Step duration map configuration parameter ported from the POA Network fork (#10902)

* step duration map configuration parameter ported from POA Network fork

* step duration map refactoring

* added a test of step duration change

* refactoring of vector search; return Err instead of panicking

* removed dead code and the Config engine error variant

* doc correction

* converted triples to struct StepDurationInfo

ethcore/engines/authority-round/src/lib.rs

@@ -33,11 +33,12 @@
 
 use std::collections::{BTreeMap, BTreeSet, HashSet};
 use std::{cmp, fmt};
-use std::iter::FromIterator;
+use std::iter::{self, FromIterator};
 use std::ops::Deref;
-use std::sync::atomic::{AtomicUsize, AtomicBool, Ordering as AtomicOrdering};
+use std::sync::atomic::{AtomicU64, AtomicBool, Ordering as AtomicOrdering};
 use std::sync::{Weak, Arc};
 use std::time::{UNIX_EPOCH, Duration};
+use std::u64;
 
 use client_traits::EngineClient;
 use engine::{Engine, ConstructedVerifier};
@@ -83,12 +84,13 @@ use self::finality::RollingFinality;
 
 /// `AuthorityRound` params.
 pub struct AuthorityRoundParams {
-	/// Time to wait before next block or authority switching,
+	/// A map defining intervals of blocks with the given times (in seconds) to wait before next
-	/// in seconds.
+	/// block or authority switching. The keys in the map are steps of starting blocks of those
+	/// periods. The entry at `0` should be defined.
 	///
-	/// Deliberately typed as u16 as too high of a value leads
+	/// Wait times (durations) are additionally required to be less than 65535 since larger values
-	/// to slow block issuance.
+	/// lead to slow block issuance.
-	pub step_duration: u16,
+	pub step_durations: BTreeMap<u64, u64>,
 	/// Starting step,
 	pub start_step: Option<u64>,
 	/// Valid validators.
@@ -121,11 +123,27 @@ const U16_MAX: usize = ::std::u16::MAX as usize;
 
 impl From<ethjson::spec::AuthorityRoundParams> for AuthorityRoundParams {
 	fn from(p: ethjson::spec::AuthorityRoundParams) -> Self {
-		let mut step_duration_usize: usize = p.step_duration.into();
+		let map_step_duration = |u: ethjson::uint::Uint| {
-		if step_duration_usize > U16_MAX {
+			let mut step_duration_usize: usize = u.into();
-			step_duration_usize = U16_MAX;
+			if step_duration_usize == 0 {
-			warn!(target: "engine", "step_duration is too high ({}), setting it to {}", step_duration_usize, U16_MAX);
+				panic!("AuthorityRoundParams: step duration cannot be 0");
 			}
+			if step_duration_usize > U16_MAX {
+				warn!(target: "engine", "step duration is too high ({}), setting it to {}", step_duration_usize, U16_MAX);
+				step_duration_usize = U16_MAX;
+			}
+			step_duration_usize as u64
+		};
+		let step_durations: BTreeMap<_, _> = match p.step_duration {
+			ethjson::spec::StepDuration::Single(u) =>
+				iter::once((0,  map_step_duration(u))).collect(),
+			ethjson::spec::StepDuration::Transitions(tr) => {
+				if tr.is_empty() {
+					panic!("AuthorityRoundParams: step duration transitions cannot be empty");
+				}
+				tr.into_iter().map(|(timestamp, u)| (timestamp.into(), map_step_duration(u))).collect()
+			}
+		};
 		let transition_block_num = p.block_reward_contract_transition.map_or(0, Into::into);
 		let mut br_transitions: BTreeMap<_, _> = p.block_reward_contract_transitions
 			.unwrap_or_default()
@@ -151,7 +169,7 @@ impl From<ethjson::spec::AuthorityRoundParams> for AuthorityRoundParams {
 			);
 		}
 		AuthorityRoundParams {
-			step_duration: step_duration_usize as u16,
+			step_durations,
 			validators: new_validator_set(p.validators),
 			start_step: p.start_step.map(Into::into),
 			validate_score_transition: p.validate_score_transition.map_or(0, Into::into),
@@ -169,53 +187,88 @@ impl From<ethjson::spec::AuthorityRoundParams> for AuthorityRoundParams {
 	}
 }
 
