Relax MSRV of utils to 1.38

Cargo.toml

@@ -5,7 +5,7 @@ name = "crossbeam"
 # - Update README.md (when increasing major or minor version)
 # - Run './tools/publish.sh crossbeam <version>'
 version = "0.8.4"
-edition = "2021"
+edition = "2018"
 rust-version = "1.61"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/crossbeam-rs/crossbeam"
@@ -47,7 +47,6 @@ rand = "0.8"
 workspace = true
 
 [workspace]
-resolver = "2"
 members = [
   ".",
   "crossbeam-channel",

crossbeam-channel/Cargo.toml

@@ -5,7 +5,7 @@ name = "crossbeam-channel"
 # - Update README.md (when increasing major or minor version)
 # - Run './tools/publish.sh crossbeam-channel <version>'
 version = "0.5.13"
-edition = "2021"
+edition = "2018"
 rust-version = "1.60"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/crossbeam-rs/crossbeam"

crossbeam-channel/benchmarks/Cargo.toml

@@ -1,7 +1,7 @@
 [package]
 name = "benchmarks"
 version = "0.0.0"
-edition = "2021"
+edition = "2018"
 publish = false
 
 [dependencies]

crossbeam-deque/Cargo.toml

@@ -5,7 +5,7 @@ name = "crossbeam-deque"
 # - Update README.md (when increasing major or minor version)
 # - Run './tools/publish.sh crossbeam-deque <version>'
 version = "0.8.5"
-edition = "2021"
+edition = "2018"
 rust-version = "1.61"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/crossbeam-rs/crossbeam"

crossbeam-deque/src/deque.rs

@@ -2,6 +2,7 @@ use std::boxed::Box;
 use std::cell::{Cell, UnsafeCell};
 use std::cmp;
 use std::fmt;
+use std::iter::FromIterator;
 use std::marker::PhantomData;
 use std::mem::{self, MaybeUninit};
 use std::ptr;

crossbeam-epoch/Cargo.toml

@@ -5,7 +5,7 @@ name = "crossbeam-epoch"
 # - Update README.md (when increasing major or minor version)
 # - Run './tools/publish.sh crossbeam-epoch <version>'
 version = "0.9.18"
-edition = "2021"
+edition = "2018"
 rust-version = "1.61"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/crossbeam-rs/crossbeam"

crossbeam-queue/Cargo.toml

@@ -5,7 +5,7 @@ name = "crossbeam-queue"
 # - Update README.md (when increasing major or minor version)
 # - Run './tools/publish.sh crossbeam-queue <version>'
 version = "0.3.11"
-edition = "2021"
+edition = "2018"
 rust-version = "1.60"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/crossbeam-rs/crossbeam"

crossbeam-skiplist/Cargo.toml

@@ -5,7 +5,7 @@ name = "crossbeam-skiplist"
 # - Update README.md (when increasing major or minor version)
 # - Run './tools/publish.sh crossbeam-skiplist <version>'
 version = "0.1.3"
-edition = "2021"
+edition = "2018"
 rust-version = "1.61"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/crossbeam-rs/crossbeam"

crossbeam-skiplist/src/map.rs

@@ -2,6 +2,7 @@
 
 use std::borrow::Borrow;
 use std::fmt;
+use std::iter::FromIterator;
 use std::mem::ManuallyDrop;
 use std::ops::{Bound, RangeBounds};
 use std::ptr;

crossbeam-skiplist/src/set.rs

@@ -2,6 +2,7 @@
 
 use std::borrow::Borrow;
 use std::fmt;
+use std::iter::FromIterator;
 use std::ops::Deref;
 use std::ops::{Bound, RangeBounds};
 

crossbeam-utils/Cargo.toml

@@ -5,8 +5,8 @@ name = "crossbeam-utils"
 # - Update README.md (when increasing major or minor version)
 # - Run './tools/publish.sh crossbeam-utils <version>'
 version = "0.8.20"
-edition = "2021"
-rust-version = "1.56"
+edition = "2018"
+rust-version = "1.38"
 license = "MIT OR Apache-2.0"
 repository = "https://github.com/crossbeam-rs/crossbeam"
 homepage = "https://github.com/crossbeam-rs/crossbeam/tree/master/crossbeam-utils"

crossbeam-utils/README.md

@@ -55,7 +55,7 @@ crossbeam-utils = "0.8"
 
 Crossbeam Utils supports stable Rust releases going back at least six months,
 and every time the minimum supported Rust version is increased, a new minor
-version is released. Currently, the minimum supported Rust version is 1.56.
+version is released. Currently, the minimum supported Rust version is 1.38.
 
 ## License
 

crossbeam-utils/src/atomic/mod.rs

@@ -3,6 +3,10 @@
 //! * [`AtomicCell`], a thread-safe mutable memory location.
 //! * [`AtomicConsume`], for reading from primitive atomic types with "consume" ordering.
 
