Pass an executor through the Configuration (#4688)

* Pass an executor through the Configuration

* Make tasks_executor mandatory

* Fix tests

substrate/client/service/src/builder.rs

@@ -1147,7 +1147,11 @@ ServiceBuilder<
 			essential_failed_rx,
 			to_spawn_tx,
 			to_spawn_rx,
-			to_poll: Vec::new(),
+			tasks_executor: if let Some(exec) = config.tasks_executor {
+				exec
+			} else {
+				return Err(Error::TasksExecutorRequired);
+			},
 			rpc_handlers,
 			_rpc: rpc,
 			_telemetry: telemetry,

substrate/client/service/src/config.rs

@@ -21,7 +21,7 @@ pub use sc_client_db::{kvdb::KeyValueDB, PruningMode};
 pub use sc_network::config::{ExtTransport, NetworkConfiguration, Roles};
 pub use sc_executor::WasmExecutionMethod;
 
-use std::{path::{PathBuf, Path}, net::SocketAddr, sync::Arc};
+use std::{future::Future, path::{PathBuf, Path}, pin::Pin, net::SocketAddr, sync::Arc};
 pub use sc_transaction_pool::txpool::Options as TransactionPoolOptions;
 use sc_chain_spec::{ChainSpec, RuntimeGenesis, Extension, NoExtension};
 use sp_core::crypto::Protected;
@@ -29,7 +29,6 @@ use target_info::Target;
 use sc_telemetry::TelemetryEndpoints;
 
 /// Service configuration.
-#[derive(Clone)]
 pub struct Configuration<C, G, E = NoExtension> {
 	/// Implementation name
 	pub impl_name: &'static str,
@@ -39,6 +38,8 @@ pub struct Configuration<C, G, E = NoExtension> {
 	pub impl_commit: &'static str,
 	/// Node roles.
 	pub roles: Roles,
+	/// How to spawn background tasks. Mandatory, otherwise creating a `Service` will error.
+	pub tasks_executor: Option<Box<dyn Fn(Pin<Box<dyn Future<Output = ()> + Send>>) + Send>>,
 	/// Extrinsic pool configuration.
 	pub transaction_pool: TransactionPoolOptions,
 	/// Network configuration.
@@ -160,6 +161,7 @@ impl<C, G, E> Configuration<C, G, E> where
 			config_dir: config_dir.clone(),
 			name: Default::default(),
 			roles: Roles::FULL,
+			tasks_executor: None,
 			transaction_pool: Default::default(),
 			network: Default::default(),
 			keystore: KeystoreConfig::None,

substrate/client/service/src/error.rs

@@ -40,6 +40,9 @@ pub enum Error {
 	/// Best chain selection strategy is missing.
 	#[display(fmt="Best chain selection strategy (SelectChain) is not provided.")]
 	SelectChainRequired,
+	/// Tasks executor is missing.
+	#[display(fmt="Tasks executor hasn't been provided.")]
+	TasksExecutorRequired,
 	/// Other error.
 	Other(String),
 }

substrate/client/service/src/lib.rs

@@ -38,7 +38,7 @@ use parking_lot::Mutex;
 use sc_client::Client;
 use exit_future::Signal;
 use futures::{
-	Future, FutureExt, Stream, StreamExt, TryFutureExt,
+	Future, FutureExt, Stream, StreamExt,
 	future::select, channel::mpsc,
 	compat::*,
 	sink::SinkExt,
@@ -95,10 +95,8 @@ pub struct Service<TBl, TCl, TSc, TNetStatus, TNet, TTxPool, TOc> {
 	to_spawn_tx: mpsc::UnboundedSender<Pin<Box<dyn Future<Output = ()> + Send>>>,
 	/// Receiver for futures that must be spawned as background tasks.
 	to_spawn_rx: mpsc::UnboundedReceiver<Pin<Box<dyn Future<Output = ()> + Send>>>,
-	/// List of futures to poll from `poll`.
-	/// If spawning a background task is not possible, we instead push the task into this `Vec`.
-	/// The elements must then be polled manually.
-	to_poll: Vec<Pin<Box<dyn Future<Output = ()> + Send>>>,
+	/// How to spawn background tasks.
+	tasks_executor: Box<dyn Fn(Pin<Box<dyn Future<Output = ()> + Send>>) + Send>,
 	rpc_handlers: sc_rpc_server::RpcHandler<sc_rpc::Metadata>,
 	_rpc: Box<dyn std::any::Any + Send + Sync>,
 	_telemetry: Option<sc_telemetry::Telemetry>,
@@ -322,22 +320,7 @@ impl<TBl: Unpin, TCl, TSc: Unpin, TNetStatus, TNet, TTxPool, TOc> Future for
 		}
 
 		while let Poll::Ready(Some(task_to_spawn)) = Pin::new(&mut this.to_spawn_rx).poll_next(cx) {
-			// TODO: Update to tokio 0.2 when libp2p get switched to std futures (#4383)
-			let executor = tokio_executor::DefaultExecutor::current();
-			use futures01::future::Executor;
-			if let Err(err) = executor.execute(task_to_spawn.unit_error().compat()) {
-				debug!(
-					target: "service",
-					"Failed to spawn background task: {:?}; falling back to manual polling",
-					err
-				);
-				this.to_poll.push(Box::pin(err.into_future().compat().map(drop)));
-			}
-		}
-
-		// Polling all the `to_poll` futures.
-		while let Some(pos) = this.to_poll.iter_mut().position(|t| Pin::new(t).poll(cx).is_ready()) {
-			let _ = this.to_poll.remove(pos);
+			(this.tasks_executor)(task_to_spawn);
 		}
 
 		// The service future never ends.