Go Concurrency Patterns

google_search.go

package main

import (
	"fmt"
	"math/rand"
	"time"
)
// Examples from https://talks.golang.org/2012/concurrency.slide, starting at slide 42, https://talks.golang.org/2012/concurrency.slide#42
var (
	Web   = fakeSearch("web")
	Image = fakeSearch("image")
	Video = fakeSearch("video")
)

type Result string

type Search func(query string) Result

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

//Google Search 1.0 - Serial invocation
func Google1(query string) (results []Result) {
	results = append(results, Web(query))
	results = append(results, Image(query))
	results = append(results, Video(query))
	return
}

//Google Search 2.0 - Concurrent invocation, wait for all results
func Google2(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
}

//Google Search 2.1 - Don't wait on slow servers
func Google21(query string, timeout time.Duration) (results []Result) {
	c := make(chan Result)
	go func() { c <- Web(query) }()
	go func() { c <- Image(query) }()
	go func() { c <- Video(query) }()

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

func main() {
	rand.Seed(time.Now().UnixNano())
	start := time.Now()
	//results := Google1("golang")
	//results := Google2("golang")
	results := Google21("golang", 80*time.Millisecond)
	elapsed := time.Since(start)
	fmt.Println(results)
	fmt.Println(elapsed)
}