Initial import of crossbeam-utils-0.8.1.
Bug: 155309706
Change-Id: I87640fade6ca771349c89b49a8dc4a1b5bc88421
diff --git a/.cargo_vcs_info.json b/.cargo_vcs_info.json
new file mode 100644
index 0000000..3dcef5c
--- /dev/null
+++ b/.cargo_vcs_info.json
@@ -0,0 +1,5 @@
+{
+ "git": {
+ "sha1": "99c3230b263202aca56497b1f8e418a7b3647a23"
+ }
+}
diff --git a/CHANGELOG.md b/CHANGELOG.md
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+++ b/CHANGELOG.md
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+# Version 0.8.1
+
+- Make `AtomicCell::is_lock_free` always const fn. (#600)
+- Fix a bug in `seq_lock_wide`. (#596)
+- Remove `const_fn` dependency. (#600)
+- `crossbeam-utils` no longer fails to compile if unable to determine rustc version. Instead, it now displays a warning. (#604)
+
+# Version 0.8.0
+
+- Bump the minimum supported Rust version to 1.36.
+- Remove deprecated `AtomicCell::get_mut()` and `Backoff::is_complete()` methods
+- Remove `alloc` feature.
+- Make `CachePadded::new()` const function.
+- Make `AtomicCell::is_lock_free()` const function at 1.46+.
+- Implement `From<T>` for `AtomicCell<T>`.
+
+# Version 0.7.2
+
+- Fix bug in release (yanking 0.7.1)
+
+# Version 0.7.1
+
+- Bump `autocfg` dependency to version 1.0. (#460)
+- Make `AtomicCell` lockfree for u8, u16, u32, u64 sized values at 1.34+. (#454)
+
+# Version 0.7.0
+
+- Bump the minimum required version to 1.28.
+- Fix breakage with nightly feature due to rust-lang/rust#65214.
+- Apply `#[repr(transparent)]` to `AtomicCell`.
+- Make `AtomicCell::new()` const function at 1.31+.
+
+# Version 0.6.6
+
+- Add `UnwindSafe` and `RefUnwindSafe` impls for `AtomicCell`.
+- Add `AtomicCell::as_ptr()`.
+- Add `AtomicCell::take()`.
+- Fix a bug in `AtomicCell::compare_exchange()` and `AtomicCell::compare_and_swap()`.
+- Various documentation improvements.
+
+# Version 0.6.5
+
+- Rename `Backoff::is_complete()` to `Backoff::is_completed()`.
+
+# Version 0.6.4
+
+- Add `WaitGroup`, `ShardedLock`, and `Backoff`.
+- Add `fetch_*` methods for `AtomicCell<i128>` and `AtomicCell<u128>`.
+- Expand documentation.
+
+# Version 0.6.3
+
+- Add `AtomicCell`.
+- Improve documentation.
+
+# Version 0.6.2
+
+- Add `Parker`.
+- Improve documentation.
+
+# Version 0.6.1
+
+- Fix a soundness bug in `Scope::spawn()`.
+- Remove the `T: 'scope` bound on `ScopedJoinHandle`.
+
+# Version 0.6.0
+
+- Move `AtomicConsume` to `atomic` module.
+- `scope()` returns a `Result` of thread joins.
+- Remove `spawn_unchecked`.
+- Fix a soundness bug due to incorrect lifetimes.
+- Improve documentation.
+- Support nested scoped spawns.
+- Implement `Copy`, `Hash`, `PartialEq`, and `Eq` for `CachePadded`.
+- Add `CachePadded::into_inner()`.
+
+# Version 0.5.0
+
+- Reorganize sub-modules and rename functions.
+
+# Version 0.4.1
+
+- Fix a documentation link.
+
+# Version 0.4.0
+
+- `CachePadded` supports types bigger than 64 bytes.
+- Fix a bug in scoped threads where unitialized memory was being dropped.
+- Minimum required Rust version is now 1.25.
+
+# Version 0.3.2
+
+- Mark `load_consume` with `#[inline]`.
+
+# Version 0.3.1
+
+- `load_consume` on ARM and AArch64.
+
+# Version 0.3.0
+
+- Add `join` for scoped thread API.
+- Add `load_consume` for atomic load-consume memory ordering.
+- Remove `AtomicOption`.
+
+# Version 0.2.2
+
+- Support Rust 1.12.1.
+- Call `T::clone` when cloning a `CachePadded<T>`.
+
+# Version 0.2.1
+
+- Add `use_std` feature.
+
+# Version 0.2.0
+
+- Add `nightly` feature.
+- Use `repr(align(64))` on `CachePadded` with the `nightly` feature.
+- Implement `Drop` for `CachePadded<T>`.
+- Implement `Clone` for `CachePadded<T>`.
+- Implement `From<T>` for `CachePadded<T>`.
+- Implement better `Debug` for `CachePadded<T>`.
+- Write more tests.
+- Add this changelog.
+- Change cache line length to 64 bytes.
+- Remove `ZerosValid`.
+
+# Version 0.1.0
+
+- Old implementation of `CachePadded` from `crossbeam` version 0.3.0
diff --git a/Cargo.toml b/Cargo.toml
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--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,40 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies
+#
+# If you believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+edition = "2018"
+name = "crossbeam-utils"
+version = "0.8.1"
+authors = ["The Crossbeam Project Developers"]
+description = "Utilities for concurrent programming"
+homepage = "https://github.com/crossbeam-rs/crossbeam/tree/master/crossbeam-utils"
+documentation = "https://docs.rs/crossbeam-utils"
+readme = "README.md"
+keywords = ["scoped", "thread", "atomic", "cache"]
+categories = ["algorithms", "concurrency", "data-structures", "no-std"]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/crossbeam-rs/crossbeam"
+[dependencies.cfg-if]
+version = "1"
+
+[dependencies.lazy_static]
+version = "1.4.0"
+optional = true
+[dev-dependencies.rand]
+version = "0.7.3"
+[build-dependencies.autocfg]
+version = "1.0.0"
+
+[features]
+default = ["std"]
+nightly = []
+std = ["lazy_static"]
diff --git a/Cargo.toml.orig b/Cargo.toml.orig
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index 0000000..6011c75
--- /dev/null
+++ b/Cargo.toml.orig
@@ -0,0 +1,40 @@
+[package]
+name = "crossbeam-utils"
+# When publishing a new version:
+# - Update CHANGELOG.md
+# - Update README.md
+# - Create "crossbeam-utils-X.Y.Z" git tag
+version = "0.8.1"
+authors = ["The Crossbeam Project Developers"]
+edition = "2018"
+license = "MIT OR Apache-2.0"
+readme = "README.md"
+repository = "https://github.com/crossbeam-rs/crossbeam"
+homepage = "https://github.com/crossbeam-rs/crossbeam/tree/master/crossbeam-utils"
+documentation = "https://docs.rs/crossbeam-utils"
+description = "Utilities for concurrent programming"
+keywords = ["scoped", "thread", "atomic", "cache"]
+categories = ["algorithms", "concurrency", "data-structures", "no-std"]
+
+[features]
+default = ["std"]
+
+# Enable to use APIs that require `std`.
+# This is enabled by default.
+std = ["lazy_static"]
+
+# Enable to use of unstable functionality.
+# This is disabled by default and requires recent nightly compiler.
+# Note that this is outside of the normal semver guarantees and minor versions
+# of crossbeam may make breaking changes to them at any time.
+nightly = []
+
+[dependencies]
+cfg-if = "1"
+lazy_static = { version = "1.4.0", optional = true }
+
+[build-dependencies]
+autocfg = "1.0.0"
+
+[dev-dependencies]
+rand = "0.7.3"
diff --git a/README.md b/README.md
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+++ b/README.md
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+# Crossbeam Utils
+
+[](
+https://github.com/crossbeam-rs/crossbeam/actions)
+[](
+https://github.com/crossbeam-rs/crossbeam/tree/master/crossbeam-utils#license)
+[](
+https://crates.io/crates/crossbeam-utils)
+[](
+https://docs.rs/crossbeam-utils)
+[](
+https://www.rust-lang.org)
+[](https://discord.gg/BBYwKq)
+
+This crate provides miscellaneous tools for concurrent programming:
+
+#### Atomics
+
+* [`AtomicCell`], a thread-safe mutable memory location.<sup>(no_std)</sup>
+* [`AtomicConsume`], for reading from primitive atomic types with "consume" ordering.<sup>(no_std)</sup>
+
+#### Thread synchronization
+
+* [`Parker`], a thread parking primitive.
