sub LockFile
{
  local $path = $_[0] ;
  local $mode = $_[1] ;
  local $flockPath = $path . '.lck' ;
  local $flockFH = $flockPath ;

  open ($flockFH, ">$flockPath") or die ("Failed to open $flockPath") ;
  if (flock ($flockFH, $mode))
  {
    use Fcntl ;
    local $fexistPath = $path . '.lck.tmp' ;
    if ($mode & LOCK_EX)
    {
      local $fexistFH = $fexistPath ;
      sysopen ($fexistFH, $fexistPath, O_WRONLY | O_CREAT | O_EXCL)
        or die ("Acquired an exclusive lock for $flockPath but cannot create $fexistPath.") ;
      close $fexistFH ;
    }
    elsif (-e $fexistPath)
    {
      die ("Acquired a shared lock for $flockPath but found that $fexistPath exists.") ;
    }
  }
  else
  {
    die ("System Busy") ;
  }
  return ($flockFH, $path, $mode) ;
}

sub UnlockFile
{
  use Fcntl ;
  local $fh = $_[0] ;
  local $path = $_[1] ;
  local $mode = $_[2] ;

  if ($mode & LOCK_EX)
  {
    local $fexistPath = $path . '.lck.tmp' ;
    unlink ($fexistPath) > 0 or die ("Failed to delete the lock file $fexistPath.") ;
  }
  close ($fh) ;
}

##</code><code>##

local ($lockFH, $lockPath, $lockMode) = LockFile ("test.txt", 2);
# Wait 10 seconds before calling UnlockFile
UnlockFile ($lockFH, $lockPath, $lockMode);