nginx源码分析—数组结构ngx_array_t
数组实现文件：文件：./src/core/ngx_array.h/.c
1.数组结构
struct ngx_array_s {
void *elts; //数组数据区起始位置
ngx_uint_t nelts; //实际存放的元素个数
size_t size; //每个元素的大小
ngx_uint_t nalloc; //数组分配的空间个数，即实际饭分配的小空间个数
ngx_pool_t *pool; //该数组在内存中的分配
};
2.数组的基本操作（5个）
ngx_array_t *ngx_array_create(ngx_pool_t *p, ngx_uint_t n, size_t size); //创建数组 //数组销毁 void ngx_array_destroy(ngx_array_t *a); //往数组中添加元素 void *ngx_array_push(ngx_array_t *a); void *ngx_array_push_n(ngx_array_t *a, ngx_uint_t n); //数组的初始化操作 static ngx_inline ngx_int_t ngx_array_init(ngx_array_t *array, ngx_pool_t *pool, ngx_uint_t n, size_t size)
2.1创建数组
创建数组的操作实现过程，首先分配数组头(20B)，然后分配数组数据区，两次分配均在传入的内存池(pool指向的内存池)中进行。然后简单初始化数组头并返回数组头的起始位置。（
分配分两个阶段完成，注意和释放过程对应
）
ngx_array_t *
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)); //从内存中分配数组头
if (a == NULL) {
return NULL;
}
a->elts = ngx_palloc(p, n * size); //分配大小为＊size的内存作为数组数据区
if (a->elts == NULL) {
return NULL;
}
a->nelts = 0; //初始化
a->size = size;
a->nalloc = n;
a->pool = p;
return a; //返回内存起始位置
}
2.2数组销毁
销毁数组的操作实现过程，包括销毁数组数据区和数组头。这里的销毁动作实际上就是修改内存池的last指针，并没有调用free等释放内存的操作，显然，这种维护效率是很高的。
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; //释放数组的数据区，只是修改内存池的last指针
}
if ((u_char *) a + sizeof(ngx_array_t) == p->d.last) {
p->d.last = (u_char *) a; //释放数组头， 再次修改内存池的last指针
}
}
2.3添加元素到数组
向数组添加元素的操作有两个，ngx_array_push和ngx_array_push_n，分别添加一个和多个元素。
但实际的添加操作并不在这两个函数中完成，例如ngx_array_push返回可以在该数组数据区中添加这个元素的位置，ngx_array_push_n则返回可以在该数组数据区中添加n个元素的起始位置，而添加操作即在获得添加位置之后进行
void *
ngx_array_push(ngx_array_t *a)
{
void *elt, *new;
size_t size;
ngx_pool_t *p;
if (a->nelts == a->nalloc) { //数据区已满
/* the array is full */
size = a->size * a->nalloc; //数组当前可用数据区大小
p = a->pool; //指向当前内存池
if ((u_char *) a->elts + size == p->d.last //条件:内存池的last指针指向数组的数据区末端
&& p->d.last + a->size <= p->d.end) //当前内存池还有可分配一个元素大小的空间
{
/*
* the array allocation is the last in the pool
* and there is space for new allocation
*/
p->d.last += a->size; //last指针后移一位
a->nalloc++; //数组元素总数+1
} else {
/* allocate a new array */
new = ngx_palloc(p, 2 * size); //重新分配2倍空间
if (new == NULL) {
return NULL;
}
ngx_memcpy(new, a->elts, size); //拷贝原来的数据
a->elts = new; //更新数组数据区指针
a->nalloc *= 2; //更新总容量
}
}
elt = (u_char *) a->elts + a->size * a->nelts;//没满，直接后移指
a->nelts++; //总数+1
return elt;
}
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;
}测试demo
#include <stdio.h>
#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 = 0x%x\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 < 1000; i++)
{
int *ptr = ngx_array_push(a);
*ptr = i + 1;
}
dump_array(a);
size_t iLen = sizeof(ngx_array_t);
printf("sizeof(ngx_array_t) == == 0x%x\n", iLen);
ngx_array_destroy(a);
ngx_destroy_pool(pool);
return 0;
}测试结果
************************************************* create a new pool: ************************************************* pool = 0x9b6b020 .d .last = 0x9b6b048 .end = 0x9b6b420 .next = 0x0 .failed = 0 .max = 984 .current = 0x9b6b020 .chain = 0x0 .large = 0x0 .cleanup = 0x0 .log = 0x0 available pool memory = 0x3d8 ------------------------------------------------- alloc an array from the pool: ------------------------------------------------- pool = 0x9b6b020 .d .last = 0x9b6b084 .end = 0x9b6b420 .next = 0x0 .failed = 0 .max = 984 .current = 0x9b6b020 .chain = 0x0 .large = 0x0 .cleanup = 0x0 .log = 0x0 available pool memory = 0x39c array = 0x9b6b048 .elts = 0x9b6b05c .nelts = 10 .size = 4 .nalloc = 10 .pool = 0x9b6b020 elements: 0x1 0x2 0x3 0x4 0x5 0x6 0x7 0x8 0x9 0xa sizeof(ngx_array_t) == == 0x14 sizeof(ngx_pool_t) === == 0x28 sizeof(ngx_pool_data_t) === === 0x10