Provisioner changes for async backing

node/core/provisioner/src/error.rs

@@ -46,6 +46,9 @@ pub enum Error {
 	#[error("failed to get votes on dispute")]
 	CanceledCandidateVotes(#[source] oneshot::Canceled),
 
+	#[error("failed to get backable candidate")]
+	CanceledProspectiveCandidateChild(#[source] oneshot::Canceled),
+
 	#[error(transparent)]
 	ChainApi(#[from] ChainApiError),
 

node/core/provisioner/src/lib.rs

@@ -21,24 +21,26 @@
 
 use bitvec::vec::BitVec;
 use futures::{
-	channel::oneshot, future::BoxFuture, prelude::*, stream::FuturesUnordered, FutureExt,
+	channel::oneshot, future::BoxFuture, lock::Mutex, prelude::*, stream::FuturesUnordered,
+	FutureExt,
 };
 use futures_timer::Delay;
 
 use polkadot_node_primitives::CandidateVotes;
 use polkadot_node_subsystem::{
 	jaeger,
 	messages::{
-		CandidateBackingMessage, ChainApiMessage, DisputeCoordinatorMessage, ProvisionableData,
-		ProvisionerInherentData, ProvisionerMessage,
+		CandidateBackingMessage, ChainApiMessage, DisputeCoordinatorMessage,
+		ProspectiveParachainsMessage, ProvisionableData, ProvisionerInherentData,
+		ProvisionerMessage,
 	},
 	overseer, ActivatedLeaf, ActiveLeavesUpdate, FromOrchestra, LeafStatus, OverseerSignal,
 	PerLeafSpan, SpawnedSubsystem, SubsystemError,
 };
-use polkadot_node_subsystem_util::{request_availability_cores, request_persisted_validation_data};
+use polkadot_node_subsystem_util::request_availability_cores;
 use polkadot_primitives::v2::{
 	BackedCandidate, BlockNumber, CandidateHash, CandidateReceipt, CoreState, DisputeState,
-	DisputeStatement, DisputeStatementSet, Hash, MultiDisputeStatementSet, OccupiedCoreAssumption,
+	DisputeStatement, DisputeStatementSet, Hash, Id as ParaId, MultiDisputeStatementSet,
 	SessionIndex, SignedAvailabilityBitfield, ValidatorIndex,
 };
 use std::collections::{BTreeMap, HashMap, HashSet};
@@ -432,6 +434,12 @@ async fn select_candidates(
 ) -> Result<Vec<BackedCandidate>, Error> {
 	let block_number = get_block_number_under_construction(relay_parent, sender).await?;
 
+	// TODO [now]: `candidates` is unused since we request from prospective paras
+	// based on core state and bitfields. Should check whether returned hash is known?
+	// Does it make sense to track candidates at all?
+
+	// Wrapped sender is shared among concurrent prospective parachains requests.
+	let wrapped_sender = Mutex::new(sender);
 	let mut selected_candidates =
 		Vec::with_capacity(candidates.len().min(availability_cores.len()));
 
@@ -443,13 +451,23 @@ async fn select_candidates(
 	);
 
 	for (core_idx, core) in availability_cores.iter().enumerate() {
-		let (scheduled_core, assumption) = match core {
-			CoreState::Scheduled(scheduled_core) => (scheduled_core, OccupiedCoreAssumption::Free),
+		let (para_id, required_path) = match core {
+			CoreState::Scheduled(scheduled_core) => {
+				// The core is free, pick the first eligible candidate from
+				// the fragment tree.
+				(scheduled_core.para_id, Vec::new())
+			},
 			CoreState::Occupied(occupied_core) => {
 				if bitfields_indicate_availability(core_idx, bitfields, &occupied_core.availability)
 				{
 					if let Some(ref scheduled_core) = occupied_core.next_up_on_available {
-						(scheduled_core, OccupiedCoreAssumption::Included)
+						// The candidate occupying the core is available, choose its
+						// child in the fragment tree.
+						//
+						// TODO [now]: doesn't work for parathreads.
+						//
+						// ?? match scheduled para id == candidate_para_id?
+						(scheduled_core.para_id, vec![occupied_core.candidate_hash])
 					} else {
 						continue
 					}
@@ -458,7 +476,8 @@ async fn select_candidates(
 						continue
 					}
 					if let Some(ref scheduled_core) = occupied_core.next_up_on_time_out {
-						(scheduled_core, OccupiedCoreAssumption::TimedOut)
+						// Candidate's availability timed out, practically same as scheduled.
+						(scheduled_core.para_id, Vec::new())
 					} else {
 						continue
 					}
@@ -467,47 +486,35 @@ async fn select_candidates(
 			CoreState::Free => continue,
 		};
 
