Redis source code-Data Structure-adlist double-ended linked list

The apsaradb for redis adlist implements a double-ended linked list in the data structure. The entire structure is as follows:
Linked List node definition:

typedef struct listNode {    struct listNode *prev;    struct listNode *next;    void *value;} listNode;

Linked list definition:

typedef struct list {    listNode *head;    listNode *tail;    void *(*dup)(void *ptr);    void (*free)(void *ptr);    int (*match)(void *ptr, void *key);    unsigned long len;} list;

The three function pointers are ignored first, and then we will see what we are doing later. In addition, we have implemented an iterator that features a bit of C ++ in it.

typedef struct listIter {    listNode *next;    int direction;} listIter;

Three elements of a linked list: Create, insert, and delete

list *listCreate(void){    struct list *list;    if ((list = malloc(sizeof(*list))) == NULL)        return NULL;    list->head = list->tail = NULL;    list->len = 0;    list->dup = NULL;    list->free = NULL;    list->match = NULL;    return list;}

Insert is divided into header insertion and tail insertion. The source code implementation header has a very clear comment, telling this function some details, the author is very careful:

list *listAddNodeHead(list *list, void *value){    listNode *node;    if ((node = malloc(sizeof(*node))) == NULL)        return NULL;    node->value = value;    if (list->len == 0) {        list->head = list->tail = node;        node->prev = node->next = NULL;    } else {        node->prev = NULL;        node->next = list->head;        list->head->prev = node;        list->head = node;    }    list->len++;    return list;}

Release memory

void listRelease(list *list){    unsigned long len;    listNode *current, *next;    current = list->head;    len = list->len;    while(len--) {        next = current->next;        if (list->free) list->free(current->value);        free(current);        current = next;    }    free(list);}

The method of creating an iterator can be followed in the future. The iterator is divided into different directions:

/* Returns a list iterator 'iter'. After the initialization every * call to listNext() will return the next element of the list. * * This function can't fail. */listIter *listGetIterator(list *list, int direction){    listIter *iter;    if ((iter = malloc(sizeof(*iter))) == NULL) return NULL;    if (direction == AL_START_HEAD)        iter->next = list->head;    else        iter->next = list->tail;    iter->direction = direction;    return iter;}

Redis source code-Data Structure-adlist double-ended linked list