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
Indicates that no more retries should be made for use in NextBackOff().
var SystemClock = systemClock{}
SystemClock implements Clock interface that uses time.Now().
func Retry(o Operation, b BackOff) error
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.
Retry sleeps the goroutine for the duration returned by BackOff after a failed operation returns.
▹ Example
func RetryNotify(operation Operation, b BackOff, notify Notify) error
RetryNotify calls notify function with the error and wait duration for each failed attempt before sleep.
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 Clock interface {
Now() time.Time
}
Clock is an interface that returns current time for BackOff.
type ConstantBackOff struct {
Interval time.Duration
}
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(d time.Duration) *ConstantBackOff
func (b *ConstantBackOff) NextBackOff() time.Duration
func (b *ConstantBackOff) Reset()
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() *ExponentialBackOff
NewExponentialBackOff creates an instance of ExponentialBackOff using default values.
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 (b *ExponentialBackOff) NextBackOff() time.Duration
NextBackOff calculates the next backoff interval using the formula:
Randomized interval = RetryInterval +/- (RandomizationFactor * RetryInterval)
func (b *ExponentialBackOff) Reset()
Reset the interval back to the initial retry interval and restarts the timer.
type Notify func(error, time.Duration)
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 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 StopBackOff struct{}
StopBackOff is a fixed backoff policy that always returns backoff.Stop for NextBackOff(), meaning that the operation should never be retried.
func (b *StopBackOff) NextBackOff() time.Duration
func (b *StopBackOff) Reset()
type Ticker struct {
C <-chan time.Time
// contains filtered or unexported fields
}
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.
▹ Example
func NewTicker(b BackOff) *Ticker
NewTicker returns a new Ticker containing a channel that will send the time at times specified by the BackOff argument. Ticker is guaranteed to tick at least once. The channel is closed when Stop method is called or BackOff stops.
func (t *Ticker) Stop()
Stop turns off a ticker. After Stop, no more ticks will be sent.
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.
func (b *ZeroBackOff) NextBackOff() time.Duration
func (b *ZeroBackOff) Reset()