+* [`ShardedLock`], a sharded reader-writer lock with fast concurrent reads.
+* [`WaitGroup`], for synchronizing the beginning or end of some computation.
+
+#### Utilities
+
+* [`Backoff`], for exponential backoff in spin loops.<sup>(no_std)</sup>
+* [`CachePadded`], for padding and aligning a value to the length of a cache line.<sup>(no_std)</sup>
+* [`scope`], for spawning threads that borrow local variables from the stack.
+
+*Features marked with <sup>(no_std)</sup> can be used in `no_std` environments.*<br/>
+
+[`AtomicCell`]: https://docs.rs/crossbeam-utils/*/crossbeam_utils/atomic/struct.AtomicCell.html
+[`AtomicConsume`]: https://docs.rs/crossbeam-utils/*/crossbeam_utils/atomic/trait.AtomicConsume.html
+[`Parker`]: https://docs.rs/crossbeam-utils/*/crossbeam_utils/sync/struct.Parker.html
+[`ShardedLock`]: https://docs.rs/crossbeam-utils/*/crossbeam_utils/sync/struct.ShardedLock.html
+[`WaitGroup`]: https://docs.rs/crossbeam-utils/*/crossbeam_utils/sync/struct.WaitGroup.html
+[`Backoff`]: https://docs.rs/crossbeam-utils/*/crossbeam_utils/struct.Backoff.html
+[`CachePadded`]: https://docs.rs/crossbeam-utils/*/crossbeam_utils/struct.CachePadded.html
+[`scope`]: https://docs.rs/crossbeam-utils/*/crossbeam_utils/thread/fn.scope.html
+
+## Usage
+
+Add this to your `Cargo.toml`:
+
+```toml
+[dependencies]
+crossbeam-utils = "0.8"
+```
+
+## Compatibility
+
+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 1.36.
+
+## License
+
+Licensed under either of
+
+ * Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
+ * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
+
+at your option.
+
+#### Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
+dual licensed as above, without any additional terms or conditions.
diff --git a/benches/atomic_cell.rs b/benches/atomic_cell.rs
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--- /dev/null
+++ b/benches/atomic_cell.rs
@@ -0,0 +1,156 @@
+#![feature(test)]
+
+extern crate test;
+
+use std::sync::Barrier;
+
+use crossbeam_utils::atomic::AtomicCell;
+use crossbeam_utils::thread;
+
+#[bench]
+fn load_u8(b: &mut test::Bencher) {
+ let a = AtomicCell::new(0u8);
+ let mut sum = 0;
+ b.iter(|| sum += a.load());
+ test::black_box(sum);
+}
+
+#[bench]
+fn store_u8(b: &mut test::Bencher) {
+ let a = AtomicCell::new(0u8);
+ b.iter(|| a.store(1));
+}
+
+#[bench]
+fn fetch_add_u8(b: &mut test::Bencher) {
+ let a = AtomicCell::new(0u8);
+ b.iter(|| a.fetch_add(1));
+}
+
+#[bench]
+fn compare_and_swap_u8(b: &mut test::Bencher) {
+ let a = AtomicCell::new(0u8);
+ let mut i = 0;
+ b.iter(|| {
+ a.compare_and_swap(i, i.wrapping_add(1));
+ i = i.wrapping_add(1);
+ });
+}
+
+#[bench]
+fn concurrent_load_u8(b: &mut test::Bencher) {
+ const THREADS: usize = 2;
+ const STEPS: usize = 1_000_000;
+
+ let start = Barrier::new(THREADS + 1);
+ let end = Barrier::new(THREADS + 1);
+ let exit = AtomicCell::new(false);
+
+ let a = AtomicCell::new(0u8);
+
+ thread::scope(|scope| {
+ for _ in 0..THREADS {
+ scope.spawn(|_| loop {
+ start.wait();
+
+ let mut sum = 0;
+ for _ in 0..STEPS {
+ sum += a.load();
+ }
+ test::black_box(sum);
+
+ end.wait();
+ if exit.load() {
+ break;
+ }
+ });
+ }
+
+ start.wait();
+ end.wait();
+
+ b.iter(|| {
+ start.wait();
+ end.wait();
+ });
+
+ start.wait();
+ exit.store(true);
+ end.wait();
+ })
+ .unwrap();
+}
+
+#[bench]
+fn load_usize(b: &mut test::Bencher) {
+ let a = AtomicCell::new(0usize);
+ let mut sum = 0;
+ b.iter(|| sum += a.load());
+ test::black_box(sum);
+}
+
+#[bench]
+fn store_usize(b: &mut test::Bencher) {
+ let a = AtomicCell::new(0usize);
+ b.iter(|| a.store(1));
+}
+
+#[bench]
+fn fetch_add_usize(b: &mut test::Bencher) {
+ let a = AtomicCell::new(0usize);
+ b.iter(|| a.fetch_add(1));
+}
+
+#[bench]
+fn compare_and_swap_usize(b: &mut test::Bencher) {
+ let a = AtomicCell::new(0usize);
+ let mut i = 0;
+ b.iter(|| {
+ a.compare_and_swap(i, i.wrapping_add(1));
+ i = i.wrapping_add(1);
+ });
+}
+
+#[bench]
+fn concurrent_load_usize(b: &mut test::Bencher) {
+ const THREADS: usize = 2;
+ const STEPS: usize = 1_000_000;
+
+ let start = Barrier::new(THREADS + 1);
+ let end = Barrier::new(THREADS + 1);
+ let exit = AtomicCell::new(false);
+
+ let a = AtomicCell::new(0usize);
+
+ thread::scope(|scope| {
+ for _ in 0..THREADS {
+ scope.spawn(|_| loop {
+ start.wait();
+
+ let mut sum = 0;
+ for _ in 0..STEPS {
+ sum += a.load();
+ }
+ test::black_box(sum);
+
+ end.wait();
+ if exit.load() {
+ break;
+ }
+ });
+ }
+
+ start.wait();
+ end.wait();
+
+ b.iter(|| {
+ start.wait();
+ end.wait();
+ });
+
+ start.wait();
+ exit.store(true);
+ end.wait();
+ })
+ .unwrap();
+}
diff --git a/build.rs b/build.rs
new file mode 100644
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--- /dev/null
+++ b/build.rs
@@ -0,0 +1,23 @@
+use autocfg::AutoCfg;
+
+// The rustc-cfg strings below are *not* public API. Please let us know by
+// opening a GitHub issue if your build environment requires some way to enable
+// these cfgs other than by executing our build script.
+fn main() {
+ let cfg = match AutoCfg::new() {
+ Ok(cfg) => cfg,
+ Err(e) => {
+ println!(
+ "cargo:warning=crossbeam-utils: unable to determine rustc version: {}",
+ e
+ );
+ return;
+ }
+ };
+
+ cfg.emit_type_cfg("core::sync::atomic::AtomicU8", "has_atomic_u8");
+ cfg.emit_type_cfg("core::sync::atomic::AtomicU16", "has_atomic_u16");
+ cfg.emit_type_cfg("core::sync::atomic::AtomicU32", "has_atomic_u32");
+ cfg.emit_type_cfg("core::sync::atomic::AtomicU64", "has_atomic_u64");
+ cfg.emit_type_cfg("core::sync::atomic::AtomicU128", "has_atomic_u128");
+}
diff --git a/src/atomic/atomic_cell.rs b/src/atomic/atomic_cell.rs
new file mode 100644
index 0000000..e8f6804
--- /dev/null
+++ b/src/atomic/atomic_cell.rs
@@ -0,0 +1,971 @@
+// Necessary for implementing atomic methods for `AtomicUnit`
+#![allow(clippy::unit_arg)]
+#![allow(clippy::let_unit_value)]
+
+use core::cell::UnsafeCell;
+use core::fmt;
+use core::mem;
+use core::ptr;
+use core::sync::atomic::{self, AtomicBool, Ordering};
+
+#[cfg(feature = "std")]
+use std::panic::{RefUnwindSafe, UnwindSafe};
+
+use super::seq_lock::SeqLock;
+
+/// A thread-safe mutable memory location.
+///
+/// This type is equivalent to [`Cell`], except it can also be shared among multiple threads.
+///
+/// Operations on `AtomicCell`s use atomic instructions whenever possible, and synchronize using
+/// global locks otherwise. You can call [`AtomicCell::<T>::is_lock_free()`] to check whether
+/// atomic instructions or locks will be used.
