Implement locktower voting (#3251)

* locktower components and tests

* integrate locktower into replay stage

* track locktower duration

* make sure threshold is checked after simulating the vote

* check vote lockouts using the VoteState program

* duplicate vote test

* epoch stakes

* disable impossible to verify tests

core/src/locktower.rs

@@ -0,0 +1,575 @@
+use crate::bank_forks::BankForks;
+use crate::staking_utils;
+use hashbrown::{HashMap, HashSet};
+use solana_runtime::bank::Bank;
+use solana_sdk::account::Account;
+use solana_sdk::pubkey::Pubkey;
+use solana_vote_api::vote_instruction::Vote;
+use solana_vote_api::vote_state::{Lockout, VoteState, MAX_LOCKOUT_HISTORY};
+
+const VOTE_THRESHOLD_DEPTH: usize = 8;
+const VOTE_THRESHOLD_SIZE: f64 = 2f64 / 3f64;
+
+#[derive(Default)]
+pub struct EpochStakes {
+    slot: u64,
+    stakes: HashMap<Pubkey, u64>,
+    total_staked: u64,
+}
+
+#[derive(Default)]
+pub struct StakeLockout {
+    lockout: u64,
+    stake: u64,
+}
+
+#[derive(Default)]
+pub struct Locktower {
+    epoch_stakes: EpochStakes,
+    threshold_depth: usize,
+    threshold_size: f64,
+    lockouts: VoteState,
+}
+
+impl EpochStakes {
+    pub fn new(slot: u64, stakes: HashMap<Pubkey, u64>) -> Self {
+        let total_staked = stakes.values().sum();
+        Self {
+            slot,
+            stakes,
+            total_staked,
+        }
+    }
+    pub fn new_for_tests(lamports: u64) -> Self {
+        Self::new(0, vec![(Pubkey::default(), lamports)].into_iter().collect())
+    }
+    pub fn new_from_stake_accounts(slot: u64, accounts: &[(Pubkey, Account)]) -> Self {
+        let stakes = accounts.iter().map(|(k, v)| (*k, v.lamports)).collect();
+        Self::new(slot, stakes)
+    }
+    pub fn new_from_bank(bank: &Bank) -> Self {
+        let bank_epoch = bank.get_epoch_and_slot_index(bank.slot()).0;
+        let stakes = staking_utils::vote_account_balances_at_epoch(bank, bank_epoch)
+            .expect("voting require a bank with stakes");
+        Self::new(bank_epoch, stakes)
+    }
+}
+
+impl Locktower {
+    pub fn new_from_forks(bank_forks: &BankForks) -> Self {
+        //TODO: which bank to start with?
+        let mut frozen_banks: Vec<_> = bank_forks.frozen_banks().values().cloned().collect();
+        frozen_banks.sort_by_key(|b| (b.parents().len(), b.slot()));
+        if let Some(bank) = frozen_banks.last() {
+            Self::new_from_bank(bank)
+        } else {
+            Self::default()
+        }
+    }
+
+    pub fn new_from_bank(bank: &Bank) -> Self {
+        let current_epoch = bank.get_epoch_and_slot_index(bank.slot()).0;
+        let mut lockouts = VoteState::default();
+        if let Some(iter) = staking_utils::node_staked_accounts_at_epoch(bank, current_epoch) {
+            for (delegate_id, _, account) in iter {
+                if *delegate_id == bank.collector_id() {
+                    let state = VoteState::deserialize(&account.data).expect("votes");
+                    if lockouts.votes.len() < state.votes.len() {
+                        //TODO: which state to init with?
+                        lockouts = state;
+                    }
+                }
+            }
+        }
+        let epoch_stakes = EpochStakes::new_from_bank(bank);
+        Self {
+            epoch_stakes,
+            threshold_depth: VOTE_THRESHOLD_DEPTH,
+            threshold_size: VOTE_THRESHOLD_SIZE,
+            lockouts,
+        }
+    }
+    pub fn new(epoch_stakes: EpochStakes, threshold_depth: usize, threshold_size: f64) -> Self {
+        Self {
+            epoch_stakes,
+            threshold_depth,
+            threshold_size,
+            lockouts: VoteState::default(),
+        }
+    }
+    pub fn collect_vote_lockouts<F>(
+        &self,
+        bank_slot: u64,
+        vote_accounts: F,
+        ancestors: &HashMap<u64, HashSet<u64>>,
+    ) -> HashMap<u64, StakeLockout>
+    where
+        F: Iterator<Item = (Pubkey, Account)>,
+    {
+        let mut stake_lockouts = HashMap::new();
+        for (key, account) in vote_accounts {
+            let lamports: u64 = *self.epoch_stakes.stakes.get(&key).unwrap_or(&0);
