A boring function

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package main

import (
	"fmt"
	"time"
)

func boring(msg string) {
	for i := 0; ; i++ {
		fmt.Println(msg, i)
		time.Sleep(time.Second)
	}
}

func main() {
	boring("boring!")
}

Slightly less boring

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

func boring(msg string) {
	for i := 0; ; i++ {
		fmt.Println(msg, i)
		time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
	}
}

func main() {
	boring("boring!")
}

Ignoring it

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

func boring(msg string) {
	for i := 0; ; i++ {
		fmt.Println(msg, i)
		time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
	}
}

func main() {
	go boring("boring!")
}

Ignoring it a little less

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

func boring(msg string) {
	for i := 0; ; i++ {
		fmt.Println(msg, i)
		time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
	}
}

func main() {
	go boring("boring!")
	fmt.Println("I'm listening.")
	time.Sleep(2 * time.Second)
	fmt.Println("You're boring; I'm leaving.")
}

Using channels

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

func boring(msg string, c chan string) {
	for i := 0; ; i++ {
		c <- fmt.Sprintf("%s %d", msg, i) // Expression to be sent can be any suitable value.
		time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
	}
}

func main() {
	c := make(chan string)
	go boring("boring!", c)
	for i := 0; i < 5; i++ {
		fmt.Printf("You say: %q\n", <-c) // Receive expression is just a value.
	}
	fmt.Println("You're boring; I'm leaving.")
}

Generator: function that returns a channel

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

func boring(msg string) <-chan string { // Returns receive-only channel of strings.
	c := make(chan string)
	go func() { // We launch the goroutine from inside the function.
		for i := 0; ; i++ {
			c <- fmt.Sprintf("%s %d", msg, i)
			time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
		}
	}()
	return c // Return the channel to the caller.
}

func main() {
	c := boring("boring!") // Function returning a channel.
	for i := 0; i < 5; i++ {
		fmt.Printf("You say: %q\n", <-c)
	}
	fmt.Println("You're boring; I'm leaving.")
}

Channels as a handle on a service

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

func boring(msg string) <-chan string { // Returns receive-only channel of strings.
	c := make(chan string)
	go func() { // We launch the goroutine from inside the function.
		for i := 0; ; i++ {
			c <- fmt.Sprintf("%s %d", msg, i)
			time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
		}
	}()
	return c // Return the channel to the caller.
}

func main() {
	joe := boring("Joe")
    ann := boring("Ann")
    for i := 0; i < 5; i++ {
        fmt.Println(<-joe)
        fmt.Println(<-ann)
    }
    fmt.Println("You're both boring; I'm leaving.")
}

Multiplexing

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

func boring(msg string) <-chan string { // Returns receive-only channel of strings.
	c := make(chan string)
	go func() { // We launch the goroutine from inside the function.
		for i := 0; ; i++ {
			c <- fmt.Sprintf("%s %d", msg, i)
			time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
		}
	}()
	return c // Return the channel to the caller.
}

func fanIn(input1, input2 <-chan string) <-chan string {
	c := make(chan string)
	go func() {
		for {
			c <- <-input1
		}
	}()
	go func() {
		for {
			c <- <-input2
		}
	}()
	return c
}

func main() {
	c := fanIn(boring("Joe"), boring("Ann"))
	for i := 0; i < 10; i++ {
		fmt.Println(<-c)
	}
	fmt.Println("You're both boring; I'm leaving.")
}

Restoring sequencing

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

type Message struct {
	str  string
	wait chan bool
}

func boring(msg string) <-chan Message { // Returns receive-only channel of strings.
	waitForIt := make(chan bool) // Shared between all messages.
	c := make(chan Message)
	go func() { // We launch the goroutine from inside the function.
		for i := 0; ; i++ {
			c <- Message{fmt.Sprintf("%s: %d", msg, i), waitForIt}
			time.Sleep(time.Duration(rand.Intn(2e3)) * time.Millisecond)
			<-waitForIt
		}
	}()
	return c // Return the channel to the caller.
}

func fanIn(input1, input2 <-chan Message) <-chan Message {
	c := make(chan Message)
	go func() {
		for {
			c <- <-input1
		}
	}()
	go func() {
		for {
			c <- <-input2
		}
	}()
	return c
}

func main() {
	c := fanIn(boring("Joe"), boring("Ann"))
	for i := 0; i < 5; i++ {
		msg1 := <-c
		fmt.Println(msg1.str)
		msg2 := <-c
		fmt.Println(msg2.str)
		msg1.wait <- true
		msg2.wait <- true
	}
	fmt.Println("You're both boring; I'm leaving.")
}

