nginx动态数组ngx_array_t

ngx_array_t是nginx中设计的动态数组，类似于STL中的vector<typename>。下面我们结合实例分析。

一、实例

<span style="font-size:18px;">#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_queue.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);                    ngx_pool_large_t*large = pool->large;       printf("*****large_pool*******\n");       while(large) {            printf("%p->",large);            large= large->next;       }       printf("\n\n");                    pool = pool->d.next;   } } typedef struct {       intarray[128]; // 128 * 4 = 512}TestNode; int main() {    ngx_pool_t *pool;     printf("--------------------------------\n");    printf("create a new pool:\n");    printf("--------------------------------\n");    pool = ngx_create_pool(1024, NULL);    dump_pool(pool);              ngx_array_t*myArray = ngx_array_create(pool, 1, sizeof(TestNode));       printf("******ngx_array_create**********\n");   dump_pool(pool);             TestNode*t1 = ngx_array_push(myArray);       TestNode*t2 = ngx_array_push(myArray);       printf("******ngx_array_push**********\n");   dump_pool(pool);             ngx_array_destroy(myArray);// 这里什么也没做       dump_pool(pool);   ngx_destroy_pool(pool);    return 0; }</span>

运行结果：

--------------------------------create a new pool:--------------------------------pool = 0x95ae020  .d   .last = 0x95ae048   .end = 0x95ae420   .next = 0x0   .failed = 0 .max = 984 .current = 0x95ae020  .chain= 0x0 .large = 0x0 .cleanup = 0x0 .log = 0x0available pool memory = 984 *****large_pool*******NULL******ngx_array_create**********pool = 0x95ae020  .d   .last = 0x95ae25c   .end = 0x95ae420   .next = 0x0   .failed = 0 .max = 984 .current = 0x95ae020 .chain = 0x0 .large = 0x0 .cleanup = 0x0 .log = 0x0available pool memory = 452 *****large_pool*******NULL******ngx_array_push**********pool = 0x95ae020  .d   .last = 0x95ae264   .end = 0x95ae420   .next = 0x0    .failed = 0 .max = 984 .current = 0x95ae020 .chain = 0x0 .large = 0x95ae25c .cleanup = 0x0 .log = 0x0available pool memory = 444 *****large_pool*******0x95ae25c->NULL******ngx_array_destroy******pool = 0x95ae020  .d   .last = 0x95ae264   .end = 0x95ae420   .next = 0x0   .failed = 0 .max = 984 .current = 0x95ae020 .chain = 0x0 .large = 0x95ae25c .cleanup = 0x0 .log = 0x0available pool memory = 444 *****large_pool*******0x95ae25c->NULL

1、 从 available pool memory 的变化可以得知，ngx_array_t、ngx_pool_large_t结构体本身所占内存是在内存池上分配内存的。

从源码中可以得到证明:

ngx_array_t *

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

{

    a = ngx_palloc(p, sizeof(ngx_array_t));

}

 

static void *

ngx_palloc_large(ngx_pool_t*pool, size_t size)

{

              // 在内存池上分配。

    large = ngx_palloc(pool,sizeof(ngx_pool_large_t));

}

2、 ngx_array_push如果扩容，并不会释放原来占用的内存。可以参考ngx_array_push的源码，在此就不贴了。

3、 如果分配动态数组的大小超过一块内存池的容量(在本例中是1024)，会调用ngx_palloc_large分配大块内存。

4、 如果动态数组所占内存是大块内存，ngx_array_destroy不会做任何事情，并且该API在nginx内核源码中没有被调用过。

编译可以参考上一遍分析ngx_queue_t结构体的文章。

 

二、参考资料：

《深入理解nginx》陶辉

http://blog.csdn.net/livelylittlefish/article/details/6586946