lock_set.c

linuxI/O的基础编程实例

/*lock_set*/
void lock_set(int fd,int type)
{
	struct flock lock;
	lock.l_whence=SEEK_SET;
	lock.l_start=0;
	lock.l_len=0;
	while(1)
	{
		lock.l_type=type;
/*根据不同的type值给文件上锁或解锁*/	
		if((fcntl(fd, F_SETLK,&lock))==0)
		{
			if(lock.l_type==F_RDLCK)
			{
				printf("read lock set by %d\n",getpid());
			}
			else if(lock.l_type==F_WRLCK)
			{
				printf("write lock set by %d\n",getpid());
			}
			else if(lock.l_type==F_UNLCK)
			{
				printf("release lock by %d\n",getpid());
			}
			return;
		}
/*判断文件是否可以上锁*/
		fcntl(fd, F_GETLK, &lock);
/*判断文件不能上锁的原因*/
		if(lock.l_type!=F_UNLCK)
		{
			/*该文件已有写入锁*/
			if(lock.l_type==F_RDLCK)
			{
				printf("read lock already set by %d\n",lock.l_pid);
			}
			/*该文件已有读取锁*/
			else if(lock.l_type==F_WRLCK)
			{
				printf("write lock already set by %d\n",lock.l_pid);
			}
			getchar();
		}
	}
}