feat: add crossbeam feature, enabled by default

CHANGELOG.md

@@ -6,6 +6,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+- Add `crossbeam` feature, enabled by default, to enable `crossbeam-utils` dependency and `AtomicLazy` struct.
+
 ## [0.2.0] - 2025-02-13
 
 ### Fixed

Cargo.toml

@@ -16,7 +16,7 @@ include = [
 
 [dependencies]
 portable-atomic = "1"
-crossbeam-utils = { version = "0.8.15", default-features = false }
+crossbeam-utils = { version = "0.8.15", default-features = false, optional = true }
 serde = { version = "1.0.171", optional = true }
 
 [target.'cfg(loom)'.dependencies]
@@ -26,5 +26,6 @@ loom =  "0.7.0"
 serde_json = "1.0.104"
 
 [features]
-default = []
-serde = ["dep:serde"]
+default = ["crossbeam"]
+crossbeam = ["dep:crossbeam-utils"]
+serde = ["dep:serde"] 

README.md

@@ -17,9 +17,10 @@ lock-free (if you know a way, please tell me).
 Both types can be used in a non-blocking way, but there are some
 blocking calls that should not be used from interrupt handlers or
 other contexts where blocking will lead to a deadlock. Blocking is
-based on
-[`crossbeam::utils::Backoff`](https://docs.rs/crossbeam/latest/crossbeam/utils/struct.Backoff.html),
-and will be reduced to a spinlock in `#[no_std]` environments.
+based on [`crossbeam::utils::Backoff`] and will be reduced to a spinlock
+in `#[no_std]` environments. This is enabled via `crossbeam` feature.
+
+[`crossbeam::utils::Backoff`]: https://docs.rs/crossbeam/latest/crossbeam/utils/struct.Backoff.html,
 
 ### Examples
 #### `AtomicOnceCell`

src/lib.rs

@@ -15,9 +15,10 @@
 //! Both types can be used in a non-blocking way, but there are some
 //! blocking calls that should not be used from interrupt handlers or
 //! other contexts where blocking will lead to a deadlock. Blocking is
-//! based on
-//! [`crossbeam::utils::Backoff`](https://docs.rs/crossbeam/latest/crossbeam/utils/struct.Backoff.html),
-//! and will be reduced to a spinlock in `#[no_std]` environments.
+//! based on [`crossbeam::utils::Backoff`] and will be reduced to a spinlock
+//! in `#[no_std]` environments. This is enabled via `crossbeam` feature.
+//!
+//! [`crossbeam::utils::Backoff`]: https://docs.rs/crossbeam/latest/crossbeam/utils/struct.Backoff.html,
 //!
 //! ## Examples
 //! ### `AtomicOnceCell`
@@ -48,13 +49,13 @@
 
 #![no_std]
 
-use core::{
-    cell::{Cell, UnsafeCell},
-    fmt,
-    ops::Deref,
-    sync::atomic::Ordering,
+use core::{cell::UnsafeCell, fmt, sync::atomic::Ordering};
+
+#[cfg(feature = "crossbeam")]
+use {
+    core::{cell::Cell, ops::Deref},
+    crossbeam_utils::Backoff,
 };
-use crossbeam_utils::Backoff;
 
 #[cfg(not(loom))]
 use portable_atomic::AtomicU8;
@@ -269,6 +270,7 @@ impl<T> AtomicOnceCell<T> {
     /// let value = cell.get_or_init(|| unreachable!());
     /// assert_eq!(value, &92);
     /// ```
+    #[cfg(feature = "crossbeam")]
     pub fn get_or_init<F>(&self, f: F) -> &T
     where
         F: FnOnce() -> T,
@@ -311,6 +313,7 @@ impl<T> AtomicOnceCell<T> {
     /// assert_eq!(value, Ok(&92));
     /// assert_eq!(cell.get(), Some(&92))
     /// ```
+    #[cfg(feature = "crossbeam")]
     pub fn get_or_try_init<F, E>(&self, f: F) -> Result<&T, E>
     where
         F: FnOnce() -> Result<T, E>,
@@ -456,12 +459,13 @@ impl<T: Serialize> Serialize for AtomicOnceCell<T> {
 ///                          // asynchronously at some point
 ///     // [...]
 /// }
-
+#[cfg(feature = "crossbeam")]
 pub struct AtomicLazy<T, F = fn() -> T> {
     cell: AtomicOnceCell<T>,
     init: Cell<Option<F>>,
 }
 
+#[cfg(feature = "crossbeam")]
 impl<T: fmt::Debug, F> fmt::Debug for AtomicLazy<T, F> {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         f.debug_struct("AtomicLazy")
@@ -471,20 +475,23 @@ impl<T: fmt::Debug, F> fmt::Debug for AtomicLazy<T, F> {
     }
 }
 
+#[cfg(feature = "crossbeam")]
 impl<T: Default> Default for AtomicLazy<T> {
     /// Creates a new lazy value using `Default` as the initializing function.
     fn default() -> AtomicLazy<T> {
         AtomicLazy::new(T::default)
     }
 }
 
+#[cfg(feature = "crossbeam")]
 unsafe impl<T, F> Sync for AtomicLazy<T, F>
 where
     T: Send + Sync,
     F: Send,
 {
 }
 
+#[cfg(feature = "crossbeam")]
 impl<T, F> AtomicLazy<T, F> {
     /// Creates a new lazy value with the given initializing function.
     ///
@@ -518,6 +525,7 @@ impl<T, F> AtomicLazy<T, F> {
     }
 }
 
+#[cfg(feature = "crossbeam")]
 impl<T, F> AtomicLazy<T, F>
 where
     F: FnOnce() -> T,
@@ -585,6 +593,7 @@ where
     }
 }
 
+#[cfg(feature = "crossbeam")]
 impl<T, F> Deref for AtomicLazy<T, F>
 where
     F: FnOnce() -> T,