Fan-in using select

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

func boring(msg string) <-chan string { // Returns receive-only channel of strings.
	c := make(chan string)
	go func() { // We launch the goroutine from inside the function.
		for i := 0; ; i++ {
			c <- fmt.Sprintf("%s %d", msg, i)
			time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
		}
	}()
	return c // Return the channel to the caller.
}

func fanIn(input1, input2 <-chan string) <-chan string {
	c := make(chan string)
	go func() {
		for {
			select {
			case s := <-input1:
				c <- s
			case s := <-input2:
				c <- s
			}
		}
	}()
	return c
}

func main() {
	c := fanIn(boring("Joe"), boring("Ann"))
	for i := 0; i < 10; i++ {
		fmt.Println(<-c)
	}
	fmt.Println("You're both boring; I'm leaving.")
}

Timeout using select

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

func boring(msg string) <-chan string { // Returns receive-only channel of strings.
	c := make(chan string)
	go func() { // We launch the goroutine from inside the function.
		for i := 0; ; i++ {
			c <- fmt.Sprintf("%s %d", msg, i)
			time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
		}
	}()
	return c // Return the channel to the caller.
}

func main() {
	c := boring("Joe")
	for {
		select {
		case s := <-c:
			fmt.Println(s)
		case <-time.After(1 * time.Second):
			fmt.Println("You're too slow.")
			return
		}
	}
}

Timeout for whole conversation using select

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

func boring(msg string) <-chan string { // Returns receive-only channel of strings.
	c := make(chan string)
	go func() { // We launch the goroutine from inside the function.
		for i := 0; ; i++ {
			c <- fmt.Sprintf("%s %d", msg, i)
			time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
		}
	}()
	return c // Return the channel to the caller.
}

func main() {
	c := boring("Joe")
    timeout := time.After(5 * time.Second)
    for {
        select {
        case s := <-c:
            fmt.Println(s)
        case <-timeout:
            fmt.Println("You talk too much.")
            return
        }
    }
}

Quit channel

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package main

import (
	"fmt"
	"math/rand"
)

func boring(msg string, quit chan bool) <-chan string { // Returns receive-only channel of strings.
	c := make(chan string)
	go func() { // We launch the goroutine from inside the function.
		for i := 0; ; i++ {
			select {
			case c <- fmt.Sprintf("%s: %d", msg, i):
				// do nothing
			case <-quit:
				return
			}
		}
	}()
	return c // Return the channel to the caller.
}

func main() {
	quit := make(chan bool)
	c := boring("Joe", quit)
	for i := rand.Intn(10); i >= 0; i-- {
		fmt.Println(<-c)
	}
	quit <- true
}

Receive on quit channel

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package main

import (
	"fmt"
	"math/rand"
)

func boring(msg string, quit chan string) <-chan string { // Returns receive-only channel of strings.
	c := make(chan string)
	go func() { // We launch the goroutine from inside the function.
		for i := 0; ; i++ {
			select {
			case c <- fmt.Sprintf("%s: %d", msg, i):
				// do nothing
			case <-quit:
				// cleanup()
				quit <- "See you!"
				return
			}
		}
	}()
	return c // Return the channel to the caller.
}

func main() {
	quit := make(chan string)
	c := boring("Joe", quit)
	for i := rand.Intn(10); i >= 0; i-- {
		fmt.Println(<-c)
	}
	quit <- "Bye!"
	fmt.Printf("Joe says: %q\n", <-quit)
}

Daisy-chain

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package main

import (
	"fmt"
)

func f(left, right chan int) {
	left <- 1 + <-right
}

func main() {
	const n = 10000
	leftmost := make(chan int)
	right := leftmost
	left := leftmost
	for i := 0; i < n; i++ {
		right = make(chan int)
		go f(left, right)
		left = right
	}
	go func(c chan int) { c <- 1 }(right)
	fmt.Println(<-leftmost)
}

Google Search 1.0

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

// var (
// 	r = rand.New(rand.NewSource(time.Now().UnixNano()))
// )

type Result string

type Search func(query string) Result

func fakeSearch(kind string) Search {
	return func(query string) Result {
		// time.Sleep(time.Duration(r.Intn(100)) * time.Millisecond)
		time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
		return Result(fmt.Sprintf("%s result for %q\n", kind, query))
	}
}

var (
	Web   = fakeSearch("web")
	Image = fakeSearch("image")
	Video = fakeSearch("video")
)

func Google(query string) (results []Result) {
	results = append(results, Web(query))
	results = append(results, Image(query))
	results = append(results, Video(query))
	return
}

func main() {
	start := time.Now()
	results := Google("golang")
	elapsed := time.Since(start)
	fmt.Println(results)
	fmt.Println(elapsed)
}

