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CSP othree

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Communicating Sequential Processes

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https://medium.com/@addyosmani/javascript-application-architecture-on-the-road-to-2015-d8125811101b

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1978

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1985

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What is CSP • Communication between processes • Born to be async • Using channel

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Process B Process A

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Process B Process A Channel msg

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Process B Process A msg PUT

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Process B Process A msg

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Process B Process A msg TAKE

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Process B Process A Channel msg

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Implements Go Clojure goroutine core.async

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https://speakerdeck.com/kachayev/channels-and-concurrency-go-clojure-erlang-haskell

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Go Example

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package main import "fmt" func main() { messages := make(chan string, 1) messages <- "ping" msg := <-messages fmt.Println(msg) }

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package main import "fmt" func main() { messages := make(chan string, 1) messages <- "ping" msg := <-messages fmt.Println(msg) }

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Short Variable Declarations • Declare variable • and assign value at the same time :=

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package main import "fmt" func main() { messages := make(chan string, 1) messages <- "ping" msg := <-messages fmt.Println(msg) }

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Receive Operator • Receive message • From channel • or channel receive message • Also imply direction of message <-

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package main import "fmt" func main() { messages := make(chan string, 1) messages <- "ping" msg := <-messages fmt.Println(msg) }

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Go Example II

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package main import "fmt" import "time" func worker(done chan bool) { fmt.Print("working...") time.Sleep(time.Second) fmt.Println("done") done <- true } func main() { done := make(chan bool, 1) go worker(done) <-done }

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package main import "fmt" import "time" func worker(done chan bool) { fmt.Print("working...") time.Sleep(time.Second) fmt.Println("done") done <- true } func main() { done := make(chan bool, 1) go worker(done) <-done }

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package main import "fmt" import "time" func worker(done chan bool) { fmt.Print("working...") time.Sleep(time.Second) fmt.Println("done") done <- true } func main() { done := make(chan bool, 1) go worker(done) <-done }

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Go Statement • Execute function as independent process(goroutine) go

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Go Pingpong Example

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package main import "fmt" import "time" type Ball struct{ hits int } func player(name string, table chan *Ball) { for { ball := <-table ball.hits++ fmt.Println(name, ball.hits) time.Sleep(100 * time.Millisecond) table <- ball } }

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package main import "fmt" import "time" type Ball struct{ hits int } func player(name string, table chan *Ball) { for { ball := <-table ball.hits++ fmt.Println(name, ball.hits) time.Sleep(100 * time.Millisecond) table <- ball } }

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player • Receive ball from channel • Hit ball(+1) • Sleep • Send ball back

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func main() { table := make(chan *Ball) go player("ping", table) go player("pong", table) table <- new(Ball) // game on; toss the ball time.Sleep(1 * time.Second) <-table // game over; grab the ball }

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func main() { table := make(chan *Ball) go player("ping", table) go player("pong", table) table <- new(Ball) // game on; toss the ball time.Sleep(1 * time.Second) <-table // game over; grab the ball }

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func main() { table := make(chan *Ball) go player("ping", table) go player("pong", table) table <- new(Ball) // game on; toss the ball time.Sleep(1 * time.Second) <-table // game over; grab the ball }

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func main() { table := make(chan *Ball) go player("ping", table) go player("pong", table) table <- new(Ball) // game on; toss the ball time.Sleep(1 * time.Second) <-table // game over; grab the ball }

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Process Channel Message players table Ball

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player pong player ping table Ball

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Key Requirement • Channel • Ability to wait(idle) message

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Channel • First class object • First in first out • Accessible across processes

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Idle • Not able to idle in JavaScript • Use recursive function call can emulate, bad performance • ES6 have async function

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async function

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function* foo(){ var index = 0; while (index <= 2) // when index reaches 3, // yield's done will be true // and its value will be undefined; yield index++; }

