solana/core/src/banking_stage/decision_maker.rs

use {
    solana_poh::poh_recorder::{BankStart, PohRecorder},
    solana_sdk::{
        clock::{
            DEFAULT_TICKS_PER_SLOT, FORWARD_TRANSACTIONS_TO_LEADER_AT_SLOT_OFFSET,
            HOLD_TRANSACTIONS_SLOT_OFFSET,
        },
        pubkey::Pubkey,
    },
    std::sync::{Arc, RwLock},
};

#[derive(Debug, Clone)]
pub enum BufferedPacketsDecision {
    Consume(BankStart),
    Forward,
    ForwardAndHold,
    Hold,
}

impl BufferedPacketsDecision {
    /// Returns the `BankStart` if the decision is `Consume`. Otherwise, returns `None`.
    pub fn bank_start(&self) -> Option<&BankStart> {
        match self {
            Self::Consume(bank_start) => Some(bank_start),
            _ => None,
        }
    }
}

pub struct DecisionMaker {
    my_pubkey: Pubkey,
    poh_recorder: Arc<RwLock<PohRecorder>>,
}

impl DecisionMaker {
    pub fn new(my_pubkey: Pubkey, poh_recorder: Arc<RwLock<PohRecorder>>) -> Self {
        Self {
            my_pubkey,
            poh_recorder,
        }
    }

    pub(crate) fn make_consume_or_forward_decision(&self) -> BufferedPacketsDecision {
        let decision;
        {
            let poh_recorder = self.poh_recorder.read().unwrap();
            decision = Self::consume_or_forward_packets(
                &self.my_pubkey,
                || {
                    poh_recorder.bank_start().filter(|bank_start| {
                        bank_start.should_working_bank_still_be_processing_txs()
                    })
                },
                || {
                    poh_recorder.would_be_leader(
                        (FORWARD_TRANSACTIONS_TO_LEADER_AT_SLOT_OFFSET - 1)
                            * DEFAULT_TICKS_PER_SLOT,
                    )
                },
                || {
                    poh_recorder
                        .would_be_leader(HOLD_TRANSACTIONS_SLOT_OFFSET * DEFAULT_TICKS_PER_SLOT)
                },
                || poh_recorder.leader_after_n_slots(FORWARD_TRANSACTIONS_TO_LEADER_AT_SLOT_OFFSET),
            );
        }

        decision
    }

    fn consume_or_forward_packets(
        my_pubkey: &Pubkey,
        bank_start_fn: impl FnOnce() -> Option<BankStart>,
        would_be_leader_shortly_fn: impl FnOnce() -> bool,
        would_be_leader_fn: impl FnOnce() -> bool,
        leader_pubkey_fn: impl FnOnce() -> Option<Pubkey>,
    ) -> BufferedPacketsDecision {
        // If has active bank, then immediately process buffered packets
        // otherwise, based on leader schedule to either forward or hold packets
        if let Some(bank_start) = bank_start_fn() {
            // If the bank is available, this node is the leader
            BufferedPacketsDecision::Consume(bank_start)
        } else if would_be_leader_shortly_fn() {
            // If the node will be the leader soon, hold the packets for now
            BufferedPacketsDecision::Hold
        } else if would_be_leader_fn() {
            // Node will be leader within ~20 slots, hold the transactions in
            // case it is the only node which produces an accepted slot.
            BufferedPacketsDecision::ForwardAndHold
        } else if let Some(x) = leader_pubkey_fn() {
            if x != *my_pubkey {
                // If the current node is not the leader, forward the buffered packets
                BufferedPacketsDecision::Forward
            } else {
                // If the current node is the leader, return the buffered packets as is
                BufferedPacketsDecision::Hold
            }
        } else {
            // We don't know the leader. Hold the packets for now
            BufferedPacketsDecision::Hold
        }
    }
}

#[cfg(test)]
mod tests {
    use {
        super::*,
        core::panic,
        solana_runtime::bank::Bank,
        std::{sync::Arc, time::Instant},
    };

    #[test]
    fn test_buffered_packet_decision_bank_start() {
        let bank = Arc::new(Bank::default_for_tests());
        let bank_start = BankStart {
            working_bank: bank,
            bank_creation_time: Arc::new(Instant::now()),
        };
        assert!(BufferedPacketsDecision::Consume(bank_start)
            .bank_start()
            .is_some());
        assert!(BufferedPacketsDecision::Forward.bank_start().is_none());
        assert!(BufferedPacketsDecision::ForwardAndHold
            .bank_start()
            .is_none());
        assert!(BufferedPacketsDecision::Hold.bank_start().is_none());
    }

    #[test]
    fn test_should_process_or_forward_packets() {
        let my_pubkey = solana_sdk::pubkey::new_rand();
        let my_pubkey1 = solana_sdk::pubkey::new_rand();
        let bank = Arc::new(Bank::default_for_tests());
        let bank_start = Some(BankStart {
            working_bank: bank,
            bank_creation_time: Arc::new(Instant::now()),
        });
        // having active bank allows to consume immediately
        assert_matches!(
            DecisionMaker::consume_or_forward_packets(
                &my_pubkey,
                || bank_start.clone(),
                || panic!("should not be called"),
                || panic!("should not be called"),
                || panic!("should not be called")
            ),
            BufferedPacketsDecision::Consume(_)
        );
        // Unknown leader, hold the packets
        assert_matches!(
            DecisionMaker::consume_or_forward_packets(
                &my_pubkey,
                || None,
                || false,
                || false,
                || None
            ),
            BufferedPacketsDecision::Hold
        );
        // Leader other than me, forward the packets
        assert_matches!(
            DecisionMaker::consume_or_forward_packets(
                &my_pubkey,
                || None,
                || false,
                || false,
                || Some(my_pubkey1),
            ),
            BufferedPacketsDecision::Forward
        );
        // Will be leader shortly, hold the packets
        assert_matches!(
            DecisionMaker::consume_or_forward_packets(
                &my_pubkey,
                || None,
                || true,
                || panic!("should not be called"),
                || panic!("should not be called"),
            ),
            BufferedPacketsDecision::Hold
        );
        // Will be leader (not shortly), forward and hold
        assert_matches!(
            DecisionMaker::consume_or_forward_packets(
                &my_pubkey,
                || None,
                || false,
                || true,
                || panic!("should not be called"),
            ),
            BufferedPacketsDecision::ForwardAndHold
        );
        // Current leader matches my pubkey, hold
        assert_matches!(
            DecisionMaker::consume_or_forward_packets(
                &my_pubkey1,
                || None,
                || false,
                || false,
                || Some(my_pubkey1),
            ),
            BufferedPacketsDecision::Hold
        );
    }
}