-// Helper for managing the step.
+/// A triple containing the first step number and the starting timestamp of the given step duration.
+#[derive(Clone, Debug)]
+struct StepDurationInfo {
+	transition_step: u64,
+	transition_timestamp: u64,
+	step_duration: u64,
+}
+
+/// Helper for managing the step.
 #[derive(Debug)]
 struct Step {
 	calibrate: bool, // whether calibration is enabled.
-	inner: AtomicUsize,
+	inner: AtomicU64,
-	duration: u16,
+	/// Planned durations of steps.
+	durations: Vec<StepDurationInfo>,
 }
 
 impl Step {
-	fn load(&self) -> u64 { self.inner.load(AtomicOrdering::SeqCst) as u64 }
+	fn load(&self) -> u64 { self.inner.load(AtomicOrdering::SeqCst) }
+
+	/// Finds the remaining duration of the current step. Panics if there was a counter under- or
+	/// overflow.
 	fn duration_remaining(&self) -> Duration {
-		let now = unix_now();
+		self.opt_duration_remaining().unwrap_or_else(|| {
-		let expected_seconds = self.load()
-			.checked_add(1)
-			.and_then(|ctr| ctr.checked_mul(self.duration as u64))
-			.map(Duration::from_secs);
-
-		match expected_seconds {
-			Some(step_end) if step_end > now => step_end - now,
-			Some(_) => Duration::from_secs(0),
-			None => {
 			let ctr = self.load();
-				error!(target: "engine", "Step counter is too high: {}, aborting", ctr);
+			error!(target: "engine", "Step counter under- or overflow: {}, aborting", ctr);
-				panic!("step counter is too high: {}", ctr)
+			panic!("step counter under- or overflow: {}", ctr)
-			},
+		})
 	}
 
+	/// Finds the remaining duration of the current step. Returns `None` if there was a counter
+	/// under- or overflow.
+	fn opt_duration_remaining(&self) -> Option<Duration> {
+		let next_step = self.load().checked_add(1)?;
+		let StepDurationInfo { transition_step, transition_timestamp, step_duration } =
+			self.durations.iter()
+			.take_while(|info| info.transition_step < next_step)
+			.last()
+			.expect("durations cannot be empty")
+			.clone();
+		let next_time = transition_timestamp
+			.checked_add(next_step.checked_sub(transition_step)?.checked_mul(step_duration)?)?;
+		Some(Duration::from_secs(next_time.saturating_sub(unix_now().as_secs())))
 	}
 
+	/// Increments the step number.
+	///
+	/// Panics if the new step number is `u64::MAX`.
 	fn increment(&self) {
-		use std::usize;
 		// fetch_add won't panic on overflow but will rather wrap
 		// around, leading to zero as the step counter, which might
 		// lead to unexpected situations, so it's better to shut down.
-		if self.inner.fetch_add(1, AtomicOrdering::SeqCst) == usize::MAX {
+		if self.inner.fetch_add(1, AtomicOrdering::SeqCst) == u64::MAX {
-			error!(target: "engine", "Step counter is too high: {}, aborting", usize::MAX);
+			error!(target: "engine", "Step counter is too high: {}, aborting", u64::MAX);
-			panic!("step counter is too high: {}", usize::MAX);
+			panic!("step counter is too high: {}", u64::MAX);
 		}
-
 	}
 
 	fn calibrate(&self) {
 		if self.calibrate {
-			let new_step = unix_now().as_secs() / (self.duration as u64);
+			if self.opt_calibrate().is_none() {
-			self.inner.store(new_step as usize, AtomicOrdering::SeqCst);
+				let ctr = self.load();
+				error!(target: "engine", "Step counter under- or overflow: {}, aborting", ctr);
+				panic!("step counter under- or overflow: {}", ctr)
 			}
 		}
+	}
+
+	/// Calibrates the AuRa step number according to the current time.
+	fn opt_calibrate(&self) -> Option<()> {
+		let now = unix_now().as_secs();
+		let StepDurationInfo { transition_step, transition_timestamp, step_duration } =
+			self.durations.iter()
+			.take_while(|info| info.transition_timestamp < now)
+			.last()
+			.expect("durations cannot be empty")
+			.clone();
+		let new_step = (now.checked_sub(transition_timestamp)? / step_duration)
+			.checked_add(transition_step)?;
+		self.inner.store(new_step, AtomicOrdering::SeqCst);
+		Some(())
+	}
 
