1.基本数据结构
1.1结点
struct ngx_list_part_s {
void *elts;
ngx_uint_t nelts;
ngx_list_part_t *next;
};
结构成员分析
void* elts :数组元素指针
ngx_uint_t :数组里面的元素数量
ngx_list_part_t* :下一个结点的指针
它类似ngx_array_t，是一个简单的数组，也可以“泛型”存储数据，但少了一些成员，还有一个next指针指向链表里的下一个节点。
1.2链表
typedef struct {
ngx_list_part_t *last;
ngx_list_part_t part;
size_t size;
ngx_uint_t nalloc;
ngx_pool_t *pool;
} ngx_list_t;
结构成员分析
last: 链表的尾结点
part：链表的头结点
size: 链表储存元素的大小
nalloc：每一个结点能够储存元素大小
pool : 使用的内存池
对比 ngx_array_t可以看到，ngx_list_t 的成员size、nalloc和pool的含义是相同的，确定了节点里数组的元信息。可以这么说，链表里的每个节点就是一个简化的ngx_array_t数组结构。
ngx_list_t 的 part成员是链表的头节点（注意不是指针)，part.next 指向链表里的第二个节点，而last则指向链表的尾节点。
1.3图形解释
2.操作函数
static ngx_inline ngx_int_t
ngx_list_init(ngx_list_t *list, ngx_pool_t *pool, ngx_uint_t n, size_t size)
{
list->part.elts = ngx_palloc(pool, n * size);
if (list->part.elts == NULL) {
return NGX_ERROR;
}
list->part.nelts = 0;
list->part.next = NULL;
list->last = &list->part;
list->size = size;
list->nalloc = n;
list->pool = pool;
return NGX_OK;
}
1. ngx_ok 是一个宏定义
2.初始化确保list已经存在
3.然后去初始化 第二个结点并且首尾相等
ngx_list_t *
ngx_list_create(ngx_pool_t *pool, ngx_uint_t n, size_t size)
{
ngx_list_t *list;
list = ngx_palloc(pool, sizeof(ngx_list_t));
if (list == NULL) {
return NULL;
}
if (ngx_list_init(list, pool, n, size) != NGX_OK) {
return NULL;
}
return list;
}
1. 分配内存
2.init函数
void *
ngx_list_push(ngx_list_t *l)
{
void *elt;
ngx_list_part_t *last;
last = l->last;
if (last->nelts == l->nalloc) {
/* the last part is full, allocate a new list part */
last = ngx_palloc(l->pool, sizeof(ngx_list_part_t));
if (last == NULL) {
return NULL;
}
last->elts = ngx_palloc(l->pool, l->nalloc * l->size);
if (last->elts == NULL) {
return NULL;
l->last->next = last;
l->last = last;
}
elt = (char *) last->elts + l->size * last->nelts;
last->nelts++;
return elt;
}
1.记住这是一个“添加元素” 后面有测试解释怎么填加
2.是往尾结点上添加！！！
3. l->last->next = last;
l->last = last;
改变尾结点
4. elt = (char *) last->elts + l->size * last->nelts;
last->nelts++;
类似与array数组！！！
note 没有销毁操作！！！
测试
理解并掌握开源软件的最好方式莫过于自己写一些测试代码，或者改写软件本身，并进行调试来进一步理解开源软件的原理和设计方法。本节给出一个创建内存池并从中分配一个链表的简单例子。在该例中，链表的每个节点(part)可存放5个元素，每个元素4字节大小，创建链表后，要向链表添加15个整型元素。
/**
* ngx_list_t test, to test ngx_list_create, ngx_list_push
*/
#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_list.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_list_part(ngx_list_t* list, ngx_list_part_t* part)
{
int *ptr = (int*)(part->elts);
int loop = 0;
printf(" .part = 0x%x\n", &(list->part));
printf(" .elts = 0x%x ", part->elts);
printf("(");
for (; loop < list->nalloc - 1; loop++)
{
printf("0x%x, ", ptr[loop]);
}
printf("0x%x)\n", ptr[loop]);
printf(" .nelts = %d\n", part->nelts);
printf(" .next = 0x%x", part->next);
if (part->next)
printf(" -->\n");
printf(" \n");
}
void dump_list(ngx_list_t* list)
{
if (list == NULL)
return;
printf("list = 0x%x\n", list);
printf(" .last = 0x%x\n", list->last);
printf(" .part = 0x%x\n", &(list->part));
printf(" .size = %d\n", list->size);
printf(" .nalloc = %d\n", list->nalloc);
printf(" .pool = 0x%x\n\n", list->pool);
printf("elements:\n");
ngx_list_part_t *part = &(list->part);
while (part)
{
dump_list_part(list, part);
part = part->next;
}
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 list from the pool:\n");
printf("--------------------------------\n");
ngx_list_t *list = ngx_list_create(pool, 5, sizeof(int));
dump_pool(pool);
for (i = 0; i < 15; i++)
{
int *ptr = ngx_list_push(list);
*ptr = i + 1;
}
printf("--------------------------------\n");
printf("the list information:\n");
printf("--------------------------------\n");
dump_list(list);
printf("--------------------------------\n");
printf("the pool at the end:\n");
printf("--------------------------------\n");
dump_pool(pool);
ngx_destroy_pool(pool);
return 0;
}解析
1.
for (i = 0; i < 15; i++)
{
int *ptr = ngx_list_push(list);
*ptr = i + 1;
}这是通过给指针赋值来实现添加元素
2.dump：(计算机内信息)转出，倾卸；转储；内容全部打印
所以dump_loop是打印所有的pool等！！！
结果
# ./ngx_list_t_test
-------------------------------- create a new pool:
-------------------------------- pool = 0x9208020 .d .last = 0x9208048
.end = 0x9208420
.next = 0x0
.failed = 0 .max = 984
.current = 0x9208020
.chain = 0x0
.large = 0x0
.cleanup = 0x0
.log = 0x0 available pool memory = 984
-------------------------------- alloc an list from the pool:
-------------------------------- pool = 0x9208020 .d .last = 0x9208078
.end = 0x9208420
.next = 0x0
.failed = 0 .max = 984
.current = 0x9208020
.chain = 0x0
.large = 0x0
.cleanup = 0x0
.log = 0x0 available pool memory = 936
-------------------------------- the list information:
-------------------------------- list = 0x9208048 .last = 0x9208098
.part = 0x920804c
.size = 4
.nalloc = 5
.pool = 0x9208020
elements: .part = 0x920804c .elts = 0x9208064 (0x1, 0x2, 0x3, 0x4, 0x5)
.nelts = 5
.next = 0x9208078 -->
.part = 0x920804c .elts = 0x9208084 (0x6, 0x7, 0x8, 0x9, 0xa)
.nelts = 5
.next = 0x9208098 -->
.part = 0x920804c .elts = 0x92080a4 (0xb, 0xc, 0xd, 0xe, 0xf)
.nelts = 5
.next = 0x0
-------------------------------- the pool at the end:
-------------------------------- pool = 0x9208020 .d .last = 0x92080b8
.end = 0x9208420
.next = 0x0
.failed = 0 .max = 984
.current = 0x9208020
.chain = 0x0
.large = 0x0
.cleanup = 0x0
.log = 0x0 available pool memory = 872
