nginx hash 구조

ngx_int_t
ngx_hash_init(ngx_hash_init_t *hinit, ngx_hash_key_t *names, ngx_uint_t nelts)
{
    u_char          *elts;
    size_t           len;
    u_short         *test;
    ngx_uint_t       i, n, key, size, start, bucket_size;
    ngx_hash_elt_t  *elt, **buckets;

    /* nginx hash       :
           hash    N  ,      N   ( <k,v>),    ,
                 N     ,        ngx_hash_elt_t   
               ngx_hash_elt_t             .
          :           
          : hash     ,    ,    .

          hash          ,                  ,    hash   .
        nginx hash    :
                         ngx_hash_init_t.bucket_size   ;
                                  .
                        ,     (   hash  %     )
                 ,           ,         ，           ,
                  ,   ngx_hash_init_t.hash.buckets     .
                       =             + void  
                ,                   .
                        ngx_hash_init_t.hash.buckets     .
                   .
               "    "  NULL

        void     :        ,   ngx_hash_find()        etl->value    NULL   .
               "    "    void*         ngx_hash_elt_t         ?
              , void*         ngx_hash_elt_t      ngx_hash_elt_t.value ,
          ngx_hash_elt_t.value      void      .

                 :                   ,           .
        
     */

    /*              +   void  ,
               
     */
    for (n = 0; n < nelts; n++) {
        if (hinit->bucket_size < NGX_HASH_ELT_SIZE(&names[n]) + sizeof(void *))
        {
            ngx_log_error(NGX_LOG_EMERG, hinit->pool->log, 0,
                          "could not build the %s, you should "
                          "increase %s_bucket_size: %i",
                          hinit->name, hinit->name, hinit->bucket_size);
            return NGX_ERROR;
        }
    }

    /*              */
    test = ngx_alloc(hinit->max_size * sizeof(u_short), hinit->pool->log);
    if (test == NULL) {
        return NGX_ERROR;
    }

    bucket_size = hinit->bucket_size - sizeof(void *);

    /*           
                NGX_HASH_ELT_SIZE(&name[n]) > (2*sizeof(void*))    
          bucket_size           bucket_size/(2*sizeof(void*))    
          nelts         start  。
     */
    start = nelts / (bucket_size / (2 * sizeof(void *)));
    start = start ? start : 1;

    if (hinit->max_size > 10000 && hinit->max_size / nelts < 99) {
        start = hinit->max_size - 1000;
    }

    /*          ，     nelts           */
    for (size = start; size < hinit->max_size; size++) {

        ngx_memzero(test, size * sizeof(u_short));

        for (n = 0; n < nelts; n++) {
            if (names[n].key.data == NULL) {
                continue;
            }

            key = names[n].key_hash % size;
            test[key] = (u_short) (test[key] + NGX_HASH_ELT_SIZE(&names[n]));

#if 0
            ngx_log_error(NGX_LOG_ALERT, hinit->pool->log, 0,
                          "%ui: %ui %ui \"%V\"",
                          size, key, test[key], &names[n].key);
#endif

            if (test[key] > (u_short) bucket_size) { /*    size   ，    nelts     */
                goto next;
            }
        }

        goto found;

    next:

        continue;
    }

    ngx_log_error(NGX_LOG_EMERG, hinit->pool->log, 0,
                  "could not build the %s, you should increase "
                  "either %s_max_size: %i or %s_bucket_size: %i",
                  hinit->name, hinit->name, hinit->max_size,
                  hinit->name, hinit->bucket_size);

    ngx_free(test);

    return NGX_ERROR;

found:

    /*              nelts       size    */
    for (i = 0; i < size; i++) {
        test[i] = sizeof(void *); /*           */
    }

    for (n = 0; n < nelts; n++) {
        if (names[n].key.data == NULL) {
            continue;
        }

        key = names[n].key_hash % size; /*    N           */
        test[key] = (u_short) (test[key] + NGX_HASH_ELT_SIZE(&names[n])); /*               n     */
    }

    len = 0;

    /*              cacheline             */
    for (i = 0; i < size; i++) {
        if (test[i] == sizeof(void *)) { /*              */
            continue;
        }

        test[i] = (u_short) (ngx_align(test[i], ngx_cacheline_size));

        len += test[i];
    }

    /*   hash NULL,     ngx_hash_wildcard_t   ,
         ngx_hash_init_t            ngx_hash_t.
            ngx_hash_wildcard_t           .
     */
    if (hinit->hash == NULL) {
        hinit->hash = ngx_pcalloc(hinit->pool, sizeof(ngx_hash_wildcard_t)
                                             + size * sizeof(ngx_hash_elt_t *));
        if (hinit->hash == NULL) {
            ngx_free(test);
            return NGX_ERROR;
        }

        /*             */
        buckets = (ngx_hash_elt_t **)
                      ((u_char *) hinit->hash + sizeof(ngx_hash_wildcard_t));

    } else {
        /*             */
        buckets = ngx_pcalloc(hinit->pool, size * sizeof(ngx_hash_elt_t *));
        if (buckets == NULL) {
            ngx_free(test);
            return NGX_ERROR;
        }
    }

    elts = ngx_palloc(hinit->pool, len + ngx_cacheline_size);
    if (elts == NULL) {
        ngx_free(test);
        return NGX_ERROR;
    }

    elts = ngx_align_ptr(elts, ngx_cacheline_size);

    for (i = 0; i < size; i++) {
        if (test[i] == sizeof(void *)) {
            continue;
        }

        /*                      */
        buckets[i] = (ngx_hash_elt_t *) elts;
        elts += test[i];

    }

    for (i = 0; i < size; i++) {
        test[i] = 0;
    }

    for (n = 0; n < nelts; n++) {
        if (names[n].key.data == NULL) {
            continue;
        }

        /*   names                ngx_hash_elt_t       ,
           names     ngx_hash_elt_t          .
         */
        key = names[n].key_hash % size;
        elt = (ngx_hash_elt_t *) ((u_char *) buckets[key] + test[key]);

        elt->value = names[n].value;
        elt->len = (u_short) names[n].key.len;

        ngx_strlow(elt->name, names[n].key.data, names[n].key.len);

        test[key] = (u_short) (test[key] + NGX_HASH_ELT_SIZE(&names[n]));
    }

    /*            NULL */
    for (i = 0; i < size; i++) {
        if (buckets[i] == NULL) {
            continue;
        }

        elt = (ngx_hash_elt_t *) ((u_char *) buckets[i] + test[i]);

        elt->value = NULL;
    }

    ngx_free(test);

    hinit->hash->buckets = buckets;
    hinit->hash->size = size;

#if 0

    for (i = 0; i < size; i++) {
        ngx_str_t   val;
        ngx_uint_t  key;

        elt = buckets[i];

        if (elt == NULL) {
            ngx_log_error(NGX_LOG_ALERT, hinit->pool->log, 0,
                          "%ui: NULL", i);
            continue;
        }

        while (elt->value) {
            val.len = elt->len;
            val.data = &elt->name[0];

            key = hinit->key(val.data, val.len);

            ngx_log_error(NGX_LOG_ALERT, hinit->pool->log, 0,
                          "%ui: %p \"%V\" %ui", i, elt, &val, key);

            elt = (ngx_hash_elt_t *) ngx_align_ptr(&elt->name[0] + elt->len,
                                                   sizeof(void *));
        }
    }

#endif

    return NGX_OK;
}