nginx源码解析之数据结构内存池

struct ngx_pool_s {
    ngx_pool_data_t       d; 		/* 内存池的数据区域*/
    size_t                max; 		/* 最大每次可分配内存 */
    ngx_pool_t           *current;  /* 指向当前的内存池指针地址。ngx_pool_t链表上最后一个缓存池结构*/
    ngx_chain_t          *chain;	/* 缓冲区链表 */
    ngx_pool_large_t     *large;    /* 存储大数据的链表 */
    ngx_pool_cleanup_t   *cleanup;  /* 可自定义回调函数，清除内存块分配的内存 */
    ngx_log_t            *log;      /* 日志 */
};
typedef struct ngx_pool_s            ngx_pool_t;

typedef struct {
    u_char               *last; /* 内存池中未使用内存的开始节点地址 */
    u_char               *end;  /* 内存池的结束地址 */
    ngx_pool_t           *next; /* 指向下一个内存池 */
    ngx_uint_t            failed;   /* 失败次数 */
} ngx_pool_data_t;

//大块数据内存池
struct ngx_pool_large_s {
    ngx_pool_large_t     *next;   /* 指向下一个存储地址 通过这个地址可以知道当前块长度 */
    void                 *alloc;  /* 数据块指针地址 */
};
typedef struct ngx_pool_large_s  ngx_pool_large_t;

//内存池回收
struct ngx_pool_cleanup_s {
    ngx_pool_cleanup_pt   handler;  /* 清理的回调函数 */
    void                 *data; 	/* 指向存储的数据地址 */
    ngx_pool_cleanup_t   *next; 	/* 下一个ngx_pool_cleanup_t */
};

ngx_alloc和ngx_calloc 主要封装了Nginx的内存分配函数malloc。 

void *
ngx_alloc(size_t size, ngx_log_t *log)
{
    void  *p;

    p = malloc(size);
    if (p == NULL) {
        ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,
                      "malloc(%uz) failed", size);
    }

    ngx_log_debug2(NGX_LOG_DEBUG_ALLOC, log, 0, "malloc: %p:%uz", p, size);

    return p;
}   


void *
ngx_calloc(size_t size, ngx_log_t *log)
{
    void  *p;

    p = ngx_alloc(size, log);

    if (p) {
        //内存数据置为0
        ngx_memzero(p, size);
    }

    return p;
}

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

    //内存开始地址，指向ngx_pool_t结构体之后数据取起始位置
    p->d.last = (u_char *) p + sizeof(ngx_pool_t);
    p->d.end = (u_char *) p + size;
    p->d.next = 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;

    p->current = p;
    p->chain = NULL;
    p->large = NULL;
    p->cleanup = NULL;
    p->log = log;

    return p;
}


//销毁内存池
void
ngx_destroy_pool(ngx_pool_t *pool)
{
    ngx_pool_t          *p, *n;
    ngx_pool_large_t    *l;
    ngx_pool_cleanup_t  *c;

    //执行内存池中的回调方法进行销毁
    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);
        }
    }

#if (NGX_DEBUG)

    /*
     * we could allocate the pool->log from this pool
     * so we cannot use this log while free()ing the pool
     */

    for (l = pool->large; l; l = l->next) {
        ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0, "free: %p", l->alloc);
    }

    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 (l = pool->large; l; l = l->next) {
        if (l->alloc) {
            ngx_free(l->alloc);
        }
    }

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

        if (n == NULL) {
            break;
        }
    }
}


//重设内存池
void ngx_reset_pool(ngx_pool_t *pool) {
	ngx_pool_t *p;
	ngx_pool_large_t *l;
 
	/* 清理pool->large链表（pool->large为单独的大数据内存块）  */
	for (l = pool->large; l; l = l->next) {
		if (l->alloc) {
			ngx_free(l->alloc);
		}
	}
 
	pool->large = NULL;
 
	/* 循环重新设置内存池data区域的 p->d.last；data区域数据并不擦除*/
	for (p = pool; p; p = p->d.next) {
		p->d.last = (u_char *) p + sizeof(ngx_pool_t);
	}
}

void *
ngx_palloc(ngx_pool_t *pool, size_t size)
{
#if !(NGX_DEBUG_PALLOC)
    if (size <= pool->max) {
        //分配小内存
        return ngx_palloc_small(pool, size, 1);
    }
#endif

    //分配大内存
    return ngx_palloc_large(pool, size);
}   


static ngx_inline void *
ngx_palloc_small(ngx_pool_t *pool, size_t size, ngx_uint_t align)
{
    u_char      *m;
    ngx_pool_t  *p;

    p = pool->current;

    do {
        m = p->d.last;

        if (align) {
            //对齐操作,会损失内存，提高内存使用速度
            m = ngx_align_ptr(m, NGX_ALIGNMENT);
        }

        if ((size_t) (p->d.end - m) >= size) {
            p->d.last = m + size;

            return m;
        }

        p = p->d.next;

    } while (p);

    //如果没有缓存池空间没有可以容纳大小为size的内存块，则需要重新申请一个缓存池pool节点
    return ngx_palloc_block(pool, size);
}

ngx_pnalloc方法则是非对齐操作分配内存

//大内存分配则是直接通过ngx_alloc分配，通过链表挂载到pool->large，所以后面的释放内存也由系统做
static void *
ngx_palloc_large(ngx_pool_t *pool, size_t size)
{
    void              *p;
    ngx_uint_t         n;
    ngx_pool_large_t  *large;

    p = ngx_alloc(size, pool->log);
    if (p == NULL) {
        return NULL;
    }

    n = 0;

    for (large = pool->large; large; large = large->next) {
        if (large->alloc == NULL) {
            large->alloc = p;
            return p;
        }

        if (n++ > 3) {
            break;
        }
    }

    large = ngx_palloc_small(pool, sizeof(ngx_pool_large_t), 1);
    if (large == NULL) {
        ngx_free(p);
        return NULL;
    }

    large->alloc = p;
    large->next = pool->large;
    pool->large = large;

    return p;
}