README
¶
Exponential Backoff 
This is a Go port of the exponential backoff algorithm from Google's HTTP Client Library for Java.
Exponential backoff is an algorithm that uses feedback to multiplicatively decrease the rate of some process, in order to gradually find an acceptable rate. The retries exponentially increase and stop increasing when a certain threshold is met.
Usage
See https://godoc.org/github.com/cenkalti/backoff#pkg-examples
Contributing
- I would like to keep this library as small as possible.
- Please don't send a PR without opening an issue and discussing it first.
- If proposed change is not a common use case, I will probably not accept it.
Documentation
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Overview ¶
Package backoff implements backoff algorithms for retrying operations.
Use Retry function for retrying operations that may fail. If Retry does not meet your needs, copy/paste the function into your project and modify as you wish.
There is also Ticker type similar to time.Ticker. You can use it if you need to work with channels.
See Examples section below for usage examples.
Index ¶
- Constants
- Variables
- func Retry(o Operation, b BackOff) error
- func RetryNotify(operation Operation, b BackOff, notify Notify) error
- type BackOff
- type BackOffContext
- type Clock
- type ConstantBackOff
- type ExponentialBackOff
- type Notify
- type Operation
- type PermanentError
- type StopBackOff
- type Ticker
- type ZeroBackOff
Constants ¶
const ( DefaultInitialInterval = 500 * time.Millisecond DefaultRandomizationFactor = 0.5 DefaultMultiplier = 1.5 DefaultMaxInterval = 60 * time.Second DefaultMaxElapsedTime = 15 * time.Minute )
Default values for ExponentialBackOff.
const Stop time.Duration = -1
Stop indicates that no more retries should be made for use in NextBackOff().
Variables ¶
var SystemClock = systemClock{}
SystemClock implements Clock interface that uses time.Now().
Functions ¶
func Retry ¶
Retry the operation o until it does not return error or BackOff stops. o is guaranteed to be run at least once. It is the caller's responsibility to reset b after Retry returns.
If o returns a *PermanentError, the operation is not retried, and the wrapped error is returned.
Retry sleeps the goroutine for the duration returned by BackOff after a failed operation returns.
Types ¶
type BackOff ¶
type BackOff interface {
// NextBackOff returns the duration to wait before retrying the operation,
// or backoff.Stop to indicate that no more retries should be made.
//
// Example usage:
//
// duration := backoff.NextBackOff();
// if (duration == backoff.Stop) {
// // Do not retry operation.
// } else {
// // Sleep for duration and retry operation.
// }
//
NextBackOff() time.Duration
// Reset to initial state.
Reset()
}
BackOff is a backoff policy for retrying an operation.
type BackOffContext ¶
BackOffContext is a backoff policy that stops retrying after the context is canceled.
func WithContext ¶
func WithContext(ctx context.Context, b BackOff) BackOffContext
WithContext returns a BackOffContext with context ctx
ctx must not be nil
type ConstantBackOff ¶
ConstantBackOff is a backoff policy that always returns the same backoff delay. This is in contrast to an exponential backoff policy, which returns a delay that grows longer as you call NextBackOff() over and over again.
func NewConstantBackOff ¶
func NewConstantBackOff(d time.Duration) *ConstantBackOff
NewConstantBackOff ...
func (*ConstantBackOff) NextBackOff ¶
func (b *ConstantBackOff) NextBackOff() time.Duration
NextBackOff ...
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
}
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().
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.
type Notify ¶
Notify is a notify-on-error function. It receives an operation error and backoff delay if the operation failed (with an error).
NOTE that if the backoff policy stated to stop retrying, the notify function isn't called.
type Operation ¶
type Operation func() error
An Operation is executing by Retry() or RetryNotify(). The operation will be retried using a backoff policy if it returns an error.
type PermanentError ¶
type PermanentError struct {
Err error
}
PermanentError signals that the operation should not be retried.
func Permanent ¶
func Permanent(err error) *PermanentError
Permanent wraps the given err in a *PermanentError.
func (*PermanentError) Error ¶
func (e *PermanentError) Error() string
type StopBackOff ¶
type StopBackOff struct{}
StopBackOff is a fixed backoff policy that always returns backoff.Stop for NextBackOff(), meaning that the operation should never be retried.
type Ticker ¶
Ticker holds a channel that delivers `ticks' of a clock at times reported by a BackOff.
Ticks will continue to arrive when the previous operation is still running, so operations that take a while to fail could run in quick succession.
type ZeroBackOff ¶
type ZeroBackOff struct{}
ZeroBackOff is a fixed backoff policy whose backoff time is always zero, meaning that the operation is retried immediately without waiting, indefinitely.
Source Files