+///
+/// Atomic loads use the [`Acquire`] ordering and atomic stores use the [`Release`] ordering.
+///
+/// [`Cell`]: std::cell::Cell
+/// [`AtomicCell::<T>::is_lock_free()`]: AtomicCell::is_lock_free
+/// [`Acquire`]: std::sync::atomic::Ordering::Acquire
+/// [`Release`]: std::sync::atomic::Ordering::Release
+#[repr(transparent)]
+pub struct AtomicCell<T: ?Sized> {
+ /// The inner value.
+ ///
+ /// If this value can be transmuted into a primitive atomic type, it will be treated as such.
+ /// Otherwise, all potentially concurrent operations on this data will be protected by a global
+ /// lock.
+ value: UnsafeCell<T>,
+}
+
+unsafe impl<T: Send> Send for AtomicCell<T> {}
+unsafe impl<T: Send> Sync for AtomicCell<T> {}
+
+#[cfg(feature = "std")]
+impl<T> UnwindSafe for AtomicCell<T> {}
+#[cfg(feature = "std")]
+impl<T> RefUnwindSafe for AtomicCell<T> {}
+
+impl<T> AtomicCell<T> {
+ /// Creates a new atomic cell initialized with `val`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(7);
+ /// ```
+ pub const fn new(val: T) -> AtomicCell<T> {
+ AtomicCell {
+ value: UnsafeCell::new(val),
+ }
+ }
+
+ /// Consumes the atomic and returns the contained value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(7);
+ /// let v = a.into_inner();
+ ///
+ /// assert_eq!(v, 7);
+ /// ```
+ pub fn into_inner(self) -> T {
+ self.value.into_inner()
+ }
+
+ /// Returns `true` if operations on values of this type are lock-free.
+ ///
+ /// If the compiler or the platform doesn't support the necessary atomic instructions,
+ /// `AtomicCell<T>` will use global locks for every potentially concurrent atomic operation.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// // This type is internally represented as `AtomicUsize` so we can just use atomic
+ /// // operations provided by it.
+ /// assert_eq!(AtomicCell::<usize>::is_lock_free(), true);
+ ///
+ /// // A wrapper struct around `isize`.
+ /// struct Foo {
+ /// bar: isize,
+ /// }
+ /// // `AtomicCell<Foo>` will be internally represented as `AtomicIsize`.
+ /// assert_eq!(AtomicCell::<Foo>::is_lock_free(), true);
+ ///
+ /// // Operations on zero-sized types are always lock-free.
+ /// assert_eq!(AtomicCell::<()>::is_lock_free(), true);
+ ///
+ /// // Very large types cannot be represented as any of the standard atomic types, so atomic
+ /// // operations on them will have to use global locks for synchronization.
+ /// assert_eq!(AtomicCell::<[u8; 1000]>::is_lock_free(), false);
+ /// ```
+ pub const fn is_lock_free() -> bool {
+ atomic_is_lock_free::<T>()
+ }
+
+ /// Stores `val` into the atomic cell.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(7);
+ ///
+ /// assert_eq!(a.load(), 7);
+ /// a.store(8);
+ /// assert_eq!(a.load(), 8);
+ /// ```
+ pub fn store(&self, val: T) {
+ if mem::needs_drop::<T>() {
+ drop(self.swap(val));
+ } else {
+ unsafe {
+ atomic_store(self.value.get(), val);
+ }
+ }
+ }
+
+ /// Stores `val` into the atomic cell and returns the previous value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(7);
+ ///
+ /// assert_eq!(a.load(), 7);
+ /// assert_eq!(a.swap(8), 7);
+ /// assert_eq!(a.load(), 8);
+ /// ```
+ pub fn swap(&self, val: T) -> T {
+ unsafe { atomic_swap(self.value.get(), val) }
+ }
+}
+
+impl<T: ?Sized> AtomicCell<T> {
+ /// Returns a raw pointer to the underlying data in this atomic cell.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(5);
+ ///
+ /// let ptr = a.as_ptr();
+ /// ```
+ #[inline]
+ pub fn as_ptr(&self) -> *mut T {
+ self.value.get()
+ }
+}
+
+impl<T: Default> AtomicCell<T> {
+ /// Takes the value of the atomic cell, leaving `Default::default()` in its place.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(5);
+ /// let five = a.take();
+ ///
+ /// assert_eq!(five, 5);
+ /// assert_eq!(a.into_inner(), 0);
+ /// ```
+ pub fn take(&self) -> T {
+ self.swap(Default::default())
+ }
+}
+
+impl<T: Copy> AtomicCell<T> {
+ /// Loads a value from the atomic cell.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(7);
+ ///
+ /// assert_eq!(a.load(), 7);
+ /// ```
+ pub fn load(&self) -> T {
+ unsafe { atomic_load(self.value.get()) }
+ }
+}
+
+impl<T: Copy + Eq> AtomicCell<T> {
+ /// If the current value equals `current`, stores `new` into the atomic cell.
+ ///
+ /// The return value is always the previous value. If it is equal to `current`, then the value
+ /// was updated.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(1);
+ ///
+ /// assert_eq!(a.compare_and_swap(2, 3), 1);
+ /// assert_eq!(a.load(), 1);
+ ///
+ /// assert_eq!(a.compare_and_swap(1, 2), 1);
+ /// assert_eq!(a.load(), 2);
+ /// ```
+ pub fn compare_and_swap(&self, current: T, new: T) -> T {
+ match self.compare_exchange(current, new) {
+ Ok(v) => v,
+ Err(v) => v,
+ }
+ }
+
+ /// If the current value equals `current`, stores `new` into the atomic cell.
+ ///
+ /// The return value is a result indicating whether the new value was written and containing
+ /// the previous value. On success this value is guaranteed to be equal to `current`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(1);
+ ///
+ /// assert_eq!(a.compare_exchange(2, 3), Err(1));
+ /// assert_eq!(a.load(), 1);
+ ///
+ /// assert_eq!(a.compare_exchange(1, 2), Ok(1));
+ /// assert_eq!(a.load(), 2);
+ /// ```
+ pub fn compare_exchange(&self, current: T, new: T) -> Result<T, T> {
+ unsafe { atomic_compare_exchange_weak(self.value.get(), current, new) }
+ }
+}
+
+macro_rules! impl_arithmetic {
+ ($t:ty, $example:tt) => {
+ impl AtomicCell<$t> {
+ /// Increments the current value by `val` and returns the previous value.
+ ///
+ /// The addition wraps on overflow.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ #[doc = $example]
+ ///
+ /// assert_eq!(a.fetch_add(3), 7);
+ /// assert_eq!(a.load(), 10);
+ /// ```
+ #[inline]
+ pub fn fetch_add(&self, val: $t) -> $t {
+ if can_transmute::<$t, atomic::AtomicUsize>() {
+ let a = unsafe { &*(self.value.get() as *const atomic::AtomicUsize) };
+ a.fetch_add(val as usize, Ordering::AcqRel) as $t
+ } else {
+ let _guard = lock(self.value.get() as usize).write();
+ let value = unsafe { &mut *(self.value.get()) };
+ let old = *value;
+ *value = value.wrapping_add(val);
+ old
+ }
+ }
+
+ /// Decrements the current value by `val` and returns the previous value.
