New contract PoA sync fixes (#5991)

* generate proofs on newly-created state

* report only missed steps after first block

* dont report skipped if not signer

* test

* finality tracing and passing valid header to `commit_block`

* avoid proposing multiple times on the same step when validator set changes

* limit benign reports

* Ordering -> AtomicOrdering

* reinstate warning now that spam is reduced

* flush pending transition changes when necessary

* ensure epochs aren't re-zoomed on every block

ethcore/src/block.rs

@@ -200,7 +200,7 @@ pub trait IsBlock {
 
 /// Trait for a object that has a state database.
 pub trait Drain {
-	/// Drop this object and return the underlieing database.
+	/// Drop this object and return the underlying database.
 	fn drain(self) -> StateDB;
 }
 
@@ -370,6 +370,22 @@ impl<'x> OpenBlock<'x> {
 		}
 	}
 
+	/// Push transactions onto the block.
+	pub fn push_transactions(&mut self, transactions: &[SignedTransaction]) -> Result<(), Error> {
+		push_transactions(self, transactions)
+	}
+
+	/// Populate self from a header.
+	pub fn populate_from(&mut self, header: &Header) {
+		self.set_difficulty(*header.difficulty());
+		self.set_gas_limit(*header.gas_limit());
+		self.set_timestamp(header.timestamp());
+		self.set_author(header.author().clone());
+		self.set_extra_data(header.extra_data().clone()).unwrap_or_else(|e| warn!("Couldn't set extradata: {}. Ignoring.", e));
+		self.set_uncles_hash(header.uncles_hash().clone());
+		self.set_transactions_root(header.transactions_root().clone());
+	}
+
 	/// Turn this into a `ClosedBlock`.
 	pub fn close(self) -> ClosedBlock {
 		let mut s = self;
@@ -579,18 +595,13 @@ pub fn enact(
 		is_epoch_begin,
 	)?;
 
-	b.set_difficulty(*header.difficulty());
-	b.set_gas_limit(*header.gas_limit());
-	b.set_timestamp(header.timestamp());
-	b.set_author(header.author().clone());
-	b.set_extra_data(header.extra_data().clone()).unwrap_or_else(|e| warn!("Couldn't set extradata: {}. Ignoring.", e));
-	b.set_uncles_hash(header.uncles_hash().clone());
-	b.set_transactions_root(header.transactions_root().clone());
+	b.populate_from(header);
+	b.push_transactions(transactions)?;
 
-	push_transactions(&mut b, transactions)?;
 	for u in uncles {
 		b.push_uncle(u.clone())?;
 	}
+
 	Ok(b.close_and_lock())
 }
 
@@ -681,7 +692,36 @@ mod tests {
 		let header = block.header();
 		let transactions: Result<Vec<_>, Error> = block.transactions().into_iter().map(SignedTransaction::new).collect();
 		let transactions = transactions?;
-		enact(&header, &transactions, &block.uncles(), engine, tracing, db, parent, last_hashes, factories, false)
+
+		{
+			if ::log::max_log_level() >= ::log::LogLevel::Trace {
+				let s = State::from_existing(db.boxed_clone(), parent.state_root().clone(), engine.account_start_nonce(parent.number() + 1), factories.clone())?;
+				trace!(target: "enact", "num={}, root={}, author={}, author_balance={}\n",
+					header.number(), s.root(), header.author(), s.balance(&header.author())?);
+			}
+		}
+
+		let mut b = OpenBlock::new(
+			engine,
+			factories,
+			tracing,
+			db,
+			parent,
+			last_hashes,
+			Address::new(),
+			(3141562.into(), 31415620.into()),
+			vec![],
+			false,
+		)?;
+
+		b.populate_from(&header);
+		b.push_transactions(&transactions)?;
+
+		for u in &block.uncles() {
+			b.push_uncle(u.clone())?;
+		}
+
+		Ok(b.close_and_lock())
 	}
 
 	/// Enact the block given by `block_bytes` using `engine` on the database `db` with given `parent` block header. Seal the block aferwards

ethcore/src/client/client.rs

@@ -530,7 +530,7 @@ impl Client {
 					} else {
 						imported_blocks.push(header.hash());
 
-						let route = self.commit_block(closed_block, &header.hash(), &block.bytes);
+						let route = self.commit_block(closed_block, &header, &block.bytes);
 						import_results.push(route);
 
 						self.report.write().accrue_block(&block);
@@ -635,10 +635,14 @@ impl Client {
 		Ok(hash)
 	}
 