Google Search 2.0

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

// var (
// 	r = rand.New(rand.NewSource(time.Now().UnixNano()))
// )

type Result string

type Search func(query string) Result

func fakeSearch(kind string) Search {
	return func(query string) Result {
		// time.Sleep(time.Duration(r.Intn(100)) * time.Millisecond)
		time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
		return Result(fmt.Sprintf("%s result for %q\n", kind, query))
	}
}

var (
	Web   = fakeSearch("web")
	Image = fakeSearch("image")
	Video = fakeSearch("video")
)

func Google(query string) (results []Result) {
	c := make(chan Result)
	go func() {
		c <- Web(query)
	}()
	go func() {
		c <- Image(query)
	}()
	go func() {
		c <- Video(query)
	}()

	for i := 0; i < 3; i++ {
		result := <-c
		results = append(results, result)
	}
	return
}

func main() {
	start := time.Now()
	results := Google("golang")
	elapsed := time.Since(start)
	fmt.Println(results)
	fmt.Println(elapsed)
}

Google Search 2.1

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

// var (
// 	r = rand.New(rand.NewSource(time.Now().UnixNano()))
// )

type Result string

type Search func(query string) Result

func fakeSearch(kind string) Search {
	return func(query string) Result {
		// time.Sleep(time.Duration(r.Intn(100)) * time.Millisecond)
		time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
		return Result(fmt.Sprintf("%s result for %q\n", kind, query))
	}
}

var (
	Web   = fakeSearch("web")
	Image = fakeSearch("image")
	Video = fakeSearch("video")
)

func Google(query string) (results []Result) {
	c := make(chan Result)
	go func() {
		c <- Web(query)
	}()
	go func() {
		c <- Image(query)
	}()
	go func() {
		c <- Video(query)
	}()

	timeout := time.After(80 * time.Millisecond)
	for i := 0; i < 3; i++ {
		select {
		case result := <-c:
			results = append(results, result)
		case <-timeout:
			fmt.Println("time out")
			return
		}
	}
	return
}

func main() {
	start := time.Now()
	results := Google("golang")
	elapsed := time.Since(start)
	fmt.Println(results)
	fmt.Println(elapsed)
}

Avoid timeout

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

// var (
// 	r = rand.New(rand.NewSource(time.Now().UnixNano()))
// )

type Result string

type Search func(query string) Result

func fakeSearch(kind string) Search {
	return func(query string) Result {
		// time.Sleep(time.Duration(r.Intn(100)) * time.Millisecond)
		time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
		return Result(fmt.Sprintf("%s result for %q\n", kind, query))
	}
}

func First(query string, replicas ...Search) Result {
	c := make(chan Result)
	searchReplica := func(i int) {
		c <- replicas[i](query)
	}
	for i := range replicas {
		go searchReplica(i)
	}
	return <-c
}

func main() {
	start := time.Now()
	result := First("golang",
		fakeSearch("replica 1"),
		fakeSearch("replica 2"))
	elapsed := time.Since(start)
	fmt.Println(result)
	fmt.Println(elapsed)
}

Google Search 3.0

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package main

import (
	"fmt"
	"math/rand"
	"time"
)

// var (
// 	r = rand.New(rand.NewSource(time.Now().UnixNano()))
// )

type Result string

type Search func(query string) Result

func fakeSearch(kind string) Search {
	return func(query string) Result {
		// time.Sleep(time.Duration(r.Intn(100)) * time.Millisecond)
		time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
		return Result(fmt.Sprintf("%s result for %q\n", kind, query))
	}
}

var (
	Web1   = fakeSearch("web1")
	Web2   = fakeSearch("web2")
	Image1 = fakeSearch("image1")
	Image2 = fakeSearch("image2")
	Video1 = fakeSearch("video1")
	Video2 = fakeSearch("video2")
)

func First(query string, replicas ...Search) Result {
	c := make(chan Result)
	searchReplica := func(i int) {
		c <- replicas[i](query)
	}
	for i := range replicas {
		go searchReplica(i)
	}
	return <-c
}

func Google(query string) (results []Result) {
	c := make(chan Result)
	go func() {
		c <- First(query, Web1, Web2)
	}()
	go func() {
		c <- First(query, Image1, Image2)
	}()
	go func() {
		c <- First(query, Video1, Video2)
	}()
	timeout := time.After(80 * time.Millisecond)
	for i := 0; i < 3; i++ {
		select {
		case result := <-c:
			results = append(results, result)
		case <-timeout:
			fmt.Println("timed out")
			return
		}
	}
	return
}

func main() {
	start := time.Now()
	results := Google("golang")
	elapsed := time.Since(start)
	fmt.Println(results)
	fmt.Println(elapsed)
}