Nginx学习笔记(五) 源码分析&内存模块&内存对齐

Nginx源码分析&内存模块

  今天总结了下C语言的内存分配问题,那么就看看Nginx的内存分配相关模型的具体实现。还有内存对齐的内容~~不懂的可以看看~~

src/os/unix/Ngx_alloc.h&Ngx_alloc.c

  先上源码:

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#ifndef _NGX_ALLOC_H_INCLUDED_
#define _NGX_ALLOC_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>


void *ngx_alloc(size_t size, ngx_log_t *log);
void *ngx_calloc(size_t size, ngx_log_t *log);

#define ngx_free          free


/*
 * Linux has memalign() or posix_memalign()
 * Solaris has memalign()
 * FreeBSD 7.0 has posix_memalign(), besides, early version's malloc()
 * aligns allocations bigger than page size at the page boundary
 */

#if (NGX_HAVE_POSIX_MEMALIGN || NGX_HAVE_MEMALIGN)

void *ngx_memalign(size_t alignment, size_t size, ngx_log_t *log);

#else

#define ngx_memalign(alignment, size, log)  ngx_alloc(size, log)

#endif


extern ngx_uint_t  ngx_pagesize;
extern ngx_uint_t  ngx_pagesize_shift;
extern ngx_uint_t  ngx_cacheline_size;


#endif /* _NGX_ALLOC_H_INCLUDED_ */
View Code

  这里部分代码是关于内存的申请的,是对Linux原有的内存申请函数的再一次封装。

  1.函数声明

void *ngx_alloc(size_t size, ngx_log_t *log);    //申请空间
void *ngx_calloc(size_t size, ngx_log_t *log);   //申请空间,并初始化为0

  2.源码解析

void * ngx_alloc(size_t size, ngx_log_t *log)
{
    void  *p;
    p = malloc(size);//malloc就是返回一个void*指针,指向分配的size大小的内存
    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);//调用上面的函数
    if (p) {
        ngx_memzero(p, size);//并初始化为0,#define ngx_memzero(buf, n) (void) memset(buf, 0, n)
  }
return p;
}

  3.POSIX_MEMALIGN与MEMALIGN申请对齐内存,可以参考Linux man page:http://man7.org/linux/man-pages/man3/valloc.3.html

#if (NGX_HAVE_POSIX_MEMALIGN || NGX_HAVE_MEMALIGN)

void *ngx_memalign(size_t alignment, size_t size, ngx_log_t *log);

#else

#define ngx_memalign(alignment, size, log)  ngx_alloc(size, log)

#endif
#if (NGX_HAVE_POSIX_MEMALIGN)
void * ngx_memalign(size_t alignment, size_t size, ngx_log_t *log)
{
    void  *p;
    int    err;
    err = posix_memalign(&p, alignment, size);//stdlib.h 新接口

    if (err) {
        ngx_log_error(NGX_LOG_EMERG, log, err,
                      "posix_memalign(%uz, %uz) failed", alignment, size);
        p = NULL;
    }
    ngx_log_debug3(NGX_LOG_DEBUG_ALLOC, log, 0,
                   "posix_memalign: %p:%uz @%uz", p, size, alignment);
    return p;
}
#elif (NGX_HAVE_MEMALIGN)
void * ngx_memalign(size_t alignment, size_t size, ngx_log_t *log)
{
    void  *p;
    p = memalign(alignment, size);//malloc.h 老接口
    if (p == NULL) {
        ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,
                      "memalign(%uz, %uz) failed", alignment, size);
    }
    ngx_log_debug3(NGX_LOG_DEBUG_ALLOC, log, 0,
                   "memalign: %p:%uz @%uz", p, size, alignment);
    return p;
}
#endif

数据对齐

概念:

  对齐跟数据在内存中的位置有关,为了使CPU能够对变量进行快速的访问,变量的起始地址应该具有某些特性,即所谓的”对齐”。 比如4字节的int型,其起始地址应该位于4字节的边界上,即起始地址能够被4整除。