+ ///
+ /// The subtraction wraps on overflow.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ #[doc = $example]
+ ///
+ /// assert_eq!(a.fetch_sub(3), 7);
+ /// assert_eq!(a.load(), 4);
+ /// ```
+ #[inline]
+ pub fn fetch_sub(&self, val: $t) -> $t {
+ if can_transmute::<$t, atomic::AtomicUsize>() {
+ let a = unsafe { &*(self.value.get() as *const atomic::AtomicUsize) };
+ a.fetch_sub(val as usize, Ordering::AcqRel) as $t
+ } else {
+ let _guard = lock(self.value.get() as usize).write();
+ let value = unsafe { &mut *(self.value.get()) };
+ let old = *value;
+ *value = value.wrapping_sub(val);
+ old
+ }
+ }
+
+ /// Applies bitwise "and" to the current value and returns the previous value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ #[doc = $example]
+ ///
+ /// assert_eq!(a.fetch_and(3), 7);
+ /// assert_eq!(a.load(), 3);
+ /// ```
+ #[inline]
+ pub fn fetch_and(&self, val: $t) -> $t {
+ if can_transmute::<$t, atomic::AtomicUsize>() {
+ let a = unsafe { &*(self.value.get() as *const atomic::AtomicUsize) };
+ a.fetch_and(val as usize, Ordering::AcqRel) as $t
+ } else {
+ let _guard = lock(self.value.get() as usize).write();
+ let value = unsafe { &mut *(self.value.get()) };
+ let old = *value;
+ *value &= val;
+ old
+ }
+ }
+
+ /// Applies bitwise "or" to the current value and returns the previous value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ #[doc = $example]
+ ///
+ /// assert_eq!(a.fetch_or(16), 7);
+ /// assert_eq!(a.load(), 23);
+ /// ```
+ #[inline]
+ pub fn fetch_or(&self, val: $t) -> $t {
+ if can_transmute::<$t, atomic::AtomicUsize>() {
+ let a = unsafe { &*(self.value.get() as *const atomic::AtomicUsize) };
+ a.fetch_or(val as usize, Ordering::AcqRel) as $t
+ } else {
+ let _guard = lock(self.value.get() as usize).write();
+ let value = unsafe { &mut *(self.value.get()) };
+ let old = *value;
+ *value |= val;
+ old
+ }
+ }
+
+ /// Applies bitwise "xor" to the current value and returns the previous value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ #[doc = $example]
+ ///
+ /// assert_eq!(a.fetch_xor(2), 7);
+ /// assert_eq!(a.load(), 5);
+ /// ```
+ #[inline]
+ pub fn fetch_xor(&self, val: $t) -> $t {
+ if can_transmute::<$t, atomic::AtomicUsize>() {
+ let a = unsafe { &*(self.value.get() as *const atomic::AtomicUsize) };
+ a.fetch_xor(val as usize, Ordering::AcqRel) as $t
+ } else {
+ let _guard = lock(self.value.get() as usize).write();
+ let value = unsafe { &mut *(self.value.get()) };
+ let old = *value;
+ *value ^= val;
+ old
+ }
+ }
+ }
+ };
+ ($t:ty, $atomic:ty, $example:tt) => {
+ impl AtomicCell<$t> {
+ /// Increments the current value by `val` and returns the previous value.
+ ///
+ /// The addition wraps on overflow.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ #[doc = $example]
+ ///
+ /// assert_eq!(a.fetch_add(3), 7);
+ /// assert_eq!(a.load(), 10);
+ /// ```
+ #[inline]
+ pub fn fetch_add(&self, val: $t) -> $t {
+ let a = unsafe { &*(self.value.get() as *const $atomic) };
+ a.fetch_add(val, Ordering::AcqRel)
+ }
+
+ /// Decrements the current value by `val` and returns the previous value.
+ ///
+ /// The subtraction wraps on overflow.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ #[doc = $example]
+ ///
+ /// assert_eq!(a.fetch_sub(3), 7);
+ /// assert_eq!(a.load(), 4);
+ /// ```
+ #[inline]
+ pub fn fetch_sub(&self, val: $t) -> $t {
+ let a = unsafe { &*(self.value.get() as *const $atomic) };
+ a.fetch_sub(val, Ordering::AcqRel)
+ }
+
+ /// Applies bitwise "and" to the current value and returns the previous value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ #[doc = $example]
+ ///
+ /// assert_eq!(a.fetch_and(3), 7);
+ /// assert_eq!(a.load(), 3);
+ /// ```
+ #[inline]
+ pub fn fetch_and(&self, val: $t) -> $t {
+ let a = unsafe { &*(self.value.get() as *const $atomic) };
+ a.fetch_and(val, Ordering::AcqRel)
+ }
+
+ /// Applies bitwise "or" to the current value and returns the previous value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ #[doc = $example]
+ ///
+ /// assert_eq!(a.fetch_or(16), 7);
+ /// assert_eq!(a.load(), 23);
+ /// ```
+ #[inline]
+ pub fn fetch_or(&self, val: $t) -> $t {
+ let a = unsafe { &*(self.value.get() as *const $atomic) };
+ a.fetch_or(val, Ordering::AcqRel)
+ }
+
+ /// Applies bitwise "xor" to the current value and returns the previous value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ #[doc = $example]
+ ///
+ /// assert_eq!(a.fetch_xor(2), 7);
+ /// assert_eq!(a.load(), 5);
+ /// ```
+ #[inline]
+ pub fn fetch_xor(&self, val: $t) -> $t {
+ let a = unsafe { &*(self.value.get() as *const $atomic) };
+ a.fetch_xor(val, Ordering::AcqRel)
+ }
+ }
+ };
+}
+
+#[cfg(has_atomic_u8)]
+impl_arithmetic!(u8, atomic::AtomicU8, "let a = AtomicCell::new(7u8);");
+#[cfg(has_atomic_u8)]
+impl_arithmetic!(i8, atomic::AtomicI8, "let a = AtomicCell::new(7i8);");
+#[cfg(has_atomic_u16)]
+impl_arithmetic!(u16, atomic::AtomicU16, "let a = AtomicCell::new(7u16);");
+#[cfg(has_atomic_u16)]
+impl_arithmetic!(i16, atomic::AtomicI16, "let a = AtomicCell::new(7i16);");
+#[cfg(has_atomic_u32)]
+impl_arithmetic!(u32, atomic::AtomicU32, "let a = AtomicCell::new(7u32);");
+#[cfg(has_atomic_u32)]
+impl_arithmetic!(i32, atomic::AtomicI32, "let a = AtomicCell::new(7i32);");
+#[cfg(has_atomic_u64)]
+impl_arithmetic!(u64, atomic::AtomicU64, "let a = AtomicCell::new(7u64);");
+#[cfg(has_atomic_u64)]
+impl_arithmetic!(i64, atomic::AtomicI64, "let a = AtomicCell::new(7i64);");
+#[cfg(has_atomic_u128)]
+impl_arithmetic!(u128, atomic::AtomicU128, "let a = AtomicCell::new(7u128);");
+#[cfg(has_atomic_u128)]
+impl_arithmetic!(i128, atomic::AtomicI128, "let a = AtomicCell::new(7i128);");
+
+impl_arithmetic!(
+ usize,
+ atomic::AtomicUsize,
+ "let a = AtomicCell::new(7usize);"
+);
+impl_arithmetic!(
+ isize,
+ atomic::AtomicIsize,
+ "let a = AtomicCell::new(7isize);"
+);
+
+impl AtomicCell<bool> {
+ /// Applies logical "and" to the current value and returns the previous value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(true);
+ ///
+ /// assert_eq!(a.fetch_and(true), true);
+ /// assert_eq!(a.load(), true);
+ ///
+ /// assert_eq!(a.fetch_and(false), true);
+ /// assert_eq!(a.load(), false);
+ /// ```
+ #[inline]
+ pub fn fetch_and(&self, val: bool) -> bool {
+ let a = unsafe { &*(self.value.get() as *const AtomicBool) };
+ a.fetch_and(val, Ordering::AcqRel)
+ }
+
+ /// Applies logical "or" to the current value and returns the previous value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(false);
+ ///
+ /// assert_eq!(a.fetch_or(false), false);
+ /// assert_eq!(a.load(), false);
+ ///
+ /// assert_eq!(a.fetch_or(true), false);
+ /// assert_eq!(a.load(), true);
+ /// ```
+ #[inline]
+ pub fn fetch_or(&self, val: bool) -> bool {
+ let a = unsafe { &*(self.value.get() as *const AtomicBool) };
+ a.fetch_or(val, Ordering::AcqRel)
+ }
+
+ /// Applies logical "xor" to the current value and returns the previous value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::atomic::AtomicCell;
+ ///
+ /// let a = AtomicCell::new(true);
+ ///
+ /// assert_eq!(a.fetch_xor(false), true);
+ /// assert_eq!(a.load(), true);
+ ///
+ /// assert_eq!(a.fetch_xor(true), true);
+ /// assert_eq!(a.load(), false);
+ /// ```
+ #[inline]
+ pub fn fetch_xor(&self, val: bool) -> bool {
+ let a = unsafe { &*(self.value.get() as *const AtomicBool) };
+ a.fetch_xor(val, Ordering::AcqRel)
+ }
+}
+
+impl<T: Default> Default for AtomicCell<T> {
+ fn default() -> AtomicCell<T> {
+ AtomicCell::new(T::default())
+ }
+}
+
+impl<T> From<T> for AtomicCell<T> {
+ #[inline]
+ fn from(val: T) -> AtomicCell<T> {
+ AtomicCell::new(val)
+ }
+}
+
+impl<T: Copy + fmt::Debug> fmt::Debug for AtomicCell<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.debug_struct("AtomicCell")
+ .field("value", &self.load())
+ .finish()
+ }
+}
+
+/// Returns `true` if values of type `A` can be transmuted into values of type `B`.
