1 传统的分配与释放内存的函数缺点:

 void *malloc(size_t size); void *calloc(size_t nmemb，size_t size);void *realloc(void *ptr, size_t size);void  free(void *ptr);

缺点1:

高并发时较小内存块使用导致系统调用频繁，降低了系统的执行效率

缺点2:

频繁使用时增加了系统内存的碎片，降低内存使用效率

缺点3:

没有垃圾回收机制，容易造成内存泄漏，导致内存枯竭

缺点4:

内存分配与释放的逻辑在程序中相隔较远时，降低程序的稳定性

2 内存池概述

在使用内存之前，先申请分配一定数量的、大小相等(一般情况下)的内存块留作备用。当有新的内存需求时，就从内存池中分出一部分内存块，若内存块不够再继续申请新的内存，统一对程序所使用的内存进行统一的分配和回收。这样做的一个显著优点是，使得内存分配效率得到很大的提升。

3 内存池架构图

4 内存池内存操作API

5 内存池源码剖析

---

5-1头文件

mem_core.h

/** Copyright (C) Igor Sysoev* Copyright (C) Nginx, Inc.*/
#ifndef _NGX_CORE_H_INCLUDED_
#define _NGX_CORE_H_INCLUDED_#define NGX_HAVE_POSIX_MEMALIGN  1typedef struct ngx_pool_s            ngx_pool_t;#define  NGX_OK          0
#define  NGX_ERROR      -1
#define  NGX_AGAIN      -2
#define  NGX_BUSY       -3
#define  NGX_DONE       -4
#define  NGX_DECLINED   -5
#define  NGX_ABORT      -6#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <error.h>
#include <sys/stat.h>
#include <stdint.h>
#include <string.h>
#include <errno.h>typedef intptr_t        ngx_int_t;
typedef uintptr_t       ngx_uint_t;#define NGX_ALIGNMENT   sizeof(unsigned long)    /* platform word */
#define ngx_align(d, a)     (((d) + (a - 1)) & ~(a - 1))
#define ngx_align_ptr(p, a)                                                   \(u_char *) (((uintptr_t) (p) + ((uintptr_t) a - 1)) & ~((uintptr_t) a - 1))#define ngx_memzero(buf, n)       (void) memset(buf, 0, n)#include "mem_alloc.h"
#include "mem_pool_palloc.h"

mem_alloc.h

/** Copyright (C) Igor Sysoev* Copyright (C) Nginx, Inc.*/
#ifndef _NGX_ALLOC_H_INCLUDED_
#define _NGX_ALLOC_H_INCLUDED_#include "mem_core.h"void *ngx_alloc(size_t size);
void *ngx_calloc(size_t size);#define ngx_free         free/** Linux has memalign() or posix_memalign()* Solaris has memalign()* FreeBSD 7.0 has posix_memalign(), besides, early version's malloc()* aligns allocations bigger than page size at the page boundary*//*#if (NGX_HAVE_POSIX_MEMALIGN || NGX_HAVE_MEMALIGN)void *ngx_memalign(size_t alignment, size_t size);#else
*/
#define ngx_memalign(alignment, size)  ngx_alloc(size)
/*
#endif
*/extern ngx_uint_t  ngx_pagesize;
extern ngx_uint_t  ngx_pagesize_shift;
extern ngx_uint_t  ngx_cacheline_size;#endif /* _NGX_ALLOC_H_INCLUDED_ */

mem_pool_palloc.h

/** Copyright (C) Igor Sysoev* Copyright (C) Nginx, Inc.*/#ifndef _NGX_PALLOC_H_INCLUDED_
#define _NGX_PALLOC_H_INCLUDED_#include "mem_core.h"/** NGX_MAX_ALLOC_FROM_POOL should be (ngx_pagesize - 1), i.e. 4095 on x86.* On Windows NT it decreases a number of locked pages in a kernel.*/
#define NGX_MAX_ALLOC_FROM_POOL  (ngx_pagesize - 1)#define