功能:

  字节对齐的作用不仅是便于cpu快速访问,同时合理的利用字节对齐可以有效地节省存储空间。

具体方法:

  指定对齐值:#pragma pack (value)时的指定对齐值value。

  取消对齐值:#pragma pach ()

具体分析:

struct A{
    char a;   //1
    int b;    //4
    short c;  //2
}

struct B{
    int b;
    char a;
    short c;
}

#pragma pack(1)
struct C{
    char a;
    int b;
    short c;
}
#pragma pack()

#pragma pach(2)
struct D{
    char a;
    int b;
    short c;
}
#pragma pack()

  代码如上,想一想答案都是多少?

    sizeof(struct A)=10  //默认情况下,1字节的a在0x00000000,而整形b只能放在0x00000004(必须从4的整数倍开始)~0x00000007,最后的c在0x00000008~0x00000009

  sizeof(struct B)=8    //分析同上

  sizeof(struct C)=7    //这里指定了对齐值为1,那么a在0x00000000,b在0x00000001~0x0000004,c在0x00000005~0x00000006

  sizeof(struct D)=8    //分析同上

A、B、C、D的内存地址如图:

地址 0x00000000 0x01 0x02 0x03 004 0x05 0x06 0x07 0x08 0x09
A a       b c
B b a   c    
C a b c      
D a   b c    

 src/core/Ngx_palloc.h&Ngx_palloc.cn内存池分析

  上源码:

/*
 * Copyright (C) Igor Sysoev
 * Copyright (C) Nginx, Inc.
 */


#ifndef _NGX_PALLOC_H_INCLUDED_
#define _NGX_PALLOC_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>


/*
 * NGX_MAX_ALLOC_FROM_POOL should be (ngx_pagesize - 1), i.e. 4095 on x86.
 * On Windows NT it decreases a number of locked pages in a kernel.
 */
#define NGX_MAX_ALLOC_FROM_POOL  (ngx_pagesize - 1)

#define NGX_DEFAULT_POOL_SIZE    (16 * 1024)

#define NGX_POOL_ALIGNMENT       16
#define NGX_MIN_POOL_SIZE                                                     \
    ngx_align((sizeof(ngx_pool_t) + 2 * sizeof(ngx_pool_large_t)),            \
              NGX_POOL_ALIGNMENT)


typedef void (*ngx_pool_cleanup_pt)(void *data);

typedef struct ngx_pool_cleanup_s  ngx_pool_cleanup_t;

struct ngx_pool_cleanup_s {
    ngx_pool_cleanup_pt   handler;
    void                 *data;
    ngx_pool_cleanup_t   *next;
};


typedef struct ngx_pool_large_s  ngx_pool_large_t;

struct ngx_pool_large_s {
    ngx_pool_large_t     *next;
    void                 *alloc;
};


typedef struct {
    u_char               *last;
    u_char               *end;
    ngx_pool_t           *next;
    ngx_uint_t            failed;
} ngx_pool_data_t;


struct ngx_pool_s {
    ngx_pool_data_t       d;
    size_t                max;
    ngx_pool_t           *current;
    ngx_chain_t          *chain;
    ngx_pool_large_t     *large;
    ngx_pool_cleanup_t   *cleanup;
    ngx_log_t            *log;
};


typedef struct {
    ngx_fd_t              fd;
    u_char               *name;
    ngx_log_t            *log;
} ngx_pool_cleanup_file_t;


void *ngx_alloc(size_t size, ngx_log_t *log);
void *ngx_calloc(size_t size, ngx_log_t *log);

ngx_pool_t *ngx_create_pool(size_t size, ngx_log_t *log);
void ngx_destroy_pool(ngx_pool_t *pool);
void ngx_reset_pool(ngx_pool_t *pool);

void *ngx_palloc(ngx_pool_t *pool, size_t size);
void *ngx_pnalloc(ngx_pool_t *pool, size_t size);
void *ngx_pcalloc(ngx_pool_t *pool, size_t size);
void *ngx_pmemalign(ngx_pool_t *pool, size_t size, size_t alignment);
ngx_int_t ngx_pfree(ngx_pool_t *pool, void *p);


ngx_pool_cleanup_t *ngx_pool_cleanup_add(ngx_pool_t *p, size_t size);
void ngx_pool_run_cleanup_file(ngx_pool_t *p, ngx_fd_t fd);
void ngx_pool_cleanup_file(void *data);
void ngx_pool_delete_file(void *data);


