[国嵌攻略][085][共享内存通讯]

共享内存

共享内存是IPC机制中的一种，它允许两个相关的进程访问同一段内存，这是传递数据的一种有效的方式。

A.c

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

#define SIZE 2048

typedef struct sharemem{
    int  flag;         //共享标志
    char data[SIZE];   //共享数据
}ShareMem;

void main(){
    //创建共享内存
    int key;
    int shmid;

    key = ftok("./", 0);
    shmid = shmget(key, sizeof(ShareMem), IPC_CREAT);

    //映射共享内存
    ShareMem *shareMem;

    shareMem = (ShareMem *)shmat(shmid, NULL, 0);

    //设置共享内存
    shareMem->flag = 0;

    while(1){
        //判断共享标志
        while(shareMem->flag != 0);

        //获取用户输入
        char buffer[SIZE];

        fgets(buffer, SIZE, stdin);

        //写入共享内存
        strncpy(shareMem->data, buffer, SIZE);
        shareMem->flag = 1;

        //判断是否退出
        if(strncmp(buffer, "quit", 4) == 0){
            break;
        }
    }

    //脱离共享内存
    shmdt((const void *)shareMem);
}

B.c

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

#define SIZE 2048

typedef struct sharemem{
    int  flag;         //共享标志
    char data[SIZE];   //共享数据
}ShareMem;

void main(){
    //打开共享内存
    int key;
    int shmid;

    key = ftok("./", 0);
    shmid = shmget(key, sizeof(ShareMem), IPC_CREAT);

    //映射共享内存
    ShareMem *shareMem;

    shareMem = (ShareMem *)shmat(shmid, NULL, 0);

    //设置共享内存
    shareMem->flag = 1;

    while(1){
        //判断共享标志
        while(shareMem->flag != 1);

        //读取共享内存
        char buffer[SIZE];

        strncpy(buffer, shareMem->data, SIZE);
        shareMem->flag = 0;

        //显示共享内存
        printf("%s", buffer);

        //判断是否退出
        if(strncmp(buffer, "quit", 4) == 0){
            break;
        }
    }

    //脱离共享内存
    shmdt((const void *)shareMem);

    //删除共享内存
    shmctl(shmid, IPC_RMID, NULL);
}