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Diffstat (limited to 'vendor/github.com/cenkalti/backoff/v4/exponential.go')
| -rw-r--r-- | vendor/github.com/cenkalti/backoff/v4/exponential.go | 161 |
1 files changed, 161 insertions, 0 deletions
diff --git a/vendor/github.com/cenkalti/backoff/v4/exponential.go b/vendor/github.com/cenkalti/backoff/v4/exponential.go new file mode 100644 index 000000000..2c56c1e71 --- /dev/null +++ b/vendor/github.com/cenkalti/backoff/v4/exponential.go @@ -0,0 +1,161 @@ +package backoff + +import ( + "math/rand" + "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. + +If the time elapsed since an ExponentialBackOff instance is created goes past the +MaxElapsedTime, then the method NextBackOff() starts returning backoff.Stop. + +The elapsed time can be reset by calling Reset(). + +Example: Given the following default arguments, for 10 tries the sequence will be, +and assuming we go over the MaxElapsedTime on the 10th try: + + 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] + 10 19.210 backoff.Stop + +Note: Implementation is not thread-safe. +*/ +type ExponentialBackOff struct { + InitialInterval time.Duration + RandomizationFactor float64 + Multiplier float64 + MaxInterval time.Duration + // After MaxElapsedTime the ExponentialBackOff returns Stop. + // It never stops if MaxElapsedTime == 0. + MaxElapsedTime time.Duration + Stop time.Duration + Clock Clock + + currentInterval time.Duration + startTime time.Time +} + +// Clock is an interface that returns current time for BackOff. +type Clock interface { + Now() time.Time +} + +// Default values for ExponentialBackOff. +const ( + DefaultInitialInterval = 500 * time.Millisecond + DefaultRandomizationFactor = 0.5 + DefaultMultiplier = 1.5 + DefaultMaxInterval = 60 * time.Second + DefaultMaxElapsedTime = 15 * time.Minute +) + +// NewExponentialBackOff creates an instance of ExponentialBackOff using default values. +func NewExponentialBackOff() *ExponentialBackOff { + b := &ExponentialBackOff{ + InitialInterval: DefaultInitialInterval, + RandomizationFactor: DefaultRandomizationFactor, + Multiplier: DefaultMultiplier, + MaxInterval: DefaultMaxInterval, + MaxElapsedTime: DefaultMaxElapsedTime, + Stop: Stop, + Clock: SystemClock, + } + b.Reset() + return b +} + +type systemClock struct{} + +func (t systemClock) Now() time.Time { + return time.Now() +} + +// SystemClock implements Clock interface that uses time.Now(). +var SystemClock = systemClock{} + +// 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 + b.startTime = b.Clock.Now() +} + +// NextBackOff calculates the next backoff interval using the formula: +// Randomized interval = RetryInterval * (1 ± RandomizationFactor) +func (b *ExponentialBackOff) NextBackOff() time.Duration { + // Make sure we have not gone over the maximum elapsed time. + elapsed := b.GetElapsedTime() + next := getRandomValueFromInterval(b.RandomizationFactor, rand.Float64(), b.currentInterval) + b.incrementCurrentInterval() + if b.MaxElapsedTime != 0 && elapsed+next > b.MaxElapsedTime { + return b.Stop + } + return next +} + +// GetElapsedTime returns the elapsed time since an ExponentialBackOff instance +// is created and is reset when Reset() is called. +// +// The elapsed time is computed using time.Now().UnixNano(). It is +// safe to call even while the backoff policy is used by a running +// ticker. +func (b *ExponentialBackOff) GetElapsedTime() time.Duration { + return b.Clock.Now().Sub(b.startTime) +} + +// 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))) +} |