Two-way linked list)

I. Introduction to two-way linked list as a common data structure, two-way linked list provides a detailed description in Yan Weimin's Data Structure book. Each data node of the two-way linked list has two pointers, it points to the successor and the precursor nodes respectively. Therefore, you can easily access any node in the two-way linked list. Ii. Two-way linked list data knot in Redis

I. Introduction to two-way linked list as a common data structure, two-way linked list provides a detailed description in Yan Weimin's Data Structure book. Each data node of the two-way linked list has two pointers, it points to the successor and the precursor nodes respectively. Therefore, you can easily access any node in the two-way linked list. Ii. Two-way linked list data knot in Redis

1. Introduction to two-way linked list

As a common data structure, the two-way linked list provides a detailed description in the Yan Weimin Data Structure book. Each data node of the two-way linked list has two pointers pointing to the successor and the front node respectively, therefore, you can easily access any node in the two-way linked list, including its predecessor and successor nodes.

Ii. Two-way linked list data structure and related macro definitions in Redis

Typedef struct listNode {struct listNode * prev; // The first pointer struct listNode * next; // The value of the subsequent pointer void * value; // The value of the node} listNode; typedef struct listIter {// listNode * next; int direction; // traversal direction} listIter; typedef struct list {// listNode * head; // listNode * tail in the linked list header; // void * (* dup) (void * ptr) at the end of the linked list; // copy function pointer void (* free) (void * ptr ); // release the memory function pointer int (* match) (void * ptr, void * key); // compare the function pointer unsigned long len; // chain table length} list;

Macro name	Function
ListLength	Returns the length of a linked list.
ListFirst	Obtain the first pointer of a linked list
ListLast	Get the end pointer of the linked list
ListPrevNode	Obtains the front-end node pointer of the current node.
ListNextNode	Obtains the successor node pointer of the current node.
ListNodeValue	Obtains the value stored by the current node.
ListSetDupMethod	Set the replication function of the linked list node value
ListSetFreeMethod	Sets the memory release function for the linked list node value.
ListSetMatchMethod	Set the comparison function of the linked list node value
ListGetDupMethod	Returns the value of a linked list node.
ListGetFree	Returns the memory release function of the linked list node value.
ListGetMatchMethod	Get the comparison function of the linked list node value

Iii. Introduction to the two-way linked list API in Redis

Name	Function	Complexity
ListCreate	Create a new two-way linked list	O (1)
ListRelease	Releases a two-way linked list and node memory.	O (N)
ListAddNodeHead	Add a node to the table header of the linked list	O (1)
ListAddNodeTail	Add a node to the end of the linked table	O (1)
ListInsertNode	Add a node after or before a given Node	O (1)
ListDelNode	Delete a given Node	O (1)
ListGetIterator	An iterator for generating a two-way linked list	O (1)
ListReleaseIterator	Release an iterator for a two-way linked list	O (1)
ListNext	Get the next node through the iterator	O (1)
ListDup	Create a copy of a given linked list	O (N)
ListSearchKey	Search nodes with the same value as the given key	O (N)
ListIndex	Returns the corresponding node based on the given index value.	O (N)
ListRewind	Reinitialize the iterator, starting from the beginning to the end of the iteration	O (1)
ListRewindTail	Reinitialize the iterator from the end to the header	O (1)
ListRotate	Remove the End Node of the linked list and insert it to the header.	O (1)

Iv. Redis two-way linked list Performance Analysis

The two-way linked list in Redis may be the simplest and easiest data structure to implement in Redis. It is very simple and easy to say for APIs. The following is a brief analysis of the performance of the two-way linked list.

ListNode has prev and next pointers, so the iterator can easily traverse the linked list from start to end or from end to header;

List has header pointers and tail as pointers. the time complexity for inserting nodes in the head or tail of the linked list is O (1 ), efficient operations of some commands in Redis;

The list contains the len field that saves the length of the linked list, so that the time complexity of calculating the length of the linked list is O (1 ).

V. Summary

Two-way linked list has two main functions: As one of the underlying implementation methods of the Redis list data type; As a general data structure, it can be used by other functional modules.

The implementation of two-way linked list is simple. Redis transformed the two-way linked list, added fields for saving the node length, and implemented its own iterative pointer, making some data operations easy.

Finally, I would like to thank Huang jianhong (huangz1990) for its Redis design and implementation and other comments on the Redis2.6 source code for my help in studying the Redis2.8 source code.