Redis源码笔记二: adlist

/* 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. */

typedef struct listNode {
    /* 前驱节点 */
    struct listNode *prev;    

    /* 后继节点 */
    struct listNode *next;

    /* 值 */
    void *value;
} listNode;/* 双链表节点 */

typedef struct listIter {    
    /* 下一节点 */
    listNode *next;

    /* 迭代方向 */
    int direction;
} listIter;/* 迭代器 */

typedef struct list {
    /* 表头指针 */
    listNode *head;

    /* 表尾指针 */
    listNode *tail;

    /* 复制函数 */
    void *(*dup)(void *ptr);

    /* 释放函数 */
    void (*free)(void *ptr);

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

    /* 节点数量 */
    unsigned long len;
} list;/* 双链表 */

/* 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 listGetFree(l) ((l)->free)
#define listGetMatchMethod(l) ((l)->match)

/* Prototypes */

/* 创建一个新链表 */
list *listCreate(void);

/* 释放一个新链表,以及该链表包含的节点 */
void listRelease(list *list);

/* 将一个包含给定值的节点添加到链表的表头  */
list *listAddNodeHead(list *list, void *value);

/* 将一个包含给定值的节点添加到链表的表尾 */
list *listAddNodeTail(list *list, void *value);

/* 将一个包含给定值的节点添加到某个节点的之前或之后 */
list *listInsertNode(list *list, listNode *old_node, void *value, int after);

/* 删除给定节点 */
void listDelNode(list *list, listNode *node);


/* 创建一个列表迭代器 */
listIter *listGetIterator(list *list, int direction);

/* 取出迭代器当前指向的节点 */
listNode *listNext(listIter *iter);

/* 释放迭代器 */
void listReleaseIterator(listIter *iter);

/* 创建一个给定链表的副本 */
list *listDup(list *orig);

/* 在链表中查找和给定key匹配的节点 */
listNode *listSearchKey(list *list, void *key);

/* 给据给定索引,返回列表中相应的节点 */
listNode *listIndex(list *list, long index);

/* 将迭代器的指针指向表头 */
void listRewind(list *list, listIter *li);

/* 将迭代器的指针指向表尾 */
void listRewindTail(list *list, listIter *li);

/* 取出链表的表尾节点,将它插入到表头 */
void listRotate(list *list);

/* Directions for iterators */
#define AL_START_HEAD 0
#define AL_START_TAIL 1

#endif /* __ADLIST_H__ */

/* 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. */
list *listCreate(void)
{
    struct list *list;

    if ((list = zmalloc(sizeof(*list))) == NULL)
        return NULL;

    /* 更新属性 */
    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. */
void listRelease(list *list)
{
    unsigned long len;
    listNode *current, *next;

    current = list->head;
    len = list->len;
    while(len--) {
        next = current->next;

        /* 如果列表有自带的free方法,那么先对节点调用它 */
        if (list->free) list->free(current->value);

        /* 之后释放节点 */
        zfree(current);
        current = next;
    }
    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. */
list *listAddNodeHead(list *list, void *value)
{
    listNode *node;

    if ((node = zmalloc(sizeof(*node))) == NULL)
        return NULL;
    node->value = value;

    /* 节点为0时,更新属性 */
    if (list->len == 0) {
        list->head = list->tail = node;
        node->prev = node->next = NULL;

    /* 节点不为0时,更新属性 */
    } else {
        node->prev = NULL;
        node->next = list->head;
        list->head->prev = node;
        list->head = node;
    }

    /* 更新节点数量 */
    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;

    /* 节点为0时,更新属性 */
    if (list->len == 0) {
        list->head = list->tail = node;
        node->prev = node->next = NULL;
    }else {    /* 节点不为0时,更新属性 */
        node->prev = list->tail;
        node->next = NULL;
        list->tail->next = node;
        list->tail = node;
    }

    /* 更新节点数量 */
    list->len++;
   
       return list;
}

/* 创建一个包含值value的节点,并根据after参数的指示,将新节点插入到old_node的之前或之后 */
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) {
        /* 将node插入到old_node之后 */
        node->prev = old_node;            
        node->next = old_node->next;    

        /* 处理表尾节点 */
        if (list->tail == old_node) {    
            list->tail = node;
        }
    } else {
        /* 将node插入到old_node之前 */
        node->next = old_node;            
        node->prev = old_node->prev;    

        /* 处理表头节点 */
        if (list->head == old_node) {    
            list->head = node;            
        }
    }

    /* 更新前置节点和后继节点的指针 */
    if (node->prev != NULL) {
        node->prev->next = node;
    }
    if (node->next != NULL) {
        node->next->prev = node;
    }

    /* 更新列表节点 */
    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. */
/* 释放列表中给定的节点 */
void listDelNode(list *list, listNode *node)
{
    /* 处理前驱节点 */
    if (node->prev)
        node->prev->next = node->next;
    else
        list->head = node->next;

    /* 处理后继节点 */
    if (node->next)
        node->next->prev = node->prev;
    else
        list->tail = node->prev;

    /* 释放节点值 */
    if (list->free) list->free(node->value);

    /* 释放节点 */
    zfree(node);

    /* 更新列表节点数目  */
    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. */
 /* 创建列表list的一个迭代器, 迭代方向由direction参数决定,每次对迭代listNext(),迭代器返回列表的下一个节点 */
listIter *listGetIterator(list *list, int direction)
{
    listIter *iter;
    
    if ((iter = zmalloc(sizeof(*iter))) == NULL) return NULL;

    /* 根据迭代器方向,将迭代器的指针指向表头或表尾 */
    if (direction == AL_START_HEAD)
        iter->next = list->head;
    else
        iter->next = list->tail;

    /* 记录方向 */
    iter->direction = direction;
    return iter;
}

/* Release the iterator memory */
/* 释放迭代器的内存 */
void listReleaseIterator(listIter *iter) {
    zfree(iter);
}

/* Create an iterator in the list private iterator structure */
/* 将迭代器iter的迭代指针倒回list的表头 */
void listRewind(list *list, listIter *li) {
    li->next = list->head;
    li->direction = AL_START_HEAD;
}

/* 将迭代器iter的迭代指针倒回list的表尾 */
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));
 * }
 *
 * */
 /* 函数要么返回当前节点,要么返回NULL,因此,常见的用法为:
  * iter = listGetIterator(list, <direction>);
  * while((node = listNext(iter)) != NULL){
  *        doSomethingWith(listNodeValue(node));      
  *     }
 */
listNode *listNext(listIter *iter)
{
    listNode *current = iter->next;

    if (current != NULL) {
        /* 根据迭代方向,选择节点 */
        if (iter->direction == AL_START_HEAD)
            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. */
/* 创建一个给定链表的副本 */
list *listDup(list *orig)
{
    list *copy;
    listIter *iter;
    listNode *node;

    if ((copy = listCreate()) == NULL)
        return NULL;

    /* 更新属性 */
    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;
}

/* 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. */
 /* 在链表中查找和给定key匹配的节点 */
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;
}

/* 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. */
/* 给据给定索引,返回列表中相应的节点 */
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;
}

/* Rotate the list removing the tail node and inserting it to the head. */
/* 取出链表中的表尾节点,将它插入到表头 */
void listRotate(list *list) {
    listNode *tail = list->tail;

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

    /* Detach 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;
}