想象一個具有大量不同路由的 Web 服務(wù)。其中一些會觸發(fā)發(fā)送給用戶的交易電子郵件。初始化郵件程序?qū)嵗坪鹾芷婀?，例如github.com/aws/aws-sdk-go/service/sns每次請求想要發(fā)送某些東西時使用的東西。相反，我假設(shè)有一個郵件程序?qū)嵗?，并且一切都發(fā)生在一個單獨(dú)的頻道上，amessage被發(fā)布到該頻道。例子我創(chuàng)建了一個簡單的例子來說明這個問題。全局Mailer實(shí)例配置一次，Index處理程序請求一個通道并傳遞一個Message.package mainimport (    "fmt"    "log"    "net/http"    "os")// Message is the custom type used to pass the channeltype Message struct {    To      string    Subject string    Body    string}// Mailer is responsible to send out emailstype Mailer struct{}// send sends out the emailfunc (m *Mailer) send(message Message) {    fmt.Printf("Sending email to:`%s`\nSubject: %s\n%s\n\n", message.To, message.Subject, message.Body)}// Messages returns the channel to which messages can be passedfunc (m *Mailer) Messages() chan<- Message {    cm := make(chan Message)    go func() {        msg := <-cm        m.send(msg)        close(cm)    }()    return cm}// mailer is a global var in this example, would probably be part of some// sort of app context that's accessible from any handler.//// Note the mailer is NOT handler-scoped.var mailer = Mailer{} // would this be thread-safe?// Index handlerfunc Index(w http.ResponseWriter, r *http.Request) {    m := Message{"email@example.com", fmt.Sprintf("visited `%s`", r.URL.Path[1:]), "Lorem ipsum"}    mailer.Messages() <- m    fmt.Fprintf(w, "Sent out email with subject line `%s`\n", m.Subject)}func main() {    http.HandleFunc("/", Index)    port := os.Getenv("PORT")    if port == "" {        port = "8080"    }    if err := http.ListenAndServe(":"+port, nil); err != nil {        log.Fatal("ListenAndServe: ", err)    }}輸出訪問http://localhost:8080/hello-world將呈現(xiàn)…發(fā)送主題為“visited `hello-world”的電子郵件...并記錄發(fā)送電子郵件到`email@example.com`：訪問了`hello-world`Lorem ipsum問題這是正確的方法嗎？它是線程安全的——如果不是，如何讓它成為線程安全的？