def retrieve_all(self, sids, default_none=False):
        """
        Retrieve all assets in `sids`.

        Parameters
        ----------
        sids : iterable of int
            Assets to retrieve.
        default_none : bool
            If True, return None for failed lookups.
            If False, raise `SidsNotFound`.

        Returns
        -------
        assets : list[Asset or None]
            A list of the same length as `sids` containing Assets (or Nones)
            corresponding to the requested sids.

        Raises
        ------
        SidsNotFound
            When a requested sid is not found and default_none=False.
        """
        sids = list(sids)
        hits, missing, failures = {}, set(), []
        for sid in sids:
            try:
                asset = self._asset_cache[sid]
                if not default_none and asset is None:
                    # Bail early if we've already cached that we don't know
                    # about an asset.
                    raise SidsNotFound(sids=[sid])
                hits[sid] = asset
            except KeyError:
                missing.add(sid)

        # All requests were cache hits.  Return requested sids in order.
        if not missing:
            return [hits[sid] for sid in sids]

        update_hits = hits.update

        # Look up cache misses by type.
        type_to_assets = self.group_by_type(missing)

        # Handle failures
        failures = {failure: None for failure in type_to_assets.pop(None, ())}
        update_hits(failures)
        self._asset_cache.update(failures)

        if failures and not default_none:
            raise SidsNotFound(sids=list(failures))

        # We don't update the asset cache here because it should already be
        # updated by `self.retrieve_equities`.
        update_hits(self.retrieve_equities(type_to_assets.pop('equity', ())))
        update_hits(
            self.retrieve_futures_contracts(type_to_assets.pop('future', ()))
        )

        # We shouldn't know about any other asset types.
        if type_to_assets:
            raise AssertionError(
                "Found asset types: %s" % list(type_to_assets.keys())
            )

        return [hits[sid] for sid in sids]