Singleflight 示例一：基础用法

多次请求共享一次请求的结果

package main

import (
    "fmt"
    "time"

    "golang.org/x/sync/singleflight"
)

func main() {
    var group singleflight.Group

    // A function that simulates an expensive operation
    expensiveOperation := func(key string) (interface{}, error) {
        time.Sleep(2 * time.Second) // Simulate delay
        return fmt.Sprintf("Result for %s", key), nil
    }

    key := "unique-key"

    // Start multiple goroutines that call the expensive operation through singleflight
    for i := 0; i < 3; i++ {
        go func(id int) {
            result, err, shared := group.Do(key, func() (interface{}, error) {
                return expensiveOperation(key)
            })

            if err != nil {
                fmt.Printf("Goroutine %d received error: %v\n", id, err)
            } else {
                fmt.Printf("Goroutine %d received result: %v (shared: %v)\n", id, result, shared)
            }
        }(i)
    }

    // Wait for goroutines to finish
    time.Sleep(3 * time.Second)
}

输出

Goroutine 0 received result: Result for unique-key (shared: true)
Goroutine 2 received result: Result for unique-key (shared: true)
Goroutine 1 received result: Result for unique-key (shared: true)

Singleflight 示例二：解决缓存击穿

这个示例集成了数据库、缓存和 HTTP API，有以下几个关键点：

1. 提供了 [GET] /gold/prcie 和 [POST] /gold 两个接口模拟黄金价格的更新与查询
2. 缓存由更新接口在更新数据后设置失效，由查询接口负责构建
3. 高并发查询场景，缓存失效的一瞬间，面临多个请求会同时访问数据库，即缓存击穿
4. 高并发查询场景，使用 Singleflight 避免缓存击穿
5. 查看访问数据库的次数，看到 Singleflight 在这个场景中的重要作用

创建表作为数据源

-- 创建表
CREATE TABLE gold_realtime_prices (
    id SERIAL PRIMARY KEY,
    price NUMERIC NOT NULL,
    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- 插入一条模拟数据
INSERT INTO gold_realtime_prices (price) VALUES (575.25);

代码示例

通关环境变量设置...