Subsystem::start takes self by-value (#1325)

* Subsystem::start takes self by-value

* fix doc-test compilation

polkadot/node/network/bridge/src/lib.rs

@@ -164,7 +164,7 @@ impl Network for Arc<sc_network::NetworkService<Block, Hash>> {
 }
 
 /// The network bridge subsystem.
-pub struct NetworkBridge<N>(Option<N>);
+pub struct NetworkBridge<N>(N);
 
 impl<N> NetworkBridge<N> {
 	/// Create a new network bridge subsystem with underlying network service.
@@ -172,7 +172,7 @@ impl<N> NetworkBridge<N> {
 	/// This assumes that the network service has had the notifications protocol for the network
 	/// bridge already registered. See [`notifications_protocol_info`](notifications_protocol_info).
 	pub fn new(net_service: N) -> Self {
-		NetworkBridge(Some(net_service))
+		NetworkBridge(net_service)
 	}
 }
 
@@ -181,18 +181,10 @@ impl<Net, Context> Subsystem<Context> for NetworkBridge<Net>
 		Net: Network,
 		Context: SubsystemContext<Message=NetworkBridgeMessage>,
 {
-	fn start(&mut self, mut ctx: Context) -> SpawnedSubsystem {
+	fn start(self, ctx: Context) -> SpawnedSubsystem {
-		SpawnedSubsystem(match self.0.take() {
+		// Swallow error because failure is fatal to the node and we log with more precision
-			None => async move { for _ in ctx.recv().await { } }.boxed(),
+		// within `run_network`.
-			Some(net) => {
+		SpawnedSubsystem(run_network(self.0, ctx).map(|_| ()).boxed())
-				// Swallow error because failure is fatal to the node and we log with more precision
-				// within `run_network`.
-				run_network(net, ctx).map(|_| ()).boxed()
-			}
-		})
-
-
-
 	}
 }
 

polkadot/node/overseer/examples/minimal-example.rs

@@ -74,7 +74,7 @@ impl Subsystem1 {
 impl<C> Subsystem<C> for Subsystem1
 	where C: SubsystemContext<Message=CandidateBackingMessage>
 {
-	fn start(&mut self, ctx: C) -> SpawnedSubsystem {
+	fn start(self, ctx: C) -> SpawnedSubsystem {
 		SpawnedSubsystem(Box::pin(async move {
 			Self::run(ctx).await;
 		}))
@@ -111,7 +111,7 @@ impl Subsystem2 {
 impl<C> Subsystem<C> for Subsystem2
 	where C: SubsystemContext<Message=CandidateValidationMessage>
 {
-	fn start(&mut self, ctx: C) -> SpawnedSubsystem {
+	fn start(self, ctx: C) -> SpawnedSubsystem {
 		SpawnedSubsystem(Box::pin(async move {
 			Self::run(ctx).await;
 		}))
@@ -129,8 +129,8 @@ fn main() {
 
 		let (overseer, _handler) = Overseer::new(
 			vec![],
-			Box::new(Subsystem2),
+			Subsystem2,
-			Box::new(Subsystem1),
+			Subsystem1,
 			spawner,
 		).unwrap();
 		let overseer_fut = overseer.run().fuse();

polkadot/node/overseer/src/lib.rs

@@ -314,7 +314,6 @@ pub type CompatibleSubsystem<M> = Box<dyn Subsystem<OverseerSubsystemContext<M>>
 /// [`Subsystem`]: trait.Subsystem.html
 #[allow(dead_code)]
 struct OverseenSubsystem<M> {
-	subsystem: CompatibleSubsystem<M>,
 	instance: Option<SubsystemInstance<M>>,
 }
 
