pub fn compose_dispatchers(
source_fragment_distribution: DistributionType,
source_fragment_actors: &HashMap<ActorId, Option<Bitmap>>,
target_fragment_id: FragmentId,
target_fragment_distribution: DistributionType,
target_fragment_actors: &HashMap<ActorId, Option<Bitmap>>,
dispatcher_type: DispatcherType,
dist_key_indices: Vec<u32>,
output_indices: Vec<u32>,
) -> HashMap<ActorId, PbDispatcher>