dict代表整个字典，内部有两个dictht, 以实现增量hash（将ht[0]中的值rehash到ht[1]中），
rehashidx是下一个需要rehash的项在ht[0]中的索引，不需要rehash时置为-1，
iterators记录当前dict中的迭代器数，主要是为了避免在有迭代器时rehash，在有迭代器时rehash可能会造成值的丢失或重复，
type的类型dictType是一组函数指针，表示该怎样哈希、复制、释放key，该怎样复制、释放value；
dictht中的table是一个数组+指针形式的hash表，size表hash数组(桶)的大小，used表示hash表的元素个数，这两个值与rehash、resize过程密切相关。sizemask等于size-1，这是为了方便将hash值映射到数组中。typedef struct dictEntry {
typedef struct dictEntry {
void *key;
void *val;
struct dictEntry *next;
} dictEntry;
typedef struct dictType {
unsigned int (*hashFunction)(const void *key);
void *(*keyDup)(void *privdata, const void *key);
void *(*valDup)(void *privdata, const void *obj);
int (*keyCompare)(void *privdata, const void *key1, const void *key2);
void (*keyDestructor)(void *privdata, void *key);
void (*valDestructor)(void *privdata, void *obj);
} 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. */
#ifdef _WIN32
typedef struct dictht {
dictEntry **table;
size_t size;
size_t sizemask;
size_t used;
} dictht;
#else
typedef struct dictht {
dictEntry **table;
unsigned long size;
unsigned long sizemask;
unsigned long used;
} dictht;
#endif
typedef struct dict {
dictType *type;
void *privdata;
dictht ht[2];
int rehashidx; /* rehashing not in progress if rehashidx == -1 */
int iterators; /* number of iterators currently running */
} dict;
/* If safe is set to 1 this is a safe iteartor, that means, you can call
* dictAdd, dictFind, and other functions against the dictionary even while
* iterating. Otherwise it is a non safe iterator, and only dictNext()
* should be called while iterating. */
typedef struct dictIterator {
dict *d;
int table, index, safe;
dictEntry *entry, *nextEntry;
} dictIterator;
/* This is the initial size of every hash table */
#define DICT_HT_INITIAL_SIZE 4
/* ------------------------------- Macros ------------------------------------*/
#define dictFreeEntryVal(d, entry) \
if ((d)->type->valDestructor) \
(d)->type->valDestructor((d)->privdata, (entry)->val)
#define dictSetHashVal(d, entry, _val_) do { \
if ((d)->type->valDup) \
entry->val = (d)->type->valDup((d)->privdata, _val_); \
else \
entry->val = (_val_); \
} while(0)
#define dictFreeEntryKey(d, entry) \
if ((d)->type->keyDestructor) \
(d)->type->keyDestructor((d)->privdata, (entry)->key)
#define dictSetHashKey(d, entry, _key_) do { \
if ((d)->type->keyDup) \
entry->key = (d)->type->keyDup((d)->privdata, _key_); \
else \
entry->key = (_key_); \
} while(0)
#define dictCompareHashKeys(d, key1, key2) \
(((d)->type->keyCompare) ? \
(d)->type->keyCompare((d)->privdata, key1, key2) : \
(key1) == (key2))
#define dictHashKey(d, key) (d)->type->hashFunction(key)
#define dictGetEntryKey(he) ((he)->key)
#define dictGetEntryVal(he) ((he)->val)
#define dictSlots(d) ((d)->ht[0].size+(d)->ht[1].size)
#define dictSize(d) ((d)->ht[0].used+(d)->ht[1].used)
#define dictIsRehashing(ht) ((ht)->rehashidx != -1)
/* API */
dict *dictCreate(dictType *type, void *privDataPtr);
#ifdef _WIN32
int dictExpand(dict *d, size_t size);
#else
int dictExpand(dict *d, unsigned long size);
#endif
int dictAdd(dict *d, void *key, void *val);
int dictReplace(dict *d, void *key, void *val);
int dictDelete(dict *d, const void *key);
int dictDeleteNoFree(dict *d, const void *key);
void dictRelease(dict *d);
dictEntry * dictFind(dict *d, const void *key);
void *dictFetchValue(dict *d, const void *key);
int dictResize(dict *d);
dictIterator *dictGetIterator(dict *d);
dictIterator *dictGetSafeIterator(dict *d);
dictEntry *dictNext(dictIterator *iter);
void dictReleaseIterator(dictIterator *iter);
dictEntry *dictGetRandomKey(dict *d);
void dictPrintStats(dict *d);
unsigned int dictGenHashFunction(const unsigned char *buf, int len);
unsigned int dictGenCaseHashFunction(const unsigned char *buf, int len);
void dictEmpty(dict *d);
void dictEnableResize(void);
void dictDisableResize(void);
int dictRehash(dict *d, int n);
int dictRehashMilliseconds(dict *d, int ms);
/* Hash table types */
extern dictType dictTypeHeapStringCopyKey;
extern dictType dictTypeHeapStrings;
extern dictType dictTypeHeapStringCopyKeyValue;