-	fn commit_block<B>(&self, block: B, hash: &H256, block_data: &[u8]) -> ImportRoute where B: IsBlock + Drain {
-		let number = block.header().number();
-		let parent = block.header().parent_hash().clone();
-		let header = block.header().clone(); // TODO: optimize and avoid copy.
+	// NOTE: the header of the block passed here is not necessarily sealed, as
+	// it is for reconstructing the state transition.
+	//
+	// The header passed is from the original block data and is sealed.
+	fn commit_block<B>(&self, block: B, header: &Header, block_data: &[u8]) -> ImportRoute where B: IsBlock + Drain {
+		let hash = &header.hash();
+		let number = header.number();
+		let parent = header.parent_hash();
 		let chain = self.chain.read();
 
 		// Commit results
@@ -648,6 +652,8 @@ impl Client {
 			.map(Into::into)
 			.collect();
 
+		assert_eq!(header.hash(), BlockView::new(block_data).header_view().sha3());
+
 		//let traces = From::from(block.traces().clone().unwrap_or_else(Vec::new));
 
 		let mut batch = DBTransaction::new();
@@ -657,6 +663,17 @@ impl Client {
 		// TODO: Prove it with a test.
 		let mut state = block.drain();
 
+		// check epoch end signal, potentially generating a proof on the current
+		// state.
+		self.check_epoch_end_signal(
+			&header,
+			block_data,
+			&receipts,
+			&state,
+			&chain,
+			&mut batch,
+		);
+
 		state.journal_under(&mut batch, number, hash).expect("DB commit failed");
 		let route = chain.insert_block(&mut batch, block_data, receipts.clone());
 
@@ -674,10 +691,6 @@ impl Client {
 		self.db.read().write_buffered(batch);
 		chain.commit();
 
-		// check for epoch end. do this after writing first batch so we can prove
-		// transactions on the block's state.
-		// TODO: work these changes into the existing DBTransaction.
-		self.check_epoch_end_signal(&header, block_data, &receipts, &chain);
 		self.check_epoch_end(&header, &chain);
 
 		self.update_last_hashes(&parent, hash);
@@ -691,38 +704,82 @@ impl Client {
 
 	// check for epoch end signal and write pending transition if it occurs.
 	// state for the given block must be available.
-	fn check_epoch_end_signal(&self, header: &Header, block: &[u8], receipts: &[Receipt], chain: &BlockChain) {
+	fn check_epoch_end_signal(
+		&self,
+		header: &Header,
+		block_bytes: &[u8],
+		receipts: &[Receipt],
+		state_db: &StateDB,
+		chain: &BlockChain,
+		batch: &mut DBTransaction,
+	) {
 		use engines::EpochChange;
 
 		let hash = header.hash();
-		match self.engine.signals_epoch_end(header, Some(block), Some(&receipts)) {
+		match self.engine.signals_epoch_end(header, Some(block_bytes), Some(&receipts)) {
 			EpochChange::Yes(proof) => {
 				use engines::epoch::PendingTransition;
 				use engines::Proof;
 
 				let proof = match proof {
 					Proof::Known(proof) => proof,
-					Proof::WithState(with_state) =>
-						match self.with_proving_caller(BlockId::Hash(hash), move |c| with_state(c)) {
+					Proof::WithState(with_state) => {
+						let env_info = EnvInfo {
+							number: header.number(),
+							author: header.author().clone(),
+							timestamp: header.timestamp(),
+							difficulty: header.difficulty().clone(),
+							last_hashes: self.build_last_hashes(header.parent_hash().clone()),
+							gas_used: U256::default(),
+							gas_limit: u64::max_value().into(),
+						};
+
+						let call = move |addr, data| {
+							let mut state_db = state_db.boxed_clone();
+							let backend = ::state::backend::Proving::new(state_db.as_hashdb_mut());
+
+							let transaction =
+								self.contract_call_tx(BlockId::Hash(*header.parent_hash()), addr, data);
+
+							let mut state = State::from_existing(
+								backend,
+								header.state_root().clone(),
+								self.engine.account_start_nonce(header.number()),
+								self.factories.clone(),
+							).expect("state known to be available for just-imported block; qed");
+
+							let options = TransactOptions { tracing: false, vm_tracing: false, check_nonce: false };
+							let res = Executive::new(&mut state, &env_info, &*self.engine)
+								.transact(&transaction, options);
+
+							let res = match res {
+								Err(ExecutionError::Internal(e)) =>
+									Err(format!("Internal error: {}", e)),
+								Err(e) => {
+									trace!(target: "client", "Proved call failed: {}", e);
+									Ok((Vec::new(), state.drop().1.extract_proof()))
+								}
+								Ok(res) => Ok((res.output, state.drop().1.extract_proof())),
+							};
+
+							res.map(|(output, proof)| (output, proof.into_iter().map(|x| x.into_vec()).collect()))
+						};
+
+						match (with_state)(&call) {
 							Ok(proof) => proof,
 							Err(e) => {
 								warn!(target: "client", "Failed to generate transition proof for block {}: {}", hash, e);
 								warn!(target: "client", "Snapshots produced by this client may be incomplete");
-
 								Vec::new()
 							}
-						},
+						}
+					}
 				};
 
