Exponential backoff does the exact opposite of what it should do

[the80srobot]

Exponential backoff is supposed to wait longer each successive time it's used. Instead, your implementation returns progressively shorter intervals.

For example, when used this way, NextBackoff will return first 500 ms and then 100 ms which is obviously wrong.

expb := backoff.NewExponentialBackOff()
expb.InitialInterval = 100 * time.Millisecond
expb.MaxInterval = 15 * time.Second
expb.Multiplier = 2
expb.RandomizationFactor = 0

[craigpastro]

I remember seeing in the following issue #30 that InitialInterval should not be set after ExponentialBackOff is created. I assume that it is still relevant. It is certainly not obvious though.

[Likhi]

With v4.2.1:

func back() {
	ctx, cancel := context.WithTimeout(context.TODO(), 20*time.Second)
	defer cancel()

	expb := backoff.NewExponentialBackOff()

	expb.InitialInterval = 1000 * time.Millisecond
	expb.MaxInterval = 15 * time.Second
	expb.Multiplier = 1.2
	expb.RandomizationFactor = 0

	fmt.Println("first backoff", expb.NextBackOff(), "\n")

	err := backoff.Retry(func() error {
		fmt.Println("elapsed", expb.GetElapsedTime())
		fmt.Println("next backoff", expb.NextBackOff(), "\n")

		select {
		case <-ctx.Done():
			return nil
		default:
			return errors.New("timeout not met")
		}

	}, expb)

	if err != nil {
		//something
	}
}

Results in:

first backoff 500ms

elapsed 0s
next backoff 1s

elapsed 1.2044503s
next backoff 1.44s

elapsed 2.9426398s
next backoff 2.0736s

elapsed 5.443746s
next backoff 2.985984s

elapsed 9.0350991s
next backoff 4.29981696s

elapsed 14.203882s
next backoff 6.191736422s

elapsed 21.6420095s
next backoff 8.916100447s