code: func (b *SimpleBackoff) Next(retry int) (time.Duration, bool) {
  	b.Lock()
  	defer b.Unlock()
  
  	if retry >= len(b.ticks) {
  		return 0, false
  	}
  
  	ms := b.ticks[retry]
  	if b.jitter {
  		ms = jitter(ms)
  	}
  	return time.Duration(ms) * time.Millisecond, true
  }
docs: // Next implements BackoffFunc for SimpleBackoff.