@@ -407,7 +406,7 @@ where
 	/// 	where C: SubsystemContext<Message=CandidateValidationMessage>
 	/// {
 	///     fn start(
-	///         &mut self,
+	///         self,
 	///         mut ctx: C,
 	///     ) -> SpawnedSubsystem {
 	///         SpawnedSubsystem(Box::pin(async move {
@@ -423,7 +422,7 @@ where
 	/// 	where C: SubsystemContext<Message=CandidateBackingMessage>
 	/// {
 	///     fn start(
-	///         &mut self,
+	///         self,
 	///         mut ctx: C,
 	///     ) -> SpawnedSubsystem {
 	///         SpawnedSubsystem(Box::pin(async move {
@@ -438,8 +437,8 @@ where
 	/// let spawner = executor::ThreadPool::new().unwrap();
 	/// let (overseer, _handler) = Overseer::new(
 	///     vec![],
-	///     Box::new(ValidationSubsystem),
+	///     ValidationSubsystem,
-	///     Box::new(CandidateBackingSubsystem),
+	///     CandidateBackingSubsystem,
 	///     spawner,
 	/// ).unwrap();
 	///
@@ -458,8 +457,8 @@ where
 	/// ```
 	pub fn new(
 		leaves: impl IntoIterator<Item = BlockInfo>,
-		validation: CompatibleSubsystem<CandidateValidationMessage>,
+		validation: impl Subsystem<OverseerSubsystemContext<CandidateValidationMessage>> + Send,
-		candidate_backing: CompatibleSubsystem<CandidateBackingMessage>,
+		candidate_backing: impl Subsystem<OverseerSubsystemContext<CandidateBackingMessage>> + Send,
 		mut s: S,
 	) -> SubsystemResult<(Self, OverseerHandler)> {
 		let (events_tx, events_rx) = mpsc::channel(CHANNEL_CAPACITY);
@@ -658,7 +657,7 @@ fn spawn<S: Spawn, M: Send + 'static>(
 	spawner: &mut S,
 	futures: &mut FuturesUnordered<RemoteHandle<()>>,
 	streams: &mut StreamUnordered<mpsc::Receiver<ToOverseer>>,
-	mut s: CompatibleSubsystem<M>,
+	s: impl Subsystem<OverseerSubsystemContext<M>>,
 ) -> SubsystemResult<OverseenSubsystem<M>> {
 	let (to_tx, to_rx) = mpsc::channel(CHANNEL_CAPACITY);
 	let (from_tx, from_rx) = mpsc::channel(CHANNEL_CAPACITY);
@@ -675,7 +674,6 @@ fn spawn<S: Spawn, M: Send + 'static>(
 	});
 
 	Ok(OverseenSubsystem {
-		subsystem: s,
 		instance,
 	})
 }
@@ -692,8 +690,8 @@ mod tests {
 	impl<C> Subsystem<C> for TestSubsystem1
 		where C: SubsystemContext<Message=CandidateValidationMessage>
 	{
-		fn start(&mut self, mut ctx: C) -> SpawnedSubsystem {
+		fn start(self, mut ctx: C) -> SpawnedSubsystem {
-			let mut sender = self.0.clone();
+			let mut sender = self.0;
 			SpawnedSubsystem(Box::pin(async move {
 				let mut i = 0;
 				loop {
@@ -717,8 +715,10 @@ mod tests {
 	impl<C> Subsystem<C> for TestSubsystem2
 		where C: SubsystemContext<Message=CandidateBackingMessage>
 	{
-		fn start(&mut self, mut ctx: C) -> SpawnedSubsystem {
+		fn start(self, mut ctx: C) -> SpawnedSubsystem {
+			let sender = self.0.clone();
 			SpawnedSubsystem(Box::pin(async move {
+				let _sender = sender;
 				let mut c: usize = 0;
 				loop {
 					if c < 10 {
@@ -759,7 +759,7 @@ mod tests {
 	impl<C> Subsystem<C> for TestSubsystem4
 		where C: SubsystemContext<Message=CandidateBackingMessage>
 	{
-		fn start(&mut self, mut _ctx: C) -> SpawnedSubsystem {
+		fn start(self, mut _ctx: C) -> SpawnedSubsystem {
 			SpawnedSubsystem(Box::pin(async move {
 				// Do nothing and exit.
 			}))
@@ -777,8 +777,8 @@ mod tests {
 
