typedef struct dictEntry {//字典的节点
    void *key;
    union {//使用的联合体
        void *val;
        uint64_t u64;//这两个参数很有用
        int64_t s64;
    } v;
    struct dictEntry *next;//下一个节点指针
} dictEntry;

typedef struct dictType {
    unsigned int (*hashFunction)(const void *key); //hash函数指针
    void *(*keyDup)(void *privdata, const void *key); //键复制函数指针
    void *(*valDup)(void *privdata, const void *obj); //值复制函数指针
    int (*keyCompare)(void *privdata, const void *key1, const void *key2); //键比较函数指针
    void (*keyDestructor)(void *privdata, void *key); //键构造函数指针
    void (*valDestructor)(void *privdata, void *obj); //值构造函数指针
} dictType;

/* This is our hash table structure. Every dictionary has two of this as we
 * implement incremental rehashing, for the old to the new table. */
typedef struct dictht { //字典hash table
    dictEntry **table;//可以看做字典数组，俗称桶bucket
    unsigned long size; //指针数组的大小，即桶的层数
    unsigned long sizemask;
    unsigned long used; //字典中当前的节点数目
} dictht;

typedef struct dict {
    dictType *type;
    void *privdata; //私有数据
    dictht ht[2];   //两个hash table
    int rehashidx; /* rehashing not in progress if rehashidx == -1 */ //rehash 索引
    int iterators; /* number of iterators currently running */ //当前该字典迭代器个数
} dict;

/* Expand or create the hash table */
int dictExpand(dict *d, unsigned long size)
{
    dictht n; /* the new hash table */
    unsigned long realsize = _dictNextPower(size); //得到需要扩展到的size

    /* the size is invalid if it is smaller than the number of
     * elements already inside the hash table */
    if (dictIsRehashing(d) || d->ht[0].used > size)
        return DICT_ERR;

    /* Allocate the new hash table and initialize all pointers to NULL */
    n.size = realsize;
    n.sizemask = realsize-1;
    n.table = zcalloc(realsize * sizeof(dictEntry*));
    n.used = 0;

    /* Is this the first initialization? If so it's not really a rehashing
     * we just set the first hash table so that it can accept keys. */
    if (d->ht[0].table == NULL) {
        d->ht[0] = n;
        return DICT_OK;
    }

    /* Prepare a second hash table for incremental rehashing */
    //准备渐进式rehash，rehash的字典table为0号
    d->ht[1] = n;
    d->rehashidx = 0;
    return DICT_OK;
}

/* Expand the hash table if needed */
static int _dictExpandIfNeeded(dict *d)
{
    /* Incremental rehashing already in progress. Return. */
    if (dictIsRehashing(d)) return DICT_OK;

    // 如果哈希表为空，那么将它扩展为初始大小
    if (d->ht[0].size == 0) return dictExpand(d, DICT_HT_INITIAL_SIZE);

    /*如果哈希表的已用节点数 >= 哈希表的大小，并且以下条件任一个为真：
       1) dict_can_resize 为真
       2) 已用节点数除以哈希表大小之比大于 dict_force_resize_ratio
       那么调用 dictExpand 对哈希表进行扩展,扩展的体积至少为已使用节点数的两倍
    */
    if (d->ht[0].used >= d->ht[0].size &&
        (dict_can_resize ||
         d->ht[0].used/d->ht[0].size > dict_force_resize_ratio))
    {
        return dictExpand(d, d->ht[0].used*2);
    }
    return DICT_OK;
}

static int _dictKeyIndex(dict *d, const void *key)
{
    unsigned int h, idx, table;
    dictEntry *he;

    /* Expand the hash table if needed */
    if (_dictExpandIfNeeded(d) == DICT_ERR)
        return -1;
    /* Compute the key hash value */
    h = dictHashKey(d, key);//通过hash函数得到key所在的bucket索引位置
    //查找在现有字典中是否出现了该key
    for (table = 0; table <= 1; table++) {
        idx = h & d->ht[table].sizemask;
        /* Search if this slot does not already contain the given key */
        he = d->ht[table].table[idx];
        while(he) {
            if (dictCompareKeys(d, key, he->key))
                return -1;
            he = he->next;
        }
        //如果系统没在rehash则不需要查找ht[1]
        if (!dictIsRehashing(d)) break;
    }
    return idx;
}

dictEntry *dictAddRaw(dict *d, void *key)
{
    int index;
    dictEntry *entry;
    dictht *ht;

    if (dictIsRehashing(d)) _dictRehashStep(d);// 尝试渐进式地 rehash 桶中一组元素

    /* Get the index of the new element, or -1 if
     * the element already exists. */
    // 查找可容纳新元素的索引位置,如果元素已存在， index 为 -1
    if ((index = _dictKeyIndex(d, key)) == -1)
        return NULL;

    /* Allocate the memory and store the new entry */
    ht = dictIsRehashing(d) ? &d->ht[1] : &d->ht[0];
    // 决定该把新元素放在那个哈希表
    entry = zmalloc(sizeof(*entry));
    //头插法，插入节点
    entry->next = ht->table[index];
    ht->table[index] = entry;
    ht->used++;

    /* Set the hash entry fields. */
    dictSetKey(d, entry, key);//关联起key
    return entry;
}

/* Add an element to the target hash table */
//添加一个元素
int dictAdd(dict *d, void *key, void *val)
{
    dictEntry *entry = dictAddRaw(d,key);

    if (!entry) return DICT_ERR;
    dictSetVal(d, entry, val);//关联起value
    return DICT_OK;
}

int dictRehash(dict *d, int n) {
    if (!dictIsRehashing(d)) return 0;

    while(n--) {
        dictEntry *de, *nextde;

        /* Check if we already rehashed the whole table... */
        if (d->ht[0].used == 0) {//已经完成
            zfree(d->ht[0].table);//释放ht[0].table
            d->ht[0] = d->ht[1]; //这里ht[0]与ht[1]都不是指针，直接赋值就替换了
            _dictReset(&d->ht[1]);//将ht[1].table设置为null
            d->rehashidx = -1;
            return 0;
        }

        /* Note that rehashidx can't overflow as we are sure there are more
         * elements because ht[0].used != 0 */
        assert(d->ht[0].size > (unsigned)d->rehashidx);
        //找到第一个不为空的数组
        while(d->ht[0].table[d->rehashidx] == NULL) d->rehashidx++;
        //指向该链表头
        de = d->ht[0].table[d->rehashidx];
        /* Move all the keys in this bucket from the old to the new hash HT */
        while(de) {//遍历链表
            unsigned int h;

            nextde = de->next;
            /* Get the index in the new hash table */
            //得到在ht[1]中的索引号，通过相应的hash函数
            h = dictHashKey(d, de->key) & d->ht[1].sizemask;

            // 添加节点到 ht[1] ，调整指针，采用的是头插法
            de->next = d->ht[1].table[h];
            d->ht[1].table[h] = de;
            d->ht[0].used--;
            d->ht[1].used++;
            de = nextde;
        }
        d->ht[0].table[d->rehashidx] = NULL;//设置为空
        d->rehashidx++;
    }
    return 1;
}