linkedlist.go
func (list *LinkedList) PeekBack() (interface{}, bool) {
	list.key.RLock()
	defer list.key.RUnlock()

	if list.last == nil {
		return nil, false
	}
	return list.last.payload, true
}
func (list *LinkedList) PeekBack() (interface{}, bool) {
	list.key.RLock()
	defer list.key.RUnlock()

	if list.last == nil {
		return nil, false
	}
	return list.last.payload, true
}
// PeekBack returns the entry logicall stored at the back of the list without removing it.