#endif /* _NGX_PALLOC_H_INCLUDED_ */
View Code

  1.#define NGX_DEFAULT_POOL_SIZE    (16 * 1024),表示NGX默认的内存池的大小为16*1024

  2.结构体ngx_pool_data_t内存数据块,ngx_pool_s内存池头部结构

 typedef struct {
   u_char      *last;  //当前内存池分配到此处,即下一次分配从此处开始
   u_char      *end;   //内存池结束位置
   ngx_pool_t  *next;  //内存池里面有很多块内存,这些内存块就是通过该指针连成链表的
   ngx_uint_t  failed; //内存池分配失败次数
 } ngx_pool_data_t;    //内存池的数据块位置信息


 struct ngx_pool_s{    //内存池头部结构
    ngx_pool_data_t     d;       //内存池的数据块
    size_t              max;     //内存池数据块的最大值
    ngx_pool_t         *current; //指向当前内存池
    ngx_chain_t        *chain;   //该指针挂接一个ngx_chain_t结构
    ngx_pool_large_t   *large;   //大块内存链表,即分配空间超过max的内存
    ngx_pool_cleanup_t *cleanup; //释放内存池的callback
    ngx_log_t          *log;     //日志信息
};

  3.创建和销毁内存池:

ngx_pool_t * ngx_create_pool(size_t size, ngx_log_t *log)//创建内存池
{ ngx_pool_t
*p; p = ngx_memalign(NGX_POOL_ALIGNMENT, size, log); //申请对齐内存空间 if (p == NULL) { return NULL; } p->d.last = (u_char *) p + sizeof(ngx_pool_t); //下一次分配的开始地址,sizeof(ngx_pool_t)为申请的P的大小 p->d.end = (u_char *) p + size;             //内存池结束位置,size是申请空间的小小 p->d.next = NULL; //内存链表的指向下一内存块的指针为空 p->d.failed = 0; //失败次数 size = size - sizeof(ngx_pool_t); // p->max = (size < NGX_MAX_ALLOC_FROM_POOL) ? size : NGX_MAX_ALLOC_FROM_POOL;                                  //内存池最大块            p->current = p; //当前指向的内存块 p->chain = NULL; p->large = NULL; p->cleanup = NULL; p->log = log; return p; } 
//该函数将遍历内存池链表,所有释放内存,如果注册了clenup(也是一个链表结构)亦将遍历该cleanup链表结构依次调用clenuphandler清理。同时,还将遍历large链表,释放大块内存
void
ngx_destroy_pool(ngx_pool_t *pool)//删除全部内存池(链上的所有内存块) { ngx_pool_t *p, *n; ngx_pool_large_t *l; ngx_pool_cleanup_t *c;   //根据注册的ngx_pool_cleanup_s 来逐个销毁内存 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);      } } //销毁大内存块 for (l = pool->large; l; l = l->next) { 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
  //普通内存池
  for (p = pool, n = pool->d.next; /* void */; p = n, n = n->d.next) { ngx_free(p); if (n == NULL) { break; } }

  4.重置内存池:

