redis源码笔记－adlist

adlist是redis自己是实现的一个通用的双向链表。

------------------------------------------------adlist.h---------------------------------------------------

#ifndef __ADLIST_H__
#define __ADLIST_H__

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

typedef struct listNode {
struct listNode *prev;
struct listNode *next;
void *value;
} listNode;        双向链表，存的结构是一个指针void*

typedef struct listIter {
listNode *next;
int direction;
} listIter;          迭代器，可以向前遍历，也可以向后遍历；

typedef struct list {
listNode *head;
listNode *tail;
void *(*dup)(void *ptr);
void (*free)(void *ptr);
int (*match)(void *ptr, void *key);
unsigned int len;
} list;                链表本身的结构，头、尾指针，同时一个函数指针dup用于在复制链表（list or listNode?）调用，一个函数指针free在释放链表时调用，一个函数指针match用来作匹配时调用，以及一个记录链表长度的字段；注意三个函数指针是list的成员，也就是被所有list node共用，因此listNode应该具有共性。

/* Functions implemented as macros */
#define listLength(l) ((l)->len)     链表长度
#define listFirst(l) ((l)->head)      链表的第一个结点
#define listLast(l) ((l)->tail)         链表的最后一个结点
#define listPrevNode(n) ((n)->prev)        当前结点的前一个结点
#define listNextNode(n) ((n)->next)        当前结点的后一个结点
#define listNodeValue(n) ((n)->value)     当前结点的值

#define listSetDupMethod(l,m) ((l)->dup = (m))       
#define listSetFreeMethod(l,m) ((l)->free = (m))
#define listSetMatchMethod(l,m) ((l)->match = (m))   set三个函数指针的方法

#define listGetDupMethod(l) ((l)->dup)
#define listGetFree(l) ((l)->free)
#define listGetMatchMethod(l) ((l)->match)       get三个函数指针的方法

/* Prototypes */
list *listCreate(void);            创建链表
void listRelease(list *list);      释放链表
list *listAddNodeHead(list *list, void *value);       在表头加一个结点
list *listAddNodeTail(list *list, void *value);         在表尾加一个结点
list *listInsertNode(list *list, listNode *old_node, void *value, int after);
void listDelNode(list *list, listNode *node);
listIter *listGetIterator(list *list, int direction);
listNode *listNext(listIter *iter);
void listReleaseIterator(listIter *iter);
list *listDup(list *orig);
listNode *listSearchKey(list *list, void *key);
listNode *listIndex(list *list, int index);
void listRewind(list *list, listIter *li);
void listRewindTail(list *list, listIter *li);

/* Directions for iterators */
#define AL_START_HEAD 0         
#define AL_START_TAIL 1          定义迭代器方向

#endif /* __ADLIST_H__ */

------------------------------------------------adlist.c---------------------------------------------------

#include <stdlib.h>
#include "adlist.h"
#include "zmalloc.h"     //redis对内存分配库函数的一个封装，用于stat目的

/* 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;
}    //这个函数创建的list是个裸的list，三个函数指针需要自行调用set赋值

/* Free the whole list.
 *
 * This function can't fail. */
void listRelease(list *list)
{
    unsigned int 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);
}       //先用free释放listNode中保存的元素，然后释放结点，最后释放链表本身。在链表操作中，注意在释放当前结点时，需要保存后续结点的值

/* 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) {
        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;
}

/* 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;
}

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;
}

/* 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. */
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;
}

/* 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)
            iter->next = current->next;
        else
            iter->next = current->prev;
    }
    return current;
}       //注意这个函数，如果对返回值作delete操作，iter并未失效

/* 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);       //这里疑似有内存泄露，如果copy->dup被指定，并为value成功分配了内存，但addNodeTail的时候失败了，这块内存就没人管了。
            listReleaseIterator(iter);
            return NULL; 
        }
    }
    listReleaseIterator(iter);
    return copy;
}  //如果没有指定dup函数则是个浅拷贝，否则是个深拷贝。

/* 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;
} //O(n)的复杂度，n是链表长度

/* 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, int index) {
    listNode *n;

    if (index < 0) {
        index = (-index)-1; //注意从后边往前数时index的处理
        n = list->tail;
        while(index-- && n) n = n->prev;
    } else {
        n = list->head;
        while(index-- && n) n = n->next;
    }
    return n;
}