Nginx源码完全注释（1）ngx_alloc.h / ngx_alloc.c

• 作者：柳大·Poechant
• 时间：2012年7月1日
• 博客：Blog.CSDN.net/Poechant

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首先看 ngx_alloc.h 文件，主要声明或宏定义了 ngx_alloc，ngx_calloc，ngx_memalign，ngx_free。

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


#ifndef _NGX_ALLOC_H_INCLUDED_
#define _NGX_ALLOC_H_INCLUDED_


#include <ngx_config h=""><span class="preprocessor" style="color: rgb(136, 0, 0); ">#include </span><ngx_core h=""><span class="keyword" style="font-weight: bold; ">void</span> *ngx_alloc(size_t size, ngx_log_t *log);
<span class="keyword" style="font-weight: bold; ">void</span> *ngx_calloc(size_t size, ngx_log_t *log);

<span class="comment" style="color: rgb(136, 136, 136); ">// 宏命名 free 为 ngx_free，Nginx 的习惯</span>
<span class="preprocessor" style="color: rgb(136, 0, 0); ">#define ngx_free          free</span>


<span class="comment" style="color: rgb(136, 136, 136); ">/*
 * 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
 */</span>

<span class="preprocessor" style="color: rgb(136, 0, 0); ">#if (NGX_HAVE_POSIX_MEMALIGN || NGX_HAVE_MEMALIGN)</span>

<span class="keyword" style="font-weight: bold; ">void</span> *ngx_memalign(size_t alignment, size_t size, ngx_log_t *log);

<span class="preprocessor" style="color: rgb(136, 0, 0); ">#else</span>

<span class="preprocessor" style="color: rgb(136, 0, 0); ">#define ngx_memalign(alignment, size, log)  ngx_alloc(size, log)</span>

<span class="preprocessor" style="color: rgb(136, 0, 0); ">#endif</span>

<span class="comment" style="color: rgb(136, 136, 136); ">// 声明三个可以被外部使用的变量</span>
<span class="keyword" style="font-weight: bold; ">extern</span> ngx_uint_t  ngx_pagesize;
<span class="keyword" style="font-weight: bold; ">extern</span> ngx_uint_t  ngx_pagesize_shift;
<span class="keyword" style="font-weight: bold; ">extern</span> ngx_uint_t  ngx_cacheline_size;


<span class="preprocessor" style="color: rgb(136, 0, 0); ">#endif /* _NGX_ALLOC_H_INCLUDED_ */</span>
</ngx_core></ngx_config>

再来看 ngx_alloc.c，实现了内存分配函数 ngx_alloc，ngx_calloc，ngx_

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


#include <ngx_config h=""><span class="preprocessor" style="color: rgb(136, 0, 0); ">#include </span><ngx_core h="">


ngx_uint_t  ngx_pagesize;
ngx_uint_t  ngx_pagesize_shift;
ngx_uint_t  ngx_cacheline_size;

<span class="comment" style="color: rgb(136, 136, 136); ">/*
 * 封装malloc，增加分配失败判断及调试日志
 */</span>
<span class="keyword" style="font-weight: bold; ">void</span> *
ngx_alloc(size_t size, ngx_log_t *log)
{
    <span class="keyword" style="font-weight: bold; ">void</span>  *p;

    p = malloc(size);
    <span class="keyword" style="font-weight: bold; ">if</span> (p == NULL) {
        ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,
                      <span class="string" style="color: rgb(136, 0, 0); ">"malloc(%uz) failed"</span>, size);
    }

    <span class="comment" style="color: rgb(136, 136, 136); ">/* 在编译时指定debug模式是否开启，如果不开启则此句仅是括号中的逗号表达式 */</span>
    ngx_log_debug2(NGX_LOG_DEBUG_ALLOC, log, <span class="number" style="color: rgb(0, 136, 0); ">0</span>, <span class="string" style="color: rgb(136, 0, 0); ">"malloc: %p:%uz"</span>, p, size);

