Redis之2-双端链表（adlist.c,adlist.h）

adlist.c 、 adlist.h 双端链表数据结构的实现。

下面的注释来源于大牛博客，这里不重复造轮子，仅仅来说说我觉得比较不一样的地方以及设计的很棒的地方：

1.整个实现使用了函数式编程思想，使用了函数指针

2.将抽象的指针操作用宏定义封装重命名便于阅读

3.自己实现迭代器，可定义方向

4.设计了自己的内存分配和释放函数

5.在list内部留有了可用于自己实现复制和释放的函数通用式接口，但

暂时没想到为什么要留下这个接口

6.使用define条件编译选项，可避免重复包含**

/* adlist.h - A generic doubly linked list implementation
*
* Copyright (c) 2006-2012, Salvatore Sanfilippo <antirez at gmail dot com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
*   * Redistributions of source code must retain the above copyright notice,
*     this list of conditions and the following disclaimer.
*   * Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in the
*     documentation and/or other materials provided with the distribution.
*   * Neither the name of Redis nor the names of its contributors may be used
*     to endorse or promote products derived from this software without
*     specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/

#ifndef __ADLIST_H__
#define __ADLIST_H__

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

/*
* 双端链表节点
*/
typedef struct listNode {

// 前置节点
struct listNode *prev;

// 后置节点
struct listNode *next;

// 节点的值
void *value;

} listNode;

/*
* 双端链表迭代器
*/
typedef struct listIter {

// 当前迭代到的节点
listNode *next;

// 迭代的方向
int direction;

} listIter;

/*
* 双端链表结构
*/
typedef struct list {

// 表头节点
listNode *head;

// 表尾节点
listNode *tail;

// 节点值复制函数
void *(*dup)(void *ptr);

// 节点值释放函数
void (*free)(void *ptr);

// 节点值对比函数
int (*match)(void *ptr, void *key);

// 链表所包含的节点数量
unsigned long len;

} list;

/* Functions implemented as macros */
// 返回给定链表所包含的节点数量
// T = O(1)
#define listLength(l) ((l)->len)
// 返回给定链表的表头节点
// T = O(1)
#define listFirst(l) ((l)->head)
// 返回给定链表的表尾节点
// T = O(1)
#define listLast(l) ((l)->tail)
// 返回给定节点的前置节点
// T = O(1)
#define listPrevNode(n) ((n)->prev)
// 返回给定节点的后置节点
// T = O(1)
#define listNextNode(n) ((n)->next)
// 返回给定节点的值
// T = O(1)
#define listNodeValue(n) ((n)->value)

// 将链表 l 的值复制函数设置为 m
// T = O(1)
#define listSetDupMethod(l,m) ((l)->dup = (m))
// 将链表 l 的值释放函数设置为 m
// T = O(1)
#define listSetFreeMethod(l,m) ((l)->free = (m))
// 将链表的对比函数设置为 m
// T = O(1)
#define listSetMatchMethod(l,m) ((l)->match = (m))

// 返回给定链表的值复制函数
// T = O(1)
#define listGetDupMethod(l) ((l)->dup)
// 返回给定链表的值释放函数
// T = O(1)
#define listGetFree(l) ((l)->free)
// 返回给定链表的值对比函数
// T = O(1)
#define listGetMatchMethod(l) ((l)->match)

/* Prototypes */
list *listCreate(void);
void listRelease(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 listRotate(list *list);

/* Directions for iterators
*
* 迭代器进行迭代的方向
*/
// 从表头向表尾进行迭代
#define AL_START_HEAD 0
// 从表尾到表头进行迭代
#define AL_START_TAIL 1

#endif /* __ADLIST_H__ */

下面是实现文件

/* adlist.c - A generic doubly linked list implementation
*
* Copyright (c) 2006-2010, Salvatore Sanfilippo <antirez at gmail dot com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
*   * Redistributions of source code must retain the above copyright notice,
*     this list of conditions and the following disclaimer.
*   * Redistributions in binary form must reproduce the above copyright
*     notice, this list of conditions and the following disclaimer in the
*     documentation and/or other materials provided with the distribution.
*   * Neither the name of Redis nor the names of its contributors may be used
*     to endorse or promote products derived from this software without
*     specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/

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

/* 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. */
/*
* 创建一个新的链表
*
* 创建成功返回链表，失败返回 NULL 。
*
* T = O(1)
*/
list *listCreate(void)
{
struct list *list;

// 分配内存
if ((list = zmalloc(sizeof(*list))) == NULL)
return NULL;