 				debug!(target: "client", "Block {} signals epoch end.", hash);
 
-				// write pending transition to DB.
-				let mut batch = DBTransaction::new();
-
 				let pending = PendingTransition { proof: proof };
-				chain.insert_pending_transition(&mut batch, hash, pending);
-
-				self.db.read().write_buffered(batch);
+				chain.insert_pending_transition(batch, hash, pending);
 			},
 			EpochChange::No => {},
 			EpochChange::Unsure(_) => {
@@ -749,7 +806,11 @@ impl Client {
 				block_number: header.number(),
 				proof: proof,
 			});
-			self.db.read().write_buffered(batch);
+
+			// always write the batch directly since epoch transition proofs are
+			// fetched from a DB iterator and DB iterators are only available on
+			// flushed data.
+			self.db.read().write(batch).expect("DB flush failed");
 		}
 	}
 
@@ -1766,7 +1827,9 @@ impl MiningBlockChainClient for Client {
 
 			let number = block.header().number();
 			let block_data = block.rlp_bytes();
-			let route = self.commit_block(block, &h, &block_data);
+			let header = block.header().clone();
+
+			let route = self.commit_block(block, &header, &block_data);
 			trace!(target: "client", "Imported sealed block #{} ({})", number, h);
 			self.state_db.lock().sync_cache(&route.enacted, &route.retracted, false);
 			route

ethcore/src/engines/authority_round/finality.rs

@@ -66,6 +66,7 @@ impl RollingFinality {
 
 				let entry = self.sign_count.entry(signer);
 				if let (true, &Entry::Vacant(_)) = (would_be_finalized, &entry) {
+					trace!(target: "finality", "Encountered already finalized block {}", hash);
 					break
 				}
 
@@ -75,6 +76,7 @@ impl RollingFinality {
 			self.headers.push_front((hash, signer));
 		}
 
+		trace!(target: "finality", "Rolling finality state: {:?}", self.headers);
 		Ok(())
 	}
 
@@ -128,6 +130,9 @@ impl RollingFinality {
 			}
 		}
 
+		trace!(target: "finality", "Blocks finalized by {:?}: {:?}", head, newly_finalized);
+
+		self.last_pushed = Some(head);
 		Ok(newly_finalized)
 	}
 }

ethcore/src/engines/authority_round/mod.rs

@@ -220,9 +220,9 @@ pub struct AuthorityRound {
 	builtins: BTreeMap<Address, Builtin>,
 	transition_service: IoService<()>,
 	step: Arc<Step>,
-	proposed: AtomicBool,
+	can_propose: AtomicBool,
 	client: RwLock<Option<Weak<EngineClient>>>,
-	signer: EngineSigner,
+	signer: RwLock<EngineSigner>,
 	validators: Box<ValidatorSet>,
 	validate_score_transition: u64,
 	eip155_transition: u64,
@@ -311,7 +311,7 @@ fn verify_external<F: Fn(Report)>(header: &Header, validators: &ValidatorSet, st
 
