Google Search (Rob Pike)

package main

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

type Result string
type Search func(query string) Result

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

// --- 1.0: Sequential ---

func Google1(query string) []Result {
	return []Result{
		Web(query),
		Image(query),
		Video(query),
	}
}

// --- 2.0: Concurrent fan-out, fan-in ---

func Google2(query string) []Result {
	c := make(chan Result)
	go func() { c <- Web(query) }()
	go func() { c <- Image(query) }()
	go func() { c <- Video(query) }()

	var results []Result
	for i := 0; i < 3; i++ {
		results = append(results, <-c)
	}
	return results
}

// --- 2.1: Add timeout ---

func Google21(query string) []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)
	var results []Result
	for i := 0; i < 3; i++ {
		select {
		case r := <-c:
			results = append(results, r)
		case <-timeout:
			fmt.Println("timed out")
			return results
		}
	}
	return results
}

// --- 3.0: Replicated + timeout ---
// Send to multiple replicas, take the fastest response.

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

var (
	Web    = fakeSearch("web")
	Web2   = fakeSearch("web")
	Image  = fakeSearch("image")
	Image2 = fakeSearch("image")
	Video  = fakeSearch("video")
	Video2 = fakeSearch("video")
)

func Google3(query string) []Result {
	c := make(chan Result)
	go func() { c <- First(query, Web, Web2) }()
	go func() { c <- First(query, Image, Image2) }()
	go func() { c <- First(query, Video, Video2) }()

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

func main() {
	rand.Seed(time.Now().UnixNano())

	for _, search := range []struct {
		name string
		fn   func(string) []Result
	}{
		{"1.0 Sequential", Google1},
		{"2.0 Concurrent", Google2},
		{"2.1 With Timeout", Google21},
		{"3.0 Replicated", Google3},
	} {
		start := time.Now()
		results := search.fn("golang")
		fmt.Printf("\n--- %s (%v) ---\n", search.name, time.Since(start))
		for _, r := range results {
			fmt.Println(" ", r)
		}
	}
}