Nginx自己实现了一个内存池组件。Nginx作为服务器，当客户端 TCP连接 &HTTP请求 到来时，Nginx会为该连接创建一个专属的内存池；这个内存池的生命周期是连接建立时创建，连接断开时销毁。客户端和Nginx通信的所有数据和操作（HTTP协议解析、HTTP数据解析等）都在内存池中完成。

/src/core/ngx_palloc.h。（相关实现在/src/core/ngx_palloc.c文件）


#ifndef _NGX_PALLOC_H_INCLUDED_
#define _NGX_PALLOC_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>


/*
 * NGX_MAX_ALLOC_FROM_POOL should be (ngx_pagesize - 1), i.e. 4095 on x86.
 * On Windows NT it decreases a number of locked pages in a kernel.
 */
#define NGX_MAX_ALLOC_FROM_POOL  (ngx_pagesize - 1)

#define NGX_DEFAULT_POOL_SIZE    (16 * 1024)

#define NGX_POOL_ALIGNMENT       16
#define NGX_MIN_POOL_SIZE                                                     \
    ngx_align((sizeof(ngx_pool_t) + 2 * sizeof(ngx_pool_large_t)),            \
              NGX_POOL_ALIGNMENT)


typedef void (*ngx_pool_cleanup_pt)(void *data);

typedef struct ngx_pool_cleanup_s  ngx_pool_cleanup_t;

struct ngx_pool_cleanup_s {
    ngx_pool_cleanup_pt   handler;
    void                 *data;
    ngx_pool_cleanup_t   *next;
};


typedef struct ngx_pool_large_s  ngx_pool_large_t;

struct ngx_pool_large_s {
    ngx_pool_large_t     *next;
    void                 *alloc;
};


typedef struct {
    u_char               *last;
    u_char               *end;
    ngx_pool_t           *next;
    ngx_uint_t            failed;
} ngx_pool_data_t;


struct ngx_pool_s {
    ngx_pool_data_t       d;
    size_t                max;
    ngx_pool_t           *current;
    ngx_chain_t          *chain;
    ngx_pool_large_t     *large;
    ngx_pool_cleanup_t   *cleanup;
    ngx_log_t            *log;
};


typedef struct {
    ngx_fd_t              fd;
    u_char               *name;
    ngx_log_t            *log;
} ngx_pool_cleanup_file_t;


ngx_pool_t *ngx_create_pool(size_t size, ngx_log_t *log);
void ngx_destroy_pool(ngx_pool_t *pool);
void ngx_reset_pool(ngx_pool_t *pool);

void *ngx_palloc(ngx_pool_t *pool, size_t size);
void *ngx_pnalloc(ngx_pool_t *pool, size_t size);
void *ngx_pcalloc(ngx_pool_t *pool, size_t size);
void *ngx_pmemalign(ngx_pool_t *pool, size_t size, size_t alignment);
ngx_int_t ngx_pfree(ngx_pool_t *pool, void *p);


ngx_pool_cleanup_t *ngx_pool_cleanup_add(ngx_pool_t *p, size_t size);
void ngx_pool_run_cleanup_file(ngx_pool_t *p, ngx_fd_t fd);
void ngx_pool_cleanup_file(void *data);
void ngx_pool_delete_file(void *data);


#endif /* _NGX_PALLOC_H_INCLUDED_ */

void *
ngx_array_push(ngx_array_t *a)
{
    void        *elt, *new;
    size_t       size;
    ngx_pool_t  *p;

    if (a->nelts == a->nalloc) {

        /* the array is full */

        size = a->size * a->nalloc;

        p = a->pool;

        if ((u_char *) a->elts + size == p->d.last
            && p->d.last + a->size <= p->d.end)
        {
            /*
             * the array allocation is the last in the pool
             * and there is space for new allocation
             */

            p->d.last += a->size;
            a->nalloc++;

        } else {
            /* allocate a new array */

            new = ngx_palloc(p, 2 * size);
            if (new == NULL) {
                return NULL;
            }

            ngx_memcpy(new, a->elts, size);
            a->elts = new;
            a->nalloc *= 2;
        }
    }

    elt = (u_char *) a->elts + a->size * a->nelts;
    a->nelts++;

    return elt;
}

// ...
typedef struct ngx_pool_s            ngx_pool_t;
// ...