 	// Give one step slack if step is lagging, double vote is still not possible.
 	if step.is_future(header_step) {
-		trace!(target: "engine", "verify_block_unordered: block from the future");
+		trace!(target: "engine", "verify_block_external: block from the future");
 		report(Report::Benign(*header.author(), header.number()));
 		Err(BlockError::InvalidSeal)?
 	} else {
@@ -321,7 +321,7 @@ fn verify_external<F: Fn(Report)>(header: &Header, validators: &ValidatorSet, st
 			!verify_address(&correct_proposer, &proposer_signature, &header.bare_hash())?;
 
 		if is_invalid_proposer {
-			trace!(target: "engine", "verify_block_unordered: bad proposer for step: {}", header_step);
+			trace!(target: "engine", "verify_block_external: bad proposer for step: {}", header_step);
 			Err(EngineError::NotProposer(Mismatch { expected: correct_proposer, found: header.author().clone() }))?
 		} else {
 			Ok(())
@@ -372,7 +372,7 @@ impl AuthorityRound {
 					calibrate: our_params.start_step.is_none(),
 					duration: our_params.step_duration,
 				}),
-				proposed: AtomicBool::new(false),
+				can_propose: AtomicBool::new(true),
 				client: RwLock::new(None),
 				signer: Default::default(),
 				validators: our_params.validators,
@@ -439,7 +439,7 @@ impl Engine for AuthorityRound {
 
 	fn step(&self) {
 		self.step.increment();
-		self.proposed.store(false, AtomicOrdering::SeqCst);
+		self.can_propose.store(true, AtomicOrdering::SeqCst);
 		if let Some(ref weak) = *self.client.read() {
 			if let Some(c) = weak.upgrade() {
 				c.update_sealing();
@@ -471,7 +471,7 @@ impl Engine for AuthorityRound {
 	}
 
 	fn seals_internally(&self) -> Option<bool> {
-		Some(self.signer.address() != Address::default())
+		Some(self.signer.read().is_some())
 	}
 
 	/// Attempt to seal the block internally.
@@ -481,7 +481,7 @@ impl Engine for AuthorityRound {
 	fn generate_seal(&self, block: &ExecutedBlock) -> Seal {
 		// first check to avoid generating signature most of the time
 		// (but there's still a race to the `compare_and_swap`)
-		if self.proposed.load(AtomicOrdering::SeqCst) { return Seal::None; }
+		if !self.can_propose.load(AtomicOrdering::SeqCst) { return Seal::None; }
 
 		let header = block.header();
 		let step = self.step.load();
@@ -512,11 +512,11 @@ impl Engine for AuthorityRound {
 		};
 
 		if is_step_proposer(validators, header.parent_hash(), step, header.author()) {
-			if let Ok(signature) = self.signer.sign(header.bare_hash()) {
+			if let Ok(signature) = self.sign(header.bare_hash()) {
 				trace!(target: "engine", "generate_seal: Issuing a block for step {}.", step);
 
 				// only issue the seal if we were the first to reach the compare_and_swap.
-				if !self.proposed.compare_and_swap(false, true, AtomicOrdering::SeqCst) {
+				if self.can_propose.compare_and_swap(true, false, AtomicOrdering::SeqCst) {
 					return Seal::Regular(vec![encode(&step).into_vec(), encode(&(&H520::from(signature) as &[u8])).into_vec()]);
 				}
 			} else {
@@ -614,16 +614,18 @@ impl Engine for AuthorityRound {
 			Err(EngineError::DoubleVote(header.author().clone()))?;
 		}
 		// Report skipped primaries.
-		if step > parent_step + 1 {
-			// TODO: use epochmanager to get correct validator set for reporting?
-			// or just rely on the fact that in general these will be the same
-			// and some reports might go missing?
-			trace!(target: "engine", "Author {} built block with step gap. current step: {}, parent step: {}",
+		if let (true, Some(me)) = (step > parent_step + 1, self.signer.read().address()) {
+			debug!(target: "engine", "Author {} built block with step gap. current step: {}, parent step: {}",
 				header.author(), step, parent_step);
-
+			let mut reported = HashSet::new();
 			for s in parent_step + 1..step {
 				let skipped_primary = step_proposer(&*self.validators, &parent.hash(), s);
-				self.validators.report_benign(&skipped_primary, header.number(), header.number());
+				// Do not report this signer.
+				if skipped_primary != me {
+					self.validators.report_benign(&skipped_primary, header.number(), header.number());
+				}
+				// Stop reporting once validators start repeating.
+				if !reported.insert(skipped_primary) { break; }
 			}
 		}
 