 			let (overseer, mut handler) = Overseer::new(
 				vec![],
-				Box::new(TestSubsystem1(s1_tx)),
+				TestSubsystem1(s1_tx),
-				Box::new(TestSubsystem2(s2_tx)),
+				TestSubsystem2(s2_tx),
 				spawner,
 			).unwrap();
 			let overseer_fut = overseer.run().fuse();
@@ -827,8 +827,8 @@ mod tests {
 			let (s1_tx, _) = mpsc::channel(64);
 			let (overseer, _handle) = Overseer::new(
 				vec![],
-				Box::new(TestSubsystem1(s1_tx)),
+				TestSubsystem1(s1_tx),
-				Box::new(TestSubsystem4),
+				TestSubsystem4,
 				spawner,
 			).unwrap();
 			let overseer_fut = overseer.run().fuse();
@@ -846,7 +846,7 @@ mod tests {
 	impl<C> Subsystem<C> for TestSubsystem5
 		where C: SubsystemContext<Message=CandidateValidationMessage>
 	{
-		fn start(&mut self, mut ctx: C) -> SpawnedSubsystem {
+		fn start(self, mut ctx: C) -> SpawnedSubsystem {
 			let mut sender = self.0.clone();
 
 			SpawnedSubsystem(Box::pin(async move {
@@ -872,7 +872,7 @@ mod tests {
 	impl<C> Subsystem<C> for TestSubsystem6
 		where C: SubsystemContext<Message=CandidateBackingMessage>
 	{
-		fn start(&mut self, mut ctx: C) -> SpawnedSubsystem {
+		fn start(self, mut ctx: C) -> SpawnedSubsystem {
 			let mut sender = self.0.clone();
 
 			SpawnedSubsystem(Box::pin(async move {
@@ -925,8 +925,8 @@ mod tests {
 
 			let (overseer, mut handler) = Overseer::new(
 				vec![first_block],
-				Box::new(TestSubsystem5(tx_5)),
+				TestSubsystem5(tx_5),
-				Box::new(TestSubsystem6(tx_6)),
+				TestSubsystem6(tx_6),
 				spawner,
 			).unwrap();
 
@@ -1010,8 +1010,8 @@ mod tests {
 			// start with two forks of different height.
 			let (overseer, mut handler) = Overseer::new(
 				vec![first_block, second_block],
-				Box::new(TestSubsystem5(tx_5)),
+				TestSubsystem5(tx_5),
-				Box::new(TestSubsystem6(tx_6)),
+				TestSubsystem6(tx_6),
 				spawner,
 			).unwrap();
 

polkadot/node/service/src/lib.rs

@@ -272,7 +272,7 @@ struct CandidateValidationSubsystem;
 impl<C> Subsystem<C> for CandidateValidationSubsystem
 	where C: SubsystemContext<Message = CandidateValidationMessage>
 {
-	fn start(&mut self, mut ctx: C) -> SpawnedSubsystem {
+	fn start(self, mut ctx: C) -> SpawnedSubsystem {
 		SpawnedSubsystem(Box::pin(async move {
 			while let Ok(_) = ctx.recv().await {}
 		}))
@@ -284,7 +284,7 @@ struct CandidateBackingSubsystem;
 impl<C> Subsystem<C> for CandidateBackingSubsystem
 	where C: SubsystemContext<Message = CandidateBackingMessage>
 {
-	fn start(&mut self, mut ctx: C) -> SpawnedSubsystem {
+	fn start(self, mut ctx: C) -> SpawnedSubsystem {
 		SpawnedSubsystem(Box::pin(async move {
 			while let Ok(_) = ctx.recv().await {}
 		}))
@@ -295,8 +295,8 @@ fn real_overseer<S: futures::task::Spawn>(
 	leaves: impl IntoIterator<Item = BlockInfo>,
 	s: S,
 ) -> Result<(Overseer<S>, OverseerHandler), ServiceError> {
-	let validation = Box::new(CandidateValidationSubsystem);
+	let validation = CandidateValidationSubsystem;
-	let candidate_backing = Box::new(CandidateBackingSubsystem);
+	let candidate_backing = CandidateBackingSubsystem;
 	Overseer::new(leaves, validation, candidate_backing, s)
 		.map_err(|e| ServiceError::Other(format!("Failed to create an Overseer: {:?}", e)))
 }

polkadot/node/subsystem/src/lib.rs

@@ -146,5 +146,5 @@ pub trait SubsystemContext: Send + 'static {
 /// [`Subsystem`]: trait.Subsystem.html
 pub trait Subsystem<C: SubsystemContext> {
 	/// Start this `Subsystem` and return `SpawnedSubsystem`.
-	fn start(&mut self, ctx: C) -> SpawnedSubsystem;
+	fn start(self, ctx: C) -> SpawnedSubsystem;
 }