海珠区有没有专门做网站的地方,营销型网站功能,wordpress andriod,百度图片搜索入口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#xff0c;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.hNgx_alloc.c 先上源码#xff1a; /** Copyright (C) Igor Sysoev* Copyright (C…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.hNgx_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.hvoid *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 versions 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)#endifextern 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; //1int b; //4short 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0x00000000b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0x000000000x010x020x030040x050x060x070x080x09Aa bcBba c Cabc Da bc src/core/Ngx_palloc.hNgx_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callbackngx_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, 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转载于:https://www.cnblogs.com/coder2012/p/3151346.html