code: def MarkForTermination(cls, flow_urn, reason=None, mutation_pool=None):
      
      # Doing a blind write here using low-level data store API. Accessing
      # the flow via AFF4 is not really possible here, because it forces a state
      # to be written in Close() method.
      if mutation_pool is None:
        raise ValueError("Mutation pool can't be none.")
  
      mutation_pool.Set(
          flow_urn,
          cls.SchemaCls.PENDING_TERMINATION.predicate,
          rdf_flow_objects.PendingFlowTermination(reason=reason),
          replace=False)
docs: Mark the flow for termination as soon as any of its states are called.