进程间通信－－共享内存

最新推荐文章于 2024-12-12 19:45:00 发布

阿磊2013

最新推荐文章于 2024-12-12 19:45:00 发布

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分类专栏： linux编程文章标签： system gcc struct 360 cmd

本文链接：https://blog.youkuaiyun.com/ubuntulover/article/details/4434726

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本文介绍了一个简单的共享内存创建和操作示例，通过C语言代码展示了如何利用系统调用创建、连接及断开共享内存段。

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1.创建

#include <sys/shm.h>

int shmget(key_t key,size_t size,int flag);

当打开一个内存段时，参数size的值为0。

//ceate_shm.c

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdlib.h>
#include <stdio.h>

#define BUFSZ 4096

int main()
{
int shm_id;
shm_id=shmget(IPC_PRIVATE,BUFSZ,0666);
if(shm_id<0){
perror("shmget");
exit(1);
}

printf("successfully created segment: %d/n",shm_id);
system("ipcs -m");

return 0;
}

结果：

alei@alei-desktop:~/linux/code/14$ gcc create_shm.c -o create_shm
alei@alei-desktop:~/linux/code/14$ ./create_shm
successfully created segment: 786451

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 0          alei      600        393216     2          dest
0x00000000 32769      alei      600        393216     2          dest
0x00000000 65538      alei      600        393216     2          dest
0x00000000 98307      alei      600        393216     2          dest
0x00000000 131076     alei      600        393216     2          dest
0x00000000 163845     alei      600        393216     2          dest
0x00000000 196614     alei      600        393216     2          dest
0x00000000 229383     alei      600        393216     2          dest
0x00000000 262152     alei      600        393216     2          dest
0x00000000 294921     alei      600        393216     2          dest
0x00000000 327690     alei      600        393216     2          dest
0x00000000 360459     alei      600        393216     2          dest
0x00000000 393228     alei      600        393216     2          dest
0x00000000 425997     alei      600        393216     2          dest
0x00000000 458766     alei      600        393216     2          dest
0x00000000 557071     alei      600        176400     2          dest
0x00000000 589840     alei      600        358620     2          dest
0x00000000 720913     alei      600        393216     2          dest
0x00000000 753682     alei      600        393216     2          dest
0x00000000 786451     alei      666        4096       0

2.共享内存的操作

使用如下函数：

#include <sys/shm.h>

int shmctl(int shm_id,int cmd,struct shmid_ds * buf);

使用shmat将一个存在的共享内存段连接到本进程空间：

#include <sys/shm.h>

void * shmat(int shm_id,const void * addr,int flag);

使用shmdt函数，将指定的共享内存段从本进程的空间中脱离出去。

#include <sys/shm.h>

int shmdt(void * addr);

//opr_shm.c

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
#include <stdlib.h>
#include <stdio.h>

int main ( int argc, char *argv[] )
{
    int shm_id ;
    char * shm_buf;

    if ( argc != 2 ){
        printf ( "USAGE: atshm <identifier>" );
        exit (1 );
    }

    shm_id = atoi(argv[1]);

    if ( (shm_buf = shmat( shm_id, 0, 0)) < (char *) 0 ){
        perror ( "shmat" );
        exit (1);
    }

    printf ( " segment attached at %p/n", shm_buf ); //输出导入的位置
    system("ipcs -m");

    sleep(3);

    if ( (shmdt(shm_buf)) < 0 ) {
        perror ( "shmdt");
        exit(1);
    }

    printf ( "segment detached /n" );
    system ( "ipcs -m " );

    exit ( 0 );
}

结果：

alei@alei-desktop:~/linux/code/14$ gcc opr_shm.c -o opr_shm
alei@alei-desktop:~/linux/code/14$ ./opr_shm
USAGE: atshm <identifier>alei@alei-desktop:~/linux/code/14$ ./opr_shm 786451
segment attached at 0xb7f11000

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 0          alei      600        393216     2          dest
0x00000000 32769      alei      600        393216     2          dest
0x00000000 65538      alei      600        393216     2          dest
0x00000000 98307      alei      600        393216     2          dest
0x00000000 131076     alei      600        393216     2          dest
0x00000000 163845     alei      600        393216     2          dest
0x00000000 196614     alei      600        393216     2          dest
0x00000000 229383     alei      600        393216     2          dest
0x00000000 262152     alei      600        393216     2          dest
0x00000000 294921     alei      600        393216     2          dest
0x00000000 327690     alei      600        393216     2          dest
0x00000000 360459     alei      600        393216     2          dest
0x00000000 393228     alei      600        393216     2          dest
0x00000000 425997     alei      600        393216     2          dest
0x00000000 458766     alei      600        393216     2          dest
0x00000000 557071     alei      600        176400     2          dest
0x00000000 589840     alei      600        358620     2          dest
0x00000000 851985     alei      600        393216     2          dest
0x00000000 884754     alei      600        393216     2          dest
0x00000000 786451     alei      666        4096       1
0x00000000 819220     alei      600        393216     2          dest

segment detached

------ Shared Memory Segments --------
key        shmid      owner      perms      bytes      nattch     status
0x00000000 0          alei      600        393216     2          dest
0x00000000 32769      alei      600        393216     2          dest
0x00000000 65538      alei      600        393216     2          dest
0x00000000 98307      alei      600        393216     2          dest
0x00000000 131076     alei      600        393216     2          dest
0x00000000 163845     alei      600        393216     2          dest
0x00000000 196614     alei      600        393216     2          dest
0x00000000 229383     alei      600        393216     2          dest
0x00000000 262152     alei      600        393216     2          dest
0x00000000 294921     alei      600        393216     2          dest
0x00000000 327690     alei      600        393216     2          dest
0x00000000 360459     alei      600        393216     2          dest
0x00000000 393228     alei      600        393216     2          dest
0x00000000 425997     alei      600        393216     2          dest
0x00000000 458766     alei      600        393216     2          dest
0x00000000 557071     alei      600        176400     2          dest
0x00000000 589840     alei      600        358620     2          dest
0x00000000 851985     alei      600        393216     2          dest
0x00000000 884754     alei      600        393216     2          dest
0x00000000 786451     alei      666        4096       0
0x00000000 819220     alei      600        393216     2          dest