想象一下具有大量不同路由的 Web 服务。其中一些会触发发送给用户的交易电子邮件。初始化一个 mailer 实例似乎很奇怪,例如每次请求想要发送一些东西时使用 github.com/aws/aws-sdk-go/service/sns
.
相反,我假设有一个 mailer 实例,并且所有事情都发生在一个单独的 channel 上,消息
被发布到该 channel 。
例子
我创建了一个简单示例来说明问题。全局 Mailer
实例配置一次,Index
处理程序请求一个 channel 并传递一个 Message
。
package main
import (
"fmt"
"log"
"net/http"
"os"
)
// Message is the custom type used to pass the channel
type Message struct {
To string
Subject string
Body string
}
// Mailer is responsible to send out emails
type Mailer struct{}
// send sends out the email
func (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 passed
func (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 handler
func 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)
}
}
输出
访问 http://localhost:8080/hello-world
将呈现...
Sent out email with subject line `visited `hello-world``
…并记录
sending email to `email@example.com`:
visited `hello-world`
Lorem ipsum
问题
- 这是正确的方法吗?
- 它是线程安全的吗?如果不是,如何让它成为线程安全的?
最佳答案
在这个例子中你并没有真正做任何事情,但是通过 channel 传递消息总是安全的—— channel 是语言中的基本并发原语之一。您让自己面临竞争条件的可能性,这取决于 send
实际上最终做了什么。另一种处理方法是让 send
从单个 channel 接收。
type Mailer struct{
Messages chan Message
}
func (m *Mailer) send() {
for message := range m.Messages {
fmt.Printf("Sending email to:`%s`\nSubject: %s\n%s\n\n", message.To, message.Subject, message.Body)
}
}
var mailer *Mailer
func 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() {
mailer = &Mailer{
// buffer up to 100 message to be sent before blocking
Messages: make(chan Message, 100),
}
// start the mailer send loop
go mailer.send()
...
关于go - 应用程序的邮件系统之类的东西是否应该像本例所示那样在单独的 channel 中运行?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/32403317/