KFSM - A Kotlin DSL for Finite State machines

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A Kotlin DSL for finite state machines - A Journey Corneil du Plessis Chief Architect, JumpCO

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Quotable quotes K.I.S.S. – Keep it simple stupid! Graeme Mitchell “Everything should be a simple as possible, but no simpler” Albert Einstein

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What is a state machine?

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Examples – Packet Reader

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Examples – Quotation Manager

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A brief history of state machines ● FSM/FSA (Finite state machines / automa) ● DFA/NFA/NDFA (Non-deterministic state machine / automa) ● State tables / charts / maps ● Mealy / Moore machines (State + Input) vs (State) ● UML state machines ● SDL state machines

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UML State Diagram

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Finite State Machines - Turnstile

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Finite State Machines – Double Lock

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Finite State Machines – Secure Turnstile

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State Event Next State Action LOCKED COIN UNLOCKED unlock PASS alarm UNLOCKED COIN return-coin PASS LOCKED lock Transition table for Turnstile

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Finite State Machines – Why and How?

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Why and How? (cont.)

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FSM Patterns ● Generate code from State Map - SMC Class per State, method per Event OR Huge switch statement ● Executable XML – SCXML ● Language Builder – Spring Statemachine

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SCXML - Turnstile

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SMC - Turnstile

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Ideal DSL

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State Machine Model

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State Machine Sequence Diagram

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Context Class

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States and Events

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State machine definition

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Creating a DSL – Lambda with argument

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Creating a DSL – Lambda as member of class

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Creating a DSL – Builder and Handler

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Creating a DSL – Using

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Definition, instance and context

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Definition, instance and context (cont.)

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Definition, instance and context (cont.)

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Definition, instance and context (cont.)

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Turnstile – Sample invocation

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Turnstile – Sequence Diagram

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Output

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Performance

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Performance – Node.js & Kotlin Native 3270 4186 2777 515 0 500 1000 1500 2000 2500 3000 3500 4000 4500 Node.js v10 Node.js v12 Kotlin Native Release Kotlin Native Debug Transitions/ms

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Performance – Graal Native 3270 4186 11477 2777 515 0 2000 4000 6000 8000 10000 12000 14000 Node.js v10 Node.js v12 Graal Native Kotlin Native Release Kotlin Native Debug Transitions/ms

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Performance - JVM 3270 4186 273 25456 20856 22163 24567 39614 11477 2777 515 0 5000 10000 15000 20000 25000 30000 35000 40000 45000 Node.js v10 Node.js v12 JDK 8 Int JDK 8 JDK 11 JDK 12 JDK 13 Graal 19.2.0.1 Graal Native Kotlin Native Release Kotlin Native Debug Transitions/ms

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Performance – Startup overhead 290 180 180 160 180 140 130 180 10 10 10 0 50 100 150 200 250 300 350 Node.js v10 Node.js v12 JDK 8 Int JDK 8 JDK 11 JDK 12 JDK 13 Graal 19.2.0.1 Graal Native Kotlin Native Release Kotlin Native Debug Overhead in ms

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Performance - Memory 42096 43528 30724 36992 58208 58804 43400 85344 6744 12036 2600 0 10000 20000 30000 40000 50000 60000 70000 80000 90000 Node.js v10 Node.js v12 JDK 8 Int JDK 8 JDK 11 JDK 12 JDK 13 Graal 19.2.0.1 Graal Native Kotlin Native Release Kotlin Native Debug Memory in Kb

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FSM other features ● Guard Expressions ● Entry / Exit Actions ● Event Parameters ● Automatic transitions ● Named State Maps ● Push / Pop transitions ● Typed Parameters ● Typed Return values

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FSM additions… ● Timeouts / Timers ● Coroutines ● Sealed Classes?

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Useless Box – State diagram

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AI Assistive technology for improved UX

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Resources ● Twitter - @corneil ● Slides - https://speakerdeck.com/corneil/kfsm-a-kotlin-dsl-for- finite-state-machines ● Project Source - https://github.com/open-jumpco/kfsm ● Samples - https://github.com/open-jumpco/kfsm-samples ● SMC - http://smc.sourceforge.net/ ● Spring Statemachine - https://projects.spring.io/spring- statemachine/ Questions?