func (f *FixedBackoff) NextDelayMillis(numAttemptsSoFar int) int64 {
	return f.delayMillis
}
NextDelayMillis return the number of milliseconds to wait for before attempting a retry.
package backoff
import (
	"fmt"
)
type FixedBackoff struct {
	delayMillis int64
}
func NewFixedBackoff(delayMillis int64) (b *FixedBackoff, err error) {
	if delayMillis >= 0 {
		b = &FixedBackoff{delayMillis: delayMillis}
	} else {
		err = fmt.Errorf("delayMillis: %d (expected: >= 0)", delayMillis)
	}
	return
}