Add RuntimeCell and RuntimeRefCell

frame/support/src/lib.rs

@@ -66,6 +66,7 @@ pub mod inherent;
 pub mod error;
 pub mod instances;
 pub mod migrations;
+pub mod sync;
 pub mod traits;
 pub mod weights;
 

frame/support/src/storage/mod.rs

@@ -48,46 +48,39 @@ pub mod unhashed;
 pub mod weak_bounded_vec;
 
 mod transaction_level_tracker {
-	use core::sync::atomic::{AtomicU32, Ordering};
+	use crate::sync::RuntimeCell;
 
 	type Layer = u32;
-	static NUM_LEVELS: AtomicU32 = AtomicU32::new(0);
+	static NUM_LEVELS: RuntimeCell<u32> = RuntimeCell::new(0);
 	const TRANSACTIONAL_LIMIT: Layer = 255;
 
 	pub fn get_transaction_level() -> Layer {
-		NUM_LEVELS.load(Ordering::SeqCst)
+		NUM_LEVELS.get()
 	}
 
 	/// Increments the transaction level. Returns an error if levels go past the limit.
 	///
 	/// Returns a guard that when dropped decrements the transaction level automatically.
 	pub fn inc_transaction_level() -> Result<StorageLayerGuard, ()> {
-		NUM_LEVELS
-			.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |existing_levels| {
-				if existing_levels >= TRANSACTIONAL_LIMIT {
-					return None
-				}
-				// Cannot overflow because of check above.
-				Some(existing_levels + 1)
-			})
-			.map_err(|_| ())?;
+		let existing_levels = get_transaction_level();
+		if existing_levels >= TRANSACTIONAL_LIMIT {
+			return Err(())
+		}
+		// Cannot overflow because of check above.
+		NUM_LEVELS.set(existing_levels + 1);
 		Ok(StorageLayerGuard)
 	}
 
 	fn dec_transaction_level() {
-		NUM_LEVELS
-			.fetch_update(Ordering::SeqCst, Ordering::SeqCst, |existing_levels| {
-				if existing_levels == 0 {
-					log::warn!(
-					"We are underflowing with calculating transactional levels. Not great, but let's not panic...",
-				);
-					None
-				} else {
-					// Cannot underflow because of checks above.
-					Some(existing_levels - 1)
-				}
-			})
-			.ok();
+		let existing_levels = get_transaction_level();
+		if existing_levels == 0 {
+			log::warn!(
+				"We are underflowing with calculating transactional levels. Not great, but let's not panic...",
+			);
+		} else {
+			// Cannot underflow because of checks above.
+			NUM_LEVELS.set(existing_levels - 1);
+		}
 	}
 
 	pub fn is_transactional() -> bool {

frame/support/src/sync.rs

@@ -0,0 +1,76 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2017-2022 Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Types used to sync access to shared data. All of these types rely on the assumption
+//! that no data parallelism exists within the runtime.
+
+use sp_std::{
+	cell::{Cell, RefCell},
+	ops::{Deref, DerefMut},
+};
+
+/// A [`Sync`] version of [`Cell`]. Safe to use within the runtime.
+pub struct RuntimeCell<T>(Cell<T>);
+
+impl<T> RuntimeCell<T> {
+	/// See [`Cell::new`]
+	pub const fn new(value: T) -> Self {
+		Self(Cell::new(value))
+	}
+}
+
+unsafe impl<T> Sync for RuntimeCell<T> {}
+
+impl<T> Deref for RuntimeCell<T> {
+	type Target = Cell<T>;
+
+	fn deref(&self) -> &Self::Target {
+		&self.0
+	}
+}
+
+impl<T> DerefMut for RuntimeCell<T> {
+	fn deref_mut(&mut self) -> &mut Self::Target {
+		&mut self.0
+	}
+}
+
+/// A [`Sync`] version of [`RefCell`]. Safe to use within the runtime.
+pub struct RuntimeRefCell<T>(RefCell<T>);
+
+impl<T> RuntimeRefCell<T> {
+	/// See [`RefCell::new`]
+	pub const fn new(value: T) -> Self {
+		Self(RefCell::new(value))
+	}
+}
+
+unsafe impl<T> Sync for RuntimeRefCell<T> {}
+
+impl<T> Deref for RuntimeRefCell<T> {
+	type Target = RefCell<T>;
+
+	fn deref(&self) -> &Self::Target {
+		&self.0
+	}
+}
+
+impl<T> DerefMut for RuntimeRefCell<T> {
+	fn deref_mut(&mut self) -> &mut Self::Target {
+		&mut self.0
+	}
+}