Go语言REST API中的Goroutine：自动并发与按需异步处理

package main

import (
    "fmt"
    "log"
    "net/http"
    "time"
)

func helloHandler(w http.ResponseWriter, r *http.Request) {
    // 这个handler的执行就运行在一个独立的Goroutine中
    log.Printf("Received request from %s for path %s", r.RemoteAddr, r.URL.Path)
    fmt.Fprintf(w, "Hello, you've hit %s\n", r.URL.Path)
}

func dbQueryHandler(w http.ResponseWriter, r *http.Request) {
    log.Printf("Simulating DB query for request from %s", r.RemoteAddr)
    time.Sleep(100 * time.Millisecond) // 模拟数据库查询耗时
    fmt.Fprintf(w, "Data retrieved from DB!\n")
}

func main() {
    http.HandleFunc("/", helloHandler)
    http.HandleFunc("/query", dbQueryHandler)

    log.Println("Server starting on port 8080...")
    // ListenAndServe会自动为每个请求创建Goroutine
    if err := http.ListenAndServe(":8080", nil); err != nil {
        log.Fatalf("Server failed to start: %v", err)
    }
}

package main

import (
    "fmt"
    "log"
    "net/http"
    "time"
)

// 模拟一个耗时的邮件发送函数
func sendEmail(recipient, subject, body string) {
    log.Printf("Starting to send email to %s (Subject: %s)...", recipient, subject)
    time.Sleep(3 * time.Second) // 模拟邮件发送耗时
    log.Printf("Email sent to %s successfully!", recipient)
}

func registerUserHandler(w http.ResponseWriter, r *http.Request) {
    // 假设这里完成了用户注册的数据库操作，并获取了用户信息
    userID := "user123"
    userEmail := "user@example.com"

    // 立即响应客户端，告知注册成功
    w.WriteHeader(http.StatusOK)
    fmt.Fprintf(w, "User %s registered successfully! Email will be sent shortly.\n", userID)

    // 在一个新的Goroutine中异步发送邮件，不阻塞当前请求的响应
    go sendEmail(userEmail, "Welcome to our service!", "Thank you for registering.")

    log.Printf("Handler for user %s registration finished, email sending initiated.", userID)
}

func main() {
    http.HandleFunc("/register", registerUserHandler)
    log.Println("Server starting on port 8080...")
    if err := http.ListenAndServe(":8080", nil); err != nil {
        log.Fatalf("Server failed to start: %v", err)
    }
}

package main

import (
    "context"
    "log"
    "time"
)

func longRunningTask(ctx context.Context, taskID string) {
    log.Printf("Task %s started.", taskID)
    for i := 0; i < 10; i++ {
        select {
        case <-time.After(1 * time.Second): // 模拟每秒进行一部分工作
            log.Printf("Task %s working... (%d/10)", taskID, i+1)
        case <-ctx.Done(): // 检查取消信号
            log.Printf("Task %s cancelled: %v", taskID, ctx.Err())
            return
        }
    }
    log.Printf("Task %s completed.", taskID)
}

func main() {
    ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second) // 5秒后自动取消
    defer cancel() // 确保在main函数退出时调用cancel

    go longRunningTask(ctx, "A")

    // 模拟主程序继续执行其他操作
    time.Sleep(7 * time.Second) // 等待超过任务超时时间
    log.Println("Main program finished.")
}