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package net
import "math"
import "math/rand"
import "time"
var randr *rand.Rand
func init() {
t := time.Now()
s := rand.NewSource(t.Unix() ^ t.UnixNano())
randr = rand.New(s)
}
// Expresses a backoff and retry specification.
//
// The nil value of this structure results in sensible defaults being used.
type Backoff struct {
// The maximum number of attempts which may be made.
// If this is 0, the number of attempts is unlimited.
MaxTries int
// The initial delay, in milliseconds. This is the delay used after the first
// failed attempt.
InitialDelay time.Duration // ms
// The maximum delay, in milliseconds. This is the maximum delay between
// attempts.
MaxDelay time.Duration // ms
// Determines when the maximum delay should be reached. If this is 5, the
// maximum delay will be reached after 5 attempts have been made.
MaxDelayAfterTries int
// Positive float expressing the maximum factor by which the delay value may
// be randomly inflated. e.g. specify 0.05 for a 5% variation. Set to zero to
// disable jitter.
Jitter float64
// The current try. You should not need to set this yourself.
CurrentTry int
}
// Initialises any nil field in Backoff with sensible defaults. You
// normally do not need to call this method yourself, as it will be called
// automatically.
func (rc *Backoff) InitDefaults() {
if rc.InitialDelay == 0 {
rc.InitialDelay = 5 * time.Second
}
if rc.MaxDelay == 0 {
rc.MaxDelay = 120 * time.Second
}
if rc.MaxDelayAfterTries == 0 {
rc.MaxDelayAfterTries = 10
}
}
// Gets the next delay in milliseconds and increments the internal try counter.
func (rc *Backoff) NextDelay() time.Duration {
rc.InitDefaults()
if rc.MaxTries != 0 && rc.CurrentTry >= rc.MaxTries {
return time.Duration(0)
}
initialDelay := float64(rc.InitialDelay)
maxDelay := float64(rc.MaxDelay)
maxDelayAfterTries := float64(rc.MaxDelayAfterTries)
currentTry := float64(rc.CurrentTry)
// [from backoff.c]
k := math.Log2(maxDelay/initialDelay) / maxDelayAfterTries
d := time.Duration(initialDelay * math.Exp2(currentTry*k))
rc.CurrentTry++
if d > rc.MaxDelay {
d = rc.MaxDelay
}
if rc.Jitter != 0 {
f := (randr.Float64() - 0.5) * 2 // random value in range [-1,1)
d = time.Duration(float64(d) * (1 + rc.Jitter*f))
}
return d
}
// Sleep for the duration returned by NextDelay().
func (rc *Backoff) Sleep() bool {
d := rc.NextDelay()
if d != 0 {
time.Sleep(d)
return true
}
return false
}
// Sets the internal try counter to zero; the next delay returned will be
// InitialDelay again.
func (rc *Backoff) Reset() {
rc.CurrentTry = 0
}
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