//添加or替换，如果key不存在就执行添加操作，返回1
//如果key存在更新value的值，返回0
int dictReplace(dict *d, void *key, void *val)
{
dictEntry *entry, auxentry;
/* Try to add the element. If the key
* does not exists dictAdd will suceed. */
//只有在这个key存在的情况下，才会返回DICT_ERR，所以如果返回为DICT_OK，
//说明key不存在，并且添加成功.
if (dictAdd(d, key, val) == DICT_OK)
return 1;
/* It already exists, get the entry */
entry = dictFind(d, key);
/* Set the new value and free the old one. Note that it is important
* to do that in this order, as the value may just be exactly the same
* as the previous one. In this context, think to reference counting,
* you want to increment (set), and then decrement (free), and not the
* reverse. */
auxentry = *entry;
//!!!这里有个疑问，这里说明必须首先设置然后再释放，但是执行了设置操作之后
//该entry的值为新的value（可能是覆盖），接下来的释放操作如果将它free了呢？
//也就是该哈希表的valDup函数为NULL，但是ValDestructor函数将free这个entry的value
//那么这就编程了一个空悬指针!!!
//有待加深理解。。。
//既然作者的注释说明这样的顺序是防止两个value为同一个对象并且使用了引用计数，
//如果这样可以简单的进行判断是否指向同一个对象，如果是直接返回
//不知道我这样理解是否违反了作者的意图~~~
dictSetVal(d, entry, val);
dictFreeVal(d, &auxentry);
return 0;
}
/* 删除字典中指定的哈希表
*
* Destroy an entire dictionary
*
* Args:
* d 被删除的哈希表所属的字典
* ht 被删除的哈希表
*
* Returns:
* DICT_OK 删除成功(这个函数不可能失败)
*/
int _dictClear(dict *d, dictht *ht)
{
unsigned long i;
// 遍历整个哈希表，删除所有节点链
/* Free all the elements */
for (i = 0; i < ht->size && ht->used > 0; i++) {
dictEntry *he, *nextHe;
// 碰到空节点链，跳到下一个节点链去
if ((he = ht->table[i]) == NULL) continue;
// 如果节点链非空，就遍历删除所有节点
while(he) {
nextHe = he->next;
dictFreeKey(d, he); // 释放 key 空间
dictFreeVal(d, he); // 释放 value 空间
zfree(he); // 释放节点
ht->used--; // 减少计数器
he = nextHe;
}
}
// 释放哈希表节点指针数组的空间
/* Free the table and the allocated cache structure */
zfree(ht->table);
// 并重置(清空)哈希表各项属性
/* Re-initialize the table */
_dictReset(ht);
return DICT_OK; /* never fails */
}
/* Destroy an entire dictionary */
int _dictClear(dict *d, dictht *ht)
{
#ifdef _WIN32
size_t i;
#else
unsigned long i;
#endif
/* Free all the elements */
for (i = 0; i < ht->size && ht->used > 0; i++) {
dictEntry *he, *nextHe;
if ((he = ht->table[i]) == NULL) continue;
while(he) {
nextHe = he->next;
dictFreeKey(d, he);
dictFreeVal(d, he);
zfree(he);
ht->used--;
he = nextHe;
}
}
/* Free the table and the allocated cache structure */
zfree(ht->table);
/* Re-initialize the table */
_dictReset(ht);
return DICT_OK; /* never fails */
}
/* 删除指定元素的底层实现代码
*
* Args:
* d
* key
* nofree 指示是否释放被删除元素的键和值
*
* Returns:
* DICT_ERR 字典为空，删除失败
* DICT_OK 删除成功
*/
static int dictGenericDelete(dict *d, const void *key, int nofree)
{
unsigned int h, idx;
dictEntry *he, *prevHe;
int table;
// 字典为空，删除失败
if (d->ht[0].size == 0)
return DICT_ERR;
// 平摊 rehash
if (dictIsRehashing(d))
_dictRehashStep(d);
// 哈希值
h = dictHashKey(d, key);
// 遍历
for (table = 0; table <= 1; table++) {
idx = h & d->ht[table].sizemask; // 地址索引
he = d->ht[table].table[idx]; // 表头节点
prevHe = NULL;
while(he) {
if (dictCompareKeys(d, key, he->key)) {
/* Unlink the element from the list */
if (prevHe)
prevHe->next = he->next;
else
d->ht[table].table[idx] = he->next;
if (!nofree) {
dictFreeKey(d, he);
dictFreeVal(d, he);
}
zfree(he);
d->ht[table].used--;
return DICT_OK;
}
// 推进指针
prevHe = he;
he = he->next;
}
if (!dictIsRehashing(d)) break;
}
return DICT_ERR; /* not found */
}
/* 将新元素添加到字典，如果 key 已经存在，那么新元素覆盖旧元素。
*
* Args:
* d
* key 新元素的关键字
* val 新元素的值
*
* Return:
* 1 key 不存在，新建元素添加成功
* 0 key 已经存在，旧元素被新元素覆盖
*/
int dictReplace(dict *d, void *key, void *val)
{
dictEntry *entry, auxentry;
// 尝试添加元素，如果 key 不存在， 那么 dictAdd 完成工作
if (dictAdd(d, key, val) == DICT_OK)
return 1;
// dictAdd 不成功，说明 key 已经存在
// 找出这个元素并更新它的值
entry = dictFind(d, key);
auxentry = *entry; // 用变量保存 entry 的引用
dictSetVal(d, entry, val); // 设置新值
dictFreeVal(d, &auxentry); // 释放旧值
return 0;
}
/* Add an element, discarding the old if the key already exists.
* Return 1 if the key was added from scratch, 0 if there was already an
* element with such key and dictReplace() just performed a value update
* operation. */
int dictReplace(dict *d, void *key, void *val)
{
dictEntry *entry, auxentry;
/* Try to add the element. If the key
* does not exists dictAdd will suceed. */
if (dictAdd(d, key, val) == DICT_OK)
return 1;
/* It already exists, get the entry */
entry = dictFind(d, key);
/* Set the new value and free the old one. Note that it is important
* to do that in this order, as the value may just be exactly the same
* as the previous one. In this context, think to reference counting,
* you want to increment (set), and then decrement (free), and not the
* reverse. */
auxentry = *entry;
dictSetVal(d, entry, val);
dictFreeVal(d, &auxentry);
return 0;
}