600 lines
		
	
	
		
			20 KiB
		
	
	
	
		
			Rust
		
	
	
	
	
	
			
		
		
	
	
			600 lines
		
	
	
		
			20 KiB
		
	
	
	
		
			Rust
		
	
	
	
	
	
//! Fork Selection Simulation
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//!
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//! Description of the algorithm can be found in [docs/src/fork-selection.md](docs/src/fork-selection.md).
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//!
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//! A test library function exists for configuring networks.
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//! ```
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//!     /// * num_partitions - 1 to 100 partitions
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//!     /// * fail_rate - 0 to 1.0 rate of packet receive failure
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//!     /// * delay_count - number of forks to observe before voting
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//!     /// * parasite_rate - number of parasite nodes that vote opposite the greedy choice
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//!     fn test_with_partitions(num_partitions: usize, fail_rate: f64, delay_count: usize, parasite_rate: f64);
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//! ```
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//! Modify the test function
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//! ```
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//! #[test]
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//! #[ignore]
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//! fn test_all_partitions() {
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//!     test_with_partitions(100, 0.0, 5, 0.25, false)
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//! }
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//! ```
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//! Run with cargo
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//!
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//! ```
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//! cargo test all_partitions --release -- --nocapture --ignored
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//! ```
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//!
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//! The output will look like this
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//! ```
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//! time: 336, tip converged: 76, trunk id: 434, trunk time: 334, trunk converged 98, trunk height 65
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//! ```
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//! * time - The current cluster time.  Each packet is transmitted to the cluster at a different time value.
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//! * tip converged - Percentage of nodes voting on the tip.
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//! * trunk id - ID of the newest most common fork for the largest converged set of nodes.
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//! * trunk time - Time when the trunk fork was created.
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//! * trunk converged - Number of voters that have converged on this fork.
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//! * trunk height - Ledger height of the trunk.
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//!
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//!
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//! ### Simulating Greedy Choice
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//!
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//! Parasitic nodes reverse the weighted function and pick the fork that has the least amount of economic finality, but without fully committing to a dead fork.
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//!
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//! ```
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//! // Each run starts with 100 partitions, and it takes about 260 forks for a dominant trunk to emerge
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//! // fully parasitic, 5 vote delay, 17% efficient
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//! test_with_partitions(100, 0.0, 5, 1.0)
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//! time: 1000, tip converged: 100, trunk id: 1095, trunk time: 995, trunk converged 100, trunk height 125
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//! // 50% parasitic, 5 vote delay, 30% efficient
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//! test_with_partitions(100, 0.0, 5, 0.5)
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//! time: 1000, tip converged: 51, trunk id: 1085, trunk time: 985, trunk converged 100, trunk
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//! height 223
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//! // 25%  parasitic, 5 vote delay, 49% efficient
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//! test_with_partitions(100, 0.0, 5, 0.25)
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//! time: 1000, tip converged: 79, trunk id: 1096, trunk time: 996, trunk converged 100, trunk
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//! height 367
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//! // 0%  parasitic, 5 vote delay, 62% efficient
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//! test_with_partitions(100, 0.0, 5, 0.0)
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//! time: 1000, tip converged: 100, trunk id: 1099, trunk time: 999, trunk converged 100, trunk height 463
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//! // 0%  parasitic, 0 vote delay, 100% efficient
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//! test_with_partitions(100, 0.0, 0, 0.0)
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//! time: 1000, tip converged: 100, trunk id: 1100, trunk time: 1000, trunk converged 100, trunk height 740
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//! ```
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//!
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//! ### Impact of Receive Errors
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//!
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//! * with 10% of packet drops, the height of the trunk is about 77% of the max possible
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//! ```
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//! time: 4007, tip converged: 94, trunk id: 4005, trunk time: 4002, trunk converged 100, trunk height 3121
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//! ```
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//! * with 90% of packet drops, the height of the trunk is about 8.6% of the max possible
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//! ```
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//! time: 4007, tip converged: 10, trunk id: 3830, trunk time: 3827, trunk converged 100, trunk height 348