// 初始化属性
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. */
/*
* 释放整个链表，以及链表中所有节点
*
* T = O(N)
*/
void listRelease(list *list)
{
unsigned long len;
listNode *current, *next;

// 指向头指针
current = list->head;
// 遍历整个链表
len = list->len;
while(len--) {
next = current->next;

// 如果有设置值释放函数，那么调用它
if (list->free) list->free(current->value);

// 释放节点结构
zfree(current);

current = next;
}

// 释放链表结构
zfree(list);
}

/* 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. */
/*
* 将一个包含有给定值指针 value 的新节点添加到链表的表头
*
* 如果为新节点分配内存出错，那么不执行任何动作，仅返回 NULL
*
* 如果执行成功，返回传入的链表指针
*
* T = O(1)
*/
list *listAddNodeHead(list *list, void *value)
{
listNode *node;

// 为节点分配内存
if ((node = zmalloc(sizeof(*node))) == NULL)
return NULL;

// 保存值指针
node->value = value;

// 添加节点到空链表
if (list->len == 0) {
list->head = list->tail = node;
node->prev = node->next = NULL;
// 添加节点到非空链表
} else {
node->prev = NULL;
node->next = list->head;
list->head->prev = node;
list->head = node;
}

// 更新链表节点数
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. */
/*
* 将一个包含有给定值指针 value 的新节点添加到链表的表尾
*
* 如果为新节点分配内存出错，那么不执行任何动作，仅返回 NULL
*
* 如果执行成功，返回传入的链表指针
*
* T = O(1)
*/
list *listAddNodeTail(list *list, void *value)
{
listNode *node;

// 为新节点分配内存
if ((node = zmalloc(sizeof(*node))) == NULL)
return NULL;

// 保存值指针
node->value = value;

// 目标链表为空
if (list->len == 0) {
list->head = list->tail = node;
node->prev = node->next = NULL;
// 目标链表非空
} else {
node->prev = list->tail;
node->next = NULL;
list->tail->next = node;
list->tail = node;
}

// 更新链表节点数
list->len++;

return list;
}

/*
* 创建一个包含值 value 的新节点，并将它插入到 old_node 的之前或之后
*
* 如果 after 为 0 ，将新节点插入到 old_node 之前。
* 如果 after 为 1 ，将新节点插入到 old_node 之后。
*
* T = O(1)
*/
list *listInsertNode(list *list, listNode *old_node, void *value, int after) {
listNode *node;

// 创建新节点
if ((node = zmalloc(sizeof(*node))) == NULL)
return NULL;

// 保存值
node->value = value;

// 将新节点添加到给定节点之后
if (after) {
node->prev = old_node;
node->next = old_node->next;
// 给定节点是原表尾节点
if (list->tail == old_node) {
list->tail = node;
}
// 将新节点添加到给定节点之前
} else {
node->next = old_node;
node->prev = old_node->prev;
// 给定节点是原表头节点
if (list->head == old_node) {
list->head = node;
}
}

// 更新新节点的前置指针
if (node->prev != NULL) {
node->prev->next = node;
}
// 更新新节点的后置指针
if (node->next != NULL) {
node->next->prev = node;
}

// 更新链表节点数
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. */
/*
* 从链表 list 中删除给定节点 node
*
* 对节点私有值(private value of the node)的释放工作由调用者进行。
*
* T = O(1)
*/
void listDelNode(list *list, listNode *node)
{
// 调整前置节点的指针
if (node->prev)
node->prev->next = node->next;
else
list->head = node->next;

// 调整后置节点的指针
if (node->next)
node->next->prev = node->prev;
else
list->tail = node->prev;

// 释放值
if (list->free) list->free(node->value);

// 释放节点
zfree(node);

// 链表数减一
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. */
/*
* 为给定链表创建一个迭代器，
* 之后每次对这个迭代器调用 listNext 都返回被迭代到的链表节点
*
* direction 参数决定了迭代器的迭代方向：
*  AL_START_HEAD ：从表头向表尾迭代
*  AL_START_TAIL ：从表尾想表头迭代
*
* T = O(1)
*/
listIter *listGetIterator(list *list, int direction)
{
// 为迭代器分配内存
listIter *iter;
if ((iter = zmalloc(sizeof(*iter))) == NULL) return NULL;

// 根据迭代方向，设置迭代器的起始节点
if (direction == AL_START_HEAD)
iter->next = list->head;
else
iter->next = list->tail;

// 记录迭代方向
iter->direction = direction;

return iter;
}

/* Release the iterator memory */
/*
* 释放迭代器
*
* T = O(1)
*/
void listReleaseIterator(listIter *iter) {
zfree(iter);
}

