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voting_round.rs
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voting_round.rs
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// Copyright 2018-2019 Parity Technologies (UK) Ltd
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//! Logic for voting and handling messages within a single round.
#[cfg(feature = "std")]
use futures::ready;
use futures::{channel::mpsc::UnboundedSender, prelude::*};
#[cfg(feature = "std")]
use log::{debug, trace, warn};
use std::{
pin::Pin,
sync::Arc,
task::{Context, Poll},
};
use super::{Buffered, Environment, FinalizedNotification};
use crate::{
round::{Round, State as RoundState},
validate_commit,
voter_set::VoterSet,
weights::VoteWeight,
BlockNumberOps, Commit, HistoricalVotes, ImportResult, Message, Precommit, Prevote,
PrimaryPropose, SignedMessage, SignedPrecommit, LOG_TARGET,
};
/// The state of a voting round.
pub(super) enum State<T, W> {
Start(T, T),
Proposed(T, T),
Prevoting(T, W),
Prevoted(T),
Precommitted,
}
impl<T, W> std::fmt::Debug for State<T, W> {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
match self {
State::Start(..) => write!(f, "Start"),
State::Proposed(..) => write!(f, "Proposed"),
State::Prevoting(..) => write!(f, "Prevoting"),
State::Prevoted(_) => write!(f, "Prevoted"),
State::Precommitted => write!(f, "Precommitted"),
}
}
}
/// Logic for a voter on a specific round.
pub(super) struct VotingRound<H, N, E: Environment<H, N>>
where
H: Clone + Eq + Ord + ::std::fmt::Debug,
N: Copy + BlockNumberOps + ::std::fmt::Debug,
{
env: Arc<E>,
voting: Voting,
votes: Round<E::Id, H, N, E::Signature>,
incoming: E::In,
outgoing: Buffered<E::Out, Message<H, N>>,
state: Option<State<E::Timer, (H, E::BestChain)>>, // state machine driving votes.
bridged_round_state: Option<crate::bridge_state::PriorView<H, N>>, // updates to later round
last_round_state: Option<crate::bridge_state::LatterView<H, N>>, // updates from prior round
primary_block: Option<(H, N)>, // a block posted by primary as a hint.
finalized_sender: UnboundedSender<FinalizedNotification<H, N, E>>,
best_finalized: Option<Commit<H, N, E::Signature, E::Id>>,
}
/// Whether we should vote in the current round (i.e. push votes to the sink.)
enum Voting {
/// Voting is disabled for the current round.
No,
/// Voting is enabled for the current round (prevotes and precommits.)
Yes,
/// Voting is enabled for the current round and we are the primary proposer
/// (we can also push primary propose messages).
Primary,
}
impl Voting {
/// Whether the voter should cast round votes (prevotes and precommits.)
fn is_active(&self) -> bool {
matches!(self, Voting::Yes | Voting::Primary)
}
/// Whether the voter is the primary proposer.
fn is_primary(&self) -> bool {
matches!(self, Voting::Primary)
}
}
impl<H, N, E: Environment<H, N>> VotingRound<H, N, E>
where
H: Clone + Eq + Ord + ::std::fmt::Debug,
N: Copy + BlockNumberOps + ::std::fmt::Debug,
{
/// Create a new voting round.
pub(super) fn new(
round_number: u64,
voters: VoterSet<E::Id>,
base: (H, N),
last_round_state: Option<crate::bridge_state::LatterView<H, N>>,
finalized_sender: UnboundedSender<FinalizedNotification<H, N, E>>,
env: Arc<E>,
) -> VotingRound<H, N, E> {
let round_data = env.round_data(round_number);
let round_params = crate::round::RoundParams { voters, base, round_number };
let votes = Round::new(round_params);
let voting = if round_data.voter_id.as_ref() == Some(votes.primary_voter().0) {
Voting::Primary
} else if round_data.voter_id.as_ref().map_or(false, |id| votes.voters().contains(id)) {
Voting::Yes
} else {
Voting::No
};
VotingRound {
votes,
voting,
incoming: round_data.incoming,
outgoing: Buffered::new(round_data.outgoing),
state: Some(State::Start(round_data.prevote_timer, round_data.precommit_timer)),
bridged_round_state: None,
primary_block: None,
best_finalized: None,
env,
last_round_state,
finalized_sender,
}
}
/// Create a voting round from a completed `Round`. We will not vote further
/// in this round.