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//! ```
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extern crate rand;
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use rand::{thread_rng, Rng};
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use std::collections::{HashMap, VecDeque};
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#[derive(Clone, Default, Debug, Hash, Eq, PartialEq)]
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pub struct Fork {
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    id: usize,
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    base: usize,
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}
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impl Fork {
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    fn is_trunk_of(&self, other: &Fork, fork_tree: &HashMap<usize, Fork>) -> bool {
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        let mut current = other;
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        loop {
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            // found it
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            if current.id == self.id {
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                return true;
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            }
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            // base is 0, and this id is 0
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            if current.base == 0 && self.id == 0 {
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                assert!(fork_tree.get(&0).is_none());
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                return true;
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            }
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            // base is 0
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            if fork_tree.get(¤t.base).is_none() {
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                return false;
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            }
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            current = fork_tree.get(¤t.base).unwrap();
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        }
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    }
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}
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#[derive(Clone, Default, Debug, Hash, Eq, PartialEq)]
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pub struct Vote {
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    fork: Fork,
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    time: usize,
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    lockout: usize,
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}
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impl Vote {
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    pub fn new(fork: Fork, time: usize) -> Vote {
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        Self {
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            fork,
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            time,
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            lockout: 2,
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        }
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    }
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    pub fn lock_height(&self) -> usize {
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        self.time + self.lockout
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    }
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    pub fn is_trunk_of(&self, other: &Vote, fork_tree: &HashMap<usize, Fork>) -> bool {
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        self.fork.is_trunk_of(&other.fork, fork_tree)
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    }
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}
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#[derive(Debug)]
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pub struct Tower {
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    votes: VecDeque<Vote>,
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    max_size: usize,
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    fork_trunk: Fork,
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    converge_depth: usize,
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    delay_count: usize,
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    delayed_votes: VecDeque<Vote>,
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    parasite: bool,
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}
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impl Tower {
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    pub fn new(max_size: usize, converge_depth: usize, delay_count: usize) -> Self {
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        Self {
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            votes: VecDeque::new(),
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            max_size,
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            fork_trunk: Fork::default(),
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            converge_depth,
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            delay_count,
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            delayed_votes: VecDeque::new(),
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            parasite: false,
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        }
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    }
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    pub fn submit_vote(
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        &mut self,
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        vote: Vote,
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        fork_tree: &HashMap<usize, Fork>,
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        converge_map: &HashMap<usize, usize>,
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        scores: &HashMap<Vote, usize>,
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    ) {
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        let is_valid = self
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            .get_vote(self.converge_depth)
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            .map(|v| v.is_trunk_of(&vote, fork_tree))
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            .unwrap_or(true);
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        if is_valid {
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            self.delayed_votes.push_front(vote);
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        }
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        loop {
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            if self.delayed_votes.len() <= self.delay_count {