-		let validation_data = match request_persisted_validation_data(
-			relay_parent,
-			scheduled_core.para_id,
-			assumption,
-			sender,
-		)
-		.await
-		.await
-		.map_err(|err| Error::CanceledPersistedValidationData(err))??
-		{
-			Some(v) => v,
-			None => continue,
-		};
+		let fut = get_backable_candidate(relay_parent, para_id, required_path, &wrapped_sender);
 
-		let computed_validation_data_hash = validation_data.hash();
+		selected_candidates.push(fut);
+	}
 
-		// we arbitrarily pick the first of the backed candidates which match the appropriate selection criteria
-		if let Some(candidate) = candidates.iter().find(|backed_candidate| {
-			let descriptor = &backed_candidate.descriptor;
-			descriptor.para_id == scheduled_core.para_id &&
-				descriptor.persisted_validation_data_hash == computed_validation_data_hash
-		}) {
-			let candidate_hash = candidate.hash();
-			gum::trace!(
-				target: LOG_TARGET,
-				leaf_hash=?relay_parent,
-				?candidate_hash,
-				para = ?candidate.descriptor.para_id,
-				core = core_idx,
-				"Selected candidate receipt",
-			);
+	let selected_candidates = futures::future::try_join_all(selected_candidates).await?;
+	let mut selected = Vec::with_capacity(selected_candidates.len());
 
-			selected_candidates.push(candidate_hash);
+	for (core_idx, candidate_hash) in selected_candidates.into_iter().enumerate() {
+		match candidate_hash {
+			Some(hash) => selected.push(hash),
+			None => {
+				gum::debug!(
+					target: LOG_TARGET,
+					leaf_hash = ?relay_parent,
+					core = core_idx,
+					"No backable candidate returned by prospective parachains",
+				);
+			},
 		}
 	}
 
+	let sender = wrapped_sender.into_inner();
+
 	// now get the backed candidates corresponding to these candidate receipts
 	let (tx, rx) = oneshot::channel();
 	sender.send_unbounded_message(CandidateBackingMessage::GetBackedCandidates(
 		relay_parent,
-		selected_candidates.clone(),
+		selected.clone(),
 		tx,
 	));
 	let mut candidates = rx.await.map_err(|err| Error::CanceledBackedCandidates(err))?;
@@ -519,8 +526,8 @@ async fn select_candidates(
 	// maps to either 0 or 1 backed candidate, and the hashes correspond. Therefore, by checking them
 	// in order, we can ensure that the backed candidates are also in order.
 	let mut backed_idx = 0;
-	for selected in selected_candidates {
-		if selected ==
+	for selected_candidate in selected {
+		if selected_candidate ==
 			candidates.get(backed_idx).ok_or(Error::BackedCandidateOrderingProblem)?.hash()
 		{
 			backed_idx += 1;
@@ -571,6 +578,29 @@ async fn get_block_number_under_construction(
 	}
 }
 
+/// Requests backable candidate from Prospective Parachains based on
+/// the given path in the fragment tree.
+async fn get_backable_candidate(
+	relay_parent: Hash,
+	para_id: ParaId,
+	required_path: Vec<CandidateHash>,
+	sender: &Mutex<&mut impl overseer::ProvisionerSenderTrait>,
+) -> Result<Option<CandidateHash>, Error> {
+	let (tx, rx) = oneshot::channel();
+	sender
+		.lock()
+		.await
+		.send_message(ProspectiveParachainsMessage::GetBackableCandidate(
+			relay_parent,
+			para_id,
+			required_path,
+			tx,
+		))
+		.await;
+
+	rx.await.map_err(Error::CanceledProspectiveCandidateChild)
+}
+
 /// The availability bitfield for a given core is the transpose
 /// of a set of signed availability bitfields. It goes like this:
 ///

node/overseer/src/lib.rs

@@ -518,6 +518,7 @@ pub struct Overseer<SupportsParachains> {
 		CandidateBackingMessage,
 		ChainApiMessage,
 		DisputeCoordinatorMessage,
+		ProspectiveParachainsMessage,
 	])]
 	provisioner: Provisioner,