/* Create an iterator in the list private iterator structure */
/*
* 将迭代器的方向设置为 AL_START_HEAD ，
* 并将迭代指针重新指向表头节点。
*
* T = O(1)
*/
void listRewind(list *list, listIter *li) {
li->next = list->head;
li->direction = AL_START_HEAD;
}

/*
* 将迭代器的方向设置为 AL_START_TAIL ，
* 并将迭代指针重新指向表尾节点。
*
* T = O(1)
*/
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));
* }
*
* */
/*
* 返回迭代器当前所指向的节点。
*
* 删除当前节点是允许的，但不能修改链表里的其他节点。
*
* 函数要么返回一个节点，要么返回 NULL ，常见的用法是：
*
* iter = listGetIterator(list,<direction>);
* while ((node = listNext(iter)) != NULL) {
*     doSomethingWith(listNodeValue(node));
* }
*
* T = O(1)
*/
listNode *listNext(listIter *iter)
{
listNode *current = iter->next;

if (current != NULL) {
// 根据方向选择下一个节点
if (iter->direction == AL_START_HEAD)
// 保存下一个节点，防止当前节点被删除而造成指针丢失
iter->next = current->next;
else
// 保存下一个节点，防止当前节点被删除而造成指针丢失
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. */
/*
* 复制整个链表。
*
* 复制成功返回输入链表的副本，
* 如果因为内存不足而造成复制失败，返回 NULL 。
*
* 如果链表有设置值复制函数 dup ，那么对值的复制将使用复制函数进行，
* 否则，新节点将和旧节点共享同一个指针。
*
* 无论复制是成功还是失败，输入节点都不会修改。
*
* T = O(N)
*/
list *listDup(list *orig)
{
list *copy;
listIter *iter;
listNode *node;

// 创建新链表
if ((copy = listCreate()) == NULL)
return NULL;

// 设置节点值处理函数
copy->dup = orig->dup;
copy->free = orig->free;
copy->match = orig->match;

// 迭代整个输入链表
iter = listGetIterator(orig, AL_START_HEAD);
while((node = listNext(iter)) != NULL) {
void *value;

// 复制节点值到新节点
if (copy->dup) {
value = copy->dup(node->value);
if (value == NULL) {
listRelease(copy);
listReleaseIterator(iter);
return NULL;
}
} else
value = node->value;

// 将节点添加到链表
if (listAddNodeTail(copy, value) == NULL) {
listRelease(copy);
listReleaseIterator(iter);
return NULL;
}
}

// 释放迭代器
listReleaseIterator(iter);

// 返回副本
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. */
/*
* 查找链表 list 中值和 key 匹配的节点。
*
* 对比操作由链表的 match 函数负责进行，
* 如果没有设置 match 函数，
* 那么直接通过对比值的指针来决定是否匹配。
*
* 如果匹配成功，那么第一个匹配的节点会被返回。
* 如果没有匹配任何节点，那么返回 NULL 。
*
* T = O(N)
*/
listNode *listSearchKey(list *list, void *key)
{
listIter *iter;
listNode *node;

// 迭代整个链表
iter = listGetIterator(list, AL_START_HEAD);
while((node = listNext(iter)) != NULL) {

// 对比
if (list->match) {
if (list->match(node->value, key)) {
listReleaseIterator(iter);
// 找到
return node;
}
} else {
if (key == node->value) {
listReleaseIterator(iter);
// 找到
return node;
}
}
}

listReleaseIterator(iter);

// 未找到
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. */
/*
* 返回链表在给定索引上的值。
*
* 索引以 0 为起始，也可以是负数， -1 表示链表最后一个节点，诸如此类。
*
* 如果索引超出范围（out of range），返回 NULL 。
*
* T = O(N)
*/
listNode *listIndex(list *list, long index) {
listNode *n;

// 如果索引为负数，从表尾开始查找
if (index < 0) {
index = (-index)-1;
n = list->tail;
while(index-- && n) n = n->prev;
// 如果索引为正数，从表头开始查找
} 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. */
/*
* 取出链表的表尾节点，并将它移动到表头，成为新的表头节点。
*
* T = O(1)
*/
void listRotate(list *list) {
listNode *tail = list->tail;

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

/* Detach current tail */
// 取出表尾节点
list->tail = tail->prev;
list->tail->next = NULL;

/* Move it as head */
// 插入到表头
list->head->prev = tail;
tail->prev = NULL;
tail->next = list->head;
list->head = tail;
}