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                break;
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            }
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            let votes = self.pop_best_votes(fork_tree, scores);
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            for vote in votes {
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                self.push_vote(vote, fork_tree, converge_map);
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            }
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        }
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        let trunk = self.votes.get(self.converge_depth).cloned();
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        if let Some(t) = trunk {
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            self.delayed_votes.retain(|v| v.fork.id > t.fork.id);
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        }
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    }
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    pub fn pop_best_votes(
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        &mut self,
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        fork_tree: &HashMap<usize, Fork>,
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        scores: &HashMap<Vote, usize>,
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    ) -> VecDeque<Vote> {
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        let mut best: Vec<(usize, usize, usize)> = self
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            .delayed_votes
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            .iter()
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            .enumerate()
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            .map(|(i, v)| (*scores.get(&v).unwrap_or(&0), v.time, i))
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            .collect();
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        // highest score, latest vote first
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        best.sort();
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        if self.parasite {
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            best.reverse();
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        }
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        // best vote is last
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        let mut votes: VecDeque<Vote> = best
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            .last()
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            .and_then(|v| self.delayed_votes.remove(v.2))
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            .into_iter()
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            .collect();
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        // plus any ancestors
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        if votes.is_empty() {
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            return votes;
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        }
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        let mut restart = true;
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        // should really be using heap here
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        while restart {
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            restart = false;
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            for i in 0..self.delayed_votes.len() {
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                let is_trunk = {
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                    let v = &self.delayed_votes[i];
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                    v.is_trunk_of(votes.front().unwrap(), fork_tree)
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                };
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                if is_trunk {
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                    votes.push_front(self.delayed_votes.remove(i).unwrap());
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                    restart = true;
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                    break;
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                }
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            }
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        }
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        votes
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    }
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    pub fn push_vote(
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        &mut self,
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        vote: Vote,
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        fork_tree: &HashMap<usize, Fork>,
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        converge_map: &HashMap<usize, usize>,
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    ) -> bool {
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        self.rollback(vote.time);
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        if !self.is_valid(&vote, fork_tree) {
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            return false;
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        }
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        if !self.is_converged(converge_map) {
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            return false;
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        }
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        self.process_vote(vote);
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        if self.is_full() {
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            self.pop_full();
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        }
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        true
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    }
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    /// check if the vote at `height` has over 50% of the cluster committed
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    fn is_converged(&self, converge_map: &HashMap<usize, usize>) -> bool {
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        self.get_vote(self.converge_depth)
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            .map(|v| {
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                let v = *converge_map.get(&v.fork.id).unwrap_or(&0);
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                // hard-coded to 100 nodes
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                assert!(v <= 100);
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                v > 50
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            })
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            .unwrap_or(true)
