utils: handle race condition gracefully (#1583)

* utils: handle race condition gracefully

* utils: add a test

* update Cargo.lock

* utils: remove a warning

* utils: init logger in tests

* utils: update the outdated comment

* util: wait for both subsystem and test_future to finish

* Revert "util: wait for both subsystem and test_future to finish"

This reverts commit 075b39242cd7200e3f4c24ea42f702c3124ce41c.

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

@@ -611,10 +611,13 @@ impl<Spawner: SpawnNamed, Job: 'static + JobTrait> Jobs<Spawner, Job> {
 	}
 
 	/// Send a message to the appropriate job for this `parent_hash`.
+	/// Will not return an error if the job is not running.
 	async fn send_msg(&mut self, parent_hash: Hash, msg: Job::ToJob) -> Result<(), Error> {
 		match self.running.get_mut(&parent_hash) {
 			Some(job) => job.send_msg(msg).await?,
-			None => return Err(Error::JobNotFound(parent_hash)),
+			None => {
+				// don't bring down the subsystem, this can happen to due a race condition
+			},
 		}
 		Ok(())
 	}
@@ -1140,6 +1143,14 @@ mod tests {
 		run_args: HashMap<Hash, Vec<FromJob>>,
 		test: impl FnOnce(OverseerHandle, mpsc::Receiver<(Option<Hash>, JobsError<Error>)>) -> T,
 	) {
+		let _ = env_logger::builder()
+			.is_test(true)
+			.filter(
+				None,
+				log::LevelFilter::Trace,
+			)
+			.try_init();
+
 		let pool = sp_core::testing::TaskExecutor::new();
 		let (context, overseer_handle) = make_subsystem_context(pool.clone());
 		let (err_tx, err_rx) = mpsc::channel(16);
@@ -1148,9 +1159,7 @@ mod tests {
 		let test_future = test(overseer_handle, err_rx);
 		let timeout = Delay::new(Duration::from_secs(2));
 
-		futures::pin_mut!(test_future);
-		futures::pin_mut!(subsystem);
-		futures::pin_mut!(timeout);
+		futures::pin_mut!(subsystem, test_future, timeout);
 
 		executor::block_on(async move {
 			futures::select! {
@@ -1213,6 +1222,29 @@ mod tests {
 		});
 	}
 
+	#[test]
+	fn sending_to_a_non_running_job_do_not_stop_the_subsystem() {
+		let run_args = HashMap::new();
+
+		test_harness(run_args, |mut overseer_handle, err_rx| async move {
+			// send to a non running job
+			overseer_handle
+				.send(FromOverseer::Communication { 
+					msg: Default::default(),
+				})
+				.await;
+
+			// the subsystem is still alive
+			assert_matches!(
+				overseer_handle.recv().await,
+				AllMessages::CandidateSelection(_)
+			);
+
+			let errs: Vec<_> = err_rx.collect().await;
+			assert_eq!(errs.len(), 0);
+		});
+	}
+
 	#[test]
 	fn test_subsystem_impl_and_name_derivation() {
 		let pool = sp_core::testing::TaskExecutor::new();