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


#ifndef _NGX_ARRAY_H_INCLUDED_
#define _NGX_ARRAY_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>


typedef struct {
    void        *elts;
    ngx_uint_t   nelts;
    size_t       size;
    ngx_uint_t   nalloc;
    ngx_pool_t  *pool;
} ngx_array_t;


ngx_array_t *ngx_array_create(ngx_pool_t *p, ngx_uint_t n, size_t size);
void ngx_array_destroy(ngx_array_t *a);
void *ngx_array_push(ngx_array_t *a);
void *ngx_array_push_n(ngx_array_t *a, ngx_uint_t n);


static ngx_inline ngx_int_t
ngx_array_init(ngx_array_t *array, ngx_pool_t *pool, ngx_uint_t n, size_t size)
{
    /*
     * set "array->nelts" before "array->elts", otherwise MSVC thinks
     * that "array->nelts" may be used without having been initialized
     */

    array->nelts = 0;
    array->size = size;
    array->nalloc = n;
    array->pool = pool;

    array->elts = ngx_palloc(pool, n * size);
    if (array->elts == NULL) {
        return NGX_ERROR;
    }

    return NGX_OK;
}


#endif /* _NGX_ARRAY_H_INCLUDED_ */

typedef struct {
    void        *elts;
    ngx_uint_t   nelts;
    size_t       size;
    ngx_uint_t   nalloc;
    ngx_pool_t  *pool;
} ngx_array_t;

nelts：指示已使用了多少个元素。

Nginx的每个进程内部都有一个自己的ngx_cycle。


#ifndef _NGX_CYCLE_H_INCLUDED_
#define _NGX_CYCLE_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>


#ifndef NGX_CYCLE_POOL_SIZE
#define NGX_CYCLE_POOL_SIZE     NGX_DEFAULT_POOL_SIZE
#endif


#define NGX_DEBUG_POINTS_STOP   1
#define NGX_DEBUG_POINTS_ABORT  2


typedef struct ngx_shm_zone_s  ngx_shm_zone_t;

typedef ngx_int_t (*ngx_shm_zone_init_pt) (ngx_shm_zone_t *zone, void *data);

struct ngx_shm_zone_s {
    void                     *data;
    ngx_shm_t                 shm;
    ngx_shm_zone_init_pt      init;
    void                     *tag;
    ngx_uint_t                noreuse;  /* unsigned  noreuse:1; */
};


struct ngx_cycle_s {
    // ...
};


typedef struct {
    // ...
} ngx_core_conf_t;


#define ngx_is_init_cycle(cycle)  (cycle->conf_ctx == NULL)


ngx_cycle_t *ngx_init_cycle(ngx_cycle_t *old_cycle);
ngx_int_t ngx_create_pidfile(ngx_str_t *name, ngx_log_t *log);
void ngx_delete_pidfile(ngx_cycle_t *cycle);
ngx_int_t ngx_signal_process(ngx_cycle_t *cycle, char *sig);
void ngx_reopen_files(ngx_cycle_t *cycle, ngx_uid_t user);
char **ngx_set_environment(ngx_cycle_t *cycle, ngx_uint_t *last);
ngx_pid_t ngx_exec_new_binary(ngx_cycle_t *cycle, char *const *argv);
ngx_cpuset_t *ngx_get_cpu_affinity(ngx_uint_t n);
ngx_shm_zone_t *ngx_shared_memory_add(ngx_conf_t *cf, ngx_str_t *name,
    size_t size, void *tag);
void ngx_set_shutdown_timer(ngx_cycle_t *cycle);


extern volatile ngx_cycle_t  *ngx_cycle;
extern ngx_array_t            ngx_old_cycles;
extern ngx_module_t           ngx_core_module;
extern ngx_uint_t             ngx_test_config;
extern ngx_uint_t             ngx_dump_config;
extern ngx_uint_t             ngx_quiet_mode;