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    }
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    pub fn score(&self, vote: &Vote, fork_tree: &HashMap<usize, Fork>) -> usize {
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        let st = self.rollback_count(vote.time);
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        if st < self.votes.len() && !self.votes[st].is_trunk_of(vote, fork_tree) {
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            return 0;
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        }
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        let mut rv = 0;
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        for i in st..self.votes.len() {
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            let lockout = self.votes[i].lockout;
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            rv += lockout;
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            if i == 0 || self.votes[i - 1].lockout * 2 == lockout {
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                // double the lockout from this vote
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                rv += lockout;
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            }
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        }
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        rv
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    }
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    fn rollback_count(&self, time: usize) -> usize {
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        let mut last: usize = 0;
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        for (i, v) in self.votes.iter().enumerate() {
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            if v.lock_height() < time {
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                last = i + 1;
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            }
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        }
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        last
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    }
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    /// if a vote is expired, pop it and all the votes leading up to it
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    fn rollback(&mut self, time: usize) {
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        let last = self.rollback_count(time);
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        for _ in 0..last {
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            self.votes.pop_front();
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        }
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    }
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    /// only add votes that are descendent from the last vote in the stack
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    fn is_valid(&self, vote: &Vote, fork_tree: &HashMap<usize, Fork>) -> bool {
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        self.last_fork().is_trunk_of(&vote.fork, fork_tree)
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    }
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    fn process_vote(&mut self, vote: Vote) {
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        let vote_time = vote.time;
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        assert!(!self.is_full());
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        assert_eq!(vote.lockout, 2);
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        // push the new vote to the front
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        self.votes.push_front(vote);
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        // double the lockouts if the threshold to double is met
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        for i in 1..self.votes.len() {
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            assert!(self.votes[i].time <= vote_time);
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            if self.votes[i].lockout == self.votes[i - 1].lockout {
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                self.votes[i].lockout *= 2;
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            }
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        }
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    }
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    fn pop_full(&mut self) {
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        assert!(self.is_full());
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        self.fork_trunk = self.votes.pop_back().unwrap().fork;
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    }
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    fn is_full(&self) -> bool {
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        assert!(self.votes.len() <= self.max_size);
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        self.votes.len() == self.max_size
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    }
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    fn last_vote(&self) -> Option<&Vote> {
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        self.votes.front()
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    }
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    fn get_vote(&self, ix: usize) -> Option<&Vote> {
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        self.votes.get(ix)
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    }
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    pub fn first_vote(&self) -> Option<&Vote> {
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        self.votes.back()
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    }
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    pub fn last_fork(&self) -> Fork {
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        self.last_vote()
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            .map(|v| v.fork.clone())
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            .unwrap_or_else(|| self.fork_trunk.clone())
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    }
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}
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#[test]
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fn test_is_trunk_of_1() {
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    let tree = HashMap::new();
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    let b1 = Fork { id: 1, base: 0 };
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    let b2 = Fork { id: 2, base: 0 };
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    assert!(!b1.is_trunk_of(&b2, &tree));
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}
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#[test]
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fn test_is_trunk_of_2() {
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    let tree = HashMap::new();
