redislock

redislock

Simplified distributed locking implementation using Redis. For more information, please see examples.

Documentation

Full documentation is available on GoDoc

Examples

import (
  "context"
  "fmt"
  "log"
  "time"

  "github.com/bsm/redislock"
  "github.com/redis/go-redis/v9"
)

func main() {
	// Connect to redis.
	client := redis.NewClient(&redis.Options{
		Network:	"tcp",
		Addr:		"127.0.0.1:6379",
	})
	defer client.Close()

	// Create a new lock client.
	locker := redislock.New(client)

	ctx := context.Background()

	// Try to obtain lock.
	lock, err := locker.Obtain(ctx, "my-key", 100*time.Millisecond, nil)
	if err == redislock.ErrNotObtained {
		fmt.Println("Could not obtain lock!")
		return
	} else if err != nil {
		log.Fatalln(err)
		return
	}

	// Don't forget to defer Release.
	defer lock.Release(ctx)
	fmt.Println("I have a lock!")

	// Sleep and check the remaining TTL.
	time.Sleep(50 * time.Millisecond)
	if ttl, err := lock.TTL(ctx); err != nil {
		log.Fatalln(err)
	} else if ttl > 0 {
		fmt.Println("Yay, I still have my lock!")
	}

	// Extend my lock.
	if err := lock.Refresh(ctx, 100*time.Millisecond, nil); err != nil {
		log.Fatalln(err)
	}

	// Sleep a little longer, then check.
	time.Sleep(100 * time.Millisecond)
	if ttl, err := lock.TTL(ctx); err != nil {
		log.Fatalln(err)
	} else if ttl == 0 {
		fmt.Println("Now, my lock has expired!")
	}

}

External watchdog

redislock deliberately does not bundle a built-in watchdog goroutine: refresh cadence and error handling are application concerns (log and continue, retry, cancel the protected work, page someone, etc.). If you need a long-running lock that outlives its initial TTL, drop a small ticker next to your work and let it call Refresh for you:

func watchdog() {
	client := redis.NewClient(&redis.Options{Network: "tcp", Addr: "127.0.0.1:6379"})
	defer client.Close()

	locker := redislock.New(client)

	ctx := context.Background()

	// Obtain a lock with a 30s TTL.
	const ttl = 30 * time.Second
	lock, err := locker.Obtain(ctx, "my-key", ttl, nil)
	if err != nil {
		log.Fatalln(err)
	}
	defer lock.Release(context.Background())

	// Start a watchdog that refreshes the lock every ttl/3. The work context
	// is cancelled if a refresh fails so the protected work can abort.
	workCtx, cancel := context.WithCancel(ctx)
	defer cancel()

	go func() {
		t := time.NewTicker(ttl / 3)
		defer t.Stop()
		for {
			select {
			case <-workCtx.Done():
				return
			case <-t.C:
				if err := lock.Refresh(workCtx, ttl, nil); err != nil {
					log.Printf("lock refresh failed: %v", err)
					cancel()
					return
				}
			}
		}
	}()

	// ... do work using workCtx ...
	fmt.Println("I have a lock!")
}

A few notes:

• Pick interval ≈ ttl/3 so a single transient redis blip still leaves room to retry before the lock expires.
• A Refresh error of redislock.ErrNotObtained means the lock was lost (expired or stolen) and is usually fatal for the protected work; cancel the work context so the caller stops.
• Release stays with the caller, so ownership is explicit.