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package backoff
import (
"math"
"math/rand"
"time"
)
// Strategy is used to calculate how long a particular Operation
// should wait between attempts.
type Strategy interface {
// Duration returns how long to wait for a given retry attempt.
Duration(attempt int) time.Duration
}
// ExponentialStrategy performs exponential backoff. The exponential backoff
// function is min(e.Min + (2^attempt * 1000) + randBetween(0, e.MaxJitter), e.Max)
type ExponentialStrategy struct {
// Min is the minimum amount of time to wait between attempts in ms.
Min float64
// Max is the maximum amount of time to wait between attempts in ms.
Max float64
// MaxJitter is the maximum amount of random jitter to insert between
// attempts in ms.
MaxJitter int
}
func (e *ExponentialStrategy) Duration(attempt int) time.Duration {
var jitter int
if e.MaxJitter > 0 {
jitter = rand.Intn(e.MaxJitter)
}
dur := e.Min + (math.Pow(2, float64(attempt)) * 1000)
dur += float64(jitter)
if dur > e.Max {
return time.Millisecond * time.Duration(e.Max)
}
return time.Millisecond * time.Duration(dur)
}
func Exponential() Strategy {
return &ExponentialStrategy{
Max: 10000,
MaxJitter: 250,
}
}
type FixedStrategy struct {
Dur time.Duration
}
func (f *FixedStrategy) Duration(attempt int) time.Duration {
return f.Dur
}
func Fixed(dur time.Duration) Strategy {
return &FixedStrategy{
Dur: dur,
}
}