allow jobs to spawn sub-tasks (#2030)

* allow jobs to spawn sub-tasks

* fix fallout in subsytems

polkadot/node/core/backing/src/lib.rs

@@ -52,6 +52,7 @@ use polkadot_node_subsystem_util::{
 	request_from_runtime,
 	Validator,
 	delegated_subsystem,
+	FromJobCommand,
 	metrics::{self, prometheus},
 };
 use statement_table::{
@@ -197,9 +198,9 @@ enum FromJob {
 	StatementDistribution(StatementDistributionMessage),
 }
 
-impl From<FromJob> for AllMessages {
+impl From<FromJob> for FromJobCommand {
-	fn from(f: FromJob) -> Self {
+	fn from(f: FromJob) -> FromJobCommand {
-		match f {
+		FromJobCommand::SendMessage(match f {
 			FromJob::AvailabilityStore(msg) => AllMessages::AvailabilityStore(msg),
 			FromJob::RuntimeApiMessage(msg) => AllMessages::RuntimeApi(msg),
 			FromJob::CandidateValidation(msg) => AllMessages::CandidateValidation(msg),
@@ -207,7 +208,7 @@ impl From<FromJob> for AllMessages {
 			FromJob::StatementDistribution(msg) => AllMessages::StatementDistribution(msg),
 			FromJob::PoVDistribution(msg) => AllMessages::PoVDistribution(msg),
 			FromJob::Provisioner(msg) => AllMessages::Provisioner(msg),
-		}
+		})
 	}
 }
 

polkadot/node/core/bitfield-signing/src/lib.rs

@@ -30,7 +30,7 @@ use polkadot_node_subsystem::{
 	errors::RuntimeApiError,
 };
 use polkadot_node_subsystem_util::{
-	self as util, JobManager, JobTrait, ToJobTrait, Validator,
+	self as util, JobManager, JobTrait, ToJobTrait, Validator, FromJobCommand,
 	metrics::{self, prometheus},
 };
 use polkadot_primitives::v1::{AvailabilityBitfield, CoreState, Hash, ValidatorIndex};
@@ -90,14 +90,14 @@ pub enum FromJob {
 	RuntimeApi(RuntimeApiMessage),
 }
 
-impl From<FromJob> for AllMessages {
+impl From<FromJob> for FromJobCommand {
-	fn from(from_job: FromJob) -> AllMessages {
+	fn from(from_job: FromJob) -> FromJobCommand {
-		match from_job {
+		FromJobCommand::SendMessage(match from_job {
 			FromJob::AvailabilityStore(asm) => AllMessages::AvailabilityStore(asm),
 			FromJob::BitfieldDistribution(bdm) => AllMessages::BitfieldDistribution(bdm),
 			FromJob::CandidateBacking(cbm) => AllMessages::CandidateBacking(cbm),
 			FromJob::RuntimeApi(ram) => AllMessages::RuntimeApi(ram),
-		}
+		})
 	}
 }
 

polkadot/node/core/candidate-selection/src/lib.rs

@@ -30,7 +30,7 @@ use polkadot_node_subsystem::{
 	},
 };
 use polkadot_node_subsystem_util::{
-	self as util, delegated_subsystem, JobTrait, ToJobTrait,
+	self as util, delegated_subsystem, JobTrait, ToJobTrait, FromJobCommand,
 	metrics::{self, prometheus},
 };
 use polkadot_primitives::v1::{CandidateReceipt, CollatorId, Hash, Id as ParaId, PoV};
@@ -89,12 +89,12 @@ enum FromJob {
 	Collator(CollatorProtocolMessage),
 }
 
-impl From<FromJob> for AllMessages {
+impl From<FromJob> for FromJobCommand {
-	fn from(from_job: FromJob) -> AllMessages {
+	fn from(from_job: FromJob) -> FromJobCommand {
-		match from_job {
+		FromJobCommand::SendMessage(match from_job {
 			FromJob::Backing(msg) => AllMessages::CandidateBacking(msg),
 			FromJob::Collator(msg) => AllMessages::CollatorProtocol(msg),
-		}
+		})
 	}
 }
 

polkadot/node/core/provisioner/src/lib.rs

@@ -33,7 +33,7 @@ use polkadot_node_subsystem::{
 };
 use polkadot_node_subsystem_util::{
 	self as util,
-	delegated_subsystem,
+	delegated_subsystem, FromJobCommand,
 	request_availability_cores, request_persisted_validation_data, JobTrait, ToJobTrait,
 	metrics::{self, prometheus},
 };
@@ -98,12 +98,12 @@ enum FromJob {
 	Runtime(RuntimeApiMessage),
 }
 
