Actor model baksia

Actor based programmingIn Erlang, Scala and F#

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Actor model baksia

• The reason• The Actor Model• Erlang• Scala• F#• OTP and AKKA

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Agenda

Actor model baksia

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The base of the problem

Actor model baksia

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Another reason

Actor model baksia

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Concurrency and shared memory model

Actor model baksia

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Shared memory model

Shared memory

Processthread

Processthread

Processthread

Actor model baksia

• Race conditions• Block contention• Deadlock

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Problems with shared memory

Actor model baksia

• Light weight processes/threads communicating through messaging

• Messages are buffered in a “mailbox”

• No shared state • Isolated from other processes• Normally event systems are inversion of control

• Adding a listener to an object• Hard to maintain in large systems

• Humans do not share memory, we communicate through messages

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What is the Actor Model

Actor model baksia

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Pattern Matching

Actor model baksia

• The world is concurrent• Things in the world don't share data• Things communicate with messages• Things fail

- Joe Armstrong

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Erlang

Actor model baksia

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Crash course in Erlang

Variables are immutable

Actor model baksia

• An atom is a global constant starting with lower case• A tuple is an ordered set of elements• Your Java or C# class would be a tuple with an atom

identifier

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Atoms and tuples

Actor model baksia

• Spawn “spawns” a new Erlang process (light weight)• Spawn returns a PID (Process identifier)• Receive waits for a message

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Spawn and process ID

Actor model baksia

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Actors in Erlang

Actor model baksia

• Object functional programming language• Everything in Scala is an object, even functions• Running on JVM and interoperable with Java language

• Also runs on Dalvik VM for Android (Java bytecode)

• Concurrent oriented programming language• Actor model programming style from Erlang• Interactive shell• No attachment to Oracle

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Crash course in Scala

Actor model baksia

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Scalatest TestStack

Actor model baksia

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Scala Actors

Actor model baksia

• React is the “normal” actor, lightweight process• Receive spins out a new Java thread • In the paper *

• 5000 threads• 1 200 000 actors

• React uses partial functions to send the process to the heap

• Receive runs on the stack and is heavyweight JVM threads (like Java)

*Actors That Unify Threads and Events P. Haller, M. Odersky

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React or receive

Actor model baksia

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Scala Actor on tuples

Actor model baksia

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Scala Actor with case classes

Actor model baksia

• F# is a object functional programming language for the .Net Framework

• Derived from ML and is largely compatible with OCaml• Interactive shell, script and compiled language• Runs on mono for Posix based systems

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Crash course in F#

Actor model baksia

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Code example F#

Actor model baksia

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F# Actor MailboxProcessor

Actor model baksia

• Erlang/OTP• Scala Akka• Erlang designed for five nines 99.999 uptime, record is

nine nines 99.999999999 • That is 31ms downtime a year

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Let it crash (supervision)

Actor model baksia

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Supervisors in Erlang/OTP and AKKA

Supervisor

ProcessProcess

Process

Actor model baksia

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Supervising supervisors

Supervisor

Process Process

Process

Supervisor

Process Process

Process

Root Supervisor

Actor model baksia

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