nginx--源码分析 array（实现动态数组）

1.基本数据结构

typedef struct {
    void        *elts;
    ngx_uint_t   nelts;
    size_t       size;
    ngx_uint_t   nalloc;
    ngx_pool_t  *pool;
} ngx_array_t;
 

结构成员定义

1.void* elts ：数组的内存位置， 即数组首地址

采用void* 近似使用模板技术,可以通过类型转化实现各种类型 例如 char*等

2. ngx_uint_t   nelts; 数组当前元素数量

(ngx_uint_t)为无符号指针

3.size_t    size   数组元素大小（已经在数组里面）

4.ngx_uint_t nalloc 数组可使用的最多元素数量

5 ngx_pool_t* pool 数组使用的内存池

图形解释

2.操作函数

初始化 static ngx_inline ngx_int_t ngx_array_init 

static ngx_inline ngx_int_t
ngx_array_init(ngx_array_t *array, ngx_pool_t *pool, ngx_uint_t n, size_t size)
{
    /*
     * set "array->nelts" before "array->elts", otherwise MSVC thinks
     * that "array->nelts" may be used without having been initialized
     */
 
    array->nelts = 0;
    array->size = size;
    array->nalloc = n;
    array->pool = pool;
 
    array->elts = ngx_palloc(pool, n * size);
    if (array->elts == NULL) {
        return NGX_ERROR;
    }

1. 解释一下 ngx_inline 

#ifndef ngx_inline
#define ngx_inline      inline
#endif

在c中,为了解决一些频繁调用的小函数大量消耗栈空间或是叫栈内存的问题，特别的引入了inline修饰符，表示为内联函数。

栈空间就是指放置程式的局部数据也就是函数内数据的内存空间，在系统下，栈空间是有限的，假如频繁大量的使用就会造成因栈空间不足所造成的程式出错的问题，函数的死循环递归调用的最终结果就是导致栈内存空间枯竭。

2.分配一个内存池给ngx_array_init

 ngx_array_t * ngx_array_create(ngx_pool_t *p, ngx_uint_t n, size_t size)

ngx_array_create(ngx_pool_t *p, ngx_uint_t n, size_t size)
{
    ngx_array_t *a;
 
    a = ngx_palloc(p, sizeof(ngx_array_t));
    if (a == NULL) {
        return NULL;
    }
 
    if (ngx_array_init(a, p, n, size) != NGX_OK) {
        return NULL;
    }
 
    return a;
}

void ngx_array_destroy(ngx_array_t *a)

void
ngx_array_destroy(ngx_array_t *a)
{
    ngx_pool_t  *p;
 
    p = a->pool;
 
    if ((u_char *) a->elts + a->size * a->nalloc == p->d.last) {
        p->d.last -= a->size * a->nalloc;
    }
 
    if ((u_char *) a + sizeof(ngx_array_t) == p->d.last) {
        p->d.last = (u_char *) a;
    }
}
 

建议阅读 Nginx源码分析--内存池_编程界的谢菲尔德的博客-CSDN博客

销毁是通过内存池覆盖的方式

插入 

 void * ngx_array_push(ngx_array_t *a)

void *ngx_array_push(ngx_array_t *a)
{
    void        *elt, *new;
    size_t       size;
    ngx_pool_t  *p;
 
    if (a->nelts == a->nalloc) {
 
        /* the array is full */
 
        size = a->size * a->nalloc;
 
        p = a->pool;
 
        if ((u_char *) a->elts + size == p->d.last
            && p->d.last + a->size <= p->d.end)
        {
            /*
             * the array allocation is the last in the pool
             * and there is space for new allocation
             */
 
 
            p->d.last += a->size;
            a->nalloc++;
 
        } else {
                 
 /* allocate a new array */
 
 
            new = ngx_palloc(p, 2 * size);
            if (new == NULL) {
                return NULL;
            }
 
            ngx_memcpy(new, a->elts, size);
            a->elts = new;
            a->nalloc *= 2;
        }
    }
elt = (u_char *) a->elts + a->size * a->nelts;
    a->nelts++;
 
    return elt;
}
 

1.判断情况 是否over capacity 

2.如果内存池还有空间就开辟内存池空间

3.如果没有就要扩容两倍！！！（并且还要移动数据位置！！！）

4.return是一个elt就是一个空指针（//数据区中实际已经存放数据的子区的末尾）需要类型转换

void *
ngx_array_push_n(ngx_array_t *a, ngx_uint_t n)
 

void *
ngx_array_push_n(ngx_array_t *a, ngx_uint_t n)
{
    void        *elt, *new;
    size_t       size;
    ngx_uint_t   nalloc;
    ngx_pool_t  *p;
 
    size = n * a->size;
 