@@ -723,6 +725,9 @@ impl Engine for AuthorityRound {
 		if epoch_manager.finality_checker.subchain_head() != Some(*chain_head.parent_hash()) {
 			// build new finality checker from ancestry of chain head,
 			// not including chain head itself yet.
+			trace!(target: "finality", "Building finality up to parent of {} ({})",
+				chain_head.hash(), chain_head.parent_hash());
+
 			let mut hash = chain_head.parent_hash().clone();
 			let epoch_transition_hash = epoch_manager.epoch_transition_hash;
 
@@ -734,6 +739,8 @@ impl Engine for AuthorityRound {
 					if header.number() == 0 { return None }
 
 					let res = (hash, header.author().clone());
+					trace!(target: "finality", "Ancestry iteration: yielding {:?}", res);
+
 					hash = header.parent_hash().clone();
 					Some(res)
 				})
@@ -766,6 +773,16 @@ impl Engine for AuthorityRound {
 						let finality_proof = ::rlp::encode_list(&finality_proof);
 						epoch_manager.note_new_epoch();
 
+						info!(target: "engine", "Applying validator set change signalled at block {}", signal_number);
+
+						// We turn off can_propose here because upon validator set change there can
+						// be two valid proposers for a single step: one from the old set and
+						// one from the new.
+						//
+						// This way, upon encountering an epoch change, the proposer from the
+						// new set will be forced to wait until the next step to avoid sealing a
+						// block that breaks the invariant that the parent's step < the block's step.
+						self.can_propose.store(false, AtomicOrdering::SeqCst);
 						return Some(combine_proofs(signal_number, &pending.proof, &*finality_proof));
 					}
 				}
@@ -816,11 +833,11 @@ impl Engine for AuthorityRound {
 	}
 
 	fn set_signer(&self, ap: Arc<AccountProvider>, address: Address, password: String) {
-		self.signer.set(ap, address, password);
+		self.signer.write().set(ap, address, password);
 	}
 
 	fn sign(&self, hash: H256) -> Result<Signature, Error> {
-		self.signer.sign(hash).map_err(Into::into)
+		self.signer.read().sign(hash).map_err(Into::into)
 	}
 
 	fn snapshot_components(&self) -> Option<Box<::snapshot::SnapshotComponents>> {
@@ -1018,6 +1035,12 @@ mod tests {
 		header.set_gas_limit(U256::from_str("222222").unwrap());
 		header.set_seal(vec![encode(&3usize).into_vec()]);
 
+		// Do not report when signer not present.
+		assert!(aura.verify_block_family(&header, &parent_header, None).is_ok());
+		assert_eq!(last_benign.load(AtomicOrdering::SeqCst), 0);
+
+		aura.set_signer(Arc::new(AccountProvider::transient_provider()), Default::default(), Default::default());
+
 		assert!(aura.verify_block_family(&header, &parent_header, None).is_ok());
 		assert_eq!(last_benign.load(AtomicOrdering::SeqCst), 1);
 	}

ethcore/src/engines/basic_authority.rs

@@ -82,7 +82,7 @@ pub struct BasicAuthority {
 	params: CommonParams,
 	gas_limit_bound_divisor: U256,
 	builtins: BTreeMap<Address, Builtin>,
-	signer: EngineSigner,
+	signer: RwLock<EngineSigner>,
 	validators: Box<ValidatorSet>,
 }
 
@@ -129,7 +129,7 @@ impl Engine for BasicAuthority {
 	}
 
 	fn seals_internally(&self) -> Option<bool> {
-		Some(self.signer.address() != Address::default())
+		Some(self.signer.read().is_some())
 	}
 
 	/// Attempt to seal the block internally.
@@ -138,7 +138,7 @@ impl Engine for BasicAuthority {
 		let author = header.author();
 		if self.validators.contains(header.parent_hash(), author) {
 			// account should be pernamently unlocked, otherwise sealing will fail
-			if let Ok(signature) = self.signer.sign(header.bare_hash()) {
+			if let Ok(signature) = self.sign(header.bare_hash()) {
 				return Seal::Regular(vec![::rlp::encode(&(&H520::from(signature) as &[u8])).into_vec()]);
 			} else {
 				trace!(target: "basicauthority", "generate_seal: FAIL: accounts secret key unavailable");
@@ -240,11 +240,11 @@ impl Engine for BasicAuthority {
 	}
 
 	fn set_signer(&self, ap: Arc<AccountProvider>, address: Address, password: String) {
-		self.signer.set(ap, address, password);
+		self.signer.write().set(ap, address, password);
 	}
 
 	fn sign(&self, hash: H256) -> Result<Signature, Error> {
-		self.signer.sign(hash).map_err(Into::into)
+		self.signer.read().sign(hash).map_err(Into::into)
 	}
 
 	fn snapshot_components(&self) -> Option<Box<::snapshot::SnapshotComponents>> {

ethcore/src/engines/signer.rs

@@ -16,21 +16,21 @@
 
 //! A signer used by Engines which need to sign messages.
 
