1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160

use rand::distributions::{Distribution, WeightedIndex};
use rand_chacha::{rand_core::SeedableRng, ChaChaRng};
use solana_sdk::pubkey::Pubkey;
use std::ops::Index;
use std::sync::Arc;

// Used for testing
#[derive(Clone, Debug)]
pub struct FixedSchedule {
    pub leader_schedule: Arc<LeaderSchedule>,
    pub start_epoch: u64,
}

/// Stake-weighted leader schedule for one epoch.
#[derive(Debug, Default, PartialEq)]
pub struct LeaderSchedule {
    slot_leaders: Vec<Pubkey>,
}

impl LeaderSchedule {
    // Note: passing in zero stakers will cause a panic.
    pub fn new(ids_and_stakes: &[(Pubkey, u64)], seed: [u8; 32], len: u64, repeat: u64) -> Self {
        let (ids, stakes): (Vec<_>, Vec<_>) = ids_and_stakes.iter().cloned().unzip();
        let rng = &mut ChaChaRng::from_seed(seed);
        let weighted_index = WeightedIndex::new(stakes).unwrap();
        let mut current_node = Pubkey::default();
        let slot_leaders = (0..len)
            .map(|i| {
                if i % repeat == 0 {
                    current_node = ids[weighted_index.sample(rng)];
                    current_node
                } else {
                    current_node
                }
            })
            .collect();
        Self { slot_leaders }
    }

    pub fn new_from_schedule(slot_leaders: Vec<Pubkey>) -> Self {
        Self { slot_leaders }
    }

    pub fn get_slot_leaders(&self) -> &[Pubkey] {
        &self.slot_leaders
    }

    pub fn num_slots(&self) -> usize {
        self.slot_leaders.len()
    }
}

impl Index<u64> for LeaderSchedule {
    type Output = Pubkey;
    fn index(&self, index: u64) -> &Pubkey {
        let index = index as usize;
        &self.slot_leaders[index % self.slot_leaders.len()]
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_leader_schedule_index() {
        let pubkey0 = solana_sdk::pubkey::new_rand();
        let pubkey1 = solana_sdk::pubkey::new_rand();
        let leader_schedule = LeaderSchedule {
            slot_leaders: vec![pubkey0, pubkey1],
        };
        assert_eq!(leader_schedule[0], pubkey0);
        assert_eq!(leader_schedule[1], pubkey1);
        assert_eq!(leader_schedule[2], pubkey0);
    }

    #[test]
    fn test_leader_schedule_basic() {
        let num_keys = 10;
        let stakes: Vec<_> = (0..num_keys)
            .map(|i| (solana_sdk::pubkey::new_rand(), i))
            .collect();

        let seed = solana_sdk::pubkey::new_rand();
        let mut seed_bytes = [0u8; 32];
        seed_bytes.copy_from_slice(seed.as_ref());
        let len = num_keys * 10;
        let leader_schedule = LeaderSchedule::new(&stakes, seed_bytes, len, 1);
        let leader_schedule2 = LeaderSchedule::new(&stakes, seed_bytes, len, 1);
        assert_eq!(leader_schedule.slot_leaders.len() as u64, len);
        // Check that the same schedule is reproducibly generated
        assert_eq!(leader_schedule, leader_schedule2);
    }

    #[test]
    fn test_repeated_leader_schedule() {
        let num_keys = 10;
        let stakes: Vec<_> = (0..num_keys)
            .map(|i| (solana_sdk::pubkey::new_rand(), i))
            .collect();

        let seed = solana_sdk::pubkey::new_rand();
        let mut seed_bytes = [0u8; 32];
        seed_bytes.copy_from_slice(seed.as_ref());
        let len = num_keys * 10;
        let repeat = 8;
        let leader_schedule = LeaderSchedule::new(&stakes, seed_bytes, len, repeat);
        assert_eq!(leader_schedule.slot_leaders.len() as u64, len);
        let mut leader_node = Pubkey::default();
        for (i, node) in leader_schedule.slot_leaders.iter().enumerate() {
            if i % repeat as usize == 0 {
                leader_node = *node;
            } else {
                assert_eq!(leader_node, *node);
            }
        }
    }

    #[test]
    fn test_repeated_leader_schedule_specific() {
        let alice_pubkey = solana_sdk::pubkey::new_rand();
        let bob_pubkey = solana_sdk::pubkey::new_rand();
        let stakes = vec![(alice_pubkey, 2), (bob_pubkey, 1)];

        let seed = Pubkey::default();
        let mut seed_bytes = [0u8; 32];
        seed_bytes.copy_from_slice(seed.as_ref());
        let len = 8;
        // What the schedule looks like without any repeats
        let leaders1 = LeaderSchedule::new(&stakes, seed_bytes, len, 1).slot_leaders;

        // What the schedule looks like with repeats
        let leaders2 = LeaderSchedule::new(&stakes, seed_bytes, len, 2).slot_leaders;
        assert_eq!(leaders1.len(), leaders2.len());

        let leaders1_expected = vec![
            alice_pubkey,
            alice_pubkey,
            alice_pubkey,
            bob_pubkey,
            alice_pubkey,
            alice_pubkey,
            alice_pubkey,
            alice_pubkey,
        ];
        let leaders2_expected = vec![
            alice_pubkey,
            alice_pubkey,
            alice_pubkey,
            alice_pubkey,
            alice_pubkey,
            alice_pubkey,
            bob_pubkey,
            bob_pubkey,
        ];

        assert_eq!(leaders1, leaders1_expected);
        assert_eq!(leaders2, leaders2_expected);
    }
}