 
    if (a->nelts + n > a->nalloc) {
 
        /* the array is full */
 
        p = a->pool;
 
        if ((u_char *) a->elts + a->size * a->nalloc == p->d.last
            && p->d.last + size <= p->d.end)
        {
            /*
             * the array allocation is the last in the pool
             * and there is space for new allocation
             */
 
            p->d.last += size;
            a->nalloc += n;
} else {
            /* allocate a new array */
 
            nalloc = 2 * ((n >= a->nalloc) ? n : a->nalloc);
 
            new = ngx_palloc(p, nalloc * a->size);
            if (new == NULL) {
                return NULL;
            }
 
            ngx_memcpy(new, a->elts, a->nelts * a->size);
            a->elts = new;
            a->nalloc = nalloc;
        }
    }
 
    elt = (u_char *) a->elts + a->size * a->nelts;
    a->nelts += n;
return elt;
}
 
                                
 

类似与push

3.测试用例

 
 
/**
 * ngx_array_t test, to test ngx_array_create, ngx_array_push
 */
 
#include 
#include "ngx_config.h"
#include "ngx_conf_file.h"
#include "nginx.h"
#include "ngx_core.h"
#include "ngx_string.h"
#include "ngx_palloc.h"
#include "ngx_array.h"
 
volatile ngx_cycle_t  *ngx_cycle;
 
void ngx_log_error_core(ngx_uint_t level, ngx_log_t *log, ngx_err_t err,
            const char *fmt, ...)
{
}
 
void dump_pool(ngx_pool_t* pool)
{
    while (pool)
    {
        printf("pool = 0x%x\n", pool);
        printf("  .d\n");
        printf("    .last = 0x%x\n", pool->d.last);
        printf("    .end = 0x%x\n", pool->d.end);
        printf("    .next = 0x%x\n", pool->d.next);
        printf("    .failed = %d\n", pool->d.failed);
        printf("  .max = %d\n", pool->max);
        printf("  .current = 0x%x\n", pool->current);
        printf("  .chain = 0x%x\n", pool->chain);
        printf("  .large = 0x%x\n", pool->large);
        printf("  .cleanup = 0x%x\n", pool->cleanup);
        printf("  .log = 0x%x\n", pool->log);
        printf("available pool memory = %d\n\n", pool->d.end - pool->d.last);
        pool = pool->d.next;
    }
}
 
void dump_array(ngx_array_t* a)
{
    if (a)
    {
        printf("array = 0x%x\n", a);
        printf("  .elts = 0x%x\n", a->elts);
        printf("  .nelts = %d\n", a->nelts);
        printf("  .size = %d\n", a->size);
        printf("  .nalloc = %d\n", a->nalloc);
        printf("  .pool = 0x%x\n", a->pool);
 
        printf("elements: ");
        int *ptr = (int*)(a->elts);
        for (; ptr < (int*)(a->elts + a->nalloc * a->size); )
        {
            printf("0x%x  ", *ptr++);
        }
        printf("\n");
    }
}
 
int main()
{
    ngx_pool_t *pool;
    int i;
 
    printf("--------------------------------\n");
    printf("create a new pool:\n");
    printf("--------------------------------\n");
    pool = ngx_create_pool(1024, NULL);
    dump_pool(pool);
 
    printf("--------------------------------\n");
    printf("alloc an array from the pool:\n");
    printf("--------------------------------\n");
    ngx_array_t *a = ngx_array_create(pool, 10, sizeof(int));
    dump_pool(pool);
 
    for (i = 0; i < 10; i++)
    {
        int *ptr = ngx_array_push(a);
        *ptr = i + 1;
    }
 
    dump_array(a);
 
    ngx_array_destroy(a);
    ngx_destroy_pool(pool);
    return 0;
 
}

结果：

# ./ngx_array_t_test
-------------------------------- create a new pool:
-------------------------------- pool = 0x860b020 .d .last = 0x860b048
    .end = 0x860b420
    .next = 0x0
    .failed = 0 .max = 984
  .current = 0x860b020
  .chain = 0x0
  .large = 0x0
  .cleanup = 0x0
  .log = 0x0 available pool memory = 984
-------------------------------- alloc an array from the pool:
-------------------------------- pool = 0x860b020 .d .last = 0x860b084
    .end = 0x860b420
    .next = 0x0
    .failed = 0 .max = 984
  .current = 0x860b020
  .chain = 0x0
  .large = 0x0
  .cleanup = 0x0
  .log = 0x0 available pool memory = 924
array = 0x860b048 .elts = 0x860b05c
  .nelts = 10
  .size = 4
  .nalloc = 10
  .pool = 0x860b020 elements: 0x1  0x2  0x3  0x4  0x5  0x6  0x7  0x8  0x9