Introduce thread pool for transaction validation. (#4051)

core/transaction-pool/Cargo.toml

@@ -7,7 +7,7 @@ edition = "2018"
 [dependencies]
 derive_more = "0.15.0"
 log = "0.4.8"
-futures-preview = "0.3.0-alpha.19"
+futures = { version = "0.3.0", features = ["thread-pool"] }
 codec = { package = "parity-scale-codec", version = "1.0.0" }
 parking_lot = "0.9.0"
 sr-primitives = { path = "../sr-primitives" }

core/transaction-pool/src/api.rs

@@ -17,11 +17,17 @@
 //! Chain api required for the transaction pool.
 
 use std::{
-	sync::Arc,
 	marker::PhantomData,
+	pin::Pin,
+	sync::Arc,
 };
 use client::{runtime_api::TaggedTransactionQueue, blockchain::HeaderBackend};
 use codec::Encode;
+use futures::{
+	channel::oneshot,
+	executor::{ThreadPool, ThreadPoolBuilder},
+	future::Future,
+};
 use txpool;
 use primitives::{
 	H256,
@@ -39,6 +45,7 @@ use crate::error;
 /// The transaction pool logic
 pub struct FullChainApi<T, Block> {
 	client: Arc<T>,
+	pool: ThreadPool,
 	_marker: PhantomData<Block>,
 }
 
@@ -49,27 +56,48 @@ impl<T, Block> FullChainApi<T, Block> where
 	pub fn new(client: Arc<T>) -> Self {
 		FullChainApi {
 			client,
+			pool: ThreadPoolBuilder::new()
+				.pool_size(2)
+				.name_prefix("txpool-verifier")
+				.create()
+				.expect("Failed to spawn verifier threads, that are critical for node operation."),
 			_marker: Default::default()
 		}
 	}
 }
 
 impl<T, Block> txpool::ChainApi for FullChainApi<T, Block> where
 	Block: traits::Block<Hash=H256>,
-	T: traits::ProvideRuntimeApi + HeaderBackend<Block>,
+	T: traits::ProvideRuntimeApi + HeaderBackend<Block> + 'static,
 	T::Api: TaggedTransactionQueue<Block>
 {
 	type Block = Block;
 	type Hash = H256;
 	type Error = error::Error;
-	type ValidationFuture = futures::future::Ready<error::Result<TransactionValidity>>;
+	type ValidationFuture = Pin<Box<dyn Future<Output=error::Result<TransactionValidity>> + Send>>;
 
 	fn validate_transaction(
 		&self,
 		at: &BlockId<Self::Block>,
 		uxt: txpool::ExtrinsicFor<Self>,
 	) -> Self::ValidationFuture {
-		futures::future::ready(self.client.runtime_api().validate_transaction(at, uxt).map_err(Into::into))
+		let (tx, rx) = oneshot::channel();
+		let client = self.client.clone();
+		let at = at.clone();
+
+		self.pool.spawn_ok(async move {
+			let res = client.runtime_api().validate_transaction(&at, uxt).map_err(Into::into);
+			if let Err(e) = tx.send(res) {
+				log::warn!("Unable to send a validate transaction result: {:?}", e);
+			}
+		});
+
+		Box::pin(async move {
+			match rx.await {
+				Ok(r) => r,
+				Err(e) => Err(client::error::Error::Msg(format!("{}", e)))?,
+			}
+		})
 	}
 
 	fn block_id_to_number(&self, at: &BlockId<Self::Block>) -> error::Result<Option<txpool::NumberFor<Self>>> {