Expose that BasicQueue expects blocking spawn (#5860)

* Expose that `BasicQueue` expects blocking spawn

Up to now `BasicQueue` expected a closure that to spawn a `Future`.
This was expected to be a closure that spawns a blocking future.
However, this wasn't documented anywhere. This pr introduces a new trait
`SpawnBlocking` that exposes this requirement to the outside.

* Feedback

substrate/client/consensus/aura/src/lib.rs

@@ -33,7 +33,7 @@ use std::{
 	collections::HashMap
 };
 
-use futures::{prelude::*, future::BoxFuture};
+use futures::prelude::*;
 use parking_lot::Mutex;
 use log::{debug, info, trace};
 
@@ -788,14 +788,14 @@ impl<Block: BlockT, C, I, P> BlockImport<Block> for AuraBlockImport<Block, C, I,
 }
 
 /// Start an import queue for the Aura consensus algorithm.
-pub fn import_queue<B, I, C, P, F>(
+pub fn import_queue<B, I, C, P, S>(
 	slot_duration: SlotDuration,
 	block_import: I,
 	justification_import: Option<BoxJustificationImport<B>>,
 	finality_proof_import: Option<BoxFinalityProofImport<B>>,
 	client: Arc<C>,
 	inherent_data_providers: InherentDataProviders,
-	spawner: F,
+	spawner: &S,
 ) -> Result<AuraImportQueue<B, sp_api::TransactionFor<C, B>>, sp_consensus::Error> where
 	B: BlockT,
 	C::Api: BlockBuilderApi<B> + AuraApi<B, AuthorityId<P>> + ApiExt<B, Error = sp_blockchain::Error>,
@@ -805,7 +805,7 @@ pub fn import_queue<B, I, C, P, F>(
 	P: Pair + Send + Sync + 'static,
 	P::Public: Clone + Eq + Send + Sync + Hash + Debug + Encode + Decode,
 	P::Signature: Encode + Decode,
-	F: Fn(BoxFuture<'static, ()>) -> (),
+	S: sp_core::traits::SpawnBlocking,
 {
 	register_aura_inherent_data_provider(&inherent_data_providers, slot_duration.get())?;
 	initialize_authorities_cache(&*client)?;
@@ -815,6 +815,7 @@ pub fn import_queue<B, I, C, P, F>(
 		inherent_data_providers,
 		phantom: PhantomData,
 	};
+
 	Ok(BasicQueue::new(
 		verifier,
 		Box::new(block_import),

substrate/client/consensus/babe/src/lib.rs

@@ -107,7 +107,7 @@ use sc_client_api::{
 };
 use sp_block_builder::BlockBuilder as BlockBuilderApi;
 
-use futures::{prelude::*, future::BoxFuture};
+use futures::prelude::*;
 use log::{debug, info, log, trace, warn};
 use sc_consensus_slots::{
 	SlotWorker, SlotInfo, SlotCompatible, StorageChanges, CheckedHeader, check_equivocation,
@@ -1272,7 +1272,7 @@ pub fn import_queue<Block: BlockT, Client, Inner>(
 	finality_proof_import: Option<BoxFinalityProofImport<Block>>,
 	client: Arc<Client>,
 	inherent_data_providers: InherentDataProviders,
-	spawner: impl Fn(BoxFuture<'static, ()>) -> (),
+	spawner: &impl sp_core::traits::SpawnBlocking,
 ) -> ClientResult<BabeImportQueue<Block, sp_api::TransactionFor<Client, Block>>> where
 	Inner: BlockImport<Block, Error = ConsensusError, Transaction = sp_api::TransactionFor<Client, Block>>
 		+ Send + Sync + 'static,

substrate/client/consensus/manual-seal/Cargo.toml

@@ -28,6 +28,7 @@ sp-blockchain = { path = "../../../primitives/blockchain" , version = "2.0.0-dev
 sp-consensus = { package = "sp-consensus", path = "../../../primitives/consensus/common" , version = "0.8.0-dev"}
 sp-inherents = { path = "../../../primitives/inherents" , version = "2.0.0-dev"}
 sp-runtime = {  path = "../../../primitives/runtime" , version = "2.0.0-dev"}
+sp-core = {  path = "../../../primitives/core" , version = "2.0.0-dev"}
 sp-transaction-pool = { path = "../../../primitives/transaction-pool" , version = "2.0.0-dev"}
 
 [dev-dependencies]

substrate/client/consensus/manual-seal/src/lib.rs

@@ -17,7 +17,7 @@
 //! A manual sealing engine: the engine listens for rpc calls to seal blocks and create forks.
 //! This is suitable for a testing environment.
 
-use futures::{prelude::*, future::BoxFuture};
+use futures::prelude::*;
 use sp_consensus::{
 	Environment, Proposer, ForkChoiceStrategy, BlockImportParams, BlockOrigin, SelectChain,
 	import_queue::{BasicQueue, CacheKeyId, Verifier, BoxBlockImport},
@@ -68,7 +68,7 @@ impl<B: BlockT> Verifier<B> for ManualSealVerifier {
 /// Instantiate the import queue for the manual seal consensus engine.
 pub fn import_queue<Block, B>(
 	block_import: BoxBlockImport<Block, TransactionFor<B, Block>>,
-	spawner: impl Fn(BoxFuture<'static, ()>) -> ()
+	spawner: &impl sp_core::traits::SpawnBlocking,
 ) -> BasicQueue<Block, TransactionFor<B, Block>>
 	where
 		Block: BlockT,

substrate/client/consensus/pow/src/lib.rs

@@ -49,12 +49,13 @@ use sp_consensus::{
 	SelectChain, Error as ConsensusError, CanAuthorWith, RecordProof, BlockImport,
 	BlockCheckParams, ImportResult,
 };
-use sp_consensus::import_queue::{BoxBlockImport, BasicQueue, Verifier, BoxJustificationImport, BoxFinalityProofImport};
+use sp_consensus::import_queue::{
+	BoxBlockImport, BasicQueue, Verifier, BoxJustificationImport, BoxFinalityProofImport,
+};
 use codec::{Encode, Decode};
 use sc_client_api;
 use log::*;
 use sp_timestamp::{InherentError as TIError, TimestampInherentData};
-use futures::future::BoxFuture;
 
 #[derive(derive_more::Display, Debug)]
 pub enum Error<B: BlockT> {
@@ -462,7 +463,7 @@ pub fn import_queue<B, Transaction, Algorithm>(
 	finality_proof_import: Option<BoxFinalityProofImport<B>>,
 	algorithm: Algorithm,
 	inherent_data_providers: InherentDataProviders,
-	spawner: impl Fn(BoxFuture<'static, ()>) -> (),
+	spawner: &impl sp_core::traits::SpawnBlocking,
 ) -> Result<
 	PowImportQueue<B, Transaction>,
 	sp_consensus::Error