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;  
}