ANNA + HANNAH #ABOUTUS...3/18/2019 Spectacle Boilerplate 1/ 87 Anna Neyzberg @Aneyzb she/her Hannah...

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AnnaNeyzberg @Aneyzb she/her

Hannah Howard @techgirlwonder

she/her

anna@carbon�ve.com

hannah@carbon�ve.co

m

ANNA + HANNAH #ABOUTUS

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GO VS. ELIXIR

A Concurrency Comparison

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BUT WE ALSOHAVE

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SO HOW ISTHIS

RELEVANT?

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“Concurrency isthe composition of

independentlyexecuting

processes, whileparallelism is the

simultaneousexecution of

computations“-

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PARALLELISMIS ABOUT

EXECUTINGMANY THINGSAT ONCE. IT'S

FOCUS ISEXECUTION

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CONCURRENCYIS ABOUT

DEALING WITHMANY THINGSAT ONCE. IT'S

FOCUS ISSTRUCTURE

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THIS REQUIRESCOORDINATION

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COORDINATIONINTRODUCES

COMPLEXITY...

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HOW DO WE

COORDINATEBETWEEN

TASKSWORKING

TOGETHER?

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THE PROBLEM

Concurrency Without Coordination

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THREADS COORDINATE BYSHARING DATA

Use same memory spaceUse mutation on shared state to

communicateUse various locks to prevent

overwriting each others work

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THREADS

Old School Concurrency

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MOST WIDELY

USEDPROGRAMMING

LANGUAGESSUPPORTTHREADS.

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MO THREADS

Mo Problems

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CHALLENGES WITHTHREADS

1. Lots of shared mutable state2. Dead locks / unpredictabiity3. Expontential complexity to manage

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THE ACTORMODEL

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INVENTED BYCARL HEWITT

1973

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ERLANGCREATED IN

1986

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CONCEPTUALMODEL TODEAL WITH

CONCURRENTCOMPUTATION

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DEFINESSOME

GENERALRULES FOR

HOW THESYSTEM’S

COMPONENTSSHOULD

BEHAVE ANDINTERACT

WITH EACHOTHER

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One ant is no ant.- https://www.brianstorti.com/the-actor-model/

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PROCCESSES1. Are not OS processes2. Light weight3. Do not share memory4. Have a unique ID

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THE ACTORMODEL IS

PHYSICALLYBASED

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DISTRIBUTEDELIXIR

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LET IT CRASH

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THE BEAM

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PREEMPTIVESCHEDULING

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ELIXIR PRIORITIES1. Scalable2. Fault Tolerant (Telco Strong)3. Fast

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GO AND CSP

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CSP:Communicating Sequential Processes

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PROCESS

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CSP PROCESS != OS PROCESS

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CHANNELS

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PROCESSESKNOW

CHANNELS,NOT OTHERPROCESSES

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Processes choose behavior by listeningon multiple channels

CHOICE:

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LOOKING AT CSP IN GO

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1. package main 2. 3. import "fmt" 4. 5. func read(incoming <-chan string, done chan<- struct{}) { 6. readValue := <-incoming 7. fmt.Printf("%s\n", readValue) 8. done <- struct{}{} 9. } 10. 11. func write(outgoing chan<- string, done chan<- struct{}) {12. outgoing <- "bananas"

Wait for both to complete

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SYNCHRONOUSCHANNELS =

COORDINATION

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Choice in Go with select!

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HOW GO IMPLEMENTS CSP

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A goroutine is alightweight thread

managed by the Goruntime.

- Of�cial Tour Of Go

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*stares Britnely*

GOROUTINES SHARE MEMORY

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BUT WAIT THERE'S MORE...

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Sync Package:

ALL THETHREAD SYNCPRIMITIVES, IN

GO!

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Do notcommunicate bysharing memory;

instead, sharememory by

communicating.- Go Docs

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This approach can be taken toofar. Reference counts may bebest done by putting a mutex

around an integer variable, forinstance. But as a high-levelapproach, using channels to

control access makes it easierto write clear, correct programs.

- Also Go Docs

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Other Go Fun Fact:GO ROUTINES ARE SCHEDULED COOPERATIVELY!

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WTF GO?

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GO COMPILES TO NATIVE CODE

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GO RUN-TIME IS SMALL (2MB)

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GO IS (ALMOST) A SYSTEMS PROGRAMMING LANGUAGE

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GO PRIORITIES1. Ease of adoption2. Speed3. Flexibility

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CSP VS ACTOR MODEL

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CSP AND ACTOR MODELSIMILARITIES

1. Abstract 'processes' managed byruntime2. Share data bycommunicating/message passing

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Erlang's syntaxderived from

Prolog and washeavily in�uencedby smalltalk, CSP

and the functionalprogramming.

- Joe Armstrong, Erlang Creator

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Difference #1:

PROCESSIDENTITY

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Difference #2:

DIRECTCOMMUNICATION

VS CHANNELS

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Difference #3:

ASYNCHRONOUSVS

SYNCHRONOUSMESSAGEPASSING

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NO SO DIFFERENT AFTER ALL?

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HOW TO GIVE CSPPROCESS AN IDENTITY

1 CSP channel+ 1 CSP Process Reading From Channel= Channel Becomes De-facto Identity

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HOW TO PASS CSPMESSAGES

ASYNCHRONOUSLYMessage Queue Process+ Channel For Sending+ Channel For Receiving= Asynchronous Message Passing

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https://medium.com/capital-one-tech/building-an-unbounded-channel-in-

go-789e175cd2cd

BUILDING AN UNBOUNDED CHANNEL IN GO:

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A GenServer in Go!

1. package counter 2. 3. type counterMessage interface { 4. handle(c * Counter) 5. } 6. 7. type Counter struct { 8. counterMessages chan counterMessage 9. 10. // do not touch outside run loop 11. value int

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HOW DO WE IMPLEMENT CHANNELS IN ELIXIR?:

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12. { queue, len, :unbuffered } ->

1. defmodule ElixirConurrency.Queue do 2. def new(max_size) do 3. { :queue.new, 0, max_size } 4. end 5. 6. def new(:unbuffered) do 7. { :queue.new, 0, :unbuffered } 8. end 9. 10. def put(bounded_queue, item ) do 11. case bounded_queue do

13. queue = :queue.in(item, queue) 14. {{:ok, queue }, len + 1} 15. { queue, len, max_size } -> 16. if len == max_size do 17. {:buffered, queue}

if queue unbuffered

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CONCLUSIONS

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http://concurrency.techgirlwonder.com

THANK YOU!