Linux进程共享通信 -- mmap实现

https://blog.csdn.net/y396397735/article/details/50651633

使用mmap内存映射实现一端写，另一端读的进程间通信

写端代码write.c

/*write.c*/
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>
/*映射内存大小*/
#define MAPLEN 0x100
/*定义一个学生信息结构体*/
struct STU
{
    int id;
    char name[20];
    char sex;
};
/*出错信息统一处理函数*/
void sys_err(char *str, int exitno)
{
    perror(str);
    exit(exitno);
}

int main(int argc, char*argv[])
{
    struct STU *pm;//STU结构体指针
    int fd, i = 0;
    if(argc < 2){
        printf("args error
");
        exit(1);
    }

    fd = open(argv[1], O_RDWR | O_CREAT, 0777); //打开一文件
    if(fd < 0){
        sys_err("open", 1);
    }

    if(lseek(fd, MAPLEN - 1, SEEK_SET) < 0){//文件偏移至分配的内存地址末端
        sys_err("lseek", 3);
    }

    if(write(fd, "", 1) < 0){  //末端赋值为''
        sys_err("write", 4);
    }
    /*将文件映射至进程的地址空间*/
    pm = mmap(NULL, MAPLEN, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if(pm == MAP_FAILED){
        sys_err("mmap", 2);
    }
    /*关闭文件描述符*/
    close(fd);
    /*对文件进行写入操作*/
    while(1){
        pm->id = i;
        sprintf(pm->name, "yu-%d", i);
        if(i % 2 == 0){
            pm->sex = 'm';
        }else{
            pm->sex = 'w';
        }
        i++;
        sleep(1);
    }
    munmap(pm, MAPLEN);

    return 0;
}

读端代码read.c

/*read.c*/
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/mman.h>

#define MANLEN 0x1000

struct STU
{
    int id;
    char name[20];
    char sex;
};

void sys_err(char *str, int exitno)
{
    perror(str);
    exit(exitno);
}

int main(int argc, char *argv[])
{
    struct STU *pm;
    int fd, i = 0;
    if (argc < 2) {
        printf("args error
");
        exit(1);
    }

    fd = open(argv[1], O_RDWR);
    if (fd < 0){
        sys_err("open", 1); 
    }

    pm = mmap(NULL, MAPLEN, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if(pm == MAP_FAILED){
        sys_err("mmap", 2);
    }
    /*关闭文件*/
    close(fd);
    /*删除文件*/
    unlink(argv[1]);
    /*在内存中读数据*/
    while(1){
        printf("%d
", pm->id);
        printf("%s
", pm->name);
        printf("%c
", pm->sex);
        sleep(1);
    }
    munmap(pm, MAPLEN);

    return 0;
}

执行过程：

yu@ubuntu:~/Linux/211/tongxin$ ls
read.c  write.c
yu@ubuntu:~/Linux/211/tongxin$ gcc -o write write.c
yu@ubuntu:~/Linux/211/tongxin$ gcc -o read read.c
yu@ubuntu:~/Linux/211/tongxin$ ls
read  read.c  write  write.c

此时执行写操作

yu@ubuntu:~/Linux/211/tongxin$ ./write myfile
//在向myfile文件中写数据

另开一终端到当前目录，执行如下读操作：

yu@ubuntu:~/Linux/211/tongxin$ ls
read  read.c  write  write.c  myfile
yu@ubuntu:~/Linux/211/tongxin$ ./read myfile
6
yu-6
m
7
yu-7
w
^C//读取写入的内容Ctrl+C退出

退出后，执行ls，可发现myfile文件已删除

yu@ubuntu:~/Linux/211/tongxin$ ls
read  read.c  write  write.c