pub(super) fn completed(
votes: Round<E::Id, H, N, E::Signature>,
finalized_sender: UnboundedSender<FinalizedNotification<H, N, E>>,
last_round_state: Option<crate::bridge_state::LatterView<H, N>>,
env: Arc<E>,
) -> VotingRound<H, N, E> {
let round_data = env.round_data(votes.number());
VotingRound {
votes,
voting: Voting::No,
incoming: round_data.incoming,
outgoing: Buffered::new(round_data.outgoing),
state: None,
bridged_round_state: None,
primary_block: None,
env,
last_round_state,
finalized_sender,
best_finalized: None,
}
}
/// Poll the round. When the round is completable and messages have been flushed, it will return `Poll::Ready` but
/// can continue to be polled.
pub(super) fn poll(&mut self, cx: &mut Context) -> Poll<Result<(), E::Error>> {
trace!(
target: LOG_TARGET,
"Polling round {}, state = {:?}, step = {:?}",
self.votes.number(),
self.votes.state(),
self.state
);
let pre_state = self.votes.state();
self.process_incoming(cx)?;
// we only cast votes when we have access to the previous round state.
// we might have started this round as a prospect "future" round to
// check whether the voter is lagging behind the current round.
let last_round_state = self.last_round_state.as_ref().map(|s| s.get(cx).clone());
if let Some(ref last_round_state) = last_round_state {
self.primary_propose(last_round_state)?;
self.prevote(cx, last_round_state)?;
self.precommit(cx, last_round_state)?;
}
ready!(self.outgoing.poll(cx))?;
self.process_incoming(cx)?; // in case we got a new message signed locally.
// broadcast finality notifications after attempting to cast votes
let post_state = self.votes.state();
self.notify(pre_state, post_state);
// early exit if the current round is not completable
if !self.votes.completable() {
return Poll::Pending
}
// make sure that the previous round estimate has been finalized
let last_round_estimate_finalized = match last_round_state {
Some(RoundState {
estimate: Some((_, last_round_estimate)),
finalized: Some((_, last_round_finalized)),
..
}) => {
// either it was already finalized in the previous round
let finalized_in_last_round = last_round_estimate <= last_round_finalized;
// or it must be finalized in the current round
let finalized_in_current_round =
self.finalized().map_or(false, |(_, current_round_finalized)| {
last_round_estimate <= *current_round_finalized
});
finalized_in_last_round || finalized_in_current_round
},
None => {
// NOTE: when we catch up to a round we complete the round
// without any last round state. in this case we already started
// a new round after we caught up so this guard is unneeded.
true
},
_ => false,
};
// the previous round estimate must be finalized
if !last_round_estimate_finalized {
trace!(
target: LOG_TARGET,
"Round {} completable but estimate not finalized.",
self.round_number()
);
self.log_participation(log::Level::Trace);
return Poll::Pending
}
debug!(
target: LOG_TARGET,
"Completed round {}, state = {:?}, step = {:?}",
self.votes.number(),
self.votes.state(),
self.state
);
self.log_participation(log::Level::Debug);
// both exit conditions verified, we can complete this round
Poll::Ready(Ok(()))
}
/// Inspect the state of this round.
pub(super) fn state(&self) -> Option<&State<E::Timer, (H, E::BestChain)>> {
self.state.as_ref()
}
/// Get access to the underlying environment.
pub(super) fn env(&self) -> &E {
&self.env
}
/// Get the round number.
