Redis源码阅读_02_adlist

A generic doubly linked list implementation

Redis的adlist.h和adlist.c共同定义了其基本数据结构list，其底层是一个带有迭代器的双向链表结构，迭代器的实现非常精巧。

adlist.h

#ifndef __ADLIST_H__
#define __ADLIST_H__

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

typedef struct listNode {		// 链表节点
    struct listNode *prev;		// 前驱
    struct listNode *next;		// 后继
    void *value;				// 值指针
} listNode;

typedef struct listIter {		// 链表迭代器，单向
    listNode *next;				// 下一节点
    int direction;				// 迭代方向，用来选择prev还是next
} listIter;

typedef struct list {			// 链表
    listNode *head;				// 头结点
    listNode *tail;				// 尾结点
    void *(*dup)(void *ptr);	// 复制函数
    void (*free)(void *ptr);	// 释放函数
    int (*match)(void *ptr, void *key); 	// 匹配函数
    unsigned long len;			// 链表长度
} list;

/* 获取链表基本信息的操作 */
#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)

/* 设置链表元素的操作函数 */
#define listSetDupMethod(l,m) ((l)->dup = (m))
#define listSetFreeMethod(l,m) ((l)->free = (m))
#define listSetMatchMethod(l,m) ((l)->match = (m))

/* 获取链表元素的操作函数 */
#define listGetDupMethod(l) ((l)->dup)
#define listGetFreeMethod(l) ((l)->free)
#define listGetMatchMethod(l) ((l)->match)

/* 函数原型，函数名含义清晰，基本实现了自注释 */
list *listCreate(void);
void listRelease(list *list);
void listEmpty(list *list);
list *listAddNodeHead(list *list, void *value);
list *listAddNodeTail(list *list, void *value);
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, long index);
void listRewind(list *list, listIter *li);
void listRewindTail(list *list, listIter *li);
void listRotateTailToHead(list *list);
void listRotateHeadToTail(list *list);
void listJoin(list *l, list *o);

/* Directions for iterators */
#define AL_START_HEAD 0		// 正向迭代方向，头--》尾
#define AL_START_TAIL 1		// 反向迭代方向，尾--》头

#endif /* __ADLIST_H__ */

adlist.c

#include <stdlib.h>
#include "adlist.h"
#include "zmalloc.h"

/* Create a new list. The created list can be freed with
 * listRelease(), but private value of every node need to be freed
 * by the user before to call listRelease(), or by setting a free method using
 * listSetFreeMethod.
 *
 * On error, NULL is returned. Otherwise the pointer to the new list. */
list *listCreate(void)
{
    struct list *list;
	// 创建一个list对象，失败返回NULL
    if ((list = zmalloc(sizeof(*list))) == NULL)
        return NULL;
    // 初始化
    list->head = list->tail = NULL;
    list->len = 0;
    list->dup = NULL;
    list->free = NULL;
    list->match = NULL;
    return list;
}

/* Remove all the elements from the list without destroying the list itself. */
/* 释放链表，但不释放list对象的空间 */ 
void listEmpty(list *list)
{
    unsigned long len;
    listNode *current, *next;

    current = list->head;
    len = list->len;
    while(len--) {
        next = current->next;
        // 若对象定义了释放函数，逐个释放对象
        if (list->free) list->free(current->value);	
        // 释放链表节点
        zfree(current);
        current = next;
    }
    // list信息置初始值
    list->head = list->tail = NULL;
    list->len = 0;
}

/* Free the whole list.
 *
 * This function can't fail. */
/* 释放链表和list，释放空间，该函数不可能失败 */
void listRelease(list *list)
{
	// 释放链表节点，list信息初始化
    listEmpty(list);
    // 释放list
    zfree(list);
}

/* 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;
    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, 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;
    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;
}

