Switch from OnceCell to LazyLock in bevy_tasks (#18506)

Remove `critical-section` from required dependencies, allowing linking
without any features.

- Switched from `OnceCell` to `LazyLock`
- Removed `std` feature from `bevy_dylib` (proof that it works)

- CI

crates/bevy_dylib/Cargo.toml

@@ -12,11 +12,7 @@ keywords = ["bevy"]
 crate-type = ["dylib"]
 
 [dependencies]
-# feature std is needed to avoid an issue when linking critical_section
+bevy_internal = { path = "../bevy_internal", version = "0.16.0-rc.1", default-features = false }
-# bevy_dylib is not expected to work in no_std
-bevy_internal = { path = "../bevy_internal", version = "0.16.0-rc.1", default-features = false, features = [
-  "std",
-] }
 
 [lints]
 workspace = true

crates/bevy_tasks/Cargo.toml

@@ -26,12 +26,7 @@ async_executor = ["std", "dep:async-executor"]
 ## Allows access to the `std` crate. Enabling this feature will prevent compilation
 ## on `no_std` targets, but provides access to certain additional features on
 ## supported platforms.
-std = [
+std = ["futures-lite/std", "async-task/std", "bevy_platform_support/std"]
-  "futures-lite/std",
-  "async-task/std",
-  "bevy_platform_support/std",
-  "once_cell/std",
-]
 
 ## `critical-section` provides the building blocks for synchronization primitives
 ## on all platforms, including `no_std`.
@@ -65,9 +60,6 @@ async-channel = { version = "2.3.0", optional = true }
 async-io = { version = "2.0.0", optional = true }
 concurrent-queue = { version = "2.0.0", optional = true }
 atomic-waker = { version = "1", default-features = false }
-once_cell = { version = "1.18", default-features = false, features = [
-  "critical-section",
-] }
 crossbeam-queue = { version = "0.3", default-features = false, features = [
   "alloc",
 ] }

crates/bevy_tasks/src/edge_executor.rs

@@ -22,9 +22,8 @@ use core::{
 
 use async_task::{Runnable, Task};
 use atomic_waker::AtomicWaker;
-use bevy_platform_support::sync::Arc;
+use bevy_platform_support::sync::{Arc, LazyLock};
 use futures_lite::FutureExt;
-use once_cell::sync::OnceCell;
 
 /// An async executor.
 ///
@@ -51,7 +50,7 @@ use once_cell::sync::OnceCell;
 ///     }));
 /// ```
 pub struct Executor<'a, const C: usize = 64> {
-    state: OnceCell<Arc<State<C>>>,
+    state: LazyLock<Arc<State<C>>>,
     _invariant: PhantomData<core::cell::UnsafeCell<&'a ()>>,
 }
 
@@ -67,7 +66,7 @@ impl<'a, const C: usize> Executor<'a, C> {
     /// ```
     pub const fn new() -> Self {
         Self {
-            state: OnceCell::new(),
+            state: LazyLock::new(|| Arc::new(State::new())),
             _invariant: PhantomData,
         }
     }
@@ -284,7 +283,7 @@ impl<'a, const C: usize> Executor<'a, C> {
 
     /// Returns a reference to the inner state.
     fn state(&self) -> &Arc<State<C>> {
-        self.state.get_or_init(|| Arc::new(State::new()))
+        &self.state
     }
 }
 
@@ -526,15 +525,15 @@ mod drop_tests {
     use core::task::{Poll, Waker};
     use std::sync::Mutex;
 
+    use bevy_platform_support::sync::LazyLock;
     use futures_lite::future;
-    use once_cell::sync::Lazy;
 
     use super::{Executor, Task};
 
     #[test]
     fn leaked_executor_leaks_everything() {
         static DROP: AtomicUsize = AtomicUsize::new(0);
-        static WAKER: Lazy<Mutex<Option<Waker>>> = Lazy::new(Default::default);
+        static WAKER: LazyLock<Mutex<Option<Waker>>> = LazyLock::new(Default::default);
 
         let ex: Executor = Default::default();