初识nginx——内存池篇

ngx_pool_t *

ngx_create_pool(size_t?size, ngx_log_t *log)

{

????ngx_pool_t *p;

????p = ngx_memalign(NGX_POOL_ALIGNMENT, size,?log);//间接调用了posix_memalign分配内存

????if?(p == NULL) {

????????return?NULL;

????}

????p->d.last = (u_char *) p +?sizeof(ngx_pool_t);//初始的前面几个字节用于储存内存池头部信息,所以下一次分配的开始应该前移头部的大小

????p->d.end = (u_char *) p + size;//内存池节点的结尾

????p->d.next = NULL;//由于当前内存池只有一个节点所以next为NULL

????p->d.failed = 0;

????size = size -?sizeof(ngx_pool_t);

????p->max = (size < NGX_MAX_ALLOC_FROM_POOL) ? size : NGX_MAX_ALLOC_FROM_POOL;//设置小块内存和大块内存的判断标准

????p->current = p;

????p->chain = NULL;

????p->large = NULL;

????p->cleanup = NULL;

????p->log?=?log;

????return?p;

}

void?*

ngx_palloc(ngx_pool_t *pool,?size_t?size)

{

????u_char *m;

????ngx_pool_t *p;

????if?(size <= pool->max)?//判断是小块内存 还是大块内存

????{

????????p = pool->current;

????????do?{

????????????m = ngx_align_ptr(p->d.last, NGX_ALIGNMENT);

????????????if?((size_t) (p->d.end - m) >= size) {//尝试在已有的内存池节点中分配内存

????????????????p->d.last = m + size;

????????????????return?m;

????????????}

????????????p = p->d.next;

????????}?while?(p);

????????return?ngx_palloc_block(pool, size);//当前已有节点都分配失败，创建一个新的内存池节点

????}

????return?ngx_palloc_large(pool, size);//分配大块内存

}

void

ngx_destroy_pool(ngx_pool_t *pool)

{

????ngx_pool_t *p, *n;

????ngx_pool_large_t *l;

????ngx_pool_cleanup_t *c;

????for?(c = pool->cleanup; c; c = c->next) {

????????if?(c->handler) {

????????????ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0,"run cleanup: %p", c);

????????????c->handler(c->data);//调用需要在内存池释放时同步调用的方法

????????}

????}

????for?(l = pool->large; l; l = l->next) {//释放大块内存

????????ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0,?"free: %p", l->alloc);

????????if?(l->alloc) {

???????????ngx_free(l->alloc);

????????}

????}

????#if (NGX_DEBUG)

????/*

????* we could allocate the pool->log from this pool

????* so we cannot use this log while free()ing the pool

????*/

????for?(p = pool, n = pool->d.next;?/* void */; p = n, n = n->d.next) {

????????ngx_log_debug2(NGX_LOG_DEBUG_ALLOC, pool->log, 0,"free: %p, unused: %uz", p, p->d.end - p->d.last);

????????if?(n == NULL) {

????????????break;

????????}

????}

????#endif

????for?(p = pool, n = pool->d.next;?/* void */; p = n, n = n->d.next) {

????????ngx_free(p);//间接调用free释放内存

????????if?(n == NULL) {

????????????break;

????????}

????}

}