fcntl_write.c

linuxI/O的基础编程实例

/*fcntl_write.c测试文件写入锁主函数部分*/
#include <unistd.h>
#include <sys/file.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>


/*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_RDLCK)
			{
				printf("write 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();
		}
	}
}





int main(void)
{
	int fd;
/*首先打开文件*/
	fd=open("hello", O_RDWR | O_CREAT, 0666);
	if(fd<0)
	{
		perror("open");
		exit(1);
	}
/*给文件上写入锁*/
	lock_set(fd,F_WRLCK);
	getchar();
/*给文件解锁*/
	lock_set(fd,F_UNLCK);
	getchar();
	close(fd);
	exit(0);
}