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    let b1 = Fork { id: 1, base: 0 };
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    let b2 = Fork { id: 0, base: 0 };
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    assert!(!b1.is_trunk_of(&b2, &tree));
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}
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#[test]
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fn test_is_trunk_of_3() {
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    let tree = HashMap::new();
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    let b1 = Fork { id: 1, base: 0 };
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    let b2 = Fork { id: 1, base: 0 };
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    assert!(b1.is_trunk_of(&b2, &tree));
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}
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#[test]
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fn test_is_trunk_of_4() {
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    let mut tree = HashMap::new();
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    let b1 = Fork { id: 1, base: 0 };
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    let b2 = Fork { id: 2, base: 1 };
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    tree.insert(b1.id, b1.clone());
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    assert!(b1.is_trunk_of(&b2, &tree));
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    assert!(!b2.is_trunk_of(&b1, &tree));
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}
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#[test]
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#[allow(clippy::cognitive_complexity)]
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fn test_push_vote() {
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    let tree = HashMap::new();
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    let bmap = HashMap::new();
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    let b0 = Fork { id: 0, base: 0 };
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    let mut tower = Tower::new(32, 7, 0);
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    let vote = Vote::new(b0.clone(), 0);
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    assert!(tower.push_vote(vote, &tree, &bmap));
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    assert_eq!(tower.votes.len(), 1);
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    let vote = Vote::new(b0.clone(), 1);
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    assert!(tower.push_vote(vote, &tree, &bmap));
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    assert_eq!(tower.votes.len(), 2);
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    let vote = Vote::new(b0.clone(), 2);
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    assert!(tower.push_vote(vote, &tree, &bmap));
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    assert_eq!(tower.votes.len(), 3);
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    let vote = Vote::new(b0.clone(), 3);
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    assert!(tower.push_vote(vote, &tree, &bmap));
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    assert_eq!(tower.votes.len(), 4);
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    assert_eq!(tower.votes[0].lockout, 2);
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    assert_eq!(tower.votes[1].lockout, 4);
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    assert_eq!(tower.votes[2].lockout, 8);
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    assert_eq!(tower.votes[3].lockout, 16);
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    assert_eq!(tower.votes[1].lock_height(), 6);
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    assert_eq!(tower.votes[2].lock_height(), 9);
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    let vote = Vote::new(b0.clone(), 7);
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    assert!(tower.push_vote(vote, &tree, &bmap));
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    assert_eq!(tower.votes[0].lockout, 2);
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    let b1 = Fork { id: 1, base: 1 };
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    let vote = Vote::new(b1, 8);
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    assert!(!tower.push_vote(vote, &tree, &bmap));
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    let vote = Vote::new(b0.clone(), 8);
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    assert!(tower.push_vote(vote, &tree, &bmap));
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    assert_eq!(tower.votes.len(), 4);
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    assert_eq!(tower.votes[0].lockout, 2);
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    assert_eq!(tower.votes[1].lockout, 4);
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    assert_eq!(tower.votes[2].lockout, 8);
 | 
						|
    assert_eq!(tower.votes[3].lockout, 16);
 | 
						|
 | 
						|
    let vote = Vote::new(b0, 10);
 | 
						|
    assert!(tower.push_vote(vote, &tree, &bmap));
 | 
						|
    assert_eq!(tower.votes.len(), 2);
 | 
						|
    assert_eq!(tower.votes[0].lockout, 2);
 | 
						|
    assert_eq!(tower.votes[1].lockout, 16);
 | 
						|
}
 | 
						|
 | 
						|
fn create_towers(sz: usize, height: usize, delay_count: usize) -> Vec<Tower> {
 | 
						|
    (0..sz)
 | 
						|
        .map(|_| Tower::new(32, height, delay_count))
 | 
						|
        .collect()
 | 
						|
}
 | 
						|
 | 
						|
/// The "height" of this fork. How many forks until it connects to fork 0
 | 
						|
fn calc_fork_depth(fork_tree: &HashMap<usize, Fork>, id: usize) -> usize {
 | 
						|
    let mut height = 0;
 | 
						|
    let mut start = fork_tree.get(&id);
 | 
						|
    loop {
 | 
						|
        if start.is_none() {
 | 
						|
            break;
 | 
						|
        }
 | 
						|
        height += 1;
 | 
						|
        start = fork_tree.get(&start.unwrap().base);
 | 
						|
    }
 | 
						|
    height
 | 
						|
}
 | 
						|
/// map of `fork id` to `tower count`
 | 
						|
/// This map contains the number of nodes that have the fork as an ancestor.
 | 
						|
/// The fork with the highest count that is the newest is the cluster "trunk".
 | 
						|
fn calc_fork_map(towers: &[Tower], fork_tree: &HashMap<usize, Fork>) -> HashMap<usize, usize> {
 | 
						|
    let mut lca_map: HashMap<usize, usize> = HashMap::new();
 | 
						|
    for tower in towers {
 | 
						|
        let mut start = tower.last_fork();
 | 
						|
        loop {
 | 
						|
            *lca_map.entry(start.id).or_insert(0) += 1;
 | 
						|
            if !fork_tree.contains_key(&start.base) {
 | 
						|
                break;
 | 
						|
            }
 | 
						|
            start = fork_tree.get(&start.base).unwrap().clone();
 | 
						|
        }
 | 
						|
    }
 | 
						|
    lca_map
 | 
						|
}
 | 
						|
