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package backoff
import (
"math/rand/v2"
"time"
)
/*
ExponentialBackOff is a backoff implementation that increases the backoff
period for each retry attempt using a randomization function that grows exponentially.
NextBackOff() is calculated using the following formula:
randomized interval =
RetryInterval * (random value in range [1 - RandomizationFactor, 1 + RandomizationFactor])
In other words NextBackOff() will range between the randomization factor
percentage below and above the retry interval.
For example, given the following parameters:
RetryInterval = 2
RandomizationFactor = 0.5
Multiplier = 2
the actual backoff period used in the next retry attempt will range between 1 and 3 seconds,
multiplied by the exponential, that is, between 2 and 6 seconds.
Note: MaxInterval caps the RetryInterval and not the randomized interval.
Example: Given the following default arguments, for 9 tries the sequence will be:
Request # RetryInterval (seconds) Randomized Interval (seconds)
1 0.5 [0.25, 0.75]
2 0.75 [0.375, 1.125]
3 1.125 [0.562, 1.687]
4 1.687 [0.8435, 2.53]
5 2.53 [1.265, 3.795]
6 3.795 [1.897, 5.692]
7 5.692 [2.846, 8.538]
8 8.538 [4.269, 12.807]
9 12.807 [6.403, 19.210]
Note: Implementation is not thread-safe.
*/
type ExponentialBackOff struct {
InitialInterval time.Duration
RandomizationFactor float64
Multiplier float64
MaxInterval time.Duration
currentInterval time.Duration
}
// Default values for ExponentialBackOff.
const (
DefaultInitialInterval = 500 * time.Millisecond
DefaultRandomizationFactor = 0.5
DefaultMultiplier = 1.5
DefaultMaxInterval = 60 * time.Second
)
// NewExponentialBackOff creates an instance of ExponentialBackOff using default values.
func NewExponentialBackOff() *ExponentialBackOff {
return &ExponentialBackOff{
InitialInterval: DefaultInitialInterval,
RandomizationFactor: DefaultRandomizationFactor,
Multiplier: DefaultMultiplier,
MaxInterval: DefaultMaxInterval,
}
}
// Reset the interval back to the initial retry interval and restarts the timer.
// Reset must be called before using b.
func (b *ExponentialBackOff) Reset() {
b.currentInterval = b.InitialInterval
}
// NextBackOff calculates the next backoff interval using the formula:
//
// Randomized interval = RetryInterval * (1 ± RandomizationFactor)
func (b *ExponentialBackOff) NextBackOff() time.Duration {
if b.currentInterval == 0 {
b.currentInterval = b.InitialInterval
}
next := getRandomValueFromInterval(b.RandomizationFactor, rand.Float64(), b.currentInterval)
b.incrementCurrentInterval()
return next
}
// Increments the current interval by multiplying it with the multiplier.
func (b *ExponentialBackOff) incrementCurrentInterval() {
// Check for overflow, if overflow is detected set the current interval to the max interval.
if float64(b.currentInterval) >= float64(b.MaxInterval)/b.Multiplier {
b.currentInterval = b.MaxInterval
} else {
b.currentInterval = time.Duration(float64(b.currentInterval) * b.Multiplier)
}
}
// Returns a random value from the following interval:
//
// [currentInterval - randomizationFactor * currentInterval, currentInterval + randomizationFactor * currentInterval].
func getRandomValueFromInterval(randomizationFactor, random float64, currentInterval time.Duration) time.Duration {
if randomizationFactor == 0 {
return currentInterval // make sure no randomness is used when randomizationFactor is 0.
}
var delta = randomizationFactor * float64(currentInterval)
var minInterval = float64(currentInterval) - delta
var maxInterval = float64(currentInterval) + delta
// Get a random value from the range [minInterval, maxInterval].
// The formula used below has a +1 because if the minInterval is 1 and the maxInterval is 3 then
// we want a 33% chance for selecting either 1, 2 or 3.
return time.Duration(minInterval + (random * (maxInterval - minInterval + 1)))
}
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