/* 在old_value的前面后者后面插入节点 */
list *listInsertNode(list *list, listNode *old_node, void *value, int after) {
    listNode *node;

    if ((node = zmalloc(sizeof(*node))) == NULL)
        return NULL;
    node->value = value;
    // 判断是前插入还是后插入，此处只更新了一半指针
    if (after) {
        node->prev = old_node;
        node->next = old_node->next;
        // 判断插入位置是不是队尾
        if (list->tail == old_node) {
            list->tail = node;
        }
    } else {
        node->next = old_node;
        node->prev = old_node->prev;
        // 判断插入位置是不是队头
        if (list->head == old_node) {
            list->head = node;
        }
    }
    // 更新前驱和后继
    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)
{
	// 有无前驱，处理不同
    if (node->prev)
        node->prev->next = node->next;
    else
        list->head = node->next;
    // 有无后继，处理不同
    if (node->next)
        node->next->prev = node->prev;
    else
        list->tail = node->prev;
    // 释放节点信息，和节点
    if (list->free) list->free(node->value);
    zfree(node);
    // 计数减一
    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;
	// 构造迭代器
    if ((iter = zmalloc(sizeof(*iter))) == NULL) return NULL;
    // 根据迭代方向，分别复制头结点或尾结点
    if (direction == AL_START_HEAD)
        iter->next = list->head;
    else
        iter->next = list->tail;
    // 赋值迭代方向
    iter->direction = direction;
    return iter;
}

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

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

/* 重置反向迭代器 */
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;
	
	// 更新迭代器指向的节点，next根据迭代方向获取下一个，prev或next
    if (current != NULL) {
        if (iter->direction == AL_START_HEAD)
            iter->next = current->next;
        else
            iter->next = current->prev;
    }
    // 返回当前
    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;

	// 构造复制list的结构，失败返回NULL
    if ((copy = listCreate()) == NULL)
        return NULL;
    // 基础属性赋值
    copy->dup = orig->dup;
    copy->free = orig->free;
    copy->match = orig->match;
    // 重绑定正向迭代器
    listRewind(orig, &iter);
    // 顺序获取链表上每个节点，并复制该节点
    while((node = listNext(&iter)) != NULL) {
        void *value;
		// 如果存在复制函数，则使用
        if (copy->dup) {
            value = copy->dup(node->value);
            // 复制函数执行失败，返回NULL，整体复制不成功
            if (value == NULL) {
                listRelease(copy);
                return NULL;
            }
        } else 
            value = node->value;
        // 将复制的节点添加在复制list的尾部，如果添加失败，整体失败，返回NULL
        if (listAddNodeTail(copy, value) == NULL) {
            listRelease(copy);
            return NULL;
        }
    }
    return copy;
}

/* 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);
    // 正向迭代器遍历所有节点，查找Key，如果有match函数，用match函数进行匹配
    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;
}

/* 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 penultimate
 * and so on. If the index is out of range NULL is returned. */
listNode *listIndex(list *list, long index) {
    listNode *n;
	// 如果index < 0，则认为是反向迭代，从-1开始
    if (index < 0) {
        index = (-index)-1;
        n = list->tail;
        while(index-- && n) n = n->prev;
    // 如果index > 0，则认为是正向迭代，从0开始
    } else {
        n = list->head;
        while(index-- && n) n = n->next;
    }
    return n;
}

/* Rotate the list removing the tail node and inserting it to the head. */
/* 旋转尾结点到头结点，调用一次，旋转一个节点 */
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;
}

/* Add all the elements of the list 'o' at the end of the
 * list 'l'. The list 'other' remains empty but otherwise valid. */
/* 将o的所有节点添加在l的尾部 */
void listJoin(list *l, list *o) {
    if (o->head)
        o->head->prev = l->tail;
        
	// 如果l的长度非0
    if (l->tail)
        l->tail->next = o->head;
    else
        l->head = o->head;

	// 如果o的长度非0
    if (o->tail) l->tail = o->tail;
    l->len += o->len;

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