-impl From<FromJob> for AllMessages {
+impl From<FromJob> for FromJobCommand {
-	fn from(from_job: FromJob) -> AllMessages {
+	fn from(from_job: FromJob) -> FromJobCommand {
-		match from_job {
+		FromJobCommand::SendMessage(match from_job {
 			FromJob::ChainApi(cam) => AllMessages::ChainApi(cam),
 			FromJob::Runtime(ram) => AllMessages::RuntimeApi(ram),
-		}
+		})
 	}
 }
 

polkadot/node/subsystem-util/src/lib.rs

@@ -476,6 +476,16 @@ pub mod metrics {
 	}
 }
 
+/// Commands from a job to the broader subsystem.
+pub enum FromJobCommand {
+	/// Send a message to another subsystem.
+	SendMessage(AllMessages),
+	/// Spawn a child task on the executor.
+	Spawn(&'static str, Pin<Box<dyn Future<Output = ()> + Send>>),
+	/// Spawn a blocking child task on the executor's dedicated thread pool.
+	SpawnBlocking(&'static str, Pin<Box<dyn Future<Output = ()> + Send>>),
+}
+
 /// This trait governs jobs.
 ///
 /// Jobs are instantiated and killed automatically on appropriate overseer messages.
@@ -485,7 +495,7 @@ pub trait JobTrait: Unpin {
 	/// Message type to the job. Typically a subset of AllMessages.
 	type ToJob: 'static + ToJobTrait + Send;
 	/// Message type from the job. Typically a subset of AllMessages.
-	type FromJob: 'static + Into<AllMessages> + Send;
+	type FromJob: 'static + Into<FromJobCommand> + Send;
 	/// Job runtime error.
 	type Error: 'static + std::error::Error + Send;
 	/// Extra arguments this job needs to run properly.
@@ -752,8 +762,11 @@ where
 					).await {
 						break
 					},
-				outgoing = jobs.next().fuse() =>
+				outgoing = jobs.next().fuse() => {
-					Self::handle_outgoing(outgoing, &mut ctx).await,
+					if let Err(e) = Self::handle_from_job(outgoing, &mut ctx).await {
+						tracing::warn!(err = ?e, "failed to handle command from job");
+					}
+				}
 				complete => break,
 			}
 		}
@@ -863,13 +876,19 @@ where
 		false
 	}
 
-	// handle an outgoing message.
+	// handle a command from a job.
-	async fn handle_outgoing(
+	async fn handle_from_job(
 		outgoing: Option<Job::FromJob>,
 		ctx: &mut Context,
-	) {
+	) -> SubsystemResult<()> {
-		let msg = outgoing.expect("the Jobs stream never ends; qed");
+		let cmd: FromJobCommand = outgoing.expect("the Jobs stream never ends; qed").into();
-		ctx.send_message(msg.into()).await;
+		match cmd {
+			FromJobCommand::SendMessage(msg) => ctx.send_message(msg).await,
+			FromJobCommand::Spawn(name, task) => ctx.spawn(name, task).await?,
+			FromJobCommand::SpawnBlocking(name, task) => ctx.spawn_blocking(name, task).await?,
+		}
+
+		Ok(())
 	}
 }
 
@@ -1031,7 +1050,7 @@ impl<F: Future> Future for Timeout<F> {
 
 #[cfg(test)]
 mod tests {
-	use super::{JobManager, JobTrait, JobsError, TimeoutExt, ToJobTrait};
+	use super::{JobManager, JobTrait, JobsError, TimeoutExt, ToJobTrait, FromJobCommand};
 	use thiserror::Error;
 	use polkadot_node_subsystem::{
 		messages::{AllMessages, CandidateSelectionMessage},
@@ -1101,9 +1120,9 @@ mod tests {
 		}
 	}
 
-	// FromJob must be infallibly convertable into AllMessages.
+	// FromJob must be infallibly convertable into FromJobCommand.
 	//
-	// It exists to be a type-safe subset of AllMessages that this job is specified to send.
+	// It exists to be a type-safe subset of FromJobCommand that this job is specified to send.
 	//
 	// Note: the Clone impl here is not generally required; it's just ueful for this test context because
 	// we include it in the RunArgs
@@ -1112,10 +1131,12 @@ mod tests {
 		Test,
 	}
 
-	impl From<FromJob> for AllMessages {
+	impl From<FromJob> for FromJobCommand {
-		fn from(from_job: FromJob) -> AllMessages {
+		fn from(from_job: FromJob) -> FromJobCommand {
 			match from_job {
-				FromJob::Test => AllMessages::CandidateSelection(CandidateSelectionMessage::default()),
+				FromJob::Test => FromJobCommand::SendMessage(
+					AllMessages::CandidateSelection(CandidateSelectionMessage::default())
+				),
 			}
 		}
 	}