+            if lamports == 0 {
+                continue;
+            }
+            let mut vote_state: VoteState = VoteState::deserialize(&account.data)
+                .expect("bank should always have valid VoteState data");
+            let start_root = vote_state.root_slot;
+            vote_state.process_vote(Vote { slot: bank_slot });
+            for vote in &vote_state.votes {
+                Self::update_ancestor_lockouts(&mut stake_lockouts, &vote, ancestors);
+            }
+            if start_root != vote_state.root_slot {
+                if let Some(root) = start_root {
+                    let vote = Lockout {
+                        confirmation_count: MAX_LOCKOUT_HISTORY as u32,
+                        slot: root,
+                    };
+                    Self::update_ancestor_lockouts(&mut stake_lockouts, &vote, ancestors);
+                }
+            }
+            if let Some(root) = vote_state.root_slot {
+                let vote = Lockout {
+                    confirmation_count: MAX_LOCKOUT_HISTORY as u32,
+                    slot: root,
+                };
+                Self::update_ancestor_lockouts(&mut stake_lockouts, &vote, ancestors);
+            }
+            // each account hash a stake for all the forks in the active tree for this bank
+            Self::update_ancestor_stakes(&mut stake_lockouts, bank_slot, lamports, ancestors);
+        }
+        stake_lockouts
+    }
+
+    pub fn update_epoch(&mut self, bank: &Bank) {
+        let bank_epoch = bank.get_epoch_and_slot_index(bank.slot()).0;
+        if bank_epoch != self.epoch_stakes.slot {
+            assert!(
+                bank_epoch > self.epoch_stakes.slot,
+                "epoch_stakes cannot move backwards"
+            );
+            self.epoch_stakes = EpochStakes::new_from_bank(bank);
+        }
+    }
+
+    pub fn record_vote(&mut self, slot: u64) {
+        self.lockouts.process_vote(Vote { slot });
+    }
+
+    pub fn calculate_weight(&self, stake_lockouts: &HashMap<u64, StakeLockout>) -> u128 {
+        let mut sum = 0u128;
+        let root_slot = self.lockouts.root_slot.unwrap_or(0);
+        for (slot, stake_lockout) in stake_lockouts {
+            if self.lockouts.root_slot.is_some() && *slot <= root_slot {
+                continue;
+            }
+            sum += u128::from(stake_lockout.lockout) * u128::from(stake_lockout.stake)
+        }
+        sum
+    }
+
+    pub fn has_voted(&self, slot: u64) -> bool {
+        for vote in &self.lockouts.votes {
+            if vote.slot == slot {
+                return true;
+            }
+        }
+        false
+    }
+
+    pub fn is_locked_out(&self, slot: u64, decendants: &HashMap<u64, HashSet<u64>>) -> bool {
+        let mut lockouts = self.lockouts.clone();
+        lockouts.process_vote(Vote { slot });
+        for vote in &lockouts.votes {
+            if vote.slot == slot {
+                continue;
+            }
+            if !decendants[&vote.slot].contains(&slot) {
+                return false;
+            }
+        }
+        if let Some(root) = lockouts.root_slot {
+            decendants[&root].contains(&slot)
+        } else {
+            true
+        }
+    }
+
+    pub fn check_vote_stake_threshold(
+        &self,
+        slot: u64,
+        stake_lockouts: &HashMap<u64, StakeLockout>,
+    ) -> bool {
+        let mut lockouts = self.lockouts.clone();
+        lockouts.process_vote(Vote { slot });
+        let vote = lockouts.nth_recent_vote(self.threshold_depth);
+        if let Some(vote) = vote {
+            if let Some(fork_stake) = stake_lockouts.get(&vote.slot) {
+                (fork_stake.stake as f64 / self.epoch_stakes.total_staked as f64)
+                    > self.threshold_size
+            } else {
+                false
+            }
+        } else {
+            true
+        }
+    }
+
+    /// Update lockouts for all the ancestors
+    fn update_ancestor_lockouts(
+        stake_lockouts: &mut HashMap<u64, StakeLockout>,
+        vote: &Lockout,
+        ancestors: &HashMap<u64, HashSet<u64>>,
+    ) {
+        let mut slot_with_ancestors = vec![vote.slot];
