/* Expand or create the hash table */
int dictExpand(dict *d, unsigned long size)
{
    dictht n; /* the new hash table */
    unsigned long realsize = _dictNextPower(size); //得到需要擴充套件到的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 */
    //準備漸進式rehash，rehash的字典table為0號
    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;

    // 如果雜湊表為空，那麼將它擴充套件為初始大小
    if (d->ht[0].size == 0) return dictExpand(d, DICT_HT_INITIAL_SIZE);

    /*如果雜湊表的已用節點數 >= 雜湊表的大小，並且以下條件任一個為真：
       1) dict_can_resize 為真
       2) 已用節點數除以雜湊表大小之比大於 dict_force_resize_ratio
       那麼呼叫 dictExpand 對雜湊表進行擴充套件,擴充套件的體積至少為已使用節點數的兩倍
    */
    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);//通過hash函式得到key所在的bucket索引位置
    //查詢在現有字典中是否出現了該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;
        }
        //如果系統沒在rehash則不需要查詢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);// 嘗試漸進式地 rehash 桶中一組元素

    /* Get the index of the new element, or -1 if
     * the element already exists. */
    // 查詢可容納新元素的索引位置,如果元素已存在， index 為 -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];
    // 決定該把新元素放在那個雜湊表
    entry = zmalloc(sizeof(*entry));
    //頭插法，插入節點
    entry->next = ht->table[index];
    ht->table[index] = entry;
    ht->used++;

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

/* Add an element to the target hash table */
//新增一個元素
int dictAdd(dict *d, void *key, void *val)
{
    dictEntry *entry = dictAddRaw(d,key);

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

字典Rehash解析