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package retry
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 * second), e.Max) + randBetween(0, e.MaxJitter)
type ExponentialStrategy struct {
// Min is the minimum amount of time to wait between attempts.
Min time.Duration
// Max is the maximum amount of time to wait between attempts.
Max time.Duration
// MaxJitter is the maximum amount of random jitter to insert between attempts.
// Jitter is added on top of the maximum, if the maximum is reached.
MaxJitter time.Duration
}
func (e *ExponentialStrategy) Duration(attempt int) time.Duration {
var jitter time.Duration // non-negative jitter
if e.MaxJitter > 0 {
jitter = time.Duration(rand.Int63n(e.MaxJitter.Nanoseconds()))
}
if attempt < 0 {
return e.Min + jitter
}
durFloat := float64(e.Min)
durFloat += math.Pow(2, float64(attempt)) * float64(time.Second)
dur := time.Duration(durFloat)
if durFloat > float64(e.Max) {
dur = e.Max
}
dur += jitter
return dur
}
func Exponential() Strategy {
return &ExponentialStrategy{
Min: 0,
Max: 10 * time.Second,
MaxJitter: 250 * time.Millisecond,
}
}
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,
}
}