//该函数将释放所有large内存,并且将d->last指针重新指向ngx_pool_t结构之后数据区的开始位置,同刚创建后的位置相同。
void
ngx_reset_pool(ngx_pool_t *pool) { ngx_pool_t *p; ngx_pool_large_t *l; //删除大内存块 for (l = pool->large; l; l = l->next) { if (l->alloc) { ngx_free(l->alloc);//专门用于释放大内存ngx_free() } } //大内存块置为空 pool->large = NULL; //重新修改每个内存块的大小 for (p = pool; p; p = p->d.next) { p->d.last = (u_char *) p + sizeof(ngx_pool_t); } }

  5.注册cleanup

//cleanup结构体
struct ngx_pool_cleanup_s {
    ngx_pool_cleanup_pt   handler;
    void                 *data;
    ngx_pool_cleanup_t   *next;
};

//注册cleanup函数,为以后清除做准备
ngx_pool_cleanup_t * ngx_pool_cleanup_add(ngx_pool_t *p, size_t size)
{
    ngx_pool_cleanup_t  *c;
    c = ngx_palloc(p, sizeof(ngx_pool_cleanup_t));//申请内存池
    if (c == NULL) {
        return NULL;
    }
    if (size) {
        c->data = ngx_palloc(p, size); //申请数据空间
        if (c->data == NULL) {
            return NULL;
        }
    } else {
        c->data = NULL;
    }
    c->handler = NULL;
    c->next = p->cleanup;
    p->cleanup = c;
    ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, p->log, 0, "add cleanup: %p", c);
    return c;
}

   6.内存分配函数

void *ngx_palloc(ngx_pool_t *pool, size_t size);
void *ngx_pnalloc(ngx_pool_t *pool, size_t size);
void *ngx_pcalloc(ngx_pool_t *pool, size_t size);
void *ngx_pmemalign(ngx_pool_t *pool, size_t size, size_t alignment);

  主要介绍一下ngx_palloc()这个函数:

void * ngx_palloc(ngx_pool_t *pool, size_t size)
{
    u_char      *m;
    ngx_pool_t  *p;

    if (size <= pool->max) {//max与待分配内存进行比较
        p = pool->current;//从当前位置开始遍历pool链表

        do {
            m = ngx_align_ptr(p->d.last, NGX_ALIGNMENT);
            if ((size_t) (p->d.end - m) >= size) {
                p->d.last = m + size;
                return m;                     //成功分配size大小的内存
            }
            p = p->d.next;
        } while (p);

        return ngx_palloc_block(pool, size);  //链表里没有能分配size大小内存的节点,则生成一个新的节点并在其中分配内存 
    }
    return ngx_palloc_large(pool, size);      //大于max值,则在large链表里分配内存
}

  其中的ngx_palloc_block()函数:

//该函数分配一块内存,并加入到内存池中
static
void * ngx_palloc_block(ngx_pool_t *pool, size_t size) { u_char *m; size_t psize; ngx_pool_t *p, *new, *current; psize = (size_t) (pool->d.end - (u_char *) pool); //计算内存池大小 m = ngx_memalign(NGX_POOL_ALIGNMENT, psize, pool->log); //申请与原来相同的大小,这样的话内存池就是以2的指数幂增大 if (m == NULL) { return NULL; } new = (ngx_pool_t *) m; //新的内存块 new->d.end = m + psize; new->d.next = NULL; new->d.failed = 0; m += sizeof(ngx_pool_data_t);//让m指向该块内存ngx_pool_data_t结构体之后数据区起始位 m = ngx_align_ptr(m, NGX_ALIGNMENT); new->d.last = m + size; //在数据区分配size大小的内存并设置last指针 current = pool->current; for (p = current; p->d.next; p = p->d.next) { if (p->d.failed++ > 4) { //失败4次以上移动current指针 current = p->d.next; } } p->d.next = new; //将这次分配的内存块new加入该内存池 pool->current = current ? current : new; return m; }

参考

http://hi.baidu.com/langwan/item/fdd3bf4a4ef66aefa4c06629

http://blog.csdn.net/wallwind/article/details/7463979

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

posted @ 2013-06-25 13:57  cococo点点  阅读(2874)  评论(0编辑  收藏  举报