 	fn check_future(&self, given: u64) -> Result<(), Option<OutOfBounds<u64>>> {
 		const REJECTED_STEP_DRIFT: u64 = 4;
@@ -234,7 +287,9 @@ impl Step {
 			Err(None)
 		// wait a bit for blocks in near future
 		} else if given > current {
-			let d = self.duration as u64;
+			let d = self.durations.iter().take_while(|info| info.transition_step <= current).last()
+				.expect("Duration map has at least a 0 entry.")
+				.step_duration;
 			Err(Some(OutOfBounds {
 				min: None,
 				max: Some(d * current),
@@ -730,23 +785,54 @@ impl<'a, A: ?Sized, B> Deref for CowLike<'a, A, B> where B: AsRef<A> {
 impl AuthorityRound {
 	/// Create a new instance of AuthorityRound engine.
 	pub fn new(our_params: AuthorityRoundParams, machine: Machine) -> Result<Arc<Self>, Error> {
-		if our_params.step_duration == 0 {
+		if !our_params.step_durations.contains_key(&0) {
-			error!(target: "engine", "Authority Round step duration can't be zero, aborting");
+			error!(target: "engine", "Authority Round step 0 duration is undefined, aborting");
-			panic!("authority_round: step duration can't be zero")
+			return Err(Error::Engine(EngineError::Custom(String::from("step 0 duration is undefined"))));
+		}
+		if our_params.step_durations.values().any(|v| *v == 0) {
+			error!(target: "engine", "Authority Round step duration cannot be 0");
+			return Err(Error::Engine(EngineError::Custom(String::from("step duration cannot be 0"))));
 		}
 		let should_timeout = our_params.start_step.is_none();
-		let initial_step = our_params.start_step.unwrap_or_else(|| (unix_now().as_secs() / (our_params.step_duration as u64)));
+		let initial_step = our_params.start_step.unwrap_or(0);
+
+		let mut durations = Vec::new();
+		let mut prev_step = 0u64;
+		let mut prev_time = 0u64;
+		let mut prev_dur = our_params.step_durations[&0];
+		durations.push(StepDurationInfo {
+			transition_step: prev_step,
+			transition_timestamp: prev_time,
+			step_duration: prev_dur
+		});
+		for (time, dur) in our_params.step_durations.iter().skip(1) {
+			let (step, time) = next_step_time_duration(
+				StepDurationInfo{
+					transition_step: prev_step,
+					transition_timestamp: prev_time,
+					step_duration: prev_dur,
+				}, *time)
+				.ok_or(BlockError::TimestampOverflow)?;
+			durations.push(StepDurationInfo {
+				transition_step: step,
+				transition_timestamp: time,
+				step_duration: *dur
+			});
+			prev_step = step;
+			prev_time = time;
+			prev_dur = *dur;
+		}
+
+		let step = Step {
+			inner: AtomicU64::new(initial_step),
+			calibrate: our_params.start_step.is_none(),
+			durations,
+		};
+		step.calibrate();
 		let engine = Arc::new(
 			AuthorityRound {
 				transition_service: IoService::<()>::start()?,
-				step: Arc::new(PermissionedStep {
+				step: Arc::new(PermissionedStep { inner: step, can_propose: AtomicBool::new(true) }),
-					inner: Step {
-						inner: AtomicUsize::new(initial_step as usize),
-						calibrate: our_params.start_step.is_none(),
-						duration: our_params.step_duration,
-					},
-					can_propose: AtomicBool::new(true),
-				}),
 				client: Arc::new(RwLock::new(None)),
 				signer: RwLock::new(None),
 				validators: our_params.validators,
@@ -994,8 +1080,10 @@ impl IoHandler<()> for TransitionHandler {
 				}
 			}
 
-			let next_run_at = AsMillis::as_millis(&self.step.inner.duration_remaining()) >> 2;
+			let next_run_at = Duration::from_millis(
-			io.register_timer_once(ENGINE_TIMEOUT_TOKEN, Duration::from_millis(next_run_at))
+				AsMillis::as_millis(&self.step.inner.duration_remaining()) >> 2
+			);
+			io.register_timer_once(ENGINE_TIMEOUT_TOKEN, next_run_at)
 				.unwrap_or_else(|e| warn!(target: "engine", "Failed to restart consensus step timer: {}.", e))
 		}
 	}
@@ -1694,12 +1782,27 @@ impl Engine for AuthorityRound {
 	}
 }
 
