前几天读了redis双链表的实现，一个标准的双链表，但是也实现了存储任意类型，用void*,真的是奇淫技巧，可能是我见识少，感觉也能实现内核链表那种感觉，今天看来记录一下。

首先是结构定义

c
/* Node, List, and Iterator are the only data structures used currently. */

typedef struct listNode { //指针和数据耦合在一起，非侵入式
    struct listNode *prev;
    struct listNode *next;
    void *value;
} listNode;



typedef struct listIter {
    listNode *next;
    int direction; //迭代方向
} listIter;

typedef struct list {
    listNode *head;
    listNode *tail;
    void *(*dup)(void *ptr);  
    void (*free)(void *ptr);  //删除释放整个链表
    int (*match)(void *ptr, void *key);  匹配节点
    unsigned long len;
} list;

然后是一些简单的操作函数,用宏来实现

c
/* Functions implemented as macros */
#define listLength(l) ((l)->len)
#define listFirst(l) ((l)->head)
#define listLast(l) ((l)->tail)
#define listPrevNode(n) ((n)->prev)
#define listNextNode(n) ((n)->next)
#define listNodeValue(n) ((n)->value)

#define listSetDupMethod(l,m) ((l)->dup = (m))
#define listSetFreeMethod(l,m) ((l)->free = (m))
#define listSetMatchMethod(l,m) ((l)->match = (m))

#define listGetDupMethod(l) ((l)->dup)
#define listGetFreeMethod(l) ((l)->free)
#define listGetMatchMethod(l) ((l)->match)

创建list并初始化

c
list *listCreate(void)
{
    struct list *list;

    if ((list = zmalloc(sizeof(*list))) == NULL)
        return NULL;
    list->head = list->tail = NULL;
    list->len = 0;
    list->dup = NULL;
    list->free = NULL;
    list->match = NULL;
    return list;
}

删所有的节点

删除所有节点，初始化长度为0

c
/* Remove all the elements from the list without destroying the list itself. */
void listEmpty(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);
        zfree(current);
        current = next;
    }
    list->head = list->tail = NULL;
    list->len = 0;
}

释放整个链表

c
/* Free the whole list.
 *
 * This function can't fail. */
void listRelease(list *list)
{
    listEmpty(list);
    zfree(list);
}

头插法插入

c
/* Add a new node to the list, to head, containing the specified 'value'
 * pointer as value.
 *
 * On error, NULL is returned and no operation is performed (i.e. the
 * list remains unaltered).
 * On success the 'list' pointer you pass to the function is returned. */
list *listAddNodeHead(list *list, void *value)
{
    listNode *node;

    if ((node = zmalloc(sizeof(*node))) == NULL)
        return NULL;
    node->value = value;
    listLinkNodeHead(list, node);
    return list;
}

/*
 * Add a node that has already been allocated to the head of list
 */
void listLinkNodeHead(list* list, listNode *node) {
    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++;
}

尾插法插入

c
/* Add a new node to the list, to tail, containing the specified 'value'
 * pointer as value.
 *
 * On error, NULL is returned and no operation is performed (i.e. the
 * list remains unaltered).
 * On success the 'list' pointer you pass to the function is returned. */
list *listAddNodeTail(list *list, void *value)
{
    listNode *node;

    if ((node = zmalloc(sizeof(*node))) == NULL)
        return NULL;
    node->value = value;
    listLinkNodeTail(list, node);
    return list;
}

/*
 * Add a node that has already been allocated to the tail of list
 */
void listLinkNodeTail(list *list, listNode *node) {
    if (list->len == 0) {
        list->head = list->tail = node;
        node->prev = node->next = NULL;
    } else {
        node->prev = list->tail;
        node->next = NULL;
        list->tail->next = node;
        list->tail = node;
    }
    list->len++;
}

往中间插入节点

c

list *listInsertNode(list *list, listNode *old_node, void *value, int after) {
    listNode *node;

    if ((node = zmalloc(sizeof(*node))) == NULL)
        return NULL;
    node->value = value;
    if (after) {
        node->prev = old_node;
        node->next = old_node->next;
        if (list->tail == old_node) {
            list->tail = node;
        }
    } else {
        node->next = old_node;
        node->prev = old_node->prev;
        if (list->head == old_node) {
            list->head = node;
        }
    }
    if (node->prev != NULL) {
        node->prev->next = node;
    }
    if (node->next != NULL) {
        node->next->prev = node;
    }
    list->len++;
    return list;
}

删除节点

/* Remove the specified node from the specified list.
 * The node is freed. If free callback is provided the value is freed as well.
 *
 * This function can't fail. */
void listDelNode(list *list, listNode *node)
{
    listUnlinkNode(list, node);
    if (list->free) list->free(node->value);
    zfree(node);
}

