Redis源碼-資料結構之Adlist雙端鏈表

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Redis的Adlist實現了資料結構中的雙端鏈表，整個結構如下：
鏈表節點定義：

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

鏈表定義：

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;

其中的三個函數指標先不用管，後面遇到了再看具體是幹什麼的，另外還實現了一個迭代器，有點c++的味道在裡面

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

鏈表三要素，建立，插入，和刪除

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;}

插入分為從頭部插入和尾部插入，原始碼實現頭部都有非常清晰的注釋，告訴這個函數的一些細節，作者很是用心：

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;}

釋放記憶體

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);}

迭代器的建立，以後可以效仿這種做法，迭代器分方向：

/* 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源碼-資料結構之Adlist雙端鏈表