Linux进程共享通信 -- mmap实现

你的名字 2022-08-20 06:29 168阅读 0赞

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\n");
            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, "\0", 1) < 0){  //末端赋值为'\0'
            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\n");
            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\n", pm->id);
            printf("%s\n", pm->name);
            printf("%c\n", 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