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_ */
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, , "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, ,
"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, ,
"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) + * 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_ */
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 = ; //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clenup的handler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, , "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, , "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, ,
"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, , "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 = ; 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++ > ) { //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