3d建模软件手机版,网站seo诊断工具,网页设计一般要多少钱,网站被百度收录吗目录 dict的基本结构dict的相关操作函数底层通用的之查找插入key-value对应该放入ht表的哪个槽rehash过程 dict的基本结构
typedef struct dict {dictType *type;void *privdata;dictht ht[2];long rehashidx; /* rehashing not in progress if rehashidx -1 */unsigned long… 目录 dict的基本结构dict的相关操作函数底层通用的之查找插入key-value对应该放入ht表的哪个槽rehash过程 dict的基本结构
typedef struct dict {dictType *type;void *privdata;dictht ht[2];long rehashidx; /* rehashing not in progress if rehashidx -1 */unsigned long iterators; /* number of iterators currently running */
} dict;Redis中dict结构体包含了两个ditcht这是为了rehash。
typedef struct dictType {uint64_t (*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;提供了dictType我认为这是用C语言实现的编译时多态在创建dict时需要将dictType传入不同的dictType可以提供不同的hashFunction、keyDup、keyCompare函数。
typedef struct dictht {dictEntry **table;unsigned long size;unsigned long sizemask;unsigned long used;
} dictht;dicht的结构中有dictEntry **table这是一个指针数组可以理解为是哈希表的array部分。
typedef struct dictEntry {void *key;union {void *val;uint64_t u64;int64_t s64;double d;} v;struct dictEntry *next;
} dictEntry;这是dict中每个entry的结构除了k和不同类型的v意外还有struct dictEntry *next;体现了这是一个链哈希即如果发生哈希冲突就通过链表指针来组织起所有位于同一个哈希槽的entry。
dict的相关操作函数
底层通用的之查找插入key-value对应该放入ht表的哪个槽
/* Returns the index of a free slot that can be populated with* an hash entry for the given key.* If the key already exists, -1 is returned. */
static int _dictKeyIndex(dict *ht, const void *key) {unsigned int h;dictEntry *he;/* Expand the hashtable if needed */if (_dictExpandIfNeeded(ht) DICT_ERR)return -1;/* Compute the key hash value */h dictHashKey(ht, key) ht-sizemask;/* Search if this slot does not already contain the given key */he ht-table[h];while(he) {if (dictCompareHashKeys(ht, key, he-key))return -1;he he-next;}return h;
}/* Expand the hash table if needed */
static int _dictExpandIfNeeded(dict *d)
{/* Incremental rehashing already in progress. Return. */if (dictIsRehashing(d)) return DICT_OK;/* If the hash table is empty expand it to the initial size. */if (d-ht[0].size 0) return dictExpand(d, DICT_HT_INITIAL_SIZE);/* If we reached the 1:1 ratio, and we are allowed to resize the hash* table (global setting) or we should avoid it but the ratio between* elements/buckets is over the safe threshold, we resize doubling* the number of buckets. */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;
}在dictExpand函数中有 _dictInit(n, ht-type, ht-privdata);n.size realsize;n.sizemask realsize-1;n.table calloc(realsize,sizeof(dictEntry*));所以一个key应该插入到ht的哪个槽呢就是_dictKeyIndex中的这一句 h dictHashKey(ht, key) ht-sizemask;可以保证h的值在[0,size-1]之间而这些槽已经被初始化了
n.table calloc(realsize,sizeof(dictEntry*));常规的dictAdd、dictDelete比较简单。
rehash过程
值得一提的是rehash过程。
int dictRehash(dict *d, int n) {int empty_visits n*10; /* Max number of empty buckets to visit. */if (!dictIsRehashing(d)) return 0;while(n-- d-ht[0].used ! 0) {dictEntry *de, *nextde;/* Note that rehashidx cant overflow as we are sure there are more* elements because ht[0].used ! 0 */assert(d-ht[0].size (unsigned long)d-rehashidx);while(d-ht[0].table[d-rehashidx] NULL) {d-rehashidx;if (--empty_visits 0) return 1;}de d-ht[0].table[d-rehashidx];/* Move all the keys in this bucket from the old to the new hash HT */while(de) {uint64_t h;nextde de-next;/* Get the index in the new hash table */h dictHashKey(d, de-key) d-ht[1].sizemask;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;d-rehashidx;}/* Check if we already rehashed the whole table... */if (d-ht[0].used 0) {zfree(d-ht[0].table);d-ht[0] d-ht[1];_dictReset(d-ht[1]);d-rehashidx -1;return 0;}/* More to rehash... */return 1;
}整体来看就是ht[0]的尺寸太小了为了效率需要把ht[0]的所有元素都搬运到扩展了尺寸的ht[1]中。 返回值为1说明rehash还没有完成。 返回值为0说明rehash已经完成。并且已经交换了ht[0]和ht[1]之后的命令写入可以往ht[0]里写了。
int dictRehashMilliseconds(dict *d, int ms) {long long start timeInMilliseconds();int rehashes 0;while(dictRehash(d,100)) {rehashes 100;if (timeInMilliseconds()-start ms) break;}return rehashes;
}int incrementallyRehash(int dbid) {/* Keys dictionary */if (dictIsRehashing(server.db[dbid].dict)) {dictRehashMilliseconds(server.db[dbid].dict,1);return 1; /* already used our millisecond for this loop... */}/* Expires */if (dictIsRehashing(server.db[dbid].expires)) {dictRehashMilliseconds(server.db[dbid].expires,1);return 1; /* already used our millisecond for this loop... */}return 0;
}实际上的rehash是在databasesCron函数里做的incrementallyRehash指定了每次进行rehash的dict和时长(1 ms)。而dicthash()又设置了每次最多进行n个槽和n*10个空槽的遍历。