    <span class="keyword" style="font-weight: bold; ">return</span> p;
}

<span class="comment" style="color: rgb(136, 136, 136); ">/*
 * 封装ngx_alloc，如果分配成功，初始化为0
 */</span>
<span class="keyword" style="font-weight: bold; ">void</span> *
ngx_calloc(size_t size, ngx_log_t *log)
{
    <span class="keyword" style="font-weight: bold; ">void</span>  *p;

    p = ngx_alloc(size, log);

    <span class="comment" style="color: rgb(136, 136, 136); ">/* 初始化为 0 */</span>
    <span class="keyword" style="font-weight: bold; ">if</span> (p) {
        ngx_memzero(p, size);
    }

    <span class="keyword" style="font-weight: bold; ">return</span> p;
}


<span class="preprocessor" style="color: rgb(136, 0, 0); ">#if (NGX_HAVE_POSIX_MEMALIGN)</span>

<span class="comment" style="color: rgb(136, 136, 136); ">// 封装 posix_memalign，如果是 Solaris 则封装 memalign</span>
<span class="keyword" style="font-weight: bold; ">void</span> *
ngx_memalign(size_t alignment, size_t size, ngx_log_t *log)
{
    <span class="keyword" style="font-weight: bold; ">void</span>  *p;
    <span class="keyword" style="font-weight: bold; ">int</span>    err;

    <span class="comment" style="color: rgb(136, 136, 136); ">/*
     * 背景：
     *      1）POSIX 1003.1d
     *      2）POSIX 标明了通过malloc( ), calloc( ), 和 realloc( ) 返回的地址对于
     *      任何的C类型来说都是对齐的
     * 功能：由posix_memalign分配的内存空间，需要由free释放。
     * 参数：
     *      p           分配好的内存空间的首地址
     *      alignment   对齐边界，Linux中，32位系统是8字节，64位系统是16字节
     *      size        指定分配size字节大小的内存
     *
     * 要求：
     *      1）要求alignment是2的幂，并且是p指针大小的倍数
     *      2）要求size是alignment的倍数
     * 返回：
     *      0       成功
     *      EINVAL  参数不满足要求
     *      ENOMEM  内存分配失败
     * 注意：
     *      1）该函数不影响errno，只能通过返回值判断
     *
     */</span>
    err = posix_memalign(&amp;p, alignment, size);

    <span class="keyword" style="font-weight: bold; ">if</span> (err) {
        ngx_log_error(NGX_LOG_EMERG, log, err,
                      <span class="string" style="color: rgb(136, 0, 0); ">"posix_memalign(%uz, %uz) failed"</span>, alignment, size);
        p = NULL;
    }

    ngx_log_debug3(NGX_LOG_DEBUG_ALLOC, log, <span class="number" style="color: rgb(0, 136, 0); ">0</span>,
                   <span class="string" style="color: rgb(136, 0, 0); ">"posix_memalign: %p:%uz @%uz"</span>, p, size, alignment);

    <span class="keyword" style="font-weight: bold; ">return</span> p;
}

<span class="preprocessor" style="color: rgb(136, 0, 0); ">#elif (NGX_HAVE_MEMALIGN)</span>

<span class="keyword" style="font-weight: bold; ">void</span> *
ngx_memalign(size_t alignment, size_t size, ngx_log_t *log)
{
    <span class="keyword" style="font-weight: bold; ">void</span>  *p;

    <span class="comment" style="color: rgb(136, 136, 136); ">// 与 posix_memalign 的不同是其将分配好的内存块首地址做为返回值</span>
    p = memalign(alignment, size);
    <span class="keyword" style="font-weight: bold; ">if</span> (p == NULL) {
        ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,
                      <span class="string" style="color: rgb(136, 0, 0); ">"memalign(%uz, %uz) failed"</span>, alignment, size);
    }

    ngx_log_debug3(NGX_LOG_DEBUG_ALLOC, log, <span class="number" style="color: rgb(0, 136, 0); ">0</span>,
                   <span class="string" style="color: rgb(136, 0, 0); ">"memalign: %p:%uz @%uz"</span>, p, size, alignment);

    <span class="keyword" style="font-weight: bold; ">return</span> p;
}

<span class="preprocessor" style="color: rgb(136, 0, 0); ">#endif</span>
</ngx_core></ngx_config>

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