#endif /* _NGX_CYCLE_H_INCLUDED_ */


#ifndef _NGX_LIST_H_INCLUDED_
#define _NGX_LIST_H_INCLUDED_


#include <ngx_config.h>
#include <ngx_core.h>


typedef struct ngx_list_part_s  ngx_list_part_t;

struct ngx_list_part_s {
    void             *elts;
    ngx_uint_t        nelts;
    ngx_list_part_t  *next;
};


typedef struct {
    ngx_list_part_t  *last;
    ngx_list_part_t   part;
    size_t            size;
    ngx_uint_t        nalloc;
    ngx_pool_t       *pool;
} ngx_list_t;


ngx_list_t *ngx_list_create(ngx_pool_t *pool, ngx_uint_t n, size_t size);

static ngx_inline ngx_int_t
ngx_list_init(ngx_list_t *list, ngx_pool_t *pool, ngx_uint_t n, size_t size)
{
    list->part.elts = ngx_palloc(pool, n * size);
    if (list->part.elts == NULL) {
        return NGX_ERROR;
    }

    list->part.nelts = 0;
    list->part.next = NULL;
    list->last = &list->part;
    list->size = size;
    list->nalloc = n;
    list->pool = pool;

    return NGX_OK;
}

void *ngx_list_push(ngx_list_t *list);


#endif /* _NGX_LIST_H_INCLUDED_ */

typedef struct ngx_list_part_s  ngx_list_part_t;

struct ngx_list_part_s {
    void             *elts;
    ngx_uint_t        nelts;
    ngx_list_part_t  *next;
};


typedef struct {
    ngx_list_part_t  *last;
    ngx_list_part_t   part;
    size_t            size;
    ngx_uint_t        nalloc;
    ngx_pool_t       *pool;
} ngx_list_t;

Nginx的内存池分成大小块，小块是要么不释放要么全部释放。ngx_create_pool(size_t size, ngx_log_t *log)里的size就是用来区分大小块的，大于size的就是大块，否则就是小块。

CXX = gcc
CXXFLAGS += -g -Wall -Wextra

NGX_ROOT = /home/fly/workspace/nginx-1.13.7

TARGETS = ngx_code
TARGETS_C_FILE = $(TARGETS).c

CLEANUP = rm -f $(TARGETS) *.o

all: $(TARGETS)

clean:
	$(CLEANUP)

CORE_INCS = -I. \
	-I$(NGX_ROOT)/src/core \
	-I$(NGX_ROOT)/src/event \
	-I$(NGX_ROOT)/src/event/modules \
	-I$(NGX_ROOT)/src/os/unix \
	-I$(NGX_ROOT)/objs \
	-I$(NGX_ROOT)/../pcre-8.41 \
	-I$(NGX_ROOT)/../openssl-1.1.0g/include/ \

NGX_PALLOC = $(NGX_ROOT)/objs/src/core/ngx_palloc.o
NGX_STRING = $(NGX_ROOT)/objs/src/core/ngx_string.o
NGX_ALLOC = $(NGX_ROOT)/objs/src/os/unix/ngx_alloc.o
NGX_ARRAY = $(NGX_ROOT)/objs/src/core/ngx_array.o
NGX_HASH = $(NGX_ROOT)/objs/src/core/ngx_hash.o
NGX_LIST = $(NGX_ROOT)/objs/src/core/ngx_list.o
NGX_QUEUE = $(NGX_ROOT)/objs/src/core/ngx_queue.o


$(TARGETS): $(TARGETS_C_FILE)
	$(CXX) $(CXXFLAGS) $(CORE_INCS) $(NGX_PALLOC) $(NGX_STRING) $(NGX_ALLOC) $(NGX_ARRAY) $(NGX_LIST) $(NGX_QUEUE)  $(NGX_HASH) $^ -o $@


注意nginx的源码路径以及所需库的路径，要写正确的。

#include <stdio.h>

#include "ngx_config.h"
#include "ngx_conf_file.h"
#include "nginx.h"
#include "ngx_core.h"
#include "ngx_string.h"
#include "ngx_palloc.h"
#include "ngx_array.h"
//#include "ngx_hash.h"

typedef struct {
	int id;
	int level;
}ngx_fly_t;

