create parallel tasks extension (#5249)

substrate/primitives/core/src/lib.rs

@@ -70,6 +70,8 @@ mod changes_trie;
 #[cfg(feature = "std")]
 pub mod traits;
 pub mod testing;
+#[cfg(feature = "std")]
+pub mod tasks;
 
 pub use self::hash::{H160, H256, H512, convert_hash};
 pub use self::uint::U256;

substrate/primitives/core/src/tasks.rs

@@ -0,0 +1,56 @@
+// Copyright 2020 Parity Technologies (UK) Ltd.
+// This file is part of Substrate.
+
+// Substrate is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+
+// Substrate is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License
+// along with Substrate.  If not, see <http://www.gnu.org/licenses/>.
+
+//! Module for low-level asynchronous processing.
+
+use crate::traits::CloneableSpawn;
+use futures::{executor, task};
+
+/// Simple task executor.
+///
+/// Uses single thread for scheduling tasks. Can be cloned and used in
+/// runtime host (implements `CloneableSpawn`).
+#[derive(Debug, Clone)]
+pub struct Executor {
+	pool: executor::ThreadPool,
+}
+
+impl Executor {
+	fn new() -> Self {
+		Self {
+			pool: executor::ThreadPool::builder().pool_size(1).create()
+				.expect("Failed to create task executor")
+		}
+	}
+}
+
+impl task::Spawn for Executor {
+	fn spawn_obj(&self, future: task::FutureObj<'static, ()>)
+	-> Result<(), task::SpawnError> {
+		self.pool.spawn_obj(future)
+	}
+}
+
+impl CloneableSpawn for Executor {
+	fn clone(&self) -> Box<dyn CloneableSpawn> {
+		Box::new(Clone::clone(self))
+	}
+}
+
+/// Create tasks executor.
+pub fn executor() -> Box<dyn CloneableSpawn> {
+	Box::new(Executor::new())
+}

substrate/primitives/core/src/traits.rs

@@ -212,3 +212,21 @@ impl CallInWasmExt {
 		Self(Box::new(inner))
 	}
 }
+
+/// Something that can spawn tasks and also can be cloned.
+pub trait CloneableSpawn: futures::task::Spawn + Send + Sync {
+	/// Clone as heap-allocated handle.
+	fn clone(&self) -> Box<dyn CloneableSpawn>;
+}
+
+sp_externalities::decl_extension! {
+	/// Task executor extension.
+	pub struct TaskExecutorExt(Box<dyn CloneableSpawn>);
+}
+
+impl TaskExecutorExt {
+	/// New instance of task executor extension.
+	pub fn new(spawn_handle: Box<dyn CloneableSpawn>) -> Self {
+		Self(spawn_handle)
+	}
+}