code: func (r *Ring) Enqueue(i interface{}) {
  	r.Lock()
  	defer r.Unlock()
  
  	r.checkInit()
  	r.set(r.head+1, i)
  	old := r.head
  	r.head = r.mod(r.head + 1)
  	if old != -1 && r.head == r.tail {
  		r.tail = r.mod(r.tail + 1)
  	}
  }
docs: /*
  Enqueue a value into the Ring buffer.
  */