prg9_1.c

配套光盘网络编程进程间的通信,网络编程进程间的通信是一本很经典的好书

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

#define	SEQFILE	"zjm.txt"
#define	MAXLINE	256
#define	FILE_MODE	(S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)

int lock_reg(int fd,int cmd,int type,off_t offset,int whence,off_t len);
pid_t lock_test(int fd, int type,off_t offset,int whence, off_t len);
/**brief 锁操作参数宏参数
 * 如果len=0 表示整个文件
 * \param fd -- 进程ID
 * \param type -- 命令类型F_RDLCK,F_WRLCK,F_UNLCK
 * \param offset -- 记录偏移量，即上锁记录的开始位置,byte offset,relative to l_whence
 * \param whence -- 是以下之中的一个：SEEK_SET,SEEK_CUR,SEEK_END
 * \param len -- 记录的长度
 */
///返回-1--错误 
#define	read_lock(fd,offset,whence,len) \
        lock_reg(fd,F_SETLK,F_RDLCK,offset,whence,len)
///返回-1--错误
#define	readw_lock(fd,offset,whence,len) \
        lock_reg(fd,F_SETLKW,F_RDLCK,offset,whence,len)
///返回-1--错误
#define	write_lock(fd,offset,whence,len) \
        lock_reg(fd,F_SETLK,F_WRLCK,offset,whence,len)
///返回-1--错误
#define	writew_lock(fd,offset,whence,len) \
        lock_reg(fd,F_SETLKW,F_WRLCK,offset,whence,len)
///返回-1--错误
#define	un_lock(fd,offset,whence,len) \
        lock_reg(fd,F_SETLK,F_UNLCK,offset,whence,len)
///返回-1 -- 错误 0 -- 没有锁定 其它 -- 已经锁,返回是拥有锁的进程ID
#define	is_read_lockable(fd,offset,whence,len) \
        !lock_test(fd,F_RDLCK,offset,whence,len)
#define	is_write_lockable(fd,offset,whence,len) \
        !lock_test(fd,F_WRLCK,offset,whence,len)


#define my_lock(fd)  (writew_lock(fd,0,SEEK_SET,0))
#define my_unlock(fd)  (un_lock(fd,0,SEEK_SET,0)) 
int main(int argc,char **argv)
{
  int	fd;
  long	i,seqno;
  pid_t	pid;
  size_t	n;
  char	line[MAXLINE+1];
  pid = getpid();
  fd = open(SEQFILE,O_RDWR,FILE_MODE);
  for(i = 0;i<20; i++)
  {
  	my_lock(fd);
  	lseek(fd,0L,SEEK_SET);
  	n = read(fd,line,MAXLINE);
  	line[n] = '\0';
  	printf("%s\n",line);
  	lseek(fd,0L,SEEK_SET);
  	write(fd,line,strlen(line));
  	my_unlock(fd);
  }
  exit(0);
}

int lock_reg(int fd,int cmd,int type,off_t offset,int whence,off_t len)
{
	struct flock lock;
	lock.l_type = type;
	lock.l_start = offset;
	lock.l_whence = whence;
	lock.l_len = len;
	return ( fcntl(fd,cmd,&lock));
}
pid_t lock_test(int fd, int type,off_t offset,int whence, off_t len)
{
	struct flock lock;
	lock.l_type = type;
	lock.l_start = offset;
	lock.l_whence = whence;
	lock.l_len = len;
	if (fcntl(fd,F_GETLK,&lock) == -1)
	  return (-1);
	if (lock.l_type == F_UNLCK)
	  return 0;
	return(lock.l_pid);
}