approval distribution: trigger assignment/votes resend based on approval checking lag (#7038)

* Send lag update message

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Process ApprovalCheckingLagUpdate

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Comput min age based on lag

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* fix comment

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Fix tests

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Fix test build

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* Make the spawnhandle optional

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

* remove unused

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

---------

Signed-off-by: Andrei Sandu <andrei-mihail@parity.io>

polkadot/node/service/src/lib.rs

@@ -763,6 +763,7 @@ where
 			basics.backend.clone(),
 			overseer_handle.clone(),
 			metrics,
+			Some(basics.task_manager.spawn_handle()),
 		)
 	} else {
 		SelectRelayChain::new_longest_chain(basics.backend.clone())

polkadot/node/service/src/relay_chain_selection.rs

@@ -40,14 +40,16 @@ use consensus_common::{Error as ConsensusError, SelectChain};
 use futures::channel::oneshot;
 use polkadot_node_primitives::MAX_FINALITY_LAG as PRIMITIVES_MAX_FINALITY_LAG;
 use polkadot_node_subsystem::messages::{
-	ApprovalVotingMessage, ChainSelectionMessage, DisputeCoordinatorMessage,
-	HighestApprovedAncestorBlock,
+	ApprovalDistributionMessage, ApprovalVotingMessage, ChainSelectionMessage,
+	DisputeCoordinatorMessage, HighestApprovedAncestorBlock,
 };
 use polkadot_node_subsystem_util::metrics::{self, prometheus};
 use polkadot_overseer::{AllMessages, Handle};
 use polkadot_primitives::{Block as PolkadotBlock, BlockNumber, Hash, Header as PolkadotHeader};
 use std::sync::Arc;
 
+pub use service::SpawnTaskHandle;
+
 /// The maximum amount of unfinalized blocks we are willing to allow due to approval checking
 /// or disputes.
 ///
@@ -162,13 +164,21 @@ where
 
 	/// Create a new [`SelectRelayChain`] wrapping the given chain backend
 	/// and a handle to the overseer.
-	pub fn new_with_overseer(backend: Arc<B>, overseer: Handle, metrics: Metrics) -> Self {
+	pub fn new_with_overseer(
+		backend: Arc<B>,
+		overseer: Handle,
+		metrics: Metrics,
+		spawn_handle: Option<SpawnTaskHandle>,
+	) -> Self {
 		gum::debug!(target: LOG_TARGET, "Using dispute aware relay-chain selection algorithm",);
 
 		SelectRelayChain {
 			longest_chain: sc_consensus::LongestChain::new(backend.clone()),
 			selection: IsDisputesAwareWithOverseer::Yes(SelectRelayChainInner::new(
-				backend, overseer, metrics,
+				backend,
+				overseer,
+				metrics,
+				spawn_handle,
 			)),
 		}
 	}
@@ -219,6 +229,7 @@ pub struct SelectRelayChainInner<B, OH> {
 	backend: Arc<B>,
 	overseer: OH,
 	metrics: Metrics,
+	spawn_handle: Option<SpawnTaskHandle>,
 }
 
 impl<B, OH> SelectRelayChainInner<B, OH>
@@ -228,8 +239,13 @@ where
 {
 	/// Create a new [`SelectRelayChainInner`] wrapping the given chain backend
 	/// and a handle to the overseer.
-	pub fn new(backend: Arc<B>, overseer: OH, metrics: Metrics) -> Self {
-		SelectRelayChainInner { backend, overseer, metrics }
+	pub fn new(
+		backend: Arc<B>,
+		overseer: OH,
+		metrics: Metrics,
+		spawn_handle: Option<SpawnTaskHandle>,
+	) -> Self {
+		SelectRelayChainInner { backend, overseer, metrics, spawn_handle }
 	}
 
 	fn block_header(&self, hash: Hash) -> Result<PolkadotHeader, ConsensusError> {
@@ -267,6 +283,7 @@ where
 			backend: self.backend.clone(),
 			overseer: self.overseer.clone(),
 			metrics: self.metrics.clone(),
+			spawn_handle: self.spawn_handle.clone(),
 		}
 	}
 }
@@ -307,7 +324,7 @@ impl OverseerHandleT for Handle {
 impl<B, OH> SelectRelayChainInner<B, OH>
 where
 	B: HeaderProviderProvider<PolkadotBlock>,
-	OH: OverseerHandleT,
+	OH: OverseerHandleT + 'static,
 {
 	/// Get all leaves of the chain, i.e. block hashes that are suitable to
 	/// build upon and have no suitable children.
@@ -455,6 +472,26 @@ where
 		let lag = initial_leaf_number.saturating_sub(subchain_number);
 		self.metrics.note_approval_checking_finality_lag(lag);
 
+		// Messages sent to `approval-distrbution` are known to have high `ToF`, we need to spawn a task for sending
+		// the message to not block here and delay finality.
+		if let Some(spawn_handle) = &self.spawn_handle {
+			let mut overseer_handle = self.overseer.clone();
+			let lag_update_task = async move {
+				overseer_handle
+					.send_msg(
+						ApprovalDistributionMessage::ApprovalCheckingLagUpdate(lag),
+						std::any::type_name::<Self>(),
+					)
+					.await;
+			};
+
+			spawn_handle.spawn(
+				"approval-checking-lag-update",
+				Some("relay-chain-selection"),
+				Box::pin(lag_update_task),
+			);
+		}
+
 		let (lag, subchain_head) = {
 			// Prevent sending flawed data to the dispute-coordinator.
 			if Some(subchain_block_descriptions.len() as _) !=

polkadot/node/service/src/tests.rs

@@ -83,6 +83,7 @@ fn test_harness<T: Future<Output = VirtualOverseer>>(
 		Arc::new(case_vars.chain.clone()),
 		context.sender().clone(),
 		Default::default(),
+		None,
 	);
 
 	let target_hash = case_vars.target_block.clone();
@@ -99,7 +100,6 @@ fn test_harness<T: Future<Output = VirtualOverseer>>(
 
 	futures::pin_mut!(test_fut);
 	futures::pin_mut!(selection_process);
-
 	futures::executor::block_on(future::join(
 		async move {
 			let _overseer = test_fut.await;