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package retry // import "gopkg.in/retry.v1"
import (
"math/rand"
"sync"
"time"
)
var (
// randomMu guards random.
randomMu sync.Mutex
// random is used as a random number source for jitter.
// We avoid using the global math/rand source
// as we don't want to be responsible for seeding it,
// and its lock may be more contended.
random = rand.New(rand.NewSource(time.Now().UnixNano()))
)
// Exponential represents an exponential backoff retry strategy.
// To limit the number of attempts or their overall duration, wrap
// this in LimitCount or LimitDuration.
type Exponential struct {
// Initial holds the initial delay.
Initial time.Duration
// Factor holds the factor that the delay time will be multiplied
// by on each iteration. If this is zero, a factor of two will be used.
Factor float64
// MaxDelay holds the maximum delay between the start
// of attempts. If this is zero, there is no maximum delay.
MaxDelay time.Duration
// Jitter specifies whether jitter should be added to the
// retry interval. The algorithm used is described as "Full Jitter"
// in https://aws.amazon.com/blogs/architecture/exponential-backoff-and-jitter/
Jitter bool
}
type exponentialTimer struct {
strategy Exponential
start time.Time
end time.Time
delay time.Duration
}
// NewTimer implements Strategy.NewTimer.
func (r Exponential) NewTimer(now time.Time) Timer {
if r.Factor <= 0 {
r.Factor = 2
}
return &exponentialTimer{
strategy: r,
start: now,
delay: r.Initial,
}
}
// NextSleep implements Timer.NextSleep.
func (a *exponentialTimer) NextSleep(now time.Time) (time.Duration, bool) {
sleep := a.delay - now.Sub(a.start)
if sleep <= 0 {
sleep = 0
}
if a.strategy.Jitter {
sleep = randDuration(sleep)
}
// Set the start of the next try.
a.start = now.Add(sleep)
a.delay = time.Duration(float64(a.delay) * a.strategy.Factor)
if a.strategy.MaxDelay > 0 && a.delay > a.strategy.MaxDelay {
a.delay = a.strategy.MaxDelay
}
return sleep, true
}
func randDuration(max time.Duration) time.Duration {
if max <= 0 {
return 0
}
randomMu.Lock()
defer randomMu.Unlock()
return time.Duration(random.Int63n(int64(max)))
}
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