+/// A helper accumulator function mapping a step duration and a step duration transition timestamp
+/// to the corresponding step number and the correct starting second of the step.
+fn next_step_time_duration(info: StepDurationInfo, time: u64) -> Option<(u64, u64)>
+{
+	let step_diff = time.checked_add(info.step_duration)?
+		.checked_sub(1)?
+		.checked_sub(info.transition_timestamp)?
+		.checked_div(info.step_duration)?;
+	Some((
+		info.transition_step.checked_add(step_diff)?,
+		step_diff.checked_mul(info.step_duration)?.checked_add(time)?,
+	))
+}
+
 #[cfg(test)]
 mod tests {
 	use std::collections::BTreeMap;
 	use std::str::FromStr;
 	use std::sync::Arc;
-	use std::sync::atomic::{AtomicUsize, Ordering as AtomicOrdering};
+	use std::sync::atomic::{AtomicUsize, AtomicU64, Ordering as AtomicOrdering};
+	use std::time::Duration;
 	use keccak_hash::keccak;
 	use accounts::AccountProvider;
 	use ethereum_types::{Address, H520, H256, U256};
@@ -1726,13 +1829,16 @@ mod tests {
 	use ethjson;
 	use serde_json;
 
-	use super::{AuthorityRoundParams, AuthorityRound, EmptyStep, SealedEmptyStep, calculate_score};
+	use super::{
+		AuthorityRoundParams, AuthorityRound, EmptyStep, SealedEmptyStep, StepDurationInfo,
+		calculate_score,
+	};
 
 	fn build_aura<F>(f: F) -> Arc<AuthorityRound> where
 		F: FnOnce(&mut AuthorityRoundParams),
 	{
 		let mut params = AuthorityRoundParams {
-			step_duration: 1,
+			step_durations: [(0, 1)].to_vec().into_iter().collect(),
 			start_step: Some(1),
 			validators: Box::new(TestSet::default()),
 			validate_score_transition: 0,
@@ -2061,29 +2167,67 @@ mod tests {
 		use super::Step;
 		let step = Step {
 			calibrate: false,
-			inner: AtomicUsize::new(::std::usize::MAX),
+			inner: AtomicU64::new(::std::u64::MAX),
-			duration: 1,
+			durations: [StepDurationInfo {
+				transition_step: 0,
+				transition_timestamp: 0,
+				step_duration: 1,
+			}].to_vec().into_iter().collect(),
 		};
 		step.increment();
 	}
 
 	#[test]
-	#[should_panic(expected="counter is too high")]
+	#[should_panic(expected="step counter under- or overflow")]
 	fn test_counter_duration_remaining_too_high() {
 		use super::Step;
 		let step = Step {
 			calibrate: false,
-			inner: AtomicUsize::new(::std::usize::MAX),
+			inner: AtomicU64::new(::std::u64::MAX),
-			duration: 1,
+			durations: [StepDurationInfo {
+				transition_step: 0,
+				transition_timestamp: 0,
+				step_duration: 1,
+			}].to_vec().into_iter().collect(),
 		};
 		step.duration_remaining();
 	}
 
 	#[test]
-	#[should_panic(expected="authority_round: step duration can't be zero")]
+	fn test_change_step_duration() {
+		use super::Step;
+		use std::thread;
+
+		let now = super::unix_now().as_secs();
+		let step = Step {
+			calibrate: true,
+			inner: AtomicU64::new(::std::u64::MAX),
+			durations: [
+				StepDurationInfo { transition_step: 0, transition_timestamp: 0, step_duration: 1 },
+				StepDurationInfo { transition_step: now, transition_timestamp: now, step_duration: 2 },
+				StepDurationInfo { transition_step: now + 1, transition_timestamp: now + 2, step_duration: 4 },
+			].to_vec().into_iter().collect(),
+		};
+		// calibrated step `now`
+		step.calibrate();
+		let duration_remaining = step.duration_remaining();
+		assert_eq!(step.inner.load(AtomicOrdering::SeqCst), now);
+		assert!(duration_remaining <= Duration::from_secs(2));
+		thread::sleep(duration_remaining);
+		step.increment();
+		// calibrated step `now + 1`
+		step.calibrate();
+		let duration_remaining = step.duration_remaining();
+		assert_eq!(step.inner.load(AtomicOrdering::SeqCst), now + 1);
+		assert!(duration_remaining > Duration::from_secs(2));
+		assert!(duration_remaining <= Duration::from_secs(4));
+	}
+
+	#[test]
+	#[should_panic(expected="called `Result::unwrap()` on an `Err` value: Engine(Custom(\"step duration cannot be 0\"))")]
 	fn test_step_duration_zero() {
 		build_aura(|params| {
-			params.step_duration = 0;
+			params.step_durations = [(0, 0)].to_vec().into_iter().collect();
 		});
 	}
 
