[Golang Single-Flight] #go #golang #singleflight #requestcollapsing #sync

singleflight.go

// https://play.golang.com/p/GoyqwZ5jW_L
// https://pkg.go.dev/golang.org/x/sync/singleflight
// https://victoriametrics.com/blog/go-singleflight/index.html

package main

import (
	"fmt"
	"math/rand"
	"sync"
	"sync/atomic"
	"time"

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

var callCount atomic.Int32
var wg sync.WaitGroup

// Simulate a function that fetches data from a database
func fetchData() (interface{}, error) {
	callCount.Add(1)
	time.Sleep(100 * time.Millisecond)
	return rand.Intn(100), nil
}

// Wrap the fetchData function with singleflight
func fetchDataWrapper(g *singleflight.Group, id int) error {
	defer wg.Done()

	time.Sleep(time.Duration(id) * 40 * time.Millisecond)
	v, err, shared := g.Do("key-fetch-data", fetchData)
	if err != nil {
		return err
	}

	fmt.Printf("Goroutine %d: result: %v, shared: %v\n", id, v, shared)
	return nil
}

func main() {
	var g singleflight.Group

	// 5 goroutines to fetch the same data
	const numGoroutines = 5
	wg.Add(numGoroutines)

	for i := 0; i < numGoroutines; i++ {
		go fetchDataWrapper(&g, i)
	}

	wg.Wait()
	fmt.Printf("Function was called %d times\n", callCount.Load())
}

// Output:
// Goroutine 0: result: 90, shared: true
// Goroutine 2: result: 90, shared: true
// Goroutine 1: result: 90, shared: true
// Goroutine 3: result: 13, shared: true
// Goroutine 4: result: 13, shared: true
// Function was called 2 times