uthash版本 :2.0.2
uthash用三个结构体来实现散列表的存储管理。
- UT_hash_table：用于散列表整体管理。
typedef struct UT_hash_table {
UT_hash_bucket *buckets;
unsigned num_buckets, log2_num_buckets;
unsigned num_items;
struct UT_hash_handle *tail; /* tail hh in app order, for fast append */
ptrdiff_t hho; /* hash handle offset (byte pos of hash handle in element */
/* in an ideal situation (all buckets used equally), no bucket would have
* more than ceil(#items/#buckets) items. that's the ideal chain length. */
unsigned ideal_chain_maxlen;
/* nonideal_items is the number of items in the hash whose chain position
* exceeds the ideal chain maxlen. these items pay the penalty for an uneven
* hash distribution; reaching them in a chain traversal takes >ideal steps */
unsigned nonideal_items;
/* ineffective expands occur when a bucket doubling was performed, but
* afterward, more than half the items in the hash had nonideal chain
* positions. If this happens on two consecutive expansions we inhibit any
* further expansion, as it's not helping; this happens when the hash
* function isn't a good fit for the key domain. When expansion is inhibited
* the hash will still work, albeit no longer in constant time. */
unsigned ineff_expands, noexpand;
uint32_t signature; /* used only to find hash tables in external analysis */
#ifdef HASH_BLOOM
uint32_t bloom_sig; /* used only to test bloom exists in external analysis */
uint8_t *bloom_bv;
uint8_t bloom_nbits;
#endif
} UT_hash_table;
- UT_hash_bucket *buckets ：指向通过uthash_malloc分配的数组结构，在第一次使用时会自动分配，个数为HASH_INITIAL_NUM_BUCKETS。
- unsigned num_buckets ：bucket的个数，也就是散列表条数。
- unsigned log2_num_buckets ：bucket的2幂次，散列表的扩容是按照2的幂次进行的，初始值为HASH_INITIAL_NUM_BUCKETS_LOG2。
- struct UT_hash_handle *tail ：指向应用最后插入的元素，用于快速扩展。
- ptrdiff_t hho ：UT_hash_handle结构在用户结构中的偏移位置，通过UT_hash_handle对象减去hho定位到用户结构对象。
- unsigned ideal_chain_maxlen ：每个bucket理想的元素数目，元素应该能平均得分配到每个bucket，这与散列函数和key值取法相关。
- unsigned nonideal_items ：buckets中超过ideal_chain_maxlen的元素个数。
- unsigned ineff_expands ：标志非平均分布，当发现bucket中元素偏离了理想分布是会职位。
- unsigned noexpand ：标志不要进行bucket幂次扩容，原因是元素已经偏离理想分布。
- uint32_t signature ：签名值。
- UThash_bucket：具有相同hashkey值，以及hashkey值与num_buckets-1与运算有相同结果的元素，将存储在相同的bucket中。
typedef struct UT_hash_bucket {
struct UT_hash_handle *hh_head;
unsigned count;
/* expand_mult is normally set to 0. In this situation, the max chain length
* threshold is enforced at its default value, HASH_BKT_CAPACITY_THRESH. (If
* the bucket's chain exceeds this length, bucket expansion is triggered).
* However, setting expand_mult to a non-zero value delays bucket expansion
* (that would be triggered by additions to this particular bucket)
* until its chain length reaches a *multiple* of HASH_BKT_CAPACITY_THRESH.
* (The multiplier is simply expand_mult+1). The whole idea of this
* multiplier is to reduce bucket expansions, since they are expensive, in
* situations where we know that a particular bucket tends to be overused.
* It is better to let its chain length grow to a longer yet-still-bounded
* value, than to do an O(n) bucket expansion too often.
*/
unsigned expand_mult;
} UT_hash_bucket;- struct UT_hash_handle *hh_head ：指向bucket中存储的头元素。
- unsigned count ：bucket中存储的元素个数。
- unsigned expand_mult ：扩容控制乘数，用于减少扩容操作。当bucket出现扩容操作时，会进行大量的计算和复制操作。
- UT_hash_handle：嵌入在用户数据结构中，代表散列表元素。
typedef struct UT_hash_handle {
struct UT_hash_table *tbl;
void *prev; /* prev element in app order */
void *next; /* next element in app order */
struct UT_hash_handle *hh_prev; /* previous hh in bucket order */
struct UT_hash_handle *hh_next; /* next hh in bucket order */
void *key; /* ptr to enclosing struct's key */
unsigned keylen; /* enclosing struct's key len */
unsigned hashv; /* result of hash-fcn(key) */
} UT_hash_handle;- struct UT_hash_table *tbl ：指向管理表。
- void *prev ：指向应用添加顺序前一个元素。
- void *next ：指向应用添加顺序后一个元素。
- struct UT_hash_handle *hh_prev ：指向在同一个bucket中的前一个UT_hash_handle。
- struct UT_hash_handle *hh_next ： 指向在同一个bucket中的后一个UT_hash_handle。
- void *key ：指向用于计算hashkey值用的数据。
- unsigned keylen ：用于计算hashkey值用的数据长度。
- unsigned hashv ：hashkey。