@@ -2473,7 +2617,7 @@ mod tests {
 	#[test]
 	fn test_empty_steps() {
 		let engine = build_aura(|p| {
-			p.step_duration = 4;
+			p.step_durations = [(0, 4)].to_vec().into_iter().collect();
 			p.empty_steps_transition = 0;
 			p.maximum_empty_steps = 0;
 		});
@@ -2507,7 +2651,7 @@ mod tests {
 		let (_spec, tap, accounts) = setup_empty_steps();
 		let engine = build_aura(|p| {
 			p.validators = Box::new(SimpleList::new(accounts.clone()));
-			p.step_duration = 4;
+			p.step_durations = [(0, 4)].to_vec().into_iter().collect();
 			p.empty_steps_transition = 0;
 			p.maximum_empty_steps = 0;
 		});
@@ -2544,7 +2688,7 @@ mod tests {
 		let (_spec, tap, accounts) = setup_empty_steps();
 		let engine = build_aura(|p| {
 			p.validators = Box::new(SimpleList::new(accounts.clone()));
-			p.step_duration = 4;
+			p.step_durations = [(0, 4)].to_vec().into_iter().collect();
 			p.empty_steps_transition = 0;
 			p.maximum_empty_steps = 0;
 		});

json/src/spec/authority_round.rs

@@ -41,7 +41,7 @@
 use std::collections::BTreeMap;
 use crate::{bytes::Bytes, hash::Address, uint::Uint};
 use serde::Deserialize;
-use super::ValidatorSet;
+use super::{StepDuration, ValidatorSet};
 
 /// Authority params deserialization.
 #[derive(Debug, PartialEq, Deserialize)]
@@ -49,7 +49,7 @@ use super::ValidatorSet;
 #[serde(rename_all = "camelCase")]
 pub struct AuthorityRoundParams {
 	/// Block duration, in seconds.
-	pub step_duration: Uint,
+	pub step_duration: StepDuration,
 	/// Valid authorities
 	pub validators: ValidatorSet,
 	/// Starting step. Determined automatically if not specified.
@@ -107,7 +107,7 @@ pub struct AuthorityRound {
 
 #[cfg(test)]
 mod tests {
-	use super::{Address, Uint};
+	use super::{Address, Uint, StepDuration};
 	use ethereum_types::{U256, H160};
 	use crate::spec::{validator_set::ValidatorSet, authority_round::AuthorityRound};
 	use std::str::FromStr;
@@ -129,7 +129,7 @@ mod tests {
 		}"#;
 
 		let deserialized: AuthorityRound = serde_json::from_str(s).unwrap();
-		assert_eq!(deserialized.params.step_duration, Uint(U256::from(0x02)));
+		assert_eq!(deserialized.params.step_duration, StepDuration::Single(Uint(U256::from(2))));
 		assert_eq!(
 			deserialized.params.validators,
 			ValidatorSet::List(vec![Address(H160::from_str("c6d9d2cd449a754c494264e1809c50e34d64562b").unwrap())]),

json/src/spec/mod.rs

@@ -32,6 +32,7 @@ pub mod null_engine;
 pub mod instant_seal;
 pub mod hardcoded_sync;
 pub mod clique;
+pub mod step_duration;
 
 pub use self::account::Account;
 pub use self::builtin::{Builtin, Pricing, Linear};
@@ -49,3 +50,4 @@ pub use self::clique::{Clique, CliqueParams};
 pub use self::null_engine::{NullEngine, NullEngineParams};
 pub use self::instant_seal::{InstantSeal, InstantSealParams};
 pub use self::hardcoded_sync::HardcodedSync;
+pub use self::step_duration::StepDuration;

json/src/spec/step_duration.rs

@@ -0,0 +1,36 @@
+// Copyright 2015-2019 Parity Technologies (UK) Ltd.
+// This file is part of Parity.
+
+// Parity is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Parity is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Parity.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Step duration configuration parameter
+
+use std::collections::BTreeMap;
+
+use serde::Deserialize;
+
+use crate::uint::Uint;
+
+/// Step duration can be specified either as a `Uint` (in seconds), in which case it will be
+/// constant, or as a list of pairs consisting of a timestamp of type `Uint` and a duration, in
+/// which case the duration of a step will be determined by a mapping arising from that list.
+#[derive(Debug, PartialEq, Deserialize)]
+#[serde(deny_unknown_fields)]
+#[serde(untagged)]
+pub enum StepDuration {
+	/// Duration of all steps.
+	Single(Uint),
+	/// Step duration transitions: a mapping of timestamp to step durations.
+	Transitions(BTreeMap<Uint, Uint>),
+}