uthash的三个数据结构

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;

/* random signature used only to find hash tables in external analysis */
#define HASH_SIGNATURE 0xa0111fe1
#define HASH_BLOOM_SIGNATURE 0xb12220f2

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;
   char bloom_nbits;
#endif

} UT_hash_table;

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;