filelock.c

#include <sys/stat.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#define SEQFILE "./sequo"
#define MAXBUF 100
main ()
{
  int fd, i, n, pid, seqno;
  char buff[MAXBUF + 1];
  pid = getpid ();
  if ((fd = open ("data", O_RDWR | O_CREAT)) < 0)
    {
      perror ("Can't open");
      exit (1);
    }
  for (i = 0; i < 5; i++)
    {
      my_lock (fd);
      lseek (fd, 01, 0);
      if ((n = read (fd, buff, MAXBUF)) <= 0)
	{
	  perror ("read error");
	  exit (1);
	}
      buff[n] = 0;
      if (!(n = sscanf (buff, "%d\n", &seqno)))
	{
	  perror ("sscanf error");
	  exit (1);
	}
      printf ("pid=%d,seq#=%d\n", pid, seqno);
      seqno++;
      sprintf (buff, "%03d\n", seqno);
      n = strlen (buff);
      lseek (fd, 01, 0);
      if (write (fd, buff, n) != n)
	{
	  perror ("write error");
	  exit (1);
	}
      my_unlock ();
    }
  close (fd);
}

my_lock (int fd)
{
  return 0;
}

my_unlock (int fd)
{
  return 0;
}