pub(super) fn round_number(&self) -> u64 {
self.votes.number()
}
/// Get the round state.
pub(super) fn round_state(&self) -> RoundState<H, N> {
self.votes.state()
}
/// Get the base block in the dag.
pub(super) fn dag_base(&self) -> (H, N) {
self.votes.base()
}
/// Get the voters in this round.
pub(super) fn voters(&self) -> &VoterSet<E::Id> {
self.votes.voters()
}
/// Get the best block finalized in this round.
pub(super) fn finalized(&self) -> Option<&(H, N)> {
self.votes.finalized()
}
/// Get the current total weight of prevotes.
pub(super) fn prevote_weight(&self) -> VoteWeight {
self.votes.prevote_participation().0
}
/// Get the current total weight of precommits.
pub(super) fn precommit_weight(&self) -> VoteWeight {
self.votes.precommit_participation().0
}
/// Get the Ids of the prevoters.
pub(super) fn prevote_ids(&self) -> impl Iterator<Item = E::Id> {
self.votes.prevotes().into_iter().map(|pv| pv.0)
}
/// Get the Ids of the precommitters.
pub(super) fn precommit_ids(&self) -> impl Iterator<Item = E::Id> {
self.votes.precommits().into_iter().map(|pv| pv.0)
}
/// Check a commit. If it's valid, import all the votes into the round as well.
/// Returns the finalized base if it checks out.
pub(super) fn check_and_import_from_commit(
&mut self,
commit: &Commit<H, N, E::Signature, E::Id>,
) -> Result<Option<(H, N)>, E::Error> {
if !validate_commit(commit, self.voters(), &*self.env)?.is_valid() {
return Ok(None)
}
for SignedPrecommit { precommit, signature, id } in commit.precommits.iter().cloned() {
let import_result =
self.votes.import_precommit(&*self.env, precommit, id, signature)?;
if let ImportResult { equivocation: Some(e), .. } = import_result {
self.env.precommit_equivocation(self.round_number(), e);
}
}
Ok(Some((commit.target_hash.clone(), commit.target_number)))
}
/// Get a clone of the finalized sender.
pub(super) fn finalized_sender(&self) -> UnboundedSender<FinalizedNotification<H, N, E>> {
self.finalized_sender.clone()
}
// call this when we build on top of a given round in order to get a handle
// to updates to the latest round-state.
pub(super) fn bridge_state(&mut self) -> crate::bridge_state::LatterView<H, N> {
let (prior_view, latter_view) = crate::bridge_state::bridge_state(self.votes.state());
if self.bridged_round_state.is_some() {
warn!(
target: LOG_TARGET,
"Bridged state from round {} more than once.",
self.votes.number()
);
}
self.bridged_round_state = Some(prior_view);
latter_view
}
/// Get a commit justifying the best finalized block.
pub(super) fn finalizing_commit(&self) -> Option<&Commit<H, N, E::Signature, E::Id>> {
self.best_finalized.as_ref()
}
/// Return all votes for the round (prevotes and precommits), sorted by
/// imported order and indicating the indices where we voted. At most two
/// prevotes and two precommits per voter are present, further equivocations
/// are not stored (as they are redundant).
pub(super) fn historical_votes(&self) -> &HistoricalVotes<H, N, E::Signature, E::Id> {
self.votes.historical_votes()
}
/// Handle a vote manually.
