redis2.6.9源码学习---adlist

源码adlist.c adlist.h，先来看看adlist的结构

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

typedef struct listNode {
    struct listNode *prev;
    struct listNode *next;
    void *value;
} listNode;
//标准的双向链表
typedef struct listIter {
    listNode *next;
    int direction;
} listIter;
//迭代器
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;
//链表本身的结构，一头一尾，三个函数指针，最后一个记录链表长度
结构很简单哦

 来看看方法

/* Create a new list. The created list can be freed with
 * AlFreeList(), but private value of every node need to be freed
 * by the user before to call AlFreeList().
 *
 * On error, NULL is returned. Otherwise the pointer to the new list. */
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;
}
/* Free the whole list.
 *
 * This function can't fail. */
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);
        zfree(current);
        current = next;
    }
    zfree(list);
}
//一个创建，一个释放，很干净的代码
//释放时取链表的头部指针，while循环，头部依次next,一个一个free

 

/* Add a new node to the list, to head, contaning 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;
    if (list->len == 0) {//如果链表长度还是0，则说明这加入的节点是唯一的节点，则头尾都是这个节点
        list->head = list->tail = node;
        node->prev = node->next = NULL;
    } else {
        //这是插入头部的，所以新插入的节点为新的head
        node->prev = NULL;
        node->next = list->head;
        list->head->prev = node;
        list->head = node;
    }
    list->len++;//记得把链表长度+1
    return list;
}

 

/* Add a new node to the list, to tail, contaning 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;
    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++;
    return list;
}
//插入尾部节点

 

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) {
//这个after意思是插入到old_node的后面(这里我来打个比方，1,2,3,5,6,把4插入到3的后面,4的前节点赋值为3,4的后节点赋值为3的现在的后节点5)
        node->prev = old_node;
        node->next = old_node->next;
        if (list->tail == old_node) {
            list->tail = node;
        }
    } else {
//4的后节点赋值为3,4的前节点赋值为3的现在的前节点2
        node->next = old_node;
        node->prev = old_node->prev;
        if (list->head == old_node) {
            list->head = node;
        }
    }
    if (node->prev != NULL) {
//先看after,4的前节点3的后节点赋值为4，不赋值前3的后节点是5
//再看非after,4的前节点2的后节点赋值为4，不赋值前2的后节点是3
        node->prev->next = node;
    }
    if (node->next != NULL) {
//先看after,4的后节点5的前节点赋值为4，不赋值前5的前节点是3,这样最后就变成了1，2，3，4，5，6
//再看非after,4的后节点3的前节点赋值为4，不赋值前3的后节点是5，这样最后就变成了1，2，4，3，5，6
        node->next->prev = node;
    }
    list->len++;//记得长度+1
    return list;
}
//如果不清楚，动手划划

 

/* Remove the specified node from the specified list.
 * It's up to the caller to free the private value of the node.
 *
 * This function can't fail. */
//把中间的删除，就是让删除的前节点的next指向删除的next,删除的后节点的prev指向删除的prev,再注意一下头尾特殊情况，长度-1
void listDelNode(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;
    if (list->free) list->free(node->value);
    zfree(node);
    list->len--;
}

 

/* 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;
}
//迭代器的创建与释放，迭代器是单向的，不是从head开始就是tail开始

 

/* 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 patter
 * 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)//判断迭代器的方向，将下一个赋值给iter的next
            iter->next = current->next;
        else
            iter->next = current->prev;
    }
    return current;
}

 

/* 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;
    iter = listGetIterator(orig, AL_START_HEAD);
    while((node = listNext(iter)) != NULL) {
        void *value;

        if (copy->dup) {
            value = copy->dup(node->value);
            if (value == NULL) {
                listRelease(copy);
                listReleaseIterator(iter);
                return NULL;
            }
        } else
            value = node->value;
        if (listAddNodeTail(copy, value) == NULL) {
            listRelease(copy);
            listReleaseIterator(iter);
            return NULL;
        }
    }
    listReleaseIterator(iter);
    return copy;
}
//复制整个list，并且释放old,利用迭代器，一个节点一个节点的复制并释放

 

/* 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;

    iter = listGetIterator(list, AL_START_HEAD);
    while((node = listNext(iter)) != NULL) {
        if (list->match) {
            if (list->match(node->value, key)) {
                listReleaseIterator(iter);
                return node;
            }
        } else {
            if (key == node->value) {
                listReleaseIterator(iter);
                return node;
            }
        }
    }
    listReleaseIterator(iter);
    return NULL;
}
//查找，迭代器遍历，注意释放迭代器，listReleaseIterator出现了三次

 

/* Return the element at the specified zero-based index
 * where 0 is the head, 1 is the element next to head
 * and so on. Negative integers are used in order to count
 * from the tail, -1 is the last element, -2 the penultimante
 * and so on. If the index is out of range NULL is returned. */
listNode *listIndex(list *list, long index) {
    listNode *n;

    if (index < 0) {
        index = (-index)-1;
        n = list->tail;
        while(index-- && n) n = n->prev;
    } else {
        n = list->head;
        while(index-- && n) n = n->next;
    }
    return n;
}
//index可以传负值，表示从尾部计算第几个，正值则是从头部计算第几个,0表示头部第一个,-1表示尾部第一个

 

/* Rotate the list removing the tail node and inserting it to the head. */
void listRotate(list *list) {
    listNode *tail = list->tail;

    if (listLength(list) <= 1) return;

    /* Detatch current 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;
}
//这个方法是将链表的尾部变成链表的头部，即1,2,3,4变成4,1,2,3

 总体来看代码比较简单，是个典型的双向链表，但代码清晰，没有多余的逻辑，以后可以做为它用。