backoff

Documentation

Index

• Constants
• Variables
• type Clock
• type ExponentialBackOff
  • func NewExponentialBackOff() *ExponentialBackOff
  • func (b *ExponentialBackOff) GetElapsedTime() time.Duration
  • func (b *ExponentialBackOff) NextBackOff() time.Duration
  • func (b *ExponentialBackOff) Reset()

Constants

const (
	DefaultInitialInterval     = 250 * time.Millisecond
	DefaultRandomizationFactor = 0.25
	DefaultMultiplier          = 1.5
	DefaultMaxInterval         = 7 * time.Second
)

Default values for ExponentialBackOff.

Variables

var SystemClock = systemClock{}

SystemClock implements Clock interface that uses time.Now().

Types

type Clock

type Clock interface {
	Now() time.Time
}

Clock is an interface that returns current time for BackOff.

type ExponentialBackOff

type ExponentialBackOff struct {
	InitialInterval     time.Duration
	RandomizationFactor float64
	Multiplier          float64
	MaxInterval         time.Duration
	// After MaxElapsedTime the ExponentialBackOff stops.
	// It never stops if MaxElapsedTime == 0.
	MaxElapsedTime time.Duration
	Clock          Clock
	// contains filtered or unexported fields
}

The MIT License (MIT)

Copyright (c) 2014 Cenk Altı

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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.

func NewExponentialBackOff

func NewExponentialBackOff() *ExponentialBackOff

NewExponentialBackOff creates an instance of ExponentialBackOff using default values.

func (*ExponentialBackOff) GetElapsedTime

func (b *ExponentialBackOff) GetElapsedTime() time.Duration

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 (*ExponentialBackOff) NextBackOff

func (b *ExponentialBackOff) NextBackOff() time.Duration

NextBackOff calculates the next backoff interval using the formula:

Randomized interval = RetryInterval +/- (RandomizationFactor * RetryInterval)

func (*ExponentialBackOff) Reset

func (b *ExponentialBackOff) Reset()

Reset the interval back to the initial retry interval and restarts the timer.