+// unsafe_op_in_unsafe_fn requires Rust 1.52, so cannot be used at crate-level,
+// but this module requires 1.60.
+#![warn(unsafe_op_in_unsafe_fn)]
+
 #[cfg(target_has_atomic = "ptr")]
 #[cfg(not(crossbeam_loom))]
 // Use "wide" sequence lock if the pointer width <= 32 for preventing its counter against wrap

crossbeam-utils/src/lib.rs

@@ -32,7 +32,7 @@
         allow(dead_code, unused_assignments, unused_variables)
     )
 ))]
-#![warn(missing_docs, unsafe_op_in_unsafe_fn)]
+#![warn(missing_docs, /* unsafe_op_in_unsafe_fn */)] // unsafe_op_in_unsafe_fn requires Rust 1.52
 #![cfg_attr(docsrs, feature(doc_cfg))]
 
 #[cfg(feature = "std")]
@@ -65,7 +65,13 @@ mod primitive {
 #[allow(unused_imports)]
 mod primitive {
     pub(crate) mod hint {
-        pub(crate) use core::hint::spin_loop;
+        // core::hint::spin_loop requires Rust 1.49
+        // pub(crate) use core::hint::spin_loop;
+        #[inline]
+        pub(crate) fn spin_loop() {
+            #[allow(deprecated)]
+            core::sync::atomic::spin_loop_hint();
+        }
     }
     pub(crate) mod sync {
         pub(crate) use core::sync::atomic;

crossbeam-utils/src/sync/mod.rs

@@ -5,6 +5,7 @@
 //! * [`WaitGroup`], for synchronizing the beginning or end of some computation.
 
 #[cfg(not(crossbeam_loom))]
+#[allow(unused_unsafe)] // once_lock.rs is also used from epoch which sets unsafe_op_in_unsafe_fn.
 mod once_lock;
 mod parker;
 #[cfg(not(crossbeam_loom))]

crossbeam-utils/src/sync/once_lock.rs

@@ -4,10 +4,13 @@
 
 use core::cell::UnsafeCell;
 use core::mem::MaybeUninit;
+use core::sync::atomic::{AtomicBool, Ordering};
 use std::sync::Once;
 
 pub(crate) struct OnceLock<T> {
     once: Once,
+    // Once::is_completed requires Rust 1.43, so use this to track of whether they have been initialized.
+    is_initialized: AtomicBool,
     value: UnsafeCell<MaybeUninit<T>>,
     // Unlike std::sync::OnceLock, we don't need PhantomData here because
     // we don't use #[may_dangle].
@@ -22,6 +25,7 @@ impl<T> OnceLock<T> {
     pub(crate) const fn new() -> Self {
         Self {
             once: Once::new(),
+            is_initialized: AtomicBool::new(false),
             value: UnsafeCell::new(MaybeUninit::uninit()),
         }
     }
@@ -46,7 +50,7 @@ impl<T> OnceLock<T> {
         F: FnOnce() -> T,
     {
         // Fast path check
-        if self.once.is_completed() {
+        if self.is_initialized() {
             // SAFETY: The inner value has been initialized
             return unsafe { self.get_unchecked() };
         }
@@ -56,31 +60,40 @@ impl<T> OnceLock<T> {
         unsafe { self.get_unchecked() }
     }
 
+    #[inline]
+    fn is_initialized(&self) -> bool {
+        self.is_initialized.load(Ordering::Acquire)
+    }
+
     #[cold]
     fn initialize<F>(&self, f: F)
     where
         F: FnOnce() -> T,
     {
         let slot = self.value.get();
+        let is_initialized = &self.is_initialized;
 
         self.once.call_once(|| {
             let value = f();
             unsafe { slot.write(MaybeUninit::new(value)) }
+            is_initialized.store(true, Ordering::Release);
         });
     }
 
     /// # Safety
     ///
     /// The value must be initialized
     unsafe fn get_unchecked(&self) -> &T {
-        debug_assert!(self.once.is_completed());
-        unsafe { (*self.value.get()).assume_init_ref() }
+        debug_assert!(self.is_initialized());
+        // assume_init_drop requires Rust 1.55
+        // unsafe { (*self.value.get()).assume_init_ref() }
+        unsafe { &*self.value.get().cast::<T>() }
     }
 }
 
 impl<T> Drop for OnceLock<T> {
     fn drop(&mut self) {
-        if self.once.is_completed() {
+        if self.is_initialized() {
             // SAFETY: The inner value has been initialized
             // assume_init_drop requires Rust 1.60
             // unsafe { (*self.value.get()).assume_init_drop() };

crossbeam-utils/src/sync/parker.rs

@@ -205,7 +205,7 @@ impl Parker {
     /// ```
     pub unsafe fn from_raw(ptr: *const ()) -> Self {
         Self {
-            unparker: unsafe { Unparker::from_raw(ptr) },
+            unparker: Unparker::from_raw(ptr),
             _marker: PhantomData,
         }
     }
@@ -293,7 +293,7 @@ impl Unparker {
     /// ```
     pub unsafe fn from_raw(ptr: *const ()) -> Self {
         Self {
-            inner: unsafe { Arc::from_raw(ptr.cast::<Inner>()) },
+            inner: Arc::from_raw(ptr.cast::<Inner>()),
         }
     }
 }

crossbeam-utils/src/thread.rs

@@ -84,7 +84,7 @@
 //! tricky because argument `s` lives *inside* the invocation of `thread::scope()` and as such
 //! cannot be borrowed by scoped threads:
 //!
-//! ```compile_fail,E0521
+//! ```compile_fail,E0373,E0521
 //! use crossbeam_utils::thread;
 //!
 //! thread::scope(|s| {