Nginx内存管理

1.源代码位置

头文件：http://trac.nginx.org/nginx/browser/nginx/src/core/ngx_palloc.h

源文件：http://trac.nginx.org/nginx/browser/nginx/src/core/ngx_palloc.c

2.数据结构定义

先来学习一下nginx内存池的几个主要数据结构：

ngx_pool_data_t（内存池数据块结构）

   1:typedef struct {
   2:     u_char               *last;        
   3:     u_char               *end;
   4:     ngx_pool_t           *next;
   5:     ngx_uint_t            failed;
   6: } ngx_pool_data_t;
last：是一个unsigned char 类型的指针，保存的是/当前内存池分配到末位地址，即下一次分配从此处开始。
end：内存池结束位置；
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，next指向下一块内存。
failed：内存池分配失败次数。
ngx_pool_s（内存池头部结构）
   1:struct ngx_pool_s {
   2:     ngx_pool_data_t       d;
   3:     size_t                max;
   4:     ngx_pool_t           *current;
   5:     ngx_chain_t          *chain;
   6:     ngx_pool_large_t     *large;
   7:     ngx_pool_cleanup_t   *cleanup;
   8:     ngx_log_t            *log;
   9: };
d：内存池的数据块；
max：内存池数据块的最大值；
current：指向当前内存池；
chain：该指针挂接一个ngx_chain_t结构；
large：大块内存链表，即分配空间超过max的情况使用；
cleanup：释放内存池的callback
log：日志信息
由ngx_pool_data_t和ngx_pool_t组成的nginx内存池结构如下图所示：
3.相关函数介绍
在分析内存池方法前，需要对几个主要的内存相关函数作一下介绍:
ngx_alloc：（只是对malloc进行了简单的封装）
<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1:void *<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   2: ngx_alloc(size_t size, ngx_log_t *log)<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   3: {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   4:     void  *p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   5:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   6:     p = malloc(size);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   7:     if (p == NULL) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   8:         ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   9:                       "malloc(%uz) failed", size);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  10:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  11:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  12:     ngx_log_debug2(NGX_LOG_DEBUG_ALLOC, log, 0, "malloc: %p:%uz", p, size);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  13:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  14:     return p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  15: }
ngx_calloc：（调用malloc并初始化为0）
<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1:void *<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   2: ngx_calloc(size_t size, ngx_log_t *log)<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   3: {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   4:     void  *p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   5:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   6:     p = ngx_alloc(size, log);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   7:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   8:     if (p) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   9:         ngx_memzero(p, size);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  10:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  11:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  12:     return p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  13: }
ngx_memzero：
<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1: #define ngx_memzero(buf, n)       (void) memset(buf, 0, n)
ngx_free ：
<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1: #define ngx_free          free
ngx_memalign：
<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1:void *<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   2: ngx_memalign(size_t alignment, size_t size, ngx_log_t *log)<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   3: {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   4:     void  *p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   5:     int    err;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   6:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   7:     err = posix_memalign(&p, alignment, size);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   8:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   9:     if (err) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  10:         ngx_log_error(NGX_LOG_EMERG, log, err,<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  11:                       "posix_memalign(%uz, %uz) failed", alignment, size);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  12:         p = NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  13:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  14:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  15:     ngx_log_debug3(NGX_LOG_DEBUG_ALLOC, log, 0,<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  16:                    "posix_memalign: %p:%uz @%uz", p, size, alignment);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  17:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  18:     return p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  19: }
这里alignment主要是针对部分unix平台需要动态的对齐，对POSIX 1003.1d提供的posix_memalign( )进行封装，在大多数情况下，编译器和C库透明地帮你处理对齐问题。nginx中通过宏NGX_HAVE_POSIX_MEMALIGN来控制；调用posix_memalign( )成功时会返回size字节的动态内存，并且这块内存的地址是alignment的倍数。参数alignment必须是2的幂，还是void指针的大小的倍数。返回的内存块的地址放在了memptr里面，函数返回值是0.
 
4.内存池基本操作
内存池对外的主要方法有：
创建内存池
ngx_pool_t *  ngx_create_pool(size_t size, ngx_log_t *log);
销毁内存池
void ngx_destroy_pool(ngx_pool_t *pool);
重置内存池
void ngx_reset_pool(ngx_pool_t *pool);
内存申请（对齐）
void *  ngx_palloc(ngx_pool_t *pool, size_t size);
内存申请（不对齐）
void *  ngx_pnalloc(ngx_pool_t *pool, size_t size);
内存清除
ngx_int_t  ngx_pfree(ngx_pool_t *pool, void *p);
4.1 创建内存池ngx_create_pool
ngx_create_pool用于创建一个内存池，我们创建时，传入我们的需要的初始大小：
<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1: ngx_pool_t *<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   2: ngx_create_pool(size_t size, ngx_log_t *log)<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   3: {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   4:     ngx_pool_t  *p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   5:     <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   6:     //以16（NGX_POOL_ALIGNMENT）字节对齐分配size内存<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   7:     p = ngx_memalign(NGX_POOL_ALIGNMENT, size, log);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   8:     if (p == NULL) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   9:         return NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  10:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  11:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  12:     //初始状态：last指向ngx_pool_t结构体之后数据取起始位置<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  13:     p->d.last = (u_char *) p + sizeof(ngx_pool_t);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  14:     //end指向分配的整个size大小的内存的末尾<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  15:     p->d.end = (u_char *) p + size;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  16:     <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  17:     p->d.next = NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  18:     p->d.failed = 0;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  19:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  20:     size = size - sizeof(ngx_pool_t);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  21:     //#define NGX_MAX_ALLOC_FROM_POOL  (ngx_pagesize - 1)，内存池最大不超过4095，x86中页的大小为4K<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  22:     p->max = (size < NGX_MAX_ALLOC_FROM_POOL) ? size : NGX_MAX_ALLOC_FROM_POOL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  23:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  24:     p->current = p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  25:     p->chain = NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  26:     p->large = NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  27:     p->cleanup = NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  28:     p->log = log;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  29:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  30:     return p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  31: }
nginx对内存的管理分为大内存与小内存，当某一个申请的内存大于某一个值时，就需要从大内存中分配空间，否则从小内存中分配空间。
nginx中的内存池是在创建的时候就设定好了大小，在以后分配小块内存的时候，如果内存不够，则是重新创建一块内存串到内存池中，而不是将原有的内存池进行扩张。当要分配大块内存是，则是在内存池外面再分配空间进行管理的，称为大块内存池。
 
4.2 内存申请 ngx_palloc
<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1:void *<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   2: ngx_palloc(ngx_pool_t *pool, size_t size)<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   3: {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   4:     u_char      *m;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   5:     ngx_pool_t  *p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   6:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   7:     //如果申请的内存大小小于内存池的max值<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   8:     if (size <= pool->max) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   9:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  10:         p = pool->current;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  11:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  12:         do {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  13:             //对内存地址进行对齐处理<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  14:             m = ngx_align_ptr(p->d.last, NGX_ALIGNMENT);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  15:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  16:             //如果当前内存块够分配内存，则直接分配<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  17:             if ((size_t) (p->d.end - m) >= size) <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  18:             {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  19:                 p->d.last = m + size;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  20:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  21:                 return m;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  22:             }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  23:             <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  24:             //如果当前内存块有效容量不够分配，则移动到下一个内存块进行分配<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  25:             p = p->d.next;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  26:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  27:         } while (p);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  28:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  29:         //当前所有内存块都没有空闲了，开辟一块新的内存，如下2详细解释<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  30:         return ngx_palloc_block(pool, size);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  31:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  32:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  33:     //分配大块内存<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  34:     return ngx_palloc_large(pool, size);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  35: }
需要说明的几点：
1、ngx_align_ptr，这是一个用来内存地址取整的宏，非常精巧，一句话就搞定了。作用不言而喻，取整可以降低CPU读取内存的次数，提高性能。因为这里并没有真正意义调用malloc等函数申请内存，而是移动指针标记而已，所以内存对齐的活，C编译器帮不了你了，得自己动手。
<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1: #define ngx_align_ptr(p, a)                                                   <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   2:      (u_char *) (((uintptr_t) (p) + ((uintptr_t) a - 1)) & ~((uintptr_t) a - 1))
2、开辟一个新的内存块 ngx_palloc_block(ngx_pool_t *pool, size_t size)
这个函数是用来分配新的内存块，为pool内存池开辟一个新的内存块，并申请使用size大小的内存；
<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1:static void *<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   2: ngx_palloc_block(ngx_pool_t *pool, size_t size)<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   3: {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   4:     u_char      *m;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   5:     size_t       psize;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   6:     ngx_pool_t  *p, *new;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   7:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   8:     //计算内存池第一个内存块的大小<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   9:     psize = (size_t) (pool->d.end - (u_char *) pool);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  10:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  11:     //分配和第一个内存块同样大小的内存块<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  12:     m = ngx_memalign(NGX_POOL_ALIGNMENT, psize, pool->log);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  13:     if (m == NULL) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  14:         return NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  15:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  16:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  17:     new = (ngx_pool_t *) m;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  18:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  19:     //设置新内存块的end<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  20:     new->d.end = m + psize;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  21:     new->d.next = NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  22:     new->d.failed = 0;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  23:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  24:     //将指针m移动到d后面的一个位置，作为起始位置<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  25:     m += sizeof(ngx_pool_data_t);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  26:     //对m指针按4字节对齐处理<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  27:     m = ngx_align_ptr(m, NGX_ALIGNMENT);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  28:     //设置新内存块的last，即申请使用size大小的内存<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  29:     new->d.last = m + size;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  30:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  31:     //这里的循环用来找最后一个链表节点，这里failed用来控制循环的长度，如果分配失败次数达到5次，就忽略，不需要每次都从头找起<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  32:     for (p = pool->current; p->d.next; p = p->d.next) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  33:         if (p->d.failed++ > 4) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  34:             pool->current = p->d.next;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  35:         }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  36:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  37:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  38:     p->d.next = new;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  39:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  40:     return m;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  41: }
3、分配大块内存 ngx_palloc_large(ngx_pool_t *pool, size_t size)
在ngx_palloc中首先会判断申请的内存大小是否超过内存块的最大限值，如果超过，则直接调用ngx_palloc_large，进入大内存块的分配流程；
<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1:static void *<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   2: ngx_palloc_large(ngx_pool_t *pool, size_t size)<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   3: {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   4:     void              *p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   5:     ngx_uint_t         n;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   6:     ngx_pool_large_t  *large;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   7:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   8:     // 直接在系统堆中分配一块大小为size的空间<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   9:     p = ngx_alloc(size, pool->log);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  10:     if (p == NULL) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  11:         return NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  12:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  13:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  14:     n = 0;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  15:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  16:     // 查找到一个空的large区，如果有，则将刚才分配的空间交由它管理  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  17:     for (large = pool->large; large; large = large->next) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  18:         if (large->alloc == NULL) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  19:             large->alloc = p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  20:             return p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  21:         }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  22:         //为了提高效率， 如果在三次内没有找到空的large结构体，则创建一个<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  23:         if (n++ > 3) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  24:             break;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  25:         }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  26:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  27:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  28:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  29:     large = ngx_palloc(pool, sizeof(ngx_pool_large_t));<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  30:     if (large == NULL) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  31:         ngx_free(p);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  32:         return NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  33:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  34:     <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  35:     //将large链接到内存池<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  36:     large->alloc = p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  37:     large->next = pool->large;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  38:     pool->large = large;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  39:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  40:     return p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  41: }
整个内存池分配如下图：
4.3 内存池重置 ngx_reset_pool
<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1:void<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   2: ngx_reset_pool(ngx_pool_t *pool)<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   3: {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   4:     ngx_pool_t        *p;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   5:     ngx_pool_large_t  *l;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   6:     <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   7:     //释放大块内存<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   8:     for (l = pool->large; l; l = l->next) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   9:         if (l->alloc) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  10:             ngx_free(l->alloc);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  11:         }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  12:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  13:     <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  14:     // 重置所有小块内存区<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  15:     for (p = pool; p; p = p->d.next) {<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  16:         p->d.last = (u_char *) p + sizeof(ngx_pool_t);<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  17:         p->d.failed = 0;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  18:     }<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  19:  <preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  20:     pool->current = pool;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  21:     pool->chain = NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  22:     pool->large = NULL;<preCourier New',courier,monospace; width:870px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  23: }
4.4 内存池释放 ngx_pfree
<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   1: ngx_int_t<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   2: ngx_pfree(ngx_pool_t *pool, void *p)<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   3: {<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   4:     ngx_pool_large_t  *l;<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   5:  <preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   6:     //只检查是否是大内存块，如果是大内存块则释放<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   7:     for (l = pool->large; l; l = l->next) {<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   8:         if (p == l->alloc) {<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">   9:             ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0,<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  10:                            "free: %p", l->alloc);<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  11:             ngx_free(l->alloc);<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  12:             l->alloc = NULL;<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  13:  <preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  14:             return NGX_OK;<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  15:         }<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  16:     }<preCourier New',courier,monospace; width:950px; padding:0px; direction:ltr; margin:0em; line-height:12pt; background-color:rgb(244,244,244)">  17:  <preCourier New',courier,monospace; width:950px; padding:


           
                
                                                

                
                
                
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