-use util::{Arc, Mutex, RwLock, H256, Address};
+use util::{Arc, H256, Address};
 use ethkey::Signature;
 use account_provider::{self, AccountProvider};
 
 /// Everything that an Engine needs to sign messages.
 pub struct EngineSigner {
-	account_provider: Mutex<Arc<AccountProvider>>,
-	address: RwLock<Address>,
-	password: RwLock<Option<String>>,
+	account_provider: Arc<AccountProvider>,
+	address: Option<Address>,
+	password: Option<String>,
 }
 
 impl Default for EngineSigner {
 	fn default() -> Self {
 		EngineSigner {
-			account_provider: Mutex::new(Arc::new(AccountProvider::transient_provider())),
+			account_provider: Arc::new(AccountProvider::transient_provider()),
 			address: Default::default(),
 			password: Default::default(),
 		}
@@ -39,25 +39,30 @@ impl Default for EngineSigner {
 
 impl EngineSigner {
 	/// Set up the signer to sign with given address and password.
-	pub fn set(&self, ap: Arc<AccountProvider>, address: Address, password: String) {
-		*self.account_provider.lock() = ap;
-		*self.address.write()	= address;
-		*self.password.write() = Some(password);
+	pub fn set(&mut self, ap: Arc<AccountProvider>, address: Address, password: String) {
+		self.account_provider = ap;
+		self.address = Some(address);
+		self.password = Some(password);
 		debug!(target: "poa", "Setting Engine signer to {}", address);
 	}
 
 	/// Sign a consensus message hash.
 	pub fn sign(&self, hash: H256) -> Result<Signature, account_provider::SignError> {
-		self.account_provider.lock().sign(*self.address.read(), self.password.read().clone(), hash)
+		self.account_provider.sign(self.address.unwrap_or_else(Default::default), self.password.clone(), hash)
 	}
 
 	/// Signing address.
-	pub fn address(&self) -> Address {
-		self.address.read().clone()
+	pub fn address(&self) -> Option<Address> {
+		self.address.clone()
 	}
 
 	/// Check if the given address is the signing address.
 	pub fn is_address(&self, address: &Address) -> bool {
-		*self.address.read() == *address
+		self.address.map_or(false, |a| a == *address)
+	}
+
+	/// Check if the signing address was set.
+	pub fn is_some(&self) -> bool {
+		self.address.is_some()
 	}
 }

ethcore/src/engines/tendermint/mod.rs

@@ -86,7 +86,7 @@ pub struct Tendermint {
 	/// Vote accumulator.
 	votes: VoteCollector<ConsensusMessage>,
 	/// Used to sign messages and proposals.
-	signer: EngineSigner,
+	signer: RwLock<EngineSigner>,
 	/// Message for the last PoLC.
 	lock_change: RwLock<Option<ConsensusMessage>>,
 	/// Last lock view.
@@ -159,19 +159,22 @@ impl Tendermint {
 		let r = self.view.load(AtomicOrdering::SeqCst);
 		let s = *self.step.read();
 		let vote_info = message_info_rlp(&VoteStep::new(h, r, s), block_hash);
-		match self.signer.sign(vote_info.sha3()).map(Into::into) {
-			Ok(signature) => {
+		match (self.signer.read().address(), self.sign(vote_info.sha3()).map(Into::into)) {
+			(Some(validator), Ok(signature)) => {
 				let message_rlp = message_full_rlp(&signature, &vote_info);
 				let message = ConsensusMessage::new(signature, h, r, s, block_hash);
-				let validator = self.signer.address();
 				self.votes.vote(message.clone(), &validator);
 				debug!(target: "engine", "Generated {:?} as {}.", message, validator);
 				self.handle_valid_message(&message);
 
