【操作系统】进程间的通信——共享内存

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/shm.h>

struct Conn_stat{
	int count;
	char ip[64];
};

int main(void){

    void *shm = NULL;
    int shmid = 0;//存储共享内存的标识
    struct Conn_stat stat = {0,"127.0.0.1"};

    //创建共享内存
    shmid = shmget((key_t)1234,sizeof(struct Conn_stat),0666 | IPC_CREAT);
    if(shmid == -1){
        fprintf(stderr, "shmget failed\n");
		exit(1);
    }
    //将共享内存挂接到当前进程的地址空间
    shm = shmat(shmid,(void*)0,0);
    if(shm == (void*)-1){
		fprintf(stderr, "shmat failed\n");
		exit(2);
	}
    printf("Memory attached at %p\n", shm);
    //设置共享内存
    struct Conn_stat *p = (struct Conn_stat*)shm;
    memcpy(p,&stat,sizeof(struct Conn_stat));
    //修改共享内存中的数据
    int i = 0;
    while((i++) < 50){
        p->count++;
        sleep(1);
    }
    //把共享内存从当前进程中分离
    if(shmdt(shm) == -1){
		fprintf(stderr, "shmdt failed\n");
		exit(3);
	}
    return 0;
}

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/shm.h>
#include <string.h>
#include <errno.h>

struct Conn_stat{
	int count;
	char ip[64];
	
};

int main(void){

    void *shm = NULL;//分配的共享内存的原始首地址
    struct Conn_stat *stat = NULL;
    int shmid;//共享内存标识符
    //创建共享内存
    shmid = shmget((key_t)1234, sizeof(struct Conn_stat), 0666|IPC_CREAT);
    if(shmid == -1){
		fprintf(stderr, "shmget failed\n");
		exit(0);
	}
    //将共享内存挂接到当前当前进程的地址空间
    shm = shmat(shmid, 0, 0);
    if(shm == (void*)-1){
		fprintf(stderr, "shmat failed\n");
		exit(1);
	}
    printf("\nMemory attached at %p\n", shm);
    //设置共享内存
    stat = (struct Conn_stat*)shm;
    int i = 0;
	while((i++) < 10){
		printf("ip = %s ,count: %d\t\t\n", stat->ip, stat->count);	
		sleep(1);
	}
    //把共享内存从当前进程中分离
    if(shmdt(shm) == -1){
		fprintf(stderr, "shmdt failed\n");
		exit(2);
	}
    //删除共享内存
    if(shmctl(shmid, IPC_RMID, 0) == -1){
		fprintf(stderr, "shmctl(IPC_RMID) failed, reason: %s\n",strerror(errno));
		exit(3);
	}
    return 0;   
}

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

struct Conn_stat{
	int count;
	char ip[64];
};

//这个进程创建映射区进行写
int main(int argc,char* argv[]){
    if(argc != 2){
        printf("Usage: %s  file.\n",argv[0]);
		exit(1);
    }
    struct Conn_stat stat =  {0,"127.0.0.1"};
    //打开文件
    int fd = open(argv[1],O_RDWR|O_CREAT|O_TRUNC,0644);
    if(fd<0){
        perror("open");
		exit(2);
    }
    //将文件截断为第二个参数这么大
    ftruncate(fd,sizeof(struct Conn_stat)); 
    //创建一个结构体大小的共享映射区。共享映射区我们可以当做数组区看待。
    struct Conn_stat *p = (struct Conn_stat*)mmap(NULL,sizeof(struct Conn_stat),PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);
    if(p == MAP_FAILED){
		perror("mmap");
		exit(3);
	}
    close(fd);//关闭不用的文件描述符
    memcpy(p,&stat,sizeof(struct Conn_stat));
    while(p->count < 30){
        p->count++;
        sleep(1);
    }
    //解除映射
    int ret = munmap(p,sizeof(struct Conn_stat));
	if(ret < 0){
		perror("mmumap");
		exit(4);
	}

	return 0;
}

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

struct Conn_stat{	
    int count;
	char ip[64];
};

int main(int argc,char *argv[]){
    if(argc != 2){
		printf("Usage: %s  file.\n",argv[0]);
		exit(1);
	}
    //打开文件-只读，注意与写中的参数不同
    int fd = open(argv[1],O_RDONLY,0644);
	if(fd < 0){
		perror("open");
		exit(2);
	}
	
	struct Conn_stat stat;
    //注意与写中的参数不同
	struct Conn_stat *p = (struct Conn_stat*)mmap(NULL,sizeof(struct Conn_stat),PROT_READ,MAP_SHARED,fd,0);
    if(p == MAP_FAILED){
		perror("mmap");
		exit(3);
	}
	close(fd);
    int i = 0;
	while((i++) < 10){
		printf("ip = %s ,count: %d\t\t\n",p->ip,p->count);	
		sleep(1);
	}
    //接触映射
	int ret = munmap(p,sizeof(stat));
	if(ret < 0){
		perror("mmumap");
		exit(4);
	}
    return 0;
}