pub(super) fn handle_vote(
&mut self,
vote: SignedMessage<H, N, E::Signature, E::Id>,
) -> Result<(), E::Error> {
let SignedMessage { message, signature, id } = vote;
if !self
.env
.is_equal_or_descendent_of(self.votes.base().0, message.target().0.clone())
{
trace!(
target: LOG_TARGET,
"Ignoring message targeting {:?} lower than round base {:?}",
message.target(),
self.votes.base(),
);
return Ok(())
}
match message {
Message::Prevote(prevote) => {
let import_result =
self.votes.import_prevote(&*self.env, prevote, id, signature)?;
if let ImportResult { equivocation: Some(e), .. } = import_result {
self.env.prevote_equivocation(self.votes.number(), e);
}
},
Message::Precommit(precommit) => {
let import_result =
self.votes.import_precommit(&*self.env, precommit, id, signature)?;
if let ImportResult { equivocation: Some(e), .. } = import_result {
self.env.precommit_equivocation(self.votes.number(), e);
}
},
Message::PrimaryPropose(primary) => {
let primary_id = self.votes.primary_voter().0.clone();
// note that id here refers to the party which has cast the vote
// and not the id of the party which has received the vote message.
if id == primary_id {
self.primary_block = Some((primary.target_hash, primary.target_number));
}
},
}
Ok(())
}
fn log_participation(&self, log_level: log::Level) {
let total_weight = self.voters().total_weight();
let threshold = self.voters().threshold();
let n_voters = self.voters().len();
let number = self.round_number();
let (prevote_weight, n_prevotes) = self.votes.prevote_participation();
let (precommit_weight, n_precommits) = self.votes.precommit_participation();
log::log!(
target: LOG_TARGET,
log_level,
"Round {}: prevotes: {}/{}/{} weight, {}/{} actual",
number,
prevote_weight,
threshold,
total_weight,
n_prevotes,
n_voters
);
log::log!(
target: LOG_TARGET,
log_level,
"Round {}: precommits: {}/{}/{} weight, {}/{} actual",
number,
precommit_weight,
threshold,
total_weight,
n_precommits,
n_voters
);
}
fn process_incoming(&mut self, cx: &mut Context) -> Result<(), E::Error> {
while let Poll::Ready(Some(incoming)) = Stream::poll_next(Pin::new(&mut self.incoming), cx)
{
trace!(target: LOG_TARGET, "Round {}: Got incoming message", self.round_number());
self.handle_vote(incoming?)?;
}
Ok(())
}
fn primary_propose(&mut self, last_round_state: &RoundState<H, N>) -> Result<(), E::Error> {
match self.state.take() {
Some(State::Start(prevote_timer, precommit_timer)) => {
let maybe_estimate = last_round_state.estimate.clone();
match (maybe_estimate, self.voting.is_primary()) {
(Some(last_round_estimate), true) => {
let maybe_finalized = last_round_state.finalized.clone();
// Last round estimate has not been finalized.
let should_send_primary =
maybe_finalized.map_or(true, |f| last_round_estimate.1 > f.1);
if should_send_primary {
debug!(
target: LOG_TARGET,
"Sending primary block hint for round {}",
self.votes.number()
);
let primary = PrimaryPropose {
target_hash: last_round_estimate.0,
target_number: last_round_estimate.1,
};
self.env.proposed(self.round_number(), primary.clone())?;
self.outgoing.push(Message::PrimaryPropose(primary));
self.state = Some(State::Proposed(prevote_timer, precommit_timer));
return Ok(())
} else {
debug!(
target: LOG_TARGET,
"Last round estimate has been finalized, \
not sending primary block hint for round {}",
self.votes.number()
);
}
},
(None, true) => {
debug!(
target: LOG_TARGET,
"Last round estimate does not exist, \
not sending primary block hint for round {}",
self.votes.number()
);
},
_ => {},
}
self.state = Some(State::Start(prevote_timer, precommit_timer));
},
x => {
self.state = x;
},
}
Ok(())
}
fn prevote(
&mut self,
cx: &mut Context,
last_round_state: &RoundState<H, N>,
) -> Result<(), E::Error> {
let state = self.state.take();
let start_prevoting = |this: &mut Self,
mut prevote_timer: E::Timer,
precommit_timer: E::Timer,
proposed: bool,
cx: &mut Context| {
let should_prevote = match prevote_timer.poll_unpin(cx) {
Poll::Ready(Err(e)) => return Err(e),
Poll::Ready(Ok(())) => true,
Poll::Pending => this.votes.completable(),
};
if should_prevote {
if this.voting.is_active() {
debug!(
target: LOG_TARGET,
"Constructing prevote for round {}",
this.votes.number()
);
let (base, best_chain) = this.construct_prevote(last_round_state);
// since we haven't polled the future above yet we need to
// manually schedule the current task to be awoken so the
// `best_chain` future is then polled below after we switch the
// state to `Prevoting`.