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var iterator = foo(); console.log(iterator.next()); // { value:0, done:false } console.log(iterator.next()); // { value:1, done:false } console.log(iterator.next()); // { value:2, done:false } console.log(iterator.next()); // { value:undefined, done:true }

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yield • Function will stop and return on yield • Next call will exec from last yield • Sort of idle

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js-csp

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js-csp • by Nguyễn Tuấn Anh • Major implementation • Use async function • Also implement `go`, dispatcher…etc

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Pingpong Example

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function* player(name, table) { while (true) { var ball = yield csp.take(table); if (ball === csp.CLOSED) { console.log(name + ": table's gone"); return; } ball.hits += 1; console.log(name + " " + ball.hits); yield csp.timeout(100); yield csp.put(table, ball); } }

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function* player(name, table) { while (true) { var ball = yield csp.take(table); if (ball === csp.CLOSED) { console.log(name + ": table's gone"); return; } ball.hits += 1; console.log(name + " " + ball.hits); yield csp.timeout(100); yield csp.put(table, ball); } } func player(name string, table chan *Ball) { for { ball := <-table ball.hits++ fmt.Println(name, ball.hits) time.Sleep(100 * time.Millisecond) table <- ball } } Go

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csp.go(function* () { var table = csp.chan(); csp.go(player, ["ping", table]); csp.go(player, ["pong", table]); yield csp.put(table, {hits: 0}); yield csp.timeout(1000); table.close(); });

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csp.go(function* () { var table = csp.chan(); csp.go(player, ["ping", table]); csp.go(player, ["pong", table]); yield csp.put(table, {hits: 0}); yield csp.timeout(1000); table.close(); }); func main() { table := make(chan *Ball) go player("ping", table) go player("pong", table) table <- new(Ball) time.Sleep(1 * time.Second) <-table } Go

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csp.go(player, ["ping", table]); go player("ping", table) yield csp.put(table, {hits: 0}); table <- new(Ball) yield csp.take(table); <-table

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csp.go(function* () { func main() { var table = csp.chan(); table := make(chan *Ball) yield csp.timeout(1000); time.Sleep(1 * time.Second)

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js-csp • Easy to port Go program • yield is annoying

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What Can Use CSP • Sequential async data • Event

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Real World Event • Might have multiple event handler on single event

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Channel Message • Only can take once

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operations alt mult mix merge onto pipe split close timeout https://clojure.github.io/core.async/

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mult • one to many

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var csp = require("./src/csp"); var mult = csp.operations.mult; var buffers = csp.buffers; var channel = csp.chan(); var m = mult(channel); https://github.com/ubolonton/js-csp/issues/31#issuecomment-68089526

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var csp = require("./src/csp"); var mult = csp.operations.mult; var buffers = csp.buffers; var channel = csp.chan(); var m = mult(channel);

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csp.go(function*() { var out = mult.tap(m, csp.chan(buffers.sliding(1))); var val = yield csp.take(out); console.log('process 1', val); }); csp.go(function*() { var out = mult.tap(m, csp.chan(buffers.sliding(1))); var val = yield csp.take(out); console.log('process 2', val); });

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csp.go(function*() { var out = mult.tap(m, csp.chan(buffers.sliding(1))); var val = yield csp.take(out); console.log('process 1', val); }); csp.go(function*() { var out = mult.tap(m, csp.chan(buffers.sliding(1))); var val = yield csp.take(out); console.log('process 2', val); });

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csp.go(function*() { var out = mult.tap(m, csp.chan(buffers.sliding(1))); var val = yield csp.take(out); console.log('process 1', val); }); csp.go(function*() { var out = mult.tap(m, csp.chan(buffers.sliding(1))); var val = yield csp.take(out); console.log('process 2', val); });

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csp.putAsync(channel, 42);

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not stable on js-csp

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Cons • Annoying yield • Not stable operations* • Lib size • Not support Web Worker

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js-csp • Syntax from Go • Operations from Clojure • Have disadvantages • Can use transducer from Clojure

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https://www.youtube.com/watch?v=7rDsRXj9-cU