+const fn can_transmute<A, B>() -> bool {
+ // Sizes must be equal, but alignment of `A` must be greater or equal than that of `B`.
+ (mem::size_of::<A>() == mem::size_of::<B>()) & (mem::align_of::<A>() >= mem::align_of::<B>())
+}
+
+/// Returns a reference to the global lock associated with the `AtomicCell` at address `addr`.
+///
+/// This function is used to protect atomic data which doesn't fit into any of the primitive atomic
+/// types in `std::sync::atomic`. Operations on such atomics must therefore use a global lock.
+///
+/// However, there is not only one global lock but an array of many locks, and one of them is
+/// picked based on the given address. Having many locks reduces contention and improves
+/// scalability.
+#[inline]
+#[must_use]
+fn lock(addr: usize) -> &'static SeqLock {
+ // The number of locks is a prime number because we want to make sure `addr % LEN` gets
+ // dispersed across all locks.
+ //
+ // Note that addresses are always aligned to some power of 2, depending on type `T` in
+ // `AtomicCell<T>`. If `LEN` was an even number, then `addr % LEN` would be an even number,
+ // too, which means only half of the locks would get utilized!
+ //
+ // It is also possible for addresses to accidentally get aligned to a number that is not a
+ // power of 2. Consider this example:
+ //
+ // ```
+ // #[repr(C)]
+ // struct Foo {
+ // a: AtomicCell<u8>,
+ // b: u8,
+ // c: u8,
+ // }
+ // ```
+ //
+ // Now, if we have a slice of type `&[Foo]`, it is possible that field `a` in all items gets
+ // stored at addresses that are multiples of 3. It'd be too bad if `LEN` was divisible by 3.
+ // In order to protect from such cases, we simply choose a large prime number for `LEN`.
+ const LEN: usize = 97;
+
+ static LOCKS: [SeqLock; LEN] = [
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ SeqLock::new(),
+ ];
+
+ // If the modulus is a constant number, the compiler will use crazy math to transform this into
+ // a sequence of cheap arithmetic operations rather than using the slow modulo instruction.
+ &LOCKS[addr % LEN]
+}
+
+/// An atomic `()`.
+///
+/// All operations are noops.
+struct AtomicUnit;
+
+impl AtomicUnit {
+ #[inline]
+ fn load(&self, _order: Ordering) {}
+
+ #[inline]
+ fn store(&self, _val: (), _order: Ordering) {}
+
+ #[inline]
+ fn swap(&self, _val: (), _order: Ordering) {}
+
+ #[inline]
+ fn compare_exchange_weak(
+ &self,
+ _current: (),
+ _new: (),
+ _success: Ordering,
+ _failure: Ordering,
+ ) -> Result<(), ()> {
+ Ok(())
+ }
+}
+
+macro_rules! atomic {
+ // If values of type `$t` can be transmuted into values of the primitive atomic type `$atomic`,
+ // declares variable `$a` of type `$atomic` and executes `$atomic_op`, breaking out of the loop.
+ (@check, $t:ty, $atomic:ty, $a:ident, $atomic_op:expr) => {
+ if can_transmute::<$t, $atomic>() {
+ let $a: &$atomic;
+ break $atomic_op;
+ }
+ };
+
+ // If values of type `$t` can be transmuted into values of a primitive atomic type, declares
+ // variable `$a` of that type and executes `$atomic_op`. Otherwise, just executes
+ // `$fallback_op`.
+ ($t:ty, $a:ident, $atomic_op:expr, $fallback_op:expr) => {
+ loop {
+ atomic!(@check, $t, AtomicUnit, $a, $atomic_op);
+ atomic!(@check, $t, atomic::AtomicUsize, $a, $atomic_op);
+
+ #[cfg(has_atomic_u8)]
+ atomic!(@check, $t, atomic::AtomicU8, $a, $atomic_op);
+ #[cfg(has_atomic_u16)]
+ atomic!(@check, $t, atomic::AtomicU16, $a, $atomic_op);
+ #[cfg(has_atomic_u32)]
+ atomic!(@check, $t, atomic::AtomicU32, $a, $atomic_op);
+ #[cfg(has_atomic_u64)]
+ atomic!(@check, $t, atomic::AtomicU64, $a, $atomic_op);
+ #[cfg(has_atomic_u128)]
+ atomic!(@check, $t, atomic::AtomicU128, $a, $atomic_op);
+
+ break $fallback_op;
+ }
+ };
+}
+
+/// Returns `true` if operations on `AtomicCell<T>` are lock-free.
+const fn atomic_is_lock_free<T>() -> bool {
+ // HACK(taiki-e): This is equivalent to `atomic! { T, _a, true, false }`, but can be used in const fn even in Rust 1.36.
+ let is_lock_free = can_transmute::<T, AtomicUnit>() | can_transmute::<T, atomic::AtomicUsize>();
+ #[cfg(has_atomic_u8)]
+ let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU8>();
+ #[cfg(has_atomic_u16)]
+ let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU16>();
+ #[cfg(has_atomic_u32)]
+ let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU32>();
+ #[cfg(has_atomic_u64)]
+ let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU64>();
+ #[cfg(has_atomic_u128)]
+ let is_lock_free = is_lock_free | can_transmute::<T, atomic::AtomicU128>();
+ is_lock_free
+}
+
+/// Atomically reads data from `src`.
+///
+/// This operation uses the `Acquire` ordering. If possible, an atomic instructions is used, and a
+/// global lock otherwise.
+unsafe fn atomic_load<T>(src: *mut T) -> T
+where
+ T: Copy,
+{
+ atomic! {
+ T, a,
+ {
+ a = &*(src as *const _ as *const _);
+ mem::transmute_copy(&a.load(Ordering::Acquire))
+ },
+ {
+ let lock = lock(src as usize);
+
+ // Try doing an optimistic read first.
+ if let Some(stamp) = lock.optimistic_read() {
+ // We need a volatile read here because other threads might concurrently modify the
+ // value. In theory, data races are *always* UB, even if we use volatile reads and
+ // discard the data when a data race is detected. The proper solution would be to
+ // do atomic reads and atomic writes, but we can't atomically read and write all
+ // kinds of data since `AtomicU8` is not available on stable Rust yet.
+ let val = ptr::read_volatile(src);
+
+ if lock.validate_read(stamp) {
+ return val;
+ }
+ }
+
+ // Grab a regular write lock so that writers don't starve this load.
+ let guard = lock.write();
+ let val = ptr::read(src);
+ // The value hasn't been changed. Drop the guard without incrementing the stamp.
+ guard.abort();
+ val
+ }
+ }
+}
+
+/// Atomically writes `val` to `dst`.
+///
+/// This operation uses the `Release` ordering. If possible, an atomic instructions is used, and a
+/// global lock otherwise.
+unsafe fn atomic_store<T>(dst: *mut T, val: T) {
+ atomic! {
+ T, a,
+ {
+ a = &*(dst as *const _ as *const _);
+ a.store(mem::transmute_copy(&val), Ordering::Release);
+ mem::forget(val);
+ },
+ {
+ let _guard = lock(dst as usize).write();
+ ptr::write(dst, val);
+ }
+ }
+}
+
+/// Atomically swaps data at `dst` with `val`.
+///
+/// This operation uses the `AcqRel` ordering. If possible, an atomic instructions is used, and a
+/// global lock otherwise.
+unsafe fn atomic_swap<T>(dst: *mut T, val: T) -> T {
+ atomic! {
+ T, a,
+ {
+ a = &*(dst as *const _ as *const _);
+ let res = mem::transmute_copy(&a.swap(mem::transmute_copy(&val), Ordering::AcqRel));
+ mem::forget(val);
+ res
+ },
+ {
+ let _guard = lock(dst as usize).write();
+ ptr::replace(dst, val)
+ }
+ }
+}
+
+/// Atomically compares data at `dst` to `current` and, if equal byte-for-byte, exchanges data at
+/// `dst` with `new`.
+///
+/// Returns the old value on success, or the current value at `dst` on failure.
+///
+/// This operation uses the `AcqRel` ordering. If possible, an atomic instructions is used, and a
+/// global lock otherwise.