// 打印内存池的数据信息
void print_pool(ngx_pool_t *pool)
{
	while (pool)
	{
		printf("avail pool memory size: %ld\n\n",
			pool->d.end - pool->d.last);
		pool=pool->d.next;
	}
}


volatile ngx_cycle_t *ngx_cycle;

#define unused(x)	(x)=(x)
void ngx_log_error_core(ngx_uint_t level, ngx_log_t *log, ngx_err_t err,
	const char *fmt, ...)
{
	unused(level);
	unused(log);
	unused(err);
	unused(fmt);
}


int main()
{
	ngx_str_t str = ngx_string("Hello World!");

	printf("string length: %ld\n", str.len);
	printf("string: %s\n", str.data);

	// 创建内存池
	ngx_pool_t *pool;

	pool = ngx_create_pool(1024, NULL);

	print_pool(pool);

	// 创建数组
	/*
	* nalloc = 32
	* size = sizeof(ngx_fly_t)
	* pool = pool
	*/
	ngx_array_t *arr = ngx_array_create(pool, 32, sizeof(ngx_fly_t));
	print_pool(pool);
	ngx_fly_t *t1 = ngx_array_push(arr); // 拿出内存
	t1->id = 101;  //赋值
	t1->level = 1; //赋值
	print_pool(pool);
	ngx_fly_t *t2 = ngx_array_push(arr); // 拿出内存
	t2->id = 102;  //赋值
	t2->level = 3; //赋值
	print_pool(pool);
	return 0;
}

使用makefile来编译，执行结果：

$ ./ngx_code

string length: 12
string: Hello World!
avail pool memory size: 944

avail pool memory size: 648

avail pool memory size: 648

avail pool memory size: 648


#include <stdio.h>

#include "ngx_config.h"
#include "ngx_conf_file.h"
#include "nginx.h"
#include "ngx_core.h"
#include "ngx_string.h"
#include "ngx_palloc.h"
#include "ngx_array.h"
//#include "ngx_hash.h"

typedef struct {
	int id;
	int level;
}ngx_fly_t;

// 打印内存池的数据信息
void print_pool(ngx_pool_t *pool)
{
	while (pool)
	{
		printf("avail pool memory size: %ld\n\n",
			pool->d.end - pool->d.last);
		pool=pool->d.next;
	}
}


volatile ngx_cycle_t *ngx_cycle;

#define unused(x)	(x)=(x)
void ngx_log_error_core(ngx_uint_t level, ngx_log_t *log, ngx_err_t err,
	const char *fmt, ...)
{
	unused(level);
	unused(log);
	unused(err);
	unused(fmt);
}


int main()
{
	ngx_str_t str = ngx_string("Hello World!");

	printf("string length: %ld\n", str.len);
	printf("string: %s\n", str.data);

	// 创建内存池
	ngx_pool_t *pool;

	pool = ngx_create_pool(1024, NULL);

	print_pool(pool);

	ngx_list_t *list=ngx_list_create(pool, 32, sizeof(ngx_fly_t));

	print_pool(pool);

	ngx_fly_t *t3 = ngx_list_push(list); // 拿出内存
	t3->id = 103;  //赋值
	t3->level = 3; //赋值
	print_pool(pool);
	ngx_fly_t *t4 = ngx_list_push(list); // 拿出内存
	t4->id = 104;  //赋值
	t4->level = 4; //赋值
	print_pool(pool);

	return 0;
}

$ ./ngx_code

string length: 12
string: Hello World!
avail pool memory size: 944

avail pool memory size: 632

avail pool memory size: 632

avail pool memory size: 632


可以发现，ngx_list相比ngx_array少了648-632 =16字节，从源码的ngx_list_create()函数可以发现，是因为多了一个ngx_list_t的头数据。

这里对ngx_string、ngx_array、ngx_list做了简单介绍和提供使用示例，其他的nginx基础组件的使用（比如dequeue、hash、log等等）也是类似的。

探索Nginx：深入理解Nginx基础组件的使用

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