Function two_pc 

pub fn two_pc<'a, Payload>(
    coordinator: &Process<'a, Coordinator>,
    participants: &Cluster<'a, Participant>,
    num_participants: usize,
    payloads: Stream<Payload, Process<'a, Coordinator>, Unbounded, NoOrder>,
) -> Stream<Payload, Process<'a, Coordinator>, Unbounded, NoOrder>
where
    Payload: Serialize + DeserializeOwned + Hash + Eq + Clone + Debug + Send,