+unsafe fn atomic_compare_exchange_weak<T>(dst: *mut T, mut current: T, new: T) -> Result<T, T>
+where
+ T: Copy + Eq,
+{
+ atomic! {
+ T, a,
+ {
+ a = &*(dst as *const _ as *const _);
+ let mut current_raw = mem::transmute_copy(¤t);
+ let new_raw = mem::transmute_copy(&new);
+
+ loop {
+ match a.compare_exchange_weak(
+ current_raw,
+ new_raw,
+ Ordering::AcqRel,
+ Ordering::Acquire,
+ ) {
+ Ok(_) => break Ok(current),
+ Err(previous_raw) => {
+ let previous = mem::transmute_copy(&previous_raw);
+
+ if !T::eq(&previous, ¤t) {
+ break Err(previous);
+ }
+
+ // The compare-exchange operation has failed and didn't store `new`. The
+ // failure is either spurious, or `previous` was semantically equal to
+ // `current` but not byte-equal. Let's retry with `previous` as the new
+ // `current`.
+ current = previous;
+ current_raw = previous_raw;
+ }
+ }
+ }
+ },
+ {
+ let guard = lock(dst as usize).write();
+
+ if T::eq(&*dst, ¤t) {
+ Ok(ptr::replace(dst, new))
+ } else {
+ let val = ptr::read(dst);
+ // The value hasn't been changed. Drop the guard without incrementing the stamp.
+ guard.abort();
+ Err(val)
+ }
+ }
+ }
+}
diff --git a/src/atomic/consume.rs b/src/atomic/consume.rs
new file mode 100644
index 0000000..584fc34
--- /dev/null
+++ b/src/atomic/consume.rs
@@ -0,0 +1,82 @@
+#[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
+use core::sync::atomic::compiler_fence;
+use core::sync::atomic::Ordering;
+
+/// Trait which allows reading from primitive atomic types with "consume" ordering.
+pub trait AtomicConsume {
+ /// Type returned by `load_consume`.
+ type Val;
+
+ /// Loads a value from the atomic using a "consume" memory ordering.
+ ///
+ /// This is similar to the "acquire" ordering, except that an ordering is
+ /// only guaranteed with operations that "depend on" the result of the load.
+ /// However consume loads are usually much faster than acquire loads on
+ /// architectures with a weak memory model since they don't require memory
+ /// fence instructions.
+ ///
+ /// The exact definition of "depend on" is a bit vague, but it works as you
+ /// would expect in practice since a lot of software, especially the Linux
+ /// kernel, rely on this behavior.
+ ///
+ /// This is currently only implemented on ARM and AArch64, where a fence
+ /// can be avoided. On other architectures this will fall back to a simple
+ /// `load(Ordering::Acquire)`.
+ fn load_consume(&self) -> Self::Val;
+}
+
+#[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
+macro_rules! impl_consume {
+ () => {
+ #[inline]
+ fn load_consume(&self) -> Self::Val {
+ let result = self.load(Ordering::Relaxed);
+ compiler_fence(Ordering::Acquire);
+ result
+ }
+ };
+}
+
+#[cfg(not(any(target_arch = "arm", target_arch = "aarch64")))]
+macro_rules! impl_consume {
+ () => {
+ #[inline]
+ fn load_consume(&self) -> Self::Val {
+ self.load(Ordering::Acquire)
+ }
+ };
+}
+
+macro_rules! impl_atomic {
+ ($atomic:ident, $val:ty) => {
+ impl AtomicConsume for ::core::sync::atomic::$atomic {
+ type Val = $val;
+ impl_consume!();
+ }
+ };
+}
+
+impl_atomic!(AtomicBool, bool);
+impl_atomic!(AtomicUsize, usize);
+impl_atomic!(AtomicIsize, isize);
+#[cfg(has_atomic_u8)]
+impl_atomic!(AtomicU8, u8);
+#[cfg(has_atomic_u8)]
+impl_atomic!(AtomicI8, i8);
+#[cfg(has_atomic_u16)]
+impl_atomic!(AtomicU16, u16);
+#[cfg(has_atomic_u16)]
+impl_atomic!(AtomicI16, i16);
+#[cfg(has_atomic_u32)]
+impl_atomic!(AtomicU32, u32);
+#[cfg(has_atomic_u32)]
+impl_atomic!(AtomicI32, i32);
+#[cfg(has_atomic_u64)]
+impl_atomic!(AtomicU64, u64);
+#[cfg(has_atomic_u64)]
+impl_atomic!(AtomicI64, i64);
+
+impl<T> AtomicConsume for ::core::sync::atomic::AtomicPtr<T> {
+ type Val = *mut T;
+ impl_consume!();
+}
diff --git a/src/atomic/mod.rs b/src/atomic/mod.rs
new file mode 100644
index 0000000..7309c16
--- /dev/null
+++ b/src/atomic/mod.rs
@@ -0,0 +1,27 @@
+//! Atomic types.
+
+use cfg_if::cfg_if;
+
+cfg_if! {
+ // Use "wide" sequence lock if the pointer width <= 32 for preventing its counter against wrap
+ // around.
+ //
+ // We are ignoring too wide architectures (pointer width >= 256), since such a system will not
+ // appear in a conceivable future.
+ //
+ // In narrow architectures (pointer width <= 16), the counter is still <= 32-bit and may be
+ // vulnerable to wrap around. But it's mostly okay, since in such a primitive hardware, the
+ // counter will not be increased that fast.
+ if #[cfg(any(target_pointer_width = "64", target_pointer_width = "128"))] {
+ mod seq_lock;
+ } else {
+ #[path = "seq_lock_wide.rs"]
+ mod seq_lock;
+ }
+}
+
+mod atomic_cell;
+mod consume;
+
+pub use self::atomic_cell::AtomicCell;
+pub use self::consume::AtomicConsume;
diff --git a/src/atomic/seq_lock.rs b/src/atomic/seq_lock.rs
new file mode 100644
index 0000000..a423bc0
--- /dev/null
+++ b/src/atomic/seq_lock.rs
@@ -0,0 +1,112 @@
+use core::mem;
+use core::sync::atomic::{self, AtomicUsize, Ordering};
+
+use crate::Backoff;
+
+/// A simple stamped lock.
+pub struct SeqLock {
+ /// The current state of the lock.
+ ///
+ /// All bits except the least significant one hold the current stamp. When locked, the state
+ /// equals 1 and doesn't contain a valid stamp.
+ state: AtomicUsize,
+}
+
+impl SeqLock {
+ pub const fn new() -> Self {
+ Self {
+ state: AtomicUsize::new(0),
+ }
+ }
+
+ /// If not locked, returns the current stamp.
+ ///
+ /// This method should be called before optimistic reads.
+ #[inline]
+ pub fn optimistic_read(&self) -> Option<usize> {
+ let state = self.state.load(Ordering::Acquire);
+ if state == 1 {
+ None
+ } else {
+ Some(state)
+ }
+ }
+
+ /// Returns `true` if the current stamp is equal to `stamp`.
+ ///
+ /// This method should be called after optimistic reads to check whether they are valid. The
+ /// argument `stamp` should correspond to the one returned by method `optimistic_read`.
+ #[inline]
+ pub fn validate_read(&self, stamp: usize) -> bool {
+ atomic::fence(Ordering::Acquire);
+ self.state.load(Ordering::Relaxed) == stamp
+ }
+
+ /// Grabs the lock for writing.
+ #[inline]
+ pub fn write(&'static self) -> SeqLockWriteGuard {
+ let backoff = Backoff::new();
+ loop {
+ let previous = self.state.swap(1, Ordering::Acquire);
+
+ if previous != 1 {
+ atomic::fence(Ordering::Release);
+
+ return SeqLockWriteGuard {
+ lock: self,
+ state: previous,
+ };
+ }
+
+ backoff.snooze();
+ }
+ }
+}
+
+/// An RAII guard that releases the lock and increments the stamp when dropped.
+pub struct SeqLockWriteGuard {
+ /// The parent lock.
+ lock: &'static SeqLock,
+
+ /// The stamp before locking.
+ state: usize,
+}
+
+impl SeqLockWriteGuard {
+ /// Releases the lock without incrementing the stamp.
+ #[inline]
+ pub fn abort(self) {
+ self.lock.state.store(self.state, Ordering::Release);
+
+ // We specifically don't want to call drop(), since that's
+ // what increments the stamp.