/// find the fork with the highest count of nodes that have it as an ancestor
 | 
						|
/// as well as with the highest possible fork id, which indicates it is the newest
 | 
						|
fn calc_newest_trunk(bmap: &HashMap<usize, usize>) -> (usize, usize) {
 | 
						|
    let mut data: Vec<_> = bmap.iter().collect();
 | 
						|
    data.sort_by_key(|x| (x.1, x.0));
 | 
						|
    data.last().map(|v| (*v.0, *v.1)).unwrap()
 | 
						|
}
 | 
						|
/// how common is the latest fork of all the nodes
 | 
						|
fn calc_tip_converged(towers: &[Tower], bmap: &HashMap<usize, usize>) -> usize {
 | 
						|
    let sum: usize = towers
 | 
						|
        .iter()
 | 
						|
        .map(|n| *bmap.get(&n.last_fork().id).unwrap_or(&0))
 | 
						|
        .sum();
 | 
						|
    sum / towers.len()
 | 
						|
}
 | 
						|
#[test]
 | 
						|
fn test_no_partitions() {
 | 
						|
    let mut tree = HashMap::new();
 | 
						|
    let len = 100;
 | 
						|
    let mut towers = create_towers(len, 32, 0);
 | 
						|
    for rounds in 0..1 {
 | 
						|
        for i in 0..towers.len() {
 | 
						|
            let time = rounds * len + i;
 | 
						|
            let base = towers[i].last_fork().clone();
 | 
						|
            let fork = Fork {
 | 
						|
                id: time + 1,
 | 
						|
                base: base.id,
 | 
						|
            };
 | 
						|
            tree.insert(fork.id, fork.clone());
 | 
						|
            let vote = Vote::new(fork, time);
 | 
						|
            let bmap = calc_fork_map(&towers, &tree);
 | 
						|
            for tower in towers.iter_mut() {
 | 
						|
                assert!(tower.push_vote(vote.clone(), &tree, &bmap));
 | 
						|
            }
 | 
						|
            println!("{} {}", time, calc_tip_converged(&towers, &bmap));
 | 
						|
        }
 | 
						|
    }
 | 
						|
    let bmap = calc_fork_map(&towers, &tree);
 | 
						|
    assert_eq!(calc_tip_converged(&towers, &bmap), len);
 | 
						|
}
 | 
						|
/// * num_partitions - 1 to 100 partitions
 | 
						|
/// * fail_rate - 0 to 1.0 rate of packet receive failure
 | 
						|
/// * delay_count - number of forks to observe before voting
 | 
						|
/// * parasite_rate - number of parasite nodes that vote opposite the greedy choice
 | 
						|
fn test_with_partitions(
 | 
						|
    num_partitions: usize,
 | 
						|
    fail_rate: f64,
 | 
						|
    delay_count: usize,
 | 
						|
    parasite_rate: f64,
 | 
						|
    break_early: bool,
 | 
						|
) {
 | 
						|
    let mut fork_tree = HashMap::new();
 | 
						|
    let len = 100;
 | 
						|
    let warmup = 8;
 | 
						|
    let mut towers = create_towers(len, warmup, delay_count);
 | 
						|
    for time in 0..warmup {
 | 
						|
        let bmap = calc_fork_map(&towers, &fork_tree);
 | 
						|
        for tower in towers.iter_mut() {
 | 
						|
            let mut fork = tower.last_fork().clone();
 | 
						|
            if fork.id == 0 {
 | 
						|
                fork.id = thread_rng().gen_range(1, 1 + num_partitions);
 | 
						|
                fork_tree.insert(fork.id, fork.clone());
 | 
						|
            }
 | 
						|
            let vote = Vote::new(fork, time);
 | 
						|
            assert!(tower.is_valid(&vote, &fork_tree));
 | 
						|
            assert!(tower.push_vote(vote, &fork_tree, &bmap));
 | 
						|
        }
 | 
						|
    }
 | 
						|
    for tower in towers.iter_mut() {
 | 
						|
        assert_eq!(tower.votes.len(), warmup);
 | 
						|
        assert_eq!(tower.first_vote().unwrap().lockout, 1 << warmup);
 | 
						|
        assert!(tower.first_vote().unwrap().lock_height() >= 1 << warmup);
 | 
						|
        tower.parasite = parasite_rate > thread_rng().gen_range(0.0, 1.0);
 | 
						|
    }
 | 
						|
    let converge_map = calc_fork_map(&towers, &fork_tree);
 | 
						|
    assert_ne!(calc_tip_converged(&towers, &converge_map), len);
 | 
						|
    for rounds in 0..10 {
 | 
						|
        for i in 0..len {
 | 
						|
            let time = warmup + rounds * len + i;
 | 
						|
            let base = towers[i].last_fork();
 | 
						|
            let fork = Fork {
 | 
						|
                id: time + num_partitions,
 | 
						|
                base: base.id,
 | 
						|
            };
 | 
						|
            fork_tree.insert(fork.id, fork.clone());
 | 
						|
            let converge_map = calc_fork_map(&towers, &fork_tree);
 | 
						|
            let vote = Vote::new(fork, time);
 | 
						|
            let mut scores: HashMap<Vote, usize> = HashMap::new();
 | 
						|
            towers.iter().for_each(|n| {
 | 
						|
                n.delayed_votes.iter().for_each(|v| {
 | 
						|
                    *scores.entry(v.clone()).or_insert(0) += n.score(&v, &fork_tree);
 | 
						|
                })
 | 
						|
            });
 | 
						|
            for tower in towers.iter_mut() {
 | 
						|
                if thread_rng().gen_range(0f64, 1.0f64) < fail_rate {
 | 
						|
                    continue;
 | 
						|
                }
 | 
						|
                tower.submit_vote(vote.clone(), &fork_tree, &converge_map, &scores);
 | 
						|
            }
 | 
						|
            let converge_map = calc_fork_map(&towers, &fork_tree);
 | 
						|
            let trunk = calc_newest_trunk(&converge_map);
 | 
						|
            let trunk_time = if trunk.0 > num_partitions {
 | 
						|
                trunk.0 - num_partitions
 | 
						|
            } else {
 | 
						|
                trunk.0
 | 
						|
            };
 | 
						|
            println!(
 | 
						|
                    "time: {}, tip converged: {}, trunk id: {}, trunk time: {}, trunk converged {}, trunk height {}",
 | 
						|
                    time,
 | 
						|
                    calc_tip_converged(&towers, &converge_map),
 | 
						|
                    trunk.0,
 | 
						|
                    trunk_time,
 | 
						|
                    trunk.1,
 | 
						|
                    calc_fork_depth(&fork_tree, trunk.0)
 | 
						|
                );
 | 
						|
            if break_early && calc_tip_converged(&towers, &converge_map) == len {
 | 
						|
                break;
 | 
						|
            }
 | 
						|
        }
 | 
						|
        if break_early {
 | 
						|
            let converge_map = calc_fork_map(&towers, &fork_tree);
 | 
						|
            if calc_tip_converged(&towers, &converge_map) == len {
 | 
						|
                break;
 | 
						|
            }
 | 
						|
        }
 | 
						|
    }
 | 
						|
    let converge_map = calc_fork_map(&towers, &fork_tree);
 | 
						|
    let trunk = calc_newest_trunk(&converge_map);
 | 
						|
    assert_eq!(trunk.1, len);
 | 
						|
}
 | 
						|
 | 
						|
#[test]
 | 
						|
#[ignore]
 | 
						|
fn test_3_partitions() {
 | 
						|
    test_with_partitions(3, 0.0, 0, 0.0, true)
 | 
						|
}
 | 
						|
#[test]
 | 
						|
#[ignore]
 | 
						|
fn test_3_partitions_large_packet_drop() {
 | 
						|
    test_with_partitions(3, 0.9, 0, 0.0, false)
 | 
						|
}
 | 
						|
#[test]
 | 
						|
#[ignore]
 | 
						|
fn test_all_partitions() {
 | 
						|
    test_with_partitions(100, 0.0, 5, 0.25, false)
 | 
						|
}
 |