def read(self, ids: torch.Tensor = None):
        """Read the feature by index.

        The returned tensor is always in GPU memory, no matter whether the
        fallback feature is in memory or on disk.

        Parameters
        ----------
        ids : torch.Tensor, optional
            The index of the feature. If specified, only the specified indices
            of the feature are read. If None, the entire feature is returned.

        Returns
        -------
        torch.Tensor
            The read feature.
        """
        if ids is None:
            return self._fallback_feature.read()
        values, missing_index, missing_keys = self._feature.query(
            ids if self._offset == 0 else ids + self._offset
        )
        missing_values = self._fallback_feature.read(
            missing_keys if self._offset == 0 else missing_keys - self._offset
        )
        values[missing_index] = missing_values
        self._feature.replace(missing_keys, missing_values)
        return values
Read the feature by index.

        The returned tensor is always in GPU memory, no matter whether the
        fallback feature is in memory or on disk.

        Parameters
        ----------
        ids : torch.Tensor, optional
            The index of the feature. If specified, only the specified indices
            of the feature are read. If None, the entire feature is returned.

        Returns
        -------
        torch.Tensor
            The read feature.
        
python/dgl/graphbolt/impl/gpu_cached_feature.py