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Nginx源码阅读(ngx_array_t)

2017-01-21 21:08 465 查看
/* src/core/ngx_array.h */

typedef struct {
void        *elts; // 数组的首地址
ngx_uint_t   nelts; // 数组中已经使用的元素个数
size_t       size; // 每个数组元素占用的字节数
ngx_uint_t   nalloc; // 数组中能够容纳的最大元素个数
ngx_pool_t  *pool;
} ngx_array_t;

ngx_array_t *ngx_array_create(ngx_pool_t *p, ngx_uint_t n, size_t size);
void ngx_array_destroy(ngx_array_t *a);
void *ngx_array_push(ngx_array_t *a);
void *ngx_array_push_n(ngx_array_t *a, ngx_uint_t n);

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;
}

return NGX_OK;
}


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));
if (a == NULL) {
return NULL;
}

if (ngx_array_init(a, p, n, size) != NGX_OK) {
return NULL;
}

return a;
}

/* 1. ngx_array_t位于第一个ngx_pool_t的尾部:只清理了ngx_array_t;
2. array位于第一个ngx_pool_t的尾部,且和ngx_array_t相邻:清理了ngx_array_t和array;
3. array位于第一个ngx_pool_t的尾部,且不和ngx_array_t相邻:只清理了array;
4. 其它情况:都没清理。 */
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) {
// the array allocation is the last in the pool
p->d.last -= a->size * a->nalloc;
}

if ((u_char *) a + sizeof(ngx_array_t) == p->d.last) {
// the ngx_array_t allocation is the last in the pool
p->d.last = (u_char *) 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;
}

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;
}


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