Struct WeightedQuorumSet 

pub struct WeightedQuorumSet<ID> { /* private fields */ }

A quorum rule that accepts an ID set whose IDs weigh at least threshold together.

Each ID of the rule has a positive weight. A set counts the weight of each of its IDs once, and an ID that the rule does not weigh adds nothing. A sum that would exceed u64::MAX exceeds every threshold, so is_quorum() saturates instead of overflowing. A threshold above the total weight gives a rule that accepts no set.

Two disjoint sets together weigh at most the total weight. So two rules with the same weights have quorum intersection when their thresholds sum to more than the total weight. This condition is sufficient but not necessary, because a set adds all of an ID’s weight or none of it. With weights {1:2, 2:2}, thresholds 3 and 1 sum to only the total weight 4, yet the only quorum of threshold 3, {1,2}, meets every quorum of threshold 1.

Examples

use std::collections::BTreeMap;

use quorum_set::{QuorumIntersection, QuorumSet, WeightedQuorumSet};

// ID 1 weighs as much as IDs 2 and 3 together; the total weight is 4.
let weights = BTreeMap::from([(1, 2), (2, 1), (3, 1)]);
let read = WeightedQuorumSet::new(3, weights.clone()).unwrap();
let write = WeightedQuorumSet::new(2, weights).unwrap();

let write_accepts_one = write.is_quorum([1].iter());
assert!(write_accepts_one);
let read_accepts_two_three = read.is_quorum([2, 3].iter());
assert!(!read_accepts_two_three);

// 3 + 2 > 4, so every read quorum intersects every write quorum.
let intersects = read.intersects_with(&write);
assert_eq!(Some(true), intersects);

Implementations

impl<ID> WeightedQuorumSet<ID>

where ID: Ord + Clone,

pub fn new( threshold: u64, weights: BTreeMap<ID, u64>, ) -> Result<Self, WeightedQuorumSetError<ID>>

Builds a rule that accepts an ID set whose IDs weigh at least threshold together, with the weight of each ID in weights.

Errors

• WeightedQuorumSetError::ZeroWeight: the first ID with weight 0, which would never count.
• WeightedQuorumSetError::ZeroThreshold: a threshold of 0, which would make the empty set a quorum.

pub fn weights(&self) -> &BTreeMap<ID, u64>

Returns the weight of each ID. QuorumSet::ids() yields its IDs.

pub fn threshold(&self) -> u64

Returns the weight that an accepted set must reach.

Trait Implementations

impl<ID: Clone> Clone for WeightedQuorumSet<ID>

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<ID: Debug> Debug for WeightedQuorumSet<ID>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<ID: Eq> Eq for WeightedQuorumSet<ID>

impl<ID: PartialEq> PartialEq for WeightedQuorumSet<ID>

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl<ID> QuorumIntersection<WeightedQuorumSet<ID>> for WeightedQuorumSet<ID>

where ID: Ord + Clone,

Sufficient quorum intersection for two weighted rules.

Two disjoint sets together weigh at most the total weight. When two rules hold the same weights and their thresholds sum to more than the total weight, a quorum of one and a quorum of the other are therefore never disjoint. The check runs in O(n) for n IDs.

fn intersects_with(&self, other: &WeightedQuorumSet<ID>) -> Option<bool>

Return Some(true) when both rules hold the same weights and their thresholds sum to more than the total weight, and None otherwise, including for every pair of rules with different weights. This check never returns Some(false).

The sums are computed in u128, so they never overflow.

impl<ID> QuorumSet for WeightedQuorumSet<ID>

where ID: Ord + Clone,

type Id = ID

Node ID type in this quorum set.

type Iter = IntoIter<ID>

Iterator over every voter ID tracked by this quorum set.

fn is_quorum<'a, I>(&self, ids: I) -> bool

where ID: 'a, I: Iterator<Item = &'a ID> + Clone,

Return true if the candidate IDs satisfy this quorum rule.

fn ids(&self) -> Self::Iter

Return all voter IDs in this quorum set.

impl<ID: PartialEq> StructuralPartialEq for WeightedQuorumSet<ID>