INTRODUCTION TO TLA + Presented by : Kevin Yeh What is TLA+ - - PowerPoint PPT Presentation

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INTRODUCTION TO TLA + Presented by : Kevin Yeh What is TLA+ - - PowerPoint PPT Presentation

Jan 20, 2024 391 likes •612 views

INTRODUCTION TO TLA + Presented by : Kevin Yeh What is TLA+ Specification Language for modelling complex or concurrent systems TLA+ toolbox performs model checks to check for correctness PlusCAL What can TLA+ do for you?

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INTRODUCTION TO TLA +

Presented by : Kevin Yeh

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What is TLA+

  • Specification Language for modelling

complex or concurrent systems

  • TLA+ toolbox performs model checks to

check for correctness

  • PlusCAL
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What can TLA+ do for you?

  • Modelling of ALGORITHMS prior to

implementation

  • Meant as a supplement to traditional test/

verification

  • Very powerful bug detection
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  • Been used successfully at Amazon, HP, and Intel
  • Two weeks before value was added

What can TLA+ do for you?

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Intangibles

  • Requires up-front system understanding
  • Adds value even after production release
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TLA+ an Overview

  • 4 parts to a specification
  • Initial predicate
  • Possible “Next” states
  • Safety Properties
  • Liveness Properties
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Alternating One-bit Clock

  • Initial Predicate
  • (b = 0 ) V (b = 1)
  • Next States
  • ((b = 0) /\ (b’ = 1)) V ((b = 1) /\ (b’ = 0 ))
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Alternating One-bit Clock

  • Initial Predicate
  • (b = 0 ) V (b = 1)
  • Next States
  • ((b = 0) /\ (b’ = 1)) V ((b = 1) /\ (b’ = 0 ))
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Die Hard Problem

  • What you have: 3-gallon jug, 5-gallon jug, and a faucet
  • Goal: Measure 4 gallons
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Die Hard Problem

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Die Hard Problem

FillSmall == /\ small’ = 3 /\ big’ = big SmallToBig == \/ /\ big+ small >5 /\ big’ = 5 /\ small’ = small – (5-big) \/ /\ big + small <= 5 /\ big’ = big + small /\ small’ = 0

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Model Checker

State Statistics Invariant Checker

  • Builds up a Directed Graph
  • f all possible states.
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Die Hard - Solution

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Safety/Liveness Properties

  • Safety Property – Define a correct behavior of your

procedure

  • Partial Correctness : (terminated) => (Correct_Output)
  • Liveness Property – Define a correct behavior that must

eventually hold

  • Termination
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Euclid’s Algorithm – a high level view

  • Find the Greatest Common Divisor of two numbers
  • General Procedure:
  • PlusCAL -> TLA+
  • Write the definition of GCD using set logic: GCD(m,n)
  • Use definition to write Safety/Liveness Properties
  • This is how TLA+ is used in industry
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Euclid’s Algorithm

  • PlusCAL code:
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Model Checking

Safety Liveness 0 BUGS!

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Questions?