IgnoreCurrentBucket lets the Reduce call ignore current bucket.

NewRollingWindow returns a RollingWindow that with size buckets and time interval, use opts to customize the RollingWindow.

WithBreakerType 预留的，可能以后有多种不同类型的breaker returns a function to set the type of a EffectiveBreaker.

WithName returns a function to set the name of a EffectiveBreaker.

WithTimeout returns a function to set the timeout param of a EffectiveBreaker.

ErrServiceUnavailable is returned when the EffectiveBreaker state is open.

Bucket defines the bucket that holds sum and num of additions.