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// Copyright 2020 TiKV Project Authors. Licensed under Apache-2.0.
use super::{AckedIndexer, Index, VoteResult};
use crate::{DefaultHashBuilder, HashSet};
use std::collections::hash_set::Iter;
use std::fmt::Formatter;
use std::mem::MaybeUninit;
use std::ops::{Deref, DerefMut};
use std::{cmp, slice, u64};
/// A set of IDs that uses majority quorums to make decisions.
#[derive(Clone, Debug, Default, PartialEq, Eq)]
pub struct Configuration {
voters: HashSet<u64>,
}
impl std::fmt::Display for Configuration {
fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
write!(
f,
"({})",
self.voters
.iter()
.map(|x| x.to_string())
.collect::<Vec<String>>()
.join(" ")
)
}
}
impl Configuration {
/// Creates a new configuration using the given IDs.
pub fn new(voters: HashSet<u64>) -> Configuration {
Configuration { voters }
}
/// Creates an empty configuration with given capacity.
pub fn with_capacity(cap: usize) -> Configuration {
Configuration {
voters: HashSet::with_capacity_and_hasher(cap, DefaultHashBuilder::default()),
}
}
/// Returns an iterator over voters.
pub fn ids(&self) -> Iter<'_, u64> {
self.voters.iter()
}
/// Returns the MajorityConfig as a sorted slice.
pub fn slice(&self) -> Vec<u64> {
let mut voters = self.raw_slice();
voters.sort_unstable();
voters
}
/// Returns the MajorityConfig as a slice.
pub fn raw_slice(&self) -> Vec<u64> {
self.voters.iter().cloned().collect()
}
/// Computes the committed index from those supplied via the
/// provided AckedIndexer (for the active config).
///
/// The bool flag indicates whether the index is computed by group commit algorithm
/// successfully.
///
/// Eg. If the matched indexes are `[2,2,2,4,5]`, it will return `2`.
/// If the matched indexes and groups are `[(1, 1), (2, 2), (3, 2)]`, it will return `1`.
pub fn committed_index(&self, use_group_commit: bool, l: &impl AckedIndexer) -> (u64, bool) {
if self.voters.is_empty() {
// This plays well with joint quorums which, when one half is the zero
// MajorityConfig, should behave like the other half.
return (u64::MAX, true);
}
let mut stack_arr: [MaybeUninit<Index>; 7] = unsafe { MaybeUninit::uninit().assume_init() };
let mut heap_arr;
let matched = if self.voters.len() <= 7 {
for (i, v) in self.voters.iter().enumerate() {
stack_arr[i] = MaybeUninit::new(l.acked_index(*v).unwrap_or_default());
}
unsafe {
slice::from_raw_parts_mut(stack_arr.as_mut_ptr() as *mut _, self.voters.len())
}
} else {
let mut buf = Vec::with_capacity(self.voters.len());
for v in &self.voters {
buf.push(l.acked_index(*v).unwrap_or_default());
}
heap_arr = Some(buf);
heap_arr.as_mut().unwrap().as_mut_slice()
};
// Reverse sort.
matched.sort_by(|a, b| b.index.cmp(&a.index));
let quorum = crate::majority(matched.len());
let quorum_index = matched[quorum - 1];
if !use_group_commit {
return (quorum_index.index, false);
}
let (quorum_commit_index, mut checked_group_id) =
(quorum_index.index, quorum_index.group_id);
let mut single_group = true;
for m in matched.iter() {
if m.group_id == 0 {
single_group = false;
continue;
}
if checked_group_id == 0 {
checked_group_id = m.group_id;
continue;
}
if checked_group_id == m.group_id {
continue;
}
return (cmp::min(m.index, quorum_commit_index), true);
}
if single_group {
(quorum_commit_index, false)
} else {
(matched.last().unwrap().index, false)
}
}
/// Takes a mapping of voters to yes/no (true/false) votes and returns
/// a result indicating whether the vote is pending (i.e. neither a quorum of
/// yes/no has been reached), won (a quorum of yes has been reached), or lost (a
/// quorum of no has been reached).
pub fn vote_result(&self, check: impl Fn(u64) -> Option<bool>) -> VoteResult {
if self.voters.is_empty() {
// By convention, the elections on an empty config win. This comes in
// handy with joint quorums because it'll make a half-populated joint
// quorum behave like a majority quorum.
return VoteResult::Won;
}
let (mut yes, mut missing) = (0, 0);
for v in &self.voters {
match check(*v) {
Some(true) => yes += 1,
None => missing += 1,
_ => (),
}
}
let q = crate::majority(self.voters.len());
if yes >= q {
VoteResult::Won
} else if yes + missing >= q {
VoteResult::Pending
} else {
VoteResult::Lost
}
}
/// Describe returns a (multi-line) representation of the commit indexes for the
/// given lookuper.
/// Including `Index`,`Id` and the number of smaller index (represented as the bar)
///
/// Print `?` if `Index` is not exist.
///
/// e.g.
/// ```txt
/// idx
/// x> 100 (id=1)
/// xx> 101 (id=2)
/// > 99 (id=3)
/// 100
/// ```
#[cfg(test)]
pub(crate) fn describe(&self, l: &impl AckedIndexer) -> String {
use std::fmt::Write;
let n = self.voters.len();
if n == 0 {
return "<empty majority quorum>".to_string();
}
struct Tup {
id: u64,
idx: Option<Index>,
// length of bar displayed for this Tup
bar: usize,
}
// Below, populate .bar so that the i-th largest commit index has bar i (we
// plot this as sort of a progress bar). The actual code is a bit more
// complicated and also makes sure that equal index => equal bar.
let mut info = Vec::with_capacity(n);
for &id in &self.voters {
let idx = l.acked_index(id);
info.push(Tup { id, idx, bar: 0 })
}
info.sort_by(|a, b| {
(a.idx.unwrap_or_default().index, a.id).cmp(&(b.idx.unwrap_or_default().index, b.id))
});
for i in 0..n {
if i > 0
&& info[i - 1].idx.unwrap_or_default().index < info[i].idx.unwrap_or_default().index
{
info[i].bar = i;
}
}
info.sort_by(|a, b| a.id.cmp(&b.id));
let mut buf = String::new();
buf.push_str(" ".repeat(n).as_str());
buf.push_str(" idx\n");
for tup in info {
match tup.idx {
Some(idx) => {
buf.push_str("x".repeat(tup.bar).as_str());
buf.push('>');
buf.push_str(" ".repeat(n - tup.bar).as_str());
writeln!(buf, " {:>5} (id={})", format!("{}", idx), tup.id)
.expect("Error occurred while trying to write in String");
}
None => {
buf.push('?');
buf.push_str(" ".repeat(n).as_str());
writeln!(
buf,
" {:>5} (id={})",
format!("{}", Index::default()),
tup.id
)
.expect("Error occurred while trying to write in String");
}
}
}
buf
}
}
impl Deref for Configuration {
type Target = HashSet<u64>;
#[inline]
fn deref(&self) -> &HashSet<u64> {
&self.voters
}
}
impl DerefMut for Configuration {
#[inline]
fn deref_mut(&mut self) -> &mut HashSet<u64> {
&mut self.voters
}
}