substack-ac-1.go

package main

import (
	"fmt"
	"sync"
	"time"

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

var sf singleflight.Group

func fetchData(key string) (interface{}, error) {
	// Simulating fetching data, e.g., from a database or external API
	time.Sleep(2 * time.Second)
	return fmt.Sprintf("Data for key: %s", key), nil
}

func SingleFlightDemo() {
	var wg sync.WaitGroup

	for i := 0; i < 5; i++ {
		wg.Add(1)
		go func(id int) {
			defer wg.Done()

			// Use the Do method to ensure that the data is fetched only once
			val, err, _ := sf.Do(fmt.Sprintf("key%d", id), func() (interface{}, error) {
				return fetchData(fmt.Sprintf("key%d", id))
			})

			if err != nil {
				fmt.Printf("Error fetching data: %v\n", err)
				return
			}

			fmt.Printf("Goroutine %d got data: %v\n", id, val)
		}(i)
	}

	wg.Wait()
}