 				Some(message_rlp)
 			},
-			Err(e) => {
-				trace!(target: "engine", "Could not sign the message {}", e);
+			(None, _) => {
+				trace!(target: "engine", "No message, since there is no engine signer.");
+				None
+			},
+			(Some(v), Err(e)) => {
+				trace!(target: "engine", "{} could not sign the message {}", v, e);
 				None
 			},
 		}
@@ -272,7 +275,7 @@ impl Tendermint {
 	/// Check if current signer is the current proposer.
 	fn is_signer_proposer(&self, bh: &H256) -> bool {
 		let proposer = self.view_proposer(bh, self.height.load(AtomicOrdering::SeqCst), self.view.load(AtomicOrdering::SeqCst));
-		self.signer.is_address(&proposer)
+		self.signer.read().is_address(&proposer)
 	}
 
 	fn is_height(&self, message: &ConsensusMessage) -> bool {
@@ -420,7 +423,7 @@ impl Engine for Tendermint {
 
 	/// Should this node participate.
 	fn seals_internally(&self) -> Option<bool> {
-		Some(self.signer.address() != Address::default())
+		Some(self.signer.read().is_some())
 	}
 
 	/// Attempt to seal generate a proposal seal.
@@ -436,7 +439,7 @@ impl Engine for Tendermint {
 		let view = self.view.load(AtomicOrdering::SeqCst);
 		let bh = Some(header.bare_hash());
 		let vote_info = message_info_rlp(&VoteStep::new(height, view, Step::Propose), bh.clone());
-		if let Ok(signature) = self.signer.sign(vote_info.sha3()).map(Into::into) {
+		if let Ok(signature) = self.sign(vote_info.sha3()).map(Into::into) {
 			// Insert Propose vote.
 			debug!(target: "engine", "Submitting proposal {} at height {} view {}.", header.bare_hash(), height, view);
 			self.votes.vote(ConsensusMessage::new(signature, height, view, Step::Propose, bh), author);
@@ -565,13 +568,13 @@ impl Engine for Tendermint {
 
 	fn set_signer(&self, ap: Arc<AccountProvider>, address: Address, password: String) {
 		{
-			self.signer.set(ap, address, password);
+			self.signer.write().set(ap, address, password);
 		}
 		self.to_step(Step::Propose);
 	}
 
 	fn sign(&self, hash: H256) -> Result<Signature, Error> {
-		self.signer.sign(hash).map_err(Into::into)
+		self.signer.read().sign(hash).map_err(Into::into)
 	}
 
 	fn stop(&self) {

ethcore/src/engines/validator_set/safe_contract.rs

@@ -110,6 +110,9 @@ fn prove_initial(provider: &Provider, header: &Header, caller: &Call) -> Result<
 		trace!(target: "engine", "obtained proof for initial set: {} validators, {} bytes",
 			validators.len(), proof.len());
 
+		info!(target: "engine", "Signal for switch to contract-based validator set.");
+		info!(target: "engine", "Initial contract validators: {:?}", validators);
+
 		proof
 	})
 }
@@ -231,9 +234,7 @@ impl ValidatorSet for ValidatorSafeContract {
 			.map(|out| (out, Vec::new()))) // generate no proofs in general
 	}
 
-	fn on_epoch_begin(&self, first: bool, _header: &Header, caller: &mut SystemCall) -> Result<(), ::error::Error> {
-		if first { return Ok(()) } // only signalled changes need to be noted.
-
+	fn on_epoch_begin(&self, _first: bool, _header: &Header, caller: &mut SystemCall) -> Result<(), ::error::Error> {
 		self.provider.finalize_change(caller)
 			.wait()
 			.map_err(::engines::EngineError::FailedSystemCall)
@@ -271,8 +272,9 @@ impl ValidatorSet for ValidatorSafeContract {
 			None => ::engines::EpochChange::Unsure(::engines::Unsure::NeedsReceipts),
 			Some(receipts) => match self.extract_from_event(bloom, header, receipts) {
 				None => ::engines::EpochChange::No,
-				Some(_) => {
-					debug!(target: "engine", "signalling transition within contract");
+				Some(list) => {
+					info!(target: "engine", "Signal for transition within contract. New list: {:?}",
+						&*list);
 
 					let proof = encode_proof(&header, receipts);
 					::engines::EpochChange::Yes(::engines::Proof::Known(proof))