非血緣關係進程間mmap通信

創建一個讀文件 mmap_r.c

#include<stdio.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>
#include<string.h>
#include<stdlib.h>
#include<sys/mman.h>


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


void sys_err(char *str)
{
        perror(str);
        exit(1);
}


int main(int argc,char *argv[])
{
        int fd;
        struct STU student;
        struct STU *mm;


        if(argc < 2){
                printf("./a.out file_shared\n");
                exit(-1);
        }


        fd = open(argv[1],O_RDONLY);
        if (fd == -1)
        sys_err("open error");

        mm = mmap(NULL,sizeof(student),PROT_READ,MAP_SHARED,fd,0);
        if (mm == MAP_FAILED)
                sys_err("mmap error");


        close(fd);


        while (1) {
                printf("id=%d\tname=%s\t%c\n", mm->id, mm->name, mm->sex);
                sleep(2);
        }
        munmap(mm, sizeof(student));
        return 0;


}

創建一個寫文件 mmap_w.c

#include<stdio.h>
#include<sys/stat.h>
#include<fcntl.h>
#include<unistd.h>
#include<string.h>
#include<stdlib.h>
#include<sys/mman.h>


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


void sys_err(char *str)
{
        perror(str);
        exit(1);
}

int main(int argc,char *argv[])
{
        int fd;
        struct STU student = {10, "xiaoming", 'm'};
        struct STU *mm;


        if(argc < 2){
                printf("./a.out file_shared\n");
                exit(-1);
        }


        fd = open(argv[1],O_RDWR | O_CREAT, 0664);
        ftruncate(fd,sizeof(student));


        mm = mmap(NULL, sizeof(student), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
        if (mm == MAP_FAILED)
                sys_err("mmap error");


        close(fd);


        while (1) {
                memcpy(mm, &student, sizeof(student));
                student.id++;
                sleep(1);
        }


        munmap(mm, sizeof(student));
        return 0;
}

創建一個共享文件 file_shared

1.分別編譯兩個文件
2.先執行寫文件 ./mmap_w file_shared
3.再打開一個終端，執行讀文件 ./mmap_r file_shared

從結果可以看出，寫端一直在覆蓋原來的id，讀端一直在讀取file_shared中的內容。