+        slot_with_ancestors.extend(&ancestors[&vote.slot]);
+        for slot in slot_with_ancestors {
+            let entry = &mut stake_lockouts.entry(slot).or_default();
+            entry.lockout += vote.lockout();
+        }
+    }
+
+    /// Update stake for all the ancestors.
+    /// Note, stake is the same for all the ancestor.
+    fn update_ancestor_stakes(
+        stake_lockouts: &mut HashMap<u64, StakeLockout>,
+        slot: u64,
+        lamports: u64,
+        ancestors: &HashMap<u64, HashSet<u64>>,
+    ) {
+        let mut slot_with_ancestors = vec![slot];
+        slot_with_ancestors.extend(&ancestors[&slot]);
+        for slot in slot_with_ancestors {
+            let entry = &mut stake_lockouts.entry(slot).or_default();
+            entry.stake += lamports;
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+    use solana_sdk::signature::{Keypair, KeypairUtil};
+
+    fn gen_accounts(stake_votes: &[(u64, &[u64])]) -> Vec<(Pubkey, Account)> {
+        let mut accounts = vec![];
+        for (lamports, votes) in stake_votes {
+            let mut account = Account::default();
+            account.data = vec![0; 1024];
+            account.lamports = *lamports;
+            let mut vote_state = VoteState::default();
+            for slot in *votes {
+                vote_state.process_vote(Vote { slot: *slot });
+            }
+            vote_state
+                .serialize(&mut account.data)
+                .expect("serialize state");
+            accounts.push((Keypair::new().pubkey(), account));
+        }
+        accounts
+    }
+
+    #[test]
+    fn test_collect_vote_lockouts_no_epoch_stakes() {
+        let accounts = gen_accounts(&[(1, &[0])]);
+        let epoch_stakes = EpochStakes::new_for_tests(2);
+        let locktower = Locktower::new(epoch_stakes, 0, 0.67);
+        let ancestors = vec![(1, vec![0].into_iter().collect()), (0, HashSet::new())]
+            .into_iter()
+            .collect();
+        let staked_lockouts = locktower.collect_vote_lockouts(1, accounts.into_iter(), &ancestors);
+        assert!(staked_lockouts.is_empty());
+    }
+
+    #[test]
+    fn test_collect_vote_lockouts_sums() {
+        //two accounts voting for slot 0 with 1 token staked
+        let accounts = gen_accounts(&[(1, &[0]), (1, &[0])]);
+        let epoch_stakes = EpochStakes::new_from_stake_accounts(0, &accounts);
+        let locktower = Locktower::new(epoch_stakes, 0, 0.67);
+        let ancestors = vec![(1, vec![0].into_iter().collect()), (0, HashSet::new())]
+            .into_iter()
+            .collect();
+        let staked_lockouts = locktower.collect_vote_lockouts(1, accounts.into_iter(), &ancestors);
+        assert_eq!(staked_lockouts[&0].stake, 2);
+        assert_eq!(staked_lockouts[&0].lockout, 2 + 2 + 4 + 4);
+    }
+
+    #[test]
+    fn test_collect_vote_lockouts_root() {
+        let votes: Vec<u64> = (0..MAX_LOCKOUT_HISTORY as u64).into_iter().collect();
+        //two accounts voting for slot 0 with 1 token staked
+        let accounts = gen_accounts(&[(1, &votes), (1, &votes)]);
+        let epoch_stakes = EpochStakes::new_from_stake_accounts(0, &accounts);
+        let mut locktower = Locktower::new(epoch_stakes, 0, 0.67);
+        let mut ancestors = HashMap::new();
+        for i in 0..(MAX_LOCKOUT_HISTORY + 1) {
+            locktower.record_vote(i as u64);
+            ancestors.insert(i as u64, (0..i as u64).into_iter().collect());
+        }
+        assert_eq!(locktower.lockouts.root_slot, Some(0));
+        let staked_lockouts = locktower.collect_vote_lockouts(
+            MAX_LOCKOUT_HISTORY as u64,
+            accounts.into_iter(),
+            &ancestors,
+        );
+        for i in 0..MAX_LOCKOUT_HISTORY {
+            assert_eq!(staked_lockouts[&(i as u64)].stake, 2);
+        }
+        // should be the sum of all the weights for root
+        assert!(staked_lockouts[&0].lockout > (2 * (1 << MAX_LOCKOUT_HISTORY)));
+    }
+
+    #[test]
+    fn test_calculate_weight_skips_root() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 0, 0.67);
+        locktower.lockouts.root_slot = Some(1);
+        let stakes = vec![
