This is a concurrent linked list implementation in Rust using RcuCell.

There are two types of linked list: SignleLinkedList and DoubleLinkedList.

The SingleLinkedList supports the following operations:

• front: Get the head entry of list.
• back: Get the tail entry of list.
• push_front: Insert a new element into the head of list.
• pop_front: Remove the element from the head of list.
• push_back: Insert a new element into the tail of list.
• iter: Iterate over the list.

each Entry that returned by instert operations could do the following operations:

• deref: Read the value of the current element.

The DoubleLinkedList supports the following operations:

• front: Get the head entry of list.
• back: Get the tail entry of list.
• push_front: Insert a new element into the head of list.
• pop_front: Remove the element from the head of list.
• push_back: Insert a new element into the tail of list.
• pop_back: Remove the element from the tail of list.
• iter: Iterate over the list.

each Entry that returned by insert operations could do the following operations:

• remove: Remove the current element from the list.
• replace: Replace the current element from the list.
• insert_after: Insert an element after the entry.
• insert_ahead: Insert an element ahead the entry.
• remove_after: Remove the element after the entry.
• remove_ahead: Remove the element ahead the entry.
• deref: Read the value of the current element.
• is_removed: Check if the element is removed from the list.
• next: Get the next entry in the list.

Any write operations like insert/remove on a removed Entry would just fail. But it's safe to read(deref) the value of a removed Entry.

1. push_front has better performance than push_back, because it doesn't need to lock the previous element.
2. pop_front has better performance than pop_back, because it doesn't need to lock the previous element.
3. pop_back could result more efficient memory recycle than pop_front, because it less likely hold the next element.
4. push_front and push_back only need to lock one element.
5. pop_front and pop_back need to lock two elements.
6. Don't hold an Entry for a long time, the drop may recursively drop next elements and cause a stack overflow.