Nginx High-level data structure source Analysis (iii)-----linked list

ngx_list_t is a linked list container in Nginx package, which is used very frequently. It has two structures, ngx_list_t describes the entire list, and ngx_list_part_t only describes one element of the linked list. For ease of understanding, we can refer to it as an array of linked lists. That is to say, ngx_list_t is a list container, and the element in the list is an array. In fact, the elements in the ngx_list_part_t array are what the user needs to store.

What are the benefits of such a structure expression:

(1) The element stored in the linked list is flexible, it can be any kind of data structure;

(2) The memory that the list element needs to occupy is managed by ngx_list_t, it has been allocated through the array;

(3) Small chunks of memory using the linked list of access efficiency is low, using an array to access memory through the offset is much more efficient.

Definition of ngx_list_t structure:

typedef struct {    ngx_list_part_t  *last;     Point to the last array element of the list

    ngx_list_part_t part   ;     The first array element of the list is    size_t            size;     One data to be stored by each user must be less than or equal to size    ngx_uint_t        nalloc;   Indicates the number of elements in an array or the number of elements in each array element??? Ask Xu    ngx_pool_t       *pool;     Memory Pool Object} ngx_list_t;

Definition of ngx_list_part_t structure:

struct ngx_list_part_s {    void             *elts;     The starting address of the pointer to the array    ngx_uint_t        nelts;    Indicates how many elements have been used in the array    ngx_list_part_t  *next;     The address of the next linked list element};

Initialize the list of arrays:

Static Ngx_inline Ngx_int_tngx_list_init (ngx_list_t *list, ngx_pool_t *pool, ngx_uint_t N, size_t size)//Initialize linked list {    List->part.elts = Ngx_palloc (pool, n * size);//Request the memory of the first array element??? Should be to apply the entire array list of                                                 //memory Ask Xu, figure out    if (list->part.elts = = NULL) {        return ngx_error;    }    list->part.nelts = 0;    There are only 0 elements in the start array element    list->part.next = NULL;    List->last = &list->part;//points to the first node    list->size = size;    List->nalloc = n;    List->pool = pool;//Memory Pool object    return NGX_OK;}

To create an array-linked list:

ngx_list_t *ngx_list_create (ngx_pool_t *pool, ngx_uint_t N, size_t size)//Create a linked list {    ngx_list_t  *list;    List = Ngx_palloc (pool, sizeof (ngx_list_t));//Application for ngx_list_t memory    if (list = = null) {        return null;    }    if (Ngx_list_init (list, pool, n, size)! = NGX_OK) {//Call initialization function to ngx_list_t initialize        return NULL;    }    return list;}

To add a new element:

void *ngx_list_push (ngx_list_t *l) {    void             *elt;    ngx_list_part_t  *last;    last = l->last;    if (last->nelts = = L->nalloc) {//To determine if the last array node is out of space */The end part was full        , allocate a new list part */        Las t = ngx_palloc (l->pool, sizeof (ngx_list_part_t));//apply a node's memory        if (last = = null) {            return null;        }        Last->elts = Ngx_palloc (L->pool, L->nalloc * l->size);//The storage memory of the application node        if (last->elts = = NULL) {            return NULL;        }        last->nelts = 0;        Last->next = NULL;        L->last->next = last;//Update the two variables        l->last = last;    }    ELT = (char *) Last->elts + l->size * last->nelts;//returns the memory address where the element can be inserted    last->nelts++;    return ELT;}

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