of

modeling timeouts.

DesignAbstract Verification

ModelImplementation

Model Checkerabstraction refinement

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Material which needs to be covered Spin Architecture

We wont cover JSpin

How to install How to use it

Promela Basic building blocks

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jSpin

Install Create a directory for mingw, and install

mingw in that directory. Create separate directory for Jspin.

Download executable for Jspin in directory, and run executable.

Running jSpin -javaw –jar jSpin.jar (with optional Promela

file). Demo jspin

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jSpin

Check Runs a syntax check.

Random Runs a random simulation.

Interactive Runs an interactive simulation.

Guided Runs a guided simulation using the trail file

created by the execution of the analyzer.

Verification with jSpin

With LTL formulas: formula must be converted to an automaton

written as a Promela never claim. Remember to do Translate. Translated LTL formula's will be saved in a *.ltl

file. Original LTL formulas can be saved in*.prp.

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Verification with jSpin

Without LTL formulas: Safety Properties

Using assertions Acceptance cycles:

Testing for acceptance cycles is generally testing for the absence of unwanted infinite behavior.

Acceptance cycle is a cycle that infinitely often visits an acceptance state.

Non-Progress cycles: Progress is the guarantee of wanted infinite behavior. Non-progress cycle is a cycle that does not visit a

progress state infinitely often.

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Promela

Promela consists of: Processes

Describes the behavior of the system. Channels

Define the environment in which the processes run.

Variables Define the environment in which the processes

run. The scope of a variable is global if it is declared

outside all process declarations, and local if it is declared within a process declaration.

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Promela

Statements in Promela: Are all conditional: A statement will only be

executed if the condition of its execution is satisfied. Hence: Statement is either Executable or Blocked.Example: (a == b) is similar to While(a != b){

// Skip}

Promela cant have unbounded Data, Channels, Processes, Process Creation.

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Promela-variables

Basic Types: Bit Bool Byte Short Int

Arrays Byte test[9]

Record Typedef test {int test1, byte test2}

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Promela-variables

Message type mtype mtype {int, byte}

Channels chan toR = [6] of {mtype, bit}

Global Variables

Variables can be given values by: assignment, argument passing and message passing.

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Promela-processes

Processes

Can be created by run or active. Can be created at any point. Processes can interact via channels or global

variables. The run statement can pass parameter values of

all basic data types to the new process.

byte state;active [2] proctype P() { (state == 1) -> state = 3}

namenumberexecution proctype P() {…

}

Init{Int pid2 = run P();}

OR

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Promela- Advanced Topics

atomic: Statements in atomic are executed as one

indivisible unit, non-interleaved with any other processes.

d_step: Similar to atomic Does not save intermediate states Can not contain non-determinism or blocking

statements

proctype P(){ atomic { (state==1) -> state = state+1 }}

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Promela-Statements

If-statement:

If more than one guard is satisfied, we have non- determinism.

If all guards are un-executable the process will block until at least one of them can be selected.

There is no restriction on the type of statements that can be used as a guard.

if:: (a >= b ) -> Stmt1 ; Stmt2 ; …:: (a < b ) -> Stmt3 ; Stmt4 ; …:: (a == b ) -> Stmt5 ; Stmt6 ; …:: else -> Stmt7fi

if:: count = count + 1:: count = count – 1fi

if:: count = count + 1:: count = count – 1fi

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Promela-Statements

Do-statement

Same as if-statement, only in a while loop.

do:: (a >= b ) -> Stmt1 ; Stmt2 ; …:: (a < b ) -> Stmt3 ; Stmt4 ; …:: (a == b ) -> Stmt5 ; Stmt6 ; …:: else -> Stmt7od

do:: count = count + 1:: count = count – 1:: (count == 0) -> breakod

do:: count = count + 1:: count = count – 1:: (count == 0) -> breakod

Promela-Communication

Processes can communicate in two ways: Global variables Channels:

chan <name> = [<dim>] of {<type1>, <type2>, ..,<typen>} Example: chan toR = [2] of {int, int}

Asynchronously : dimension > 0 Synchronously : dimension = 0 Actions:

Sending : ch ! <expr_1>, ..,<expr_n> Receiving: ch ? var_1,..,var_n

If send and receive can not happen, process will block.

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toR!(1,5)…….toR?(x1,x2)

toR!(1,5)…….toR?(x1,x2)

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Promela-Statements

Special Statements: goto skip: same as 1 or true, run assert (<expr>)

check whether certain properties hold. Gives an error if violated.

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Promela- Advanced Topics

Timeout Promela has no real-time features The timeout statement can only be executed when no

other statement in the system can be executed Can help get out of deadlock The timeout models a special condition that allows a

process to abort the waiting for a condition that may never become true, e.g. an input from an empty channel.

Example:do:: guard1 -> Stmt1; …:: timeout -> break ;…od

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Conclusion

Spin is suitable for concurrent systems Can not model time JSpin is easy to install and use via the

graphical interface Promela is similar to C, therefore easy

to cope with. Beware of state explosion Need basic knowledge of LTL.

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References

Spin official page http://spinroot.com

Spin online tutorials http://spinroot.com/spin/Man/index.html

Jspin http://stwww.weizmann.ac.il/g-cs/benari/spin

Erigone http://stwww.weizmann.ac.il/g-cs/benari/

erigone