Go Synchronized Andrej Vckovski

What I want to transmit

Go is useful and neat for heavily concurrent applications Webrockets socks!

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A small poll

Point your [smartphone] browser to

nca.me/l Go synchronized 3

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nca.me/l

About go

Started by Robert Griesemer, Rob Pike and Ken Thompson in Fall 2007, Open-sourced 2009, Go 1 March 2012

Main features – C/Pascal/Modula-like, garbage collected, no pointer

arithmetics, type safe, very fast compiler – Simple type system without hierarchies – Concepts for concurrent programming in the “CSP”-style – Embeds dependency management – Today about similar memory/execution-performance as

Java or Node.

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Concurrency?

Separate, potentially simultaneously executed computations

Usually somehow interacting Candidates to leverage multi-{core|cpu|node}

environments Usually but not necessarily correspond to multiple users Often on the server side

And hard to make it right

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Go and concurrency

Communicating Sequential Processes (CSP) pattern (C. A. R. Hoare, 1978) 1. Channels 2. Go-routines 3. select-statement

“Do not communicate by sharing memory; instead, share memory by communicating”

Occam, Erlang, Newsqueak, Limbo, Clojure and many more

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Example

package main import ("fmt"; "time"; "math/rand") func main() { table := make(chan string) for _, player := range [...]string{"alice", "bob"} { go func(who string) { num := 0; for { ball := <- table; fmt.Printf("player %s: %s\n", who, ball) table <- fmt.Sprintf("tick-%s-%d",who,num) time.Sleep(time.Millisecond * time.Duration(rand.Intn(1000))) num++ } }(player) } table <- "go" time.Sleep(10 * time.Second) }

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The application: Very Instant Massive (Audience) Polling Presentations

like this one TV shows with

added interactivity

Pause entertainment in a stadium

Flipped Classrooms

© Loozrboy

© Chris Lawrence

© Jeff Chenqinyi

© Nhenze

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Browser that

displays questions

and allows voting

Presentation Software (e.g., PowerPoint)

Browser that displays voting results

ipoll server

System context

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Browser that

displays questions

and allows voting

Browser that

displays questions

and allows voting

go

JS

JS

JS

JS

Browser that

displays questions

and allows voting

Presentation Software (e.g., PowerPoint)

Browser that displays voting results

ipoll server

Browser that

displays questions

and allows voting

Browser that

displays questions

and allows voting

go

JS

JS

JS

JS

WebSockets

Full-duplex conversation over TCP connection

RFC 6455 Available in most modern

browsers Simple JavaScript binding Handshake by HTTP, then

user-defined messages over the same socket

Client (Browser) Server

HTTP GET Request, special attributes

HTTP response “switch protocol”

Message

Message

Message

Message

Message

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Browser that

displays questions

and allows voting

Presentation Software (e.g., PowerPoint)

Browser that displays voting results

ipoll server

Multiplexer and

Demultiplexer

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Browser that

displays questions

and allows voting

Browser that

displays questions

and allows voting

Small Demo

Point your smartphone browser to

nca.me/l Go synchronized 14

Demo: New Question 1

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nca.me/l

Demo: New Question 2

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nca.me/l

Demo: New Question 3

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nca.me/l

WebSocket on server side (go) func startWebserver() {

// [...]

http.HandleFunc("/svy", surveyHandler)

// [...]

}

func surveyHandler(c http.ResponseWriter, req *http.Request) { // [...]

go websocket.Handler(func (ws *websocket.Conn) { s.VoterHandler(ws)} ).ServeHTTP(c, req) // [...]

}

func (s *Survey) VoterHandler(ws *websocket.Conn) { defer func() { s.voterChan <- voter{ws, false} log.Printf("connection closed by client") ws.Close() }() s.voterChan <- voter{ws, true} // notify hub of a new voter for { // [...]

len, err := ws.Read(buf) // [...]

var v vote err = json.Unmarshal(buf, &v) if err == nil { s.voteChan <- v } else { // [...]

} } }

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Core data massaged at a single place: The “model” implements an event-loop

func (s *Survey) surveyHub() { // [...] t := time.NewTicker(100 * time.Millisecond) // [...] for { select { case _ = <-t.C: // tick arrived // [...] case ctrl := <-s.controlChan: // control message // [...] case voter := <-s.voterChan: // voter subscribed // [...] case viewer := <-s.viewerChan: // viewer subscribed // [...] case admin := <-s.adminChan: // admin subscribed // [...] case vote := <-s.voteChan: // a vote arrived // [...] } } }

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Conclusions

Go (or “CSP”-design) has massively simplified the concurrency challenges WebSockets are easy to use and will be

increasingly popular

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(mascot by Renée French)

Rob Pike on “concurrency is not parallelism”: http://vimeo.com/49718712

http://golang.org

Bonus poll

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nca.me/l

Thanks for the attention!

andrej.vckovski@netcetera.com netcetera.com

ipoll.ch (coming soon)