+            (
+                0,
+                StakeLockout {
+                    stake: 1,
+                    lockout: 8,
+                },
+            ),
+            (
+                1,
+                StakeLockout {
+                    stake: 1,
+                    lockout: 8,
+                },
+            ),
+        ]
+        .into_iter()
+        .collect();
+        assert_eq!(locktower.calculate_weight(&stakes), 0u128);
+    }
+
+    #[test]
+    fn test_calculate_weight() {
+        let locktower = Locktower::new(EpochStakes::new_for_tests(2), 0, 0.67);
+        let stakes = vec![(
+            0,
+            StakeLockout {
+                stake: 1,
+                lockout: 8,
+            },
+        )]
+        .into_iter()
+        .collect();
+        assert_eq!(locktower.calculate_weight(&stakes), 8u128);
+    }
+
+    #[test]
+    fn test_check_vote_threshold_without_votes() {
+        let locktower = Locktower::new(EpochStakes::new_for_tests(2), 1, 0.67);
+        let stakes = vec![(
+            0,
+            StakeLockout {
+                stake: 1,
+                lockout: 8,
+            },
+        )]
+        .into_iter()
+        .collect();
+        assert!(locktower.check_vote_stake_threshold(0, &stakes));
+    }
+
+    #[test]
+    fn test_is_locked_out_empty() {
+        let locktower = Locktower::new(EpochStakes::new_for_tests(2), 0, 0.67);
+        let decendants = HashMap::new();
+        assert!(locktower.is_locked_out(0, &decendants));
+    }
+
+    #[test]
+    fn test_is_locked_out_root_slot_child() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 0, 0.67);
+        let decendants = vec![(0, vec![1].into_iter().collect())]
+            .into_iter()
+            .collect();
+        locktower.lockouts.root_slot = Some(0);
+        assert!(locktower.is_locked_out(1, &decendants));
+    }
+
+    #[test]
+    fn test_is_locked_out_root_slot_sibling() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 0, 0.67);
+        let decendants = vec![(0, vec![1].into_iter().collect())]
+            .into_iter()
+            .collect();
+        locktower.lockouts.root_slot = Some(0);
+        assert!(!locktower.is_locked_out(2, &decendants));
+    }
+
+    #[test]
+    fn test_check_already_voted() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 0, 0.67);
+        locktower.record_vote(0);
+        assert!(locktower.has_voted(0));
+        assert!(!locktower.has_voted(1));
+    }
+
+    #[test]
+    fn test_is_locked_out_double_vote() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 0, 0.67);
+        let decendants = vec![(0, vec![1].into_iter().collect()), (1, HashSet::new())]
+            .into_iter()
+            .collect();
+        locktower.record_vote(0);
+        locktower.record_vote(1);
+        assert!(!locktower.is_locked_out(0, &decendants));
+    }
+
+    #[test]
+    fn test_is_locked_out_child() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 0, 0.67);
+        let decendants = vec![(0, vec![1].into_iter().collect())]
+            .into_iter()
+            .collect();
+        locktower.record_vote(0);
+        assert!(locktower.is_locked_out(1, &decendants));
+    }
+
+    #[test]
+    fn test_is_locked_out_sibling() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 0, 0.67);
+        let decendants = vec![
+            (0, vec![1, 2].into_iter().collect()),
+            (1, HashSet::new()),
+            (2, HashSet::new()),
+        ]
+        .into_iter()
+        .collect();
+        locktower.record_vote(0);
+        locktower.record_vote(1);
+        assert!(!locktower.is_locked_out(2, &decendants));
+    }
+
+    #[test]
+    fn test_is_locked_out_last_vote_expired() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 0, 0.67);
+        let decendants = vec![(0, vec![1, 4].into_iter().collect()), (1, HashSet::new())]
+            .into_iter()
+            .collect();
+        locktower.record_vote(0);
+        locktower.record_vote(1);
+        assert!(locktower.is_locked_out(4, &decendants));
+        locktower.record_vote(4);
+        assert_eq!(locktower.lockouts.votes[0].slot, 0);
