code: def clear(self):
          
          self._lock.acquire_write()  # TODO: read access is enough?
          try:
              was_closed = self._dict is None
              if was_closed:
                  self.open()
              if len(self._dict):
                  self._dict.clear()
                  self._dict.sync()
              if was_closed:
                  self.close()
          finally:
              self._lock.release()
docs: Delete all entries.