+ mem::forget(self);
+ }
+}
+
+impl Drop for SeqLockWriteGuard {
+ #[inline]
+ fn drop(&mut self) {
+ // Release the lock and increment the stamp.
+ self.lock
+ .state
+ .store(self.state.wrapping_add(2), Ordering::Release);
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::SeqLock;
+
+ #[test]
+ fn test_abort() {
+ static LK: SeqLock = SeqLock::new();
+ let before = LK.optimistic_read().unwrap();
+ {
+ let guard = LK.write();
+ guard.abort();
+ }
+ let after = LK.optimistic_read().unwrap();
+ assert_eq!(before, after, "aborted write does not update the stamp");
+ }
+}
diff --git a/src/atomic/seq_lock_wide.rs b/src/atomic/seq_lock_wide.rs
new file mode 100644
index 0000000..871a93d
--- /dev/null
+++ b/src/atomic/seq_lock_wide.rs
@@ -0,0 +1,155 @@
+use core::mem;
+use core::sync::atomic::{self, AtomicUsize, Ordering};
+
+use crate::Backoff;
+
+/// A simple stamped lock.
+///
+/// The state is represented as two `AtomicUsize`: `state_hi` for high bits and `state_lo` for low
+/// bits.
+pub struct SeqLock {
+ /// The high bits of the current state of the lock.
+ state_hi: AtomicUsize,
+
+ /// The low bits of the current state of the lock.
+ ///
+ /// All bits except the least significant one hold the current stamp. When locked, the state_lo
+ /// equals 1 and doesn't contain a valid stamp.
+ state_lo: AtomicUsize,
+}
+
+impl SeqLock {
+ pub const fn new() -> Self {
+ Self {
+ state_hi: AtomicUsize::new(0),
+ state_lo: AtomicUsize::new(0),
+ }
+ }
+
+ /// If not locked, returns the current stamp.
+ ///
+ /// This method should be called before optimistic reads.
+ #[inline]
+ pub fn optimistic_read(&self) -> Option<(usize, usize)> {
+ // The acquire loads from `state_hi` and `state_lo` synchronize with the release stores in
+ // `SeqLockWriteGuard::drop`.
+ //
+ // As a consequence, we can make sure that (1) all writes within the era of `state_hi - 1`
+ // happens before now; and therefore, (2) if `state_lo` is even, all writes within the
+ // critical section of (`state_hi`, `state_lo`) happens before now.
+ let state_hi = self.state_hi.load(Ordering::Acquire);
+ let state_lo = self.state_lo.load(Ordering::Acquire);
+ if state_lo == 1 {
+ None
+ } else {
+ Some((state_hi, state_lo))
+ }
+ }
+
+ /// Returns `true` if the current stamp is equal to `stamp`.
+ ///
+ /// This method should be called after optimistic reads to check whether they are valid. The
+ /// argument `stamp` should correspond to the one returned by method `optimistic_read`.
+ #[inline]
+ pub fn validate_read(&self, stamp: (usize, usize)) -> bool {
+ // Thanks to the fence, if we're noticing any modification to the data at the critical
+ // section of `(a, b)`, then the critical section's write of 1 to state_lo should be
+ // visible.
+ atomic::fence(Ordering::Acquire);
+
+ // So if `state_lo` coincides with `stamp.1`, then either (1) we're noticing no modification
+ // to the data after the critical section of `(stamp.0, stamp.1)`, or (2) `state_lo` wrapped
+ // around.
+ //
+ // If (2) is the case, the acquire ordering ensures we see the new value of `state_hi`.
+ let state_lo = self.state_lo.load(Ordering::Acquire);
+
+ // If (2) is the case and `state_hi` coincides with `stamp.0`, then `state_hi` also wrapped
+ // around, which we give up to correctly validate the read.
+ let state_hi = self.state_hi.load(Ordering::Relaxed);
+
+ // Except for the case that both `state_hi` and `state_lo` wrapped around, the following
+ // condition implies that we're noticing no modification to the data after the critical
+ // section of `(stamp.0, stamp.1)`.
+ (state_hi, state_lo) == stamp
+ }
+
+ /// Grabs the lock for writing.
+ #[inline]
+ pub fn write(&'static self) -> SeqLockWriteGuard {
+ let backoff = Backoff::new();
+ loop {
+ let previous = self.state_lo.swap(1, Ordering::Acquire);
+
+ if previous != 1 {
+ // To synchronize with the acquire fence in `validate_read` via any modification to
+ // the data at the critical section of `(state_hi, previous)`.
+ atomic::fence(Ordering::Release);
+
+ return SeqLockWriteGuard {
+ lock: self,
+ state_lo: previous,
+ };
+ }
+
+ backoff.snooze();
+ }
+ }
+}
+
+/// An RAII guard that releases the lock and increments the stamp when dropped.
+pub struct SeqLockWriteGuard {
+ /// The parent lock.
+ lock: &'static SeqLock,
+
+ /// The stamp before locking.
+ state_lo: usize,
+}
+
+impl SeqLockWriteGuard {
+ /// Releases the lock without incrementing the stamp.
+ #[inline]
+ pub fn abort(self) {
+ self.lock.state_lo.store(self.state_lo, Ordering::Release);
+ mem::forget(self);
+ }
+}
+
+impl Drop for SeqLockWriteGuard {
+ #[inline]
+ fn drop(&mut self) {
+ let state_lo = self.state_lo.wrapping_add(2);
+
+ // Increase the high bits if the low bits wrap around.
+ //
+ // Release ordering for synchronizing with `optimistic_read`.
+ if state_lo == 0 {
+ let state_hi = self.lock.state_hi.load(Ordering::Relaxed);
+ self.lock
+ .state_hi
+ .store(state_hi.wrapping_add(1), Ordering::Release);
+ }
+
+ // Release the lock and increment the stamp.
+ //
+ // Release ordering for synchronizing with `optimistic_read`.
+ self.lock.state_lo.store(state_lo, Ordering::Release);
+ }
+}
+
+#[cfg(test)]
+mod tests {
+ use super::SeqLock;
+
+ #[test]
+ fn test_abort() {
+ static LK: SeqLock = SeqLock::new();
+ let before = LK.optimistic_read().unwrap();
+ {
+ let guard = LK.write();
+ guard.abort();
+ }
+ let after = LK.optimistic_read().unwrap();
+ assert_eq!(before, after, "aborted write does not update the stamp");
+ }
+}
diff --git a/src/backoff.rs b/src/backoff.rs
new file mode 100644
index 0000000..2391dd1
--- /dev/null
+++ b/src/backoff.rs
@@ -0,0 +1,285 @@
+use core::cell::Cell;
+use core::fmt;
+use core::sync::atomic;
+
+const SPIN_LIMIT: u32 = 6;
+const YIELD_LIMIT: u32 = 10;
+
+/// Performs exponential backoff in spin loops.
+///
+/// Backing off in spin loops reduces contention and improves overall performance.
+///
+/// This primitive can execute *YIELD* and *PAUSE* instructions, yield the current thread to the OS
+/// scheduler, and tell when is a good time to block the thread using a different synchronization
+/// mechanism. Each step of the back off procedure takes roughly twice as long as the previous
+/// step.
+///
+/// # Examples
+///
+/// Backing off in a lock-free loop:
+///
+/// ```
+/// use crossbeam_utils::Backoff;
+/// use std::sync::atomic::AtomicUsize;
+/// use std::sync::atomic::Ordering::SeqCst;
+///
+/// fn fetch_mul(a: &AtomicUsize, b: usize) -> usize {
+/// let backoff = Backoff::new();
+/// loop {
+/// let val = a.load(SeqCst);
+/// if a.compare_and_swap(val, val.wrapping_mul(b), SeqCst) == val {
+/// return val;
+/// }
+/// backoff.spin();
+/// }
+/// }
+/// ```
+///
+/// Waiting for an [`AtomicBool`] to become `true`:
+///
+/// ```
+/// use crossbeam_utils::Backoff;
+/// use std::sync::atomic::AtomicBool;
+/// use std::sync::atomic::Ordering::SeqCst;
+///
+/// fn spin_wait(ready: &AtomicBool) {
+/// let backoff = Backoff::new();
+/// while !ready.load(SeqCst) {
+/// backoff.snooze();
+/// }
+/// }
+/// ```
+///
+/// Waiting for an [`AtomicBool`] to become `true` and parking the thread after a long wait.
