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）
<span> 1:</span><span>typedef</span> <span>struct</span> {<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 2:</span> u_char *last; <pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 3:</span> u_char *end;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 4:</span> ngx_pool_t *next;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 5:</span> ngx_uint_t failed;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 6:</span> } 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）
<span> 1:</span><span>struct</span> ngx_pool_s {<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 2:</span> ngx_pool_data_t d;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 3:</span> size_t max;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 4:</span> ngx_pool_t *current;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 5:</span> ngx_chain_t *chain;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 6:</span> ngx_pool_large_t *large;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 7:</span> ngx_pool_cleanup_t *cleanup;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 8:</span> ngx_log_t *log;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 9:</span> };
- 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）
<span> 1:</span><span>void</span> *<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 2:</span> ngx_alloc(size_t size, ngx_log_t *log)<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 3:</span> {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 4:</span> <span>void</span> *p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 5:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 6:</span> p = malloc(size);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 7:</span> <span>if</span> (p == NULL) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 8:</span> ngx_log_error(NGX_LOG_EMERG, log, ngx_errno,<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 9:</span> <span>"malloc(%uz) failed"</span>, size);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 10:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 11:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 12:</span> ngx_log_debug2(NGX_LOG_DEBUG_ALLOC, log, 0, <span>"malloc: %p:%uz"</span>, p, size);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 13:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 14:</span> <span>return</span> p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 15:</span> }
ngx_calloc：（调用malloc并初始化为0）
<span> 1:</span><span>void</span> *<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 2:</span> ngx_calloc(size_t size, ngx_log_t *log)<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 3:</span> {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 4:</span> <span>void</span> *p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 5:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 6:</span> p = ngx_alloc(size, log);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 7:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 8:</span> <span>if</span> (p) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 9:</span> ngx_memzero(p, size);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 10:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 11:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 12:</span> <span>return</span> p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 13:</span> }
ngx_memzero：
ngx_free ：
ngx_memalign：
<span> 1:</span><span>void</span> *<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 2:</span> ngx_memalign(size_t alignment, size_t size, ngx_log_t *log)<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 3:</span> {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 4:</span> <span>void</span> *p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 5:</span> <span>int</span> err;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 6:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 7:</span> err = posix_memalign(&p, alignment, size);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 8:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 9:</span> <span>if</span> (err) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 10:</span> ngx_log_error(NGX_LOG_EMERG, log, err,<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 11:</span> <span>"posix_memalign(%uz, %uz) failed"</span>, alignment, size);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 12:</span> p = NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 13:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 14:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 15:</span> ngx_log_debug3(NGX_LOG_DEBUG_ALLOC, log, 0,<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 16:</span> <span>"posix_memalign: %p:%uz @%uz"</span>, p, size, alignment);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 17:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 18:</span> <span>return</span> p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 19:</span> }
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：
<span> 1:</span> ngx_pool_t *<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 2:</span> ngx_create_pool(size_t size, ngx_log_t *log)<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 3:</span> {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 4:</span> ngx_pool_t *p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 5:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 6:</span> <span>//以16（NGX_POOL_ALIGNMENT）字节对齐分配size内存</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 7:</span> p = ngx_memalign(NGX_POOL_ALIGNMENT, size, log);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 8:</span> <span>if</span> (p == NULL) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 9:</span> <span>return</span> NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 10:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 11:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 12:</span> <span>//初始状态：last指向ngx_pool_t结构体之后数据取起始位置</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 13:</span> p->d.last = (u_char *) p + <span>sizeof</span>(ngx_pool_t);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 14:</span> <span>//end指向分配的整个size大小的内存的末尾</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 15:</span> p->d.end = (u_char *) p + size;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 16:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 17:</span> p->d.next = NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 18:</span> p->d.failed = 0;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 19:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 20:</span> size = size - <span>sizeof</span>(ngx_pool_t);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 21:</span> <span>//#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</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 22:</span> p->max = (size <span> 23:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 24:</span> p->current = p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 25:</span> p->chain = NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 26:</span> p->large = NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 27:</span> p->cleanup = NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 28:</span> p->log = log;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 29:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 30:</span> <span>return</span> p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 31:</span> }
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
<span> 1:</span><span>void</span> *<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 2:</span> ngx_palloc(ngx_pool_t *pool, size_t size)<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 3:</span> {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 4:</span> u_char *m;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 5:</span> ngx_pool_t *p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 6:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 7:</span> <span>//如果申请的内存大小小于内存池的max值</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 8:</span> <span>if</span> (size max) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 9:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 10:</span> p = pool->current;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 11:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 12:</span> <span>do</span> {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 13:</span> <span>//对内存地址进行对齐处理</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 14:</span> m = ngx_align_ptr(p->d.last, NGX_ALIGNMENT);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 15:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 16:</span> <span>//如果当前内存块够分配内存，则直接分配</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 17:</span> <span>if</span> ((size_t) (p->d.end - m) >= size) <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 18:</span> {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 19:</span> p->d.last = m + size;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 20:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 21:</span> <span>return</span> m;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 22:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 23:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 24:</span> <span>//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</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 25:</span> p = p->d.next;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 26:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 27:</span> } <span>while</span> (p);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 28:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 29:</span> <span>//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</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 30:</span> <span>return</span> ngx_palloc_block(pool, size);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 31:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 32:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 33:</span> <span>//分配大块内存</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 34:</span> <span>return</span> ngx_palloc_large(pool, size);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 35:</span> }
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。
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；
<span> 1:</span><span>static</span> <span>void</span> *<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 2:</span> ngx_palloc_block(ngx_pool_t *pool, size_t size)<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 3:</span> {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 4:</span> u_char *m;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 5:</span> size_t psize;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 6:</span> ngx_pool_t *p, *<span>new</span>;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 7:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 8:</span> <span>//计算内存池第一个内存块的大小</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 9:</span> psize = (size_t) (pool->d.end - (u_char *) pool);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 10:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 11:</span> <span>//分配和第一个内存块同样大小的内存块</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 12:</span> m = ngx_memalign(NGX_POOL_ALIGNMENT, psize, pool->log);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 13:</span> <span>if</span> (m == NULL) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 14:</span> <span>return</span> NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 15:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 16:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 17:</span> <span>new</span> = (ngx_pool_t *) m;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 18:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 19:</span> <span>//设置新内存块的end</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 20:</span> <span>new</span>->d.end = m + psize;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 21:</span> <span>new</span>->d.next = NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 22:</span> <span>new</span>->d.failed = 0;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 23:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 24:</span> <span>//将指针m移动到d后面的一个位置，作为起始位置</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 25:</span> m += <span>sizeof</span>(ngx_pool_data_t);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 26:</span> <span>//对m指针按4字节对齐处理</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 27:</span> m = ngx_align_ptr(m, NGX_ALIGNMENT);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 28:</span> <span>//设置新内存块的last，即申请使用size大小的内存</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 29:</span> <span>new</span>->d.last = m + size;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 30:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 31:</span> <span>//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</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 32:</span> <span>for</span> (p = pool->current; p->d.next; p = p->d.next) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 33:</span> <span>if</span> (p->d.failed++ > 4) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 34:</span> pool->current = p->d.next;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 35:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 36:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 37:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 38:</span> p->d.next = <span>new</span>;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 39:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 40:</span> <span>return</span> m;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 41:</span> }
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；
<span> 1:</span><span>static</span> <span>void</span> *<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 2:</span> ngx_palloc_large(ngx_pool_t *pool, size_t size)<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 3:</span> {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 4:</span> <span>void</span> *p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 5:</span> ngx_uint_t n;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 6:</span> ngx_pool_large_t *large;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 7:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 8:</span> <span>// 直接在系统堆中分配一块大小为size的空间</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 9:</span> p = ngx_alloc(size, pool->log);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 10:</span> <span>if</span> (p == NULL) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 11:</span> <span>return</span> NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 12:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 13:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 14:</span> n = 0;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 15:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 16:</span> <span>// 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 </span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 17:</span> <span>for</span> (large = pool->large; large; large = large->next) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 18:</span> <span>if</span> (large->alloc == NULL) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 19:</span> large->alloc = p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 20:</span> <span>return</span> p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 21:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 22:</span> <span>//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</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 23:</span> <span>if</span> (n++ > 3) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 24:</span> <span>break</span>;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 25:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 26:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 27:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 28:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 29:</span> large = ngx_palloc(pool, <span>sizeof</span>(ngx_pool_large_t));<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 30:</span> <span>if</span> (large == NULL) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 31:</span> ngx_free(p);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 32:</span> <span>return</span> NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 33:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 34:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 35:</span> <span>//将large链接到内存池</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 36:</span> large->alloc = p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 37:</span> large->next = pool->large;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 38:</span> pool->large = large;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 39:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 40:</span> <span>return</span> p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 41:</span> }
整个内存池分配如下图：
4.3 内存池重置 ngx_reset_pool
<span> 1:</span><span>void</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 2:</span> ngx_reset_pool(ngx_pool_t *pool)<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 3:</span> {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 4:</span> ngx_pool_t *p;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 5:</span> ngx_pool_large_t *l;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 6:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 7:</span> <span>//释放大块内存</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 8:</span> <span>for</span> (l = pool->large; l; l = l->next) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 9:</span> <span>if</span> (l->alloc) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 10:</span> ngx_free(l->alloc);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 11:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 12:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 13:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 14:</span> <span>// 重置所有小块内存区</span><pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 15:</span> <span>for</span> (p = pool; p; p = p->d.next) {<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 16:</span> p->d.last = (u_char *) p + <span>sizeof</span>(ngx_pool_t);<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 17:</span> p->d.failed = 0;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 18:</span> }<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 19:</span> <pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 20:</span> pool->current = pool;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 21:</span> pool->chain = NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 22:</span> pool->large = NULL;<pre class="brush:php;toolbar:false;" courier new width:870px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 23:</span> }
4.4 内存池释放 ngx_pfree
<span> 1:</span> ngx_int_t<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 2:</span> ngx_pfree(ngx_pool_t *pool, <span>void</span> *p)<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 3:</span> {<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 4:</span> ngx_pool_large_t *l;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 5:</span> <pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 6:</span> <span>//只检查是否是大内存块，如果是大内存块则释放</span><pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 7:</span> <span>for</span> (l = pool->large; l; l = l->next) {<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 8:</span> <span>if</span> (p == l->alloc) {<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 9:</span> ngx_log_debug1(NGX_LOG_DEBUG_ALLOC, pool->log, 0,<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 10:</span> <span>"free: %p"</span>, l->alloc);<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 11:</span> ngx_free(l->alloc);<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 12:</span> l->alloc = NULL;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 13:</span> <pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 14:</span> <span>return</span> NGX_OK;<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 15:</span> }<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 16:</span> }<pre class="brush:php;toolbar:false;" courier new width:950px padding:0px direction:ltr margin:0em line-height:12pt background-color:rgb><span> 17:</span> <pre class="brush:php;toolbar:false;" courier new width:950px padding:>
