Create a lock file as flag for other instances, mark our instance as lock-holder

        :raise IOError: if a lock was already present or a lock file could not be written

def _obtain_lock_or_raise(self):
        """Create a lock file as flag for other instances, mark our instance as lock-holder

        :raise IOError: if a lock was already present or a lock file could not be written"""
        if self._has_lock():
            return
        lock_file = self._lock_file_path()
        if os.path.isfile(lock_file):
            raise IOError("Lock for file %r did already exist, delete %r in case the lock is illegal" % (self._file_path, lock_file))

        try:
            fd = os.open(lock_file, os.O_WRONLY | os.O_CREAT | os.O_EXCL, 0)
            os.close(fd)
        except OSError,e:
            raise IOError(str(e))

        self._owns_lock = True