/*
 * Remove the specified node from the list without freeing it.
 */
void listUnlinkNode(list *list, listNode *node) {
    if (node->prev)
        node->prev->next = node->next;
    else
        list->head = node->next;
    if (node->next)
        node->next->prev = node->prev;
    else
        list->tail = node->prev;

    node->next = NULL;
    node->prev = NULL;

    list->len--;
}

迭代器相关

c
/* 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 = zmalloc(sizeof(*iter))) == NULL) return NULL;
    if (direction == AL_START_HEAD)
        iter->next = list->head;
    else
        iter->next = list->tail;
    iter->direction = direction;
    return iter;
}

/* Release the iterator memory */
void listReleaseIterator(listIter *iter) {
    zfree(iter);
}


/* Create an iterator in the list private iterator structure */
void listRewind(list *list, listIter *li) {
    li->next = list->head;
    li->direction = AL_START_HEAD;
}

void listRewindTail(list *list, listIter *li) {
    li->next = list->tail;
    li->direction = AL_START_TAIL;
}

/* Return the next element of an iterator.
 * It's valid to remove the currently returned element using
 * listDelNode(), but not to remove other elements.
 *
 * The function returns a pointer to the next element of the list,
 * or NULL if there are no more elements, so the classical usage
 * pattern is:
 *
 * iter = listGetIterator(list,<direction>);
 * while ((node = listNext(iter)) != NULL) {
 *     doSomethingWith(listNodeValue(node));
 * }
 *
 * */
listNode *listNext(listIter *iter)
{
    listNode *current = iter->next;

    if (current != NULL) {
        if (iter->direction == AL_START_HEAD)
            iter->next = current->next;
        else
            iter->next = current->prev;
    }
    return current;
}

复制链表

c
/* Duplicate the whole list. On out of memory NULL is returned.
 * On success a copy of the original list is returned.
 *
 * The 'Dup' method set with listSetDupMethod() function is used
 * to copy the node value. Otherwise the same pointer value of
 * the original node is used as value of the copied node.
 *
 * The original list both on success or error is never modified. */
list *listDup(list *orig)
{
    list *copy;
    listIter iter;
    listNode *node;

    if ((copy = listCreate()) == NULL)
        return NULL;
    copy->dup = orig->dup;
    copy->free = orig->free;
    copy->match = orig->match;
    listRewind(orig, &iter);
    while((node = listNext(&iter)) != NULL) {
        void *value;

        if (copy->dup) {
            value = copy->dup(node->value);
            if (value == NULL) {
                listRelease(copy);
                return NULL;
            }
        } else {
            value = node->value;
        }
        
        if (listAddNodeTail(copy, value) == NULL) {
            /* Free value if dup succeed but listAddNodeTail failed. */
            if (copy->free) copy->free(value);

            listRelease(copy);
            return NULL;
        }
    }
    return copy;
}

搜索值

c
/* Search the list for a node matching a given key.
 * The match is performed using the 'match' method
 * set with listSetMatchMethod(). If no 'match' method
 * is set, the 'value' pointer of every node is directly
 * compared with the 'key' pointer.
 *
 * On success the first matching node pointer is returned
 * (search starts from head). If no matching node exists
 * NULL is returned. */
listNode *listSearchKey(list *list, void *key)
{
    listIter iter;
    listNode *node;

    listRewind(list, &iter);
    while((node = listNext(&iter)) != NULL) {
        if (list->match) {
            if (list->match(node->value, key)) {
                return node;
            }
        } else {
            if (key == node->value) {
                return node;
            }
        }
    }
    return NULL;
}

把一个链表加入另一个链表

被加入的链表清空

c
/* Add all the elements of the list 'o' at the end of the
 * list 'l'. The list 'other' remains empty but otherwise valid. */
void listJoin(list *l, list *o) {
    if (o->len == 0) return;

    o->head->prev = l->tail;

    if (l->tail)
        l->tail->next = o->head;
    else
        l->head = o->head;

    l->tail = o->tail;
    l->len += o->len;

    /* Setup other as an empty list. */
    o->head = o->tail = NULL;
    o->len = 0;
}

/* Initializes the node's value and sets its pointers
 * so that it is initially not a member of any list.
 */
void listInitNode(listNode *node, void *value) {
    node->prev = NULL;
    node->next = NULL;
    node->value = value;
}

链接头尾

c
/* Rotate the list removing the tail node and inserting it to the head. */
void listRotateTailToHead(list *list) {
    if (listLength(list) <= 1) return;

    /* Detach current tail */
    listNode *tail = list->tail;
    list->tail = tail->prev;
    list->tail->next = NULL;
    /* Move it as head */
    list->head->prev = tail;
    tail->prev = NULL;
    tail->next = list->head;
    list->head = tail;
}

/* Rotate the list removing the head node and inserting it to the tail. */
void listRotateHeadToTail(list *list) {
    if (listLength(list) <= 1) return;

    listNode *head = list->head;
    /* Detach current head */
    list->head = head->next;
    list->head->prev = NULL;
    /* Move it as tail */
    list->tail->next = head;
    head->next = NULL;
    head->prev = list->tail;
    list->tail = head;
}

差不多，就是一个很正常的双向链表，但是也很多奇淫技巧。