cx.waker().wake_by_ref();
this.state = Some(State::Prevoting(precommit_timer, (base, best_chain)));
} else {
this.state = Some(State::Prevoted(precommit_timer));
}
} else if proposed {
this.state = Some(State::Proposed(prevote_timer, precommit_timer));
} else {
this.state = Some(State::Start(prevote_timer, precommit_timer));
}
Ok(())
};
let finish_prevoting = |this: &mut Self,
precommit_timer: E::Timer,
base: H,
mut best_chain: E::BestChain,
cx: &mut Context| {
let best_chain = match best_chain.poll_unpin(cx) {
Poll::Ready(Err(e)) => return Err(e),
Poll::Ready(Ok(best_chain)) => best_chain,
Poll::Pending => {
this.state = Some(State::Prevoting(precommit_timer, (base, best_chain)));
return Ok(())
},
};
if let Some(target) = best_chain {
let prevote = Prevote { target_hash: target.0, target_number: target.1 };
debug!(target: LOG_TARGET, "Casting prevote for round {}", this.votes.number());
this.env.prevoted(this.round_number(), prevote.clone())?;
this.votes.set_prevoted_index();
this.outgoing.push(Message::Prevote(prevote));
this.state = Some(State::Prevoted(precommit_timer));
} else {
// if this block is considered unknown, something has gone wrong.
// log and handle, but skip casting a vote.
warn!(
target: LOG_TARGET,
"Could not cast prevote: previously known block {:?} has disappeared", base,
);
// when we can't construct a prevote, we shouldn't precommit.
this.state = None;
this.voting = Voting::No;
}
Ok(())
};
match state {
Some(State::Start(prevote_timer, precommit_timer)) => {
start_prevoting(self, prevote_timer, precommit_timer, false, cx)?;
},
Some(State::Proposed(prevote_timer, precommit_timer)) => {
start_prevoting(self, prevote_timer, precommit_timer, true, cx)?;
},
Some(State::Prevoting(precommit_timer, (base, best_chain))) => {
finish_prevoting(self, precommit_timer, base, best_chain, cx)?;
},
x => {
self.state = x;
},
}
Ok(())
}
fn precommit(
&mut self,
cx: &mut Context,
last_round_state: &RoundState<H, N>,
) -> Result<(), E::Error> {
match self.state.take() {
Some(State::Prevoted(mut precommit_timer)) => {
let last_round_estimate = last_round_state
.estimate
.clone()
.expect("Rounds only started when prior round completable; qed");
let should_precommit = {
// we wait for the last round's estimate to be equal to or
// the ancestor of the current round's p-Ghost before precommitting.
self.votes.state().prevote_ghost.as_ref().map_or(false, |p_g| {
p_g == &last_round_estimate ||
self.env
.is_equal_or_descendent_of(last_round_estimate.0, p_g.0.clone())
})
} && match precommit_timer.poll_unpin(cx) {
Poll::Ready(Err(e)) => return Err(e),
Poll::Ready(Ok(())) => true,
Poll::Pending => self.votes.completable(),
};
if should_precommit {
if self.voting.is_active() {
debug!(
target: LOG_TARGET,
"Casting precommit for round {}",
self.votes.number()
);
let precommit = self.construct_precommit();
self.env.precommitted(self.round_number(), precommit.clone())?;
self.votes.set_precommitted_index();
self.outgoing.push(Message::Precommit(precommit));
}
self.state = Some(State::Precommitted);
} else {
self.state = Some(State::Prevoted(precommit_timer));
}
},
x => {
self.state = x;
},
}
Ok(())
}
// construct a prevote message based on local state.
