Question

我正在玩Golang，我创建了这个小应用程序，使用goroutines进行了多个并发的api调用。

在应用程序正常运行的同时，调用完成后，该应用程序被卡住了，这是有道理的，因为由于通道未关闭，它无法退出 range c 循环。

我不确定以哪种方式可以更好地关闭渠道。

package main

import "fmt"
import "net/http"

func main() {
    links := []string{
        "https://github.com/fabpot",
        "https://github.com/andrew",
        "https://github.com/taylorotwell",
        "https://github.com/egoist",
        "https://github.com/HugoGiraudel",
    }

    checkUrls(links)
}

func checkUrls(urls []string) {
    c := make(chan string)

    for _, link := range urls {
        go checkUrl(link, c)
    }

    for msg := range c {
        fmt.Println(msg)
    }

    close(c) //this won't get hit
}

func checkUrl(url string, c chan string) {
    _, err := http.Get(url)

    if err != nil {
        c <- "We could not reach:" + url
    } else {
        c <- "Success reaching the website:" + url
    }
}

Answer 1

当没有更多值要发送时，您将关闭通道，因此在这种情况下，所有checkUrl goroutine已完成。

var wg sync.WaitGroup

func checkUrls(urls []string) {
    c := make(chan string)

    for _, link := range urls {
        wg.Add(1)
        go checkUrl(link, c)
    }

    go func() {
        wg.Wait()
        close(c)
    }()

    for msg := range c {
        fmt.Println(msg)
    }
}

func checkUrl(url string, c chan string) {
    defer wg.Done()
    _, err := http.Get(url)

    if err != nil {
        c <- "We could not reach:" + url
    } else {
        c <- "Success reaching the website:" + url
    }
}

（请注意，error中的http.Get只会反映连接和协议错误。如果您也希望看到HTTP服务器错误，那么它将不会包含http服务器错误。如何检查路径，而不仅仅是主机。）

Answer 2

在使用通道和goroutine在Go中编写程序时，请始终考虑谁（哪个函数）拥有通道。我更喜欢让拥有频道的函数关闭它的做法。如果我要写这个，我将按照以下所示进行操作。

注意：处理这种情况的更好方法是扇出，扇入并发模式。请参阅（https://blog.golang.org/pipelines）Go Concurrency Patterns

package main

import "fmt"
import "net/http"
import "sync"

func main() {
    links := []string{
        "https://github.com/fabpot",
        "https://github.com/andrew",
        "https://github.com/taylorotwell",
        "https://github.com/egoist",
        "https://github.com/HugoGiraudel",
    }


    processURLS(links)
    fmt.Println("End of Main")
}

func processURLS(links []string) {
    resultsChan := checkUrls(links)

    for msg := range resultsChan {
        fmt.Println(msg)
    }

}     

func checkUrls(urls []string) chan string {

    outChan := make(chan string)

    go func(urls []string) {
       defer close(outChan)

       var wg sync.WaitGroup
       for _, url := range urls {
         wg.Add(1)
          go checkUrl(&wg, url, outChan)
       }
       wg.Wait()

    }(urls)

    return outChan
}

func checkUrl(wg *sync.WaitGroup, url string, c chan string) {
    defer wg.Done()
    _, err := http.Get(url)

    if err != nil {
        c <- "We could not reach:" + url
    } else {
        c <- "Success reaching the website:" + url
    }
}

遍历通道时关闭通道的最佳时间

2 个答案: