n-r-w/singleflight

Golang Singleflight group with generics

singleflight

Fork from golang.org/x/sync/singleflight with generics and context support.

Usage

Singleflight is a concurrency method to prevent duplicate work from being executed due to multiple calls for the same resource. V2 contains breaking changes from V1, because it adds context and reorders the output parameters of the Do method (putting the error last). Context cancellation should be handled inside the function passed to Do, because singleflight does not interrupt the function execution if the context is canceled.

go get github.com/n-r-w/singleflight/v2

package main

import (
    "log"
    "time"

    "github.com/n-r-w/singleflight/v2"
    "golang.org/x/sync/errgroup"
)

func main() {
    var (
        g singleflight.Group[int, string]
        errGroup errgroup.Group
        ctx = context.Background()
    )

    const key = 1

    // 10 goroutines are trying to get the value for the same key,
    // but only one of them will call the function and the others will wait for the result.
    for i := 0; i < 10; i++ {
        iCopy := i
        errGroup.Go(func() error {
            _, _, err := g.Do(ctx, key, func(_ context.Context) (string, error) {
                log.Println("called for", iCopy)
                time.Sleep(1 * time.Second)
                return "Hello, world!", nil
            })
            return err
        })
    }

    if err := errGroup.Wait(); err != nil {
        log.Println(err)
    }
}