Linux共享内存使用常见陷阱与分析 - 51CTO.COM http://os.51cto.com/art/201311/418977_all.htmIPC---共享内存

 #include <sys/types.h>
 #include <sys/shm.h>

 void *shmat(int shmid, const void *shmaddr, int shmflg);

#include <sys/types.h>
#include <sys/shm.h>

int shmdt(const void *shmaddr);

 #include <sys/ipc.h>
 #include <sys/shm.h>
      
  int shmctl(int shmid, int cmd, struct shmid_ds *buf);

 struct shmid_ds {
               struct ipc_perm shm_perm;    /* Ownership and permissions */
               size_t          shm_segsz;   /* Size of segment (bytes) */
               time_t          shm_atime;   /* Last attach time */
               time_t          shm_dtime;   /* Last detach time */
               time_t          shm_ctime;   /* Last change time */
               pid_t           shm_cpid;    /* PID of creator */
               pid_t           shm_lpid;    /* PID of last shmat(2)/shmdt(2) */
               shmatt_t        shm_nattch;  /* No. of current attaches */
               ...
           };

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

#define MAX_SIZE   2048
#define BUF_SIZE   2047

#define ERR_EXIT(m) 	do  	{   		perror(m);   		exit(EXIT_FAILURE);  	}while(0)
		
struct share_memory 
{
	int  WR_RD;          //非0表示可写，0表示可读
	char text[MAX_SIZE];
};

int main()
{
	int shmid;     
	char buffer[BUF_SIZE+1];   //用于保存输入的文本
	shmid = shmget(1234,sizeof(struct share_memory),0666 | IPC_CREAT);    //创建共享内存
	if(shmid==-1)
	    ERR_EXIT("shmget failed\n");
	
	struct share_memory *sh_mem;  
	void *sh=NULL;
	sh = shmat(shmid,0,0);     //将共享内存连接到当前进程的地址空间
	if(sh ==(void *)-1)
		ERR_EXIT("shmat failed\n");
	else
		printf("Memory attached at9 %x\n",(int)sh);   
	
	sh_mem=(struct share_memory *)sh;
	sh_mem->WR_RD=1;   // 置为可写
	int flag=1;
	
	while(1)
	{
		while(!sh_mem->WR_RD)     //共享内存为可读，表示内存里的数据还未被读取，不能写，此时堵塞
		{
			if(flag)
			{
				printf("memory is not empty,waiting.....\n");
				flag=0;
			}
			
			sleep(1);
		}
		
		flag=1;
		/*向共享内存写入数据*/
		printf("Enter some text(Enter ‘end‘ to quit): \n");
		fgets(buffer,BUF_SIZE,stdin);
		strncpy(sh_mem->text,buffer,sizeof(buffer));
		
		sh_mem->WR_RD=0;    //写完数据之后设置共享内存可读
		
		if(strncmp(buffer,"end",3)==0)
			break;                //输入end结束循环
		
	}
	
	if(shmdt(sh)==-1)
		ERR_EXIT("shmdt failed\n");    //将共享内存从当前进程分离
	
	sleep(2);
	return 0;
	
}

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


#define MAX_SIZE   2048

#define ERR_EXIT(m) 	do  	{   		perror(m);   		exit(EXIT_FAILURE);  	}while(0)
		
struct share_memory 
{
	int  WR_RD;          //非0表示可写，0表示可读
	char text[MAX_SIZE];
};

int main()
{
	int shmid;     
	
	srand(getpid());
	
	shmid = shmget(1234,sizeof(struct share_memory),0666 | IPC_CREAT);    //创建共享内存
	if(shmid==-1)
	    ERR_EXIT("shmget failed\n");
	
	struct share_memory *sh_mem;  
	void *sh=NULL;
	sh = shmat(shmid,0,0);     //将共享内存连接到当前进程的地址空间
	if(sh ==(void *)-1)
		ERR_EXIT("shmat failed\n");
	else
		printf("Memory attached at %x\n",(int)sh);   
	
	sh_mem=(struct share_memory*)sh;
	//sh_mem->WR_RD=ture;   // 置为可写
	
	while(1)
	
		if(!sh_mem->WR_RD)     //共享内存为可读，从共享内存读取数据
		{
			printf("your wrote: %s", sh_mem->text);
			sleep(rand()%3);
			sh_mem->WR_RD=1;    //读完数据之后设置共享内存可写
		
			if(strncmp(sh_mem->text,"end",3)==0)
				break;                //输入end结束循环
		}
		else           //表示内存为空，不能读，此时堵塞
		{
			//printf("memory is empty,waiting.....\n");
			sleep(1);
		}
	
	
	
	if(shmdt(sh)==-1)
		ERR_EXIT("shmdt failed\n");    //将共享内存从当前进程分离
	
	if(shmctl(shmid,IPC_RMID,0)==-1)
		ERR_EXIT("shmctl failed\n");
	
	return 0;
	
}