fn construct_prevote(&self, last_round_state: &RoundState<H, N>) -> (H, E::BestChain) {
let last_round_estimate = last_round_state
.estimate
.clone()
.expect("Rounds only started when prior round completable; qed");
let find_descendent_of = match self.primary_block {
None => {
// vote for best chain containing prior round-estimate.
last_round_estimate.0
},
Some(ref primary_block) => {
// we will vote for the best chain containing `p_hash` iff
// the last round's prevote-GHOST included that block and
// that block is a strict descendent of the last round-estimate that we are
// aware of.
let last_prevote_g = last_round_state
.prevote_ghost
.clone()
.expect("Rounds only started when prior round completable; qed");
// if the blocks are equal, we don't check ancestry.
if primary_block == &last_prevote_g {
primary_block.0.clone()
} else if primary_block.1 >= last_prevote_g.1 {
last_round_estimate.0
} else {
// from this point onwards, the number of the primary-broadcasted
// block is less than the last prevote-GHOST's number.
// if the primary block is in the ancestry of p-G we vote for the
// best chain containing it.
let &(ref p_hash, p_num) = primary_block;
match self.env.ancestry(last_round_estimate.0.clone(), last_prevote_g.0.clone())
{
Ok(ancestry) => {
let to_sub = p_num + N::one();
let offset: usize = if last_prevote_g.1 < to_sub {
0
} else {
(last_prevote_g.1 - to_sub).as_()
};
if ancestry.get(offset).map_or(false, |b| b == p_hash) {
p_hash.clone()
} else {
last_round_estimate.0
}
},
Err(crate::Error::NotDescendent) => {
// This is only possible in case of massive equivocation
warn!(
target: LOG_TARGET,
"Possible case of massive equivocation: \
last round prevote GHOST: {:?} is not a descendant of last round estimate: {:?}",
last_prevote_g,
last_round_estimate,
);
last_round_estimate.0
},
}
}
},
};
(find_descendent_of.clone(), self.env.best_chain_containing(find_descendent_of))
}
// construct a precommit message based on local state.
fn construct_precommit(&self) -> Precommit<H, N> {
let t = match self.votes.state().prevote_ghost {
Some(target) => target,
None => self.votes.base(),
};
Precommit { target_hash: t.0, target_number: t.1 }
}
// notify when new blocks are finalized or when the round-estimate is updated
fn notify(&mut self, last_state: RoundState<H, N>, new_state: RoundState<H, N>) {
if last_state != new_state {
if let Some(ref b) = self.bridged_round_state {
b.update(new_state.clone());
}
}
// send notification only when the round is completable and we've cast votes.
// this is a workaround that ensures when we re-instantiate the voter after
// a shutdown, we never re-create the same round with a base that was finalized
// in this round or after.
// we try to notify if either the round state changed or if we haven't
// sent any notification yet (this is to guard against seeing enough
// votes to finalize before having precommited)
let state_changed = last_state.finalized != new_state.finalized;
let sent_finality_notifications = self.best_finalized.is_some();
if new_state.completable && (state_changed || !sent_finality_notifications) {
let precommitted = matches!(self.state, Some(State::Precommitted));
// we only cast votes when we have access to the previous round state,
// which won't be the case whenever we catch up to a later round.
let cant_vote = self.last_round_state.is_none();
if precommitted || cant_vote {
if let Some((f_hash, f_number)) = new_state.finalized {
let commit = Commit {
target_hash: f_hash.clone(),
target_number: f_number,
precommits: self.votes.finalizing_precommits(&*self.env)
.expect("always returns none if something was finalized; this is checked above; qed")
.collect(),
};
let finalized = (f_hash, f_number, self.votes.number(), commit.clone());
let _ = self.finalized_sender.unbounded_send(finalized);
self.best_finalized = Some(commit);
}
}
}
}
}