实例说明golang并发

package main

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

func main() {
    rand.Seed(time.Now().UnixNano())
    start := time.Now()
    results := Google("golang")
    fmt.Println(results)
    fmt.Printf("%s", time.Since(start))
}

type Result string

type Search func(key string) Result

func ResourceSearch(kind string) Search {
    return func(key string) Result {
        time.Sleep(time.Duration(rand.Intn(100)) * time.Millisecond)
        return Result(fmt.Sprintf("<%s from %s server>\n", key, kind))
    }
}

func FirstSearch(servers []Search, key string) Result {
    result := make(chan Result)
    done := make(chan struct{})
    defer close(done)
    first := func(i int) {
        select {
        case <-done:
            return
        case result <- servers[i](key):
        }
    }
    for i := range servers {
        go first(i)
    }
    return <-result
}

func Google(key string) (results []Result) {
    var images []Search
    var videos []Search
    var voices []Search
    for i := 0; i < 3; i++ {
        images = append(images, ResourceSearch(fmt.Sprintf("image-%d", i)))
        videos = append(videos, ResourceSearch(fmt.Sprintf("video-%d", i)))
        voices = append(voices, ResourceSearch(fmt.Sprintf("voice-%d", i)))
    }
    chanResults := make(chan Result)
    go func() {
        chanResults <- FirstSearch(images, key)
    }()
    go func() {
        chanResults <- FirstSearch(videos, key)
    }()
    go func() {
        chanResults <- FirstSearch(voices, key)
    }()
    after := time.After(80 * time.Millisecond)
    for i := 0; i < 3; i++ {
        select {
        case r := <-chanResults:
            results = append(results, r)
        case <-after:
            fmt.Println("timeout")
            return
        }
    }
    return
}