在从共享内存中读数据时添加信号灯集中的灯资源

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

#define PROJ_ID 'k'
#define SHM_SZ 4096

//./read /home/ubuntu
int main(int argc, const char *argv[])
{
int shmid = 0;
int semid = 0;
char *paddr = NULL;
pid_t perr_pid = 0;
key_t key;

if(argc < 2)
{
fprintf(stderr,"Usage : %s argv[1].\n",argv[0]);
exit(EXIT_FAILURE);
}

key = ftok(argv[1],PROJ_ID);
if(key < 0)
{
perror("Fail to shmget");
exit(EXIT_FAILURE);
}

//创建共享内存
shmid = shmget(key,SHM_SZ,IPC_CREAT | 0666);
if(shmid < 0)
{
perror("Fail to shmget");
exit(EXIT_FAILURE);
}
//将共享内存映射进进程的虚拟地址空间
paddr = (char *)shmat(shmid,NULL,0);
if(paddr == (char *)-1)
{
perror("Fail to shmat");
exit(EXIT_FAILURE);
}

//初始化信号灯集，创建0和1两个读写资源
semid = init_semaphore(argv[1],2);

//获得共享内存映射到当前进程的地址
//向共享内存中写入数据
while(1)
{
//申请读资源
P(semid,0);
printf("read %d bytes : %s\n",strlen(paddr),paddr);

//释放写资源
V(semid,1);

if(strncmp(paddr,"quit",4) == 0)
break;
}

//解除映射
if(shmdt(paddr) < 0)
{
perror("Fail to shmdt");
exit(EXIT_FAILURE);
}

//删除共享内存
if(shmctl(shmid,IPC_RMID,NULL) < 0)
{
perror("Fail to shmctl");
exit(EXIT_FAILURE);
}

//删除信号灯集
if(semctl(semid,0,IPC_RMID) < 0)
{
perror("Fail to semctl");
exit(EXIT_FAILURE);
}
return 0;
}