From be9e97afb28956a4f9207222c795214299799a99 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Drwi=C4=99ga?= <tomusdrw@users.noreply.github.com>
Date: Tue, 23 Jul 2019 10:59:01 +0200
Subject: [PATCH] Run each offchain worker in a separate thread. (#3169)

* Run each offchain worker in a separate thread.

* Start a thread only on supported targets.

* Flip conditions.

* Remove platform-specific code.
---
 substrate/core/offchain/src/lib.rs | 36 +++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 5 deletions(-)

diff --git a/substrate/core/offchain/src/lib.rs b/substrate/core/offchain/src/lib.rs
index e187bbc0e3..d4947e271f 100644
--- a/substrate/core/offchain/src/lib.rs
+++ b/substrate/core/offchain/src/lib.rs
@@ -128,9 +128,9 @@ impl<Client, Storage, KeyProvider, Block> OffchainWorkers<
 	Block,
 > where
 	Block: traits::Block,
-	Client: ProvideRuntimeApi,
+	Client: ProvideRuntimeApi + Send + Sync + 'static,
 	Client::Api: OffchainWorkerApi<Block>,
-	KeyProvider: AuthorityKeyProvider<Block>,
+	KeyProvider: AuthorityKeyProvider<Block> + Send,
 	Storage: client::backend::OffchainStorage + 'static,
 {
 	/// Start the offchain workers after given block.
@@ -157,9 +157,22 @@ impl<Client, Storage, KeyProvider, Block> OffchainWorkers<
 				at.clone(),
 				network_state.clone(),
 			);
-			debug!("Running offchain workers at {:?}", at);
-			let api = Box::new(api);
-			runtime.offchain_worker_with_context(&at, ExecutionContext::OffchainWorker(api), *number).unwrap();
+			debug!("Spawning offchain workers at {:?}", at);
+			let number = *number;
+			let client = self.client.clone();
+			spawn_worker(move || {
+				let runtime = client.runtime_api();
+				let api = Box::new(api);
+				debug!("Running offchain workers at {:?}", at);
+				let run = runtime.offchain_worker_with_context(
+					&at,
+					ExecutionContext::OffchainWorker(api),
+					number
+				);
+				if let Err(e) =	run {
+					log::error!("Error running offchain workers at {:?}: {:?}", at, e);
+				}
+			});
 			futures::future::Either::A(runner.process())
 		} else {
 			futures::future::Either::B(futures::future::ok(()))
@@ -167,6 +180,19 @@ impl<Client, Storage, KeyProvider, Block> OffchainWorkers<
 	}
 }
 
+/// Spawns a new offchain worker.
+///
+/// We spawn offchain workers for each block in a separate thread,
+/// since they can run for a significant amount of time
+/// in a blocking fashion and we don't want to block the runtime.
+///
+/// Note that we should avoid that if we switch to future-based runtime in the future,
+/// alternatively:
+/// TODO [ToDr] (#1458) we can consider using a thread pool instead.
+fn spawn_worker(f: impl FnOnce() -> () + Send + 'static) {
+	std::thread::spawn(f);
+}
+
 #[cfg(test)]
 mod tests {
 	use super::*;