+        assert_eq!(locktower.lockouts.votes[0].confirmation_count, 2);
+        assert_eq!(locktower.lockouts.votes[1].slot, 4);
+        assert_eq!(locktower.lockouts.votes[1].confirmation_count, 1);
+    }
+
+    #[test]
+    fn test_check_vote_threshold_below_threshold() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 1, 0.67);
+        let stakes = vec![(
+            0,
+            StakeLockout {
+                stake: 1,
+                lockout: 8,
+            },
+        )]
+        .into_iter()
+        .collect();
+        locktower.record_vote(0);
+        assert!(!locktower.check_vote_stake_threshold(1, &stakes));
+    }
+    #[test]
+    fn test_check_vote_threshold_above_threshold() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 1, 0.67);
+        let stakes = vec![(
+            0,
+            StakeLockout {
+                stake: 2,
+                lockout: 8,
+            },
+        )]
+        .into_iter()
+        .collect();
+        locktower.record_vote(0);
+        assert!(locktower.check_vote_stake_threshold(1, &stakes));
+    }
+
+    #[test]
+    fn test_check_vote_threshold_above_threshold_after_pop() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 1, 0.67);
+        let stakes = vec![(
+            0,
+            StakeLockout {
+                stake: 2,
+                lockout: 8,
+            },
+        )]
+        .into_iter()
+        .collect();
+        locktower.record_vote(0);
+        locktower.record_vote(1);
+        locktower.record_vote(2);
+        assert!(locktower.check_vote_stake_threshold(6, &stakes));
+    }
+
+    #[test]
+    fn test_check_vote_threshold_above_threshold_no_stake() {
+        let mut locktower = Locktower::new(EpochStakes::new_for_tests(2), 1, 0.67);
+        let stakes = HashMap::new();
+        locktower.record_vote(0);
+        assert!(!locktower.check_vote_stake_threshold(1, &stakes));
+    }
+
+    #[test]
+    fn test_lockout_is_updated_for_entire_branch() {
+        let mut stake_lockouts = HashMap::new();
+        let vote = Lockout {
+            slot: 2,
+            confirmation_count: 1,
+        };
+        let set: HashSet<u64> = vec![0u64, 1u64].into_iter().collect();
+        let mut ancestors = HashMap::new();
+        ancestors.insert(2, set);
+        let set: HashSet<u64> = vec![0u64].into_iter().collect();
+        ancestors.insert(1, set);
+        Locktower::update_ancestor_lockouts(&mut stake_lockouts, &vote, &ancestors);
+        assert_eq!(stake_lockouts[&0].lockout, 2);
+        assert_eq!(stake_lockouts[&1].lockout, 2);
+        assert_eq!(stake_lockouts[&2].lockout, 2);
+    }
+
+    #[test]
+    fn test_lockout_is_updated_for_slot_or_lower() {
+        let mut stake_lockouts = HashMap::new();
+        let set: HashSet<u64> = vec![0u64, 1u64].into_iter().collect();
+        let mut ancestors = HashMap::new();
+        ancestors.insert(2, set);
+        let set: HashSet<u64> = vec![0u64].into_iter().collect();
+        ancestors.insert(1, set);
+        let vote = Lockout {
+            slot: 2,
+            confirmation_count: 1,
+        };
+        Locktower::update_ancestor_lockouts(&mut stake_lockouts, &vote, &ancestors);
+        let vote = Lockout {
+            slot: 1,
+            confirmation_count: 2,
+        };
+        Locktower::update_ancestor_lockouts(&mut stake_lockouts, &vote, &ancestors);
+        assert_eq!(stake_lockouts[&0].lockout, 2 + 4);
+        assert_eq!(stake_lockouts[&1].lockout, 2 + 4);
+        assert_eq!(stake_lockouts[&2].lockout, 2);
+    }
+
+    #[test]
+    fn test_stake_is_updated_for_entire_branch() {
+        let mut stake_lockouts = HashMap::new();
+        let mut account = Account::default();
+        account.lamports = 1;
+        let set: HashSet<u64> = vec![0u64, 1u64].into_iter().collect();
+        let ancestors: HashMap<u64, HashSet<u64>> = [(2u64, set)].into_iter().cloned().collect();
+        Locktower::update_ancestor_stakes(&mut stake_lockouts, 2, account.lamports, &ancestors);
+        assert_eq!(stake_lockouts[&0].stake, 1);
+        assert_eq!(stake_lockouts[&1].stake, 1);
+        assert_eq!(stake_lockouts[&2].stake, 1);
+    }
+}