+/// Note that whoever sets the atomic variable to `true` must notify the parked thread by calling
+/// [`unpark()`]:
+///
+/// ```
+/// use crossbeam_utils::Backoff;
+/// use std::sync::atomic::AtomicBool;
+/// use std::sync::atomic::Ordering::SeqCst;
+/// use std::thread;
+///
+/// fn blocking_wait(ready: &AtomicBool) {
+/// let backoff = Backoff::new();
+/// while !ready.load(SeqCst) {
+/// if backoff.is_completed() {
+/// thread::park();
+/// } else {
+/// backoff.snooze();
+/// }
+/// }
+/// }
+/// ```
+///
+/// [`is_completed`]: Backoff::is_completed
+/// [`std::thread::park()`]: std::thread::park
+/// [`Condvar`]: std::sync::Condvar
+/// [`AtomicBool`]: std::sync::atomic::AtomicBool
+/// [`unpark()`]: std::thread::Thread::unpark
+pub struct Backoff {
+ step: Cell<u32>,
+}
+
+impl Backoff {
+ /// Creates a new `Backoff`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::Backoff;
+ ///
+ /// let backoff = Backoff::new();
+ /// ```
+ #[inline]
+ pub fn new() -> Self {
+ Backoff { step: Cell::new(0) }
+ }
+
+ /// Resets the `Backoff`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::Backoff;
+ ///
+ /// let backoff = Backoff::new();
+ /// backoff.reset();
+ /// ```
+ #[inline]
+ pub fn reset(&self) {
+ self.step.set(0);
+ }
+
+ /// Backs off in a lock-free loop.
+ ///
+ /// This method should be used when we need to retry an operation because another thread made
+ /// progress.
+ ///
+ /// The processor may yield using the *YIELD* or *PAUSE* instruction.
+ ///
+ /// # Examples
+ ///
+ /// Backing off in a lock-free loop:
+ ///
+ /// ```
+ /// use crossbeam_utils::Backoff;
+ /// use std::sync::atomic::AtomicUsize;
+ /// use std::sync::atomic::Ordering::SeqCst;
+ ///
+ /// fn fetch_mul(a: &AtomicUsize, b: usize) -> usize {
+ /// let backoff = Backoff::new();
+ /// loop {
+ /// let val = a.load(SeqCst);
+ /// if a.compare_and_swap(val, val.wrapping_mul(b), SeqCst) == val {
+ /// return val;
+ /// }
+ /// backoff.spin();
+ /// }
+ /// }
+ ///
+ /// let a = AtomicUsize::new(7);
+ /// assert_eq!(fetch_mul(&a, 8), 7);
+ /// assert_eq!(a.load(SeqCst), 56);
+ /// ```
+ #[inline]
+ pub fn spin(&self) {
+ for _ in 0..1 << self.step.get().min(SPIN_LIMIT) {
+ atomic::spin_loop_hint();
+ }
+
+ if self.step.get() <= SPIN_LIMIT {
+ self.step.set(self.step.get() + 1);
+ }
+ }
+
+ /// Backs off in a blocking loop.
+ ///
+ /// This method should be used when we need to wait for another thread to make progress.
+ ///
+ /// The processor may yield using the *YIELD* or *PAUSE* instruction and the current thread
+ /// may yield by giving up a timeslice to the OS scheduler.
+ ///
+ /// In `#[no_std]` environments, this method is equivalent to [`spin`].
+ ///
+ /// If possible, use [`is_completed`] to check when it is advised to stop using backoff and
+ /// block the current thread using a different synchronization mechanism instead.
+ ///
+ /// [`spin`]: Backoff::spin
+ /// [`is_completed`]: Backoff::is_completed
+ ///
+ /// # Examples
+ ///
+ /// Waiting for an [`AtomicBool`] to become `true`:
+ ///
+ /// ```
+ /// use crossbeam_utils::Backoff;
+ /// use std::sync::Arc;
+ /// use std::sync::atomic::AtomicBool;
+ /// use std::sync::atomic::Ordering::SeqCst;
+ /// use std::thread;
+ /// use std::time::Duration;
+ ///
+ /// fn spin_wait(ready: &AtomicBool) {
+ /// let backoff = Backoff::new();
+ /// while !ready.load(SeqCst) {
+ /// backoff.snooze();
+ /// }
+ /// }
+ ///
+ /// let ready = Arc::new(AtomicBool::new(false));
+ /// let ready2 = ready.clone();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_millis(100));
+ /// ready2.store(true, SeqCst);
+ /// });
+ ///
+ /// assert_eq!(ready.load(SeqCst), false);
+ /// spin_wait(&ready);
+ /// assert_eq!(ready.load(SeqCst), true);
+ /// ```
+ ///
+ /// [`AtomicBool`]: std::sync::atomic::AtomicBool
+ #[inline]
+ pub fn snooze(&self) {
+ if self.step.get() <= SPIN_LIMIT {
+ for _ in 0..1 << self.step.get() {
+ atomic::spin_loop_hint();
+ }
+ } else {
+ #[cfg(not(feature = "std"))]
+ for _ in 0..1 << self.step.get() {
+ atomic::spin_loop_hint();
+ }
+
+ #[cfg(feature = "std")]
+ ::std::thread::yield_now();
+ }
+
+ if self.step.get() <= YIELD_LIMIT {
+ self.step.set(self.step.get() + 1);
+ }
+ }
+
+ /// Returns `true` if exponential backoff has completed and blocking the thread is advised.
+ ///
+ /// # Examples
+ ///
+ /// Waiting for an [`AtomicBool`] to become `true` and parking the thread after a long wait:
+ ///
+ /// ```
+ /// use crossbeam_utils::Backoff;
+ /// use std::sync::Arc;
+ /// use std::sync::atomic::AtomicBool;
+ /// use std::sync::atomic::Ordering::SeqCst;
+ /// use std::thread;
+ /// use std::time::Duration;
+ ///
+ /// fn blocking_wait(ready: &AtomicBool) {
+ /// let backoff = Backoff::new();
+ /// while !ready.load(SeqCst) {
+ /// if backoff.is_completed() {
+ /// thread::park();
+ /// } else {
+ /// backoff.snooze();
+ /// }
+ /// }
+ /// }
+ ///
+ /// let ready = Arc::new(AtomicBool::new(false));
+ /// let ready2 = ready.clone();
+ /// let waiter = thread::current();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_millis(100));
+ /// ready2.store(true, SeqCst);
+ /// waiter.unpark();
+ /// });
+ ///
+ /// assert_eq!(ready.load(SeqCst), false);
+ /// blocking_wait(&ready);
+ /// assert_eq!(ready.load(SeqCst), true);
+ /// ```
+ ///
+ /// [`AtomicBool`]: std::sync::atomic::AtomicBool
+ #[inline]
+ pub fn is_completed(&self) -> bool {
+ self.step.get() > YIELD_LIMIT
+ }
+}
+
+impl fmt::Debug for Backoff {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.debug_struct("Backoff")
+ .field("step", &self.step)
+ .field("is_completed", &self.is_completed())
+ .finish()
+ }
+}
+
+impl Default for Backoff {
+ fn default() -> Backoff {
+ Backoff::new()
+ }
+}
diff --git a/src/cache_padded.rs b/src/cache_padded.rs
new file mode 100644
index 0000000..62c686b
--- /dev/null
+++ b/src/cache_padded.rs
@@ -0,0 +1,139 @@
+use core::fmt;
+use core::ops::{Deref, DerefMut};
+
+/// Pads and aligns a value to the length of a cache line.
+///
+/// In concurrent programming, sometimes it is desirable to make sure commonly accessed pieces of
+/// data are not placed into the same cache line. Updating an atomic value invalidates the whole
+/// cache line it belongs to, which makes the next access to the same cache line slower for other
+/// CPU cores. Use `CachePadded` to ensure updating one piece of data doesn't invalidate other
+/// cached data.
+///
+/// # Size and alignment
+///
+/// Cache lines are assumed to be N bytes long, depending on the architecture:
+///
+/// * On x86-64 and aarch64, N = 128.
+/// * On all others, N = 64.
+///
+/// Note that N is just a reasonable guess and is not guaranteed to match the actual cache line
+/// length of the machine the program is running on. On modern Intel architectures, spatial
+/// prefetcher is pulling pairs of 64-byte cache lines at a time, so we pessimistically assume that
+/// cache lines are 128 bytes long.
+///
+/// The size of `CachePadded<T>` is the smallest multiple of N bytes large enough to accommodate
+/// a value of type `T`.
+///
+/// The alignