code: def chain_update(self, block, receipts):
          
          with self._lock:
              for batch_id in self._pending.copy():
                  if self._batch_committed(batch_id):
                      self._pending.remove(batch_id)
                      self._update_observers(batch_id,
                                             ClientBatchStatus.COMMITTED)
docs: Removes batches from the pending cache if found in the block store,
          and notifies any observers.