迭代通道时关闭通道的最佳时间

Question

我正在使用 Golang，我创建了这个小应用程序来使用 goroutine 进行多个并发 api 调用。

当应用程序工作时，调用完成后，应用程序会卡住，这是有道理的，因为它无法退出范围c循环，因为通道未关闭。

我不知道在这种模式下哪里可以更好地关闭通道。

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

当没有更多的值要发送时，您将关闭通道，因此在本例中，是在所有checkUrlgoroutine 完成时关闭。var wg sync.WaitGroupfunc checkUrls(urls []string) {&nbsp; &nbsp; c := make(chan string)&nbsp; &nbsp; for _, link := range urls {&nbsp; &nbsp; &nbsp; &nbsp; wg.Add(1)&nbsp; &nbsp; &nbsp; &nbsp; go checkUrl(link, c)&nbsp; &nbsp; }&nbsp; &nbsp; go func() {&nbsp; &nbsp; &nbsp; &nbsp; wg.Wait()&nbsp; &nbsp; &nbsp; &nbsp; close(c)&nbsp; &nbsp; }()&nbsp; &nbsp; for msg := range c {&nbsp; &nbsp; &nbsp; &nbsp; fmt.Println(msg)&nbsp; &nbsp; }}func checkUrl(url string, c chan string) {&nbsp; &nbsp; defer wg.Done()&nbsp; &nbsp; _, err := http.Get(url)&nbsp; &nbsp; if err != nil {&nbsp; &nbsp; &nbsp; &nbsp; c <- "We could not reach:" + url&nbsp; &nbsp; } else {&nbsp; &nbsp; &nbsp; &nbsp; c <- "Success reaching the website:" + url&nbsp; &nbsp; }}（请注意，errorfromhttp.Get仅反映连接和协议错误。如果您也期望这些错误，那么它不会包含 http 服务器错误，您必须看到如何检查路径而不仅仅是主机。）

Answer 2

当使用通道和 goroutine 在 Go 中编写程序时，始终要考虑谁（哪个函数）拥有通道。我更喜欢让拥有通道的函数关闭它的做法。如果我要写这个，我会这样做，如下所示。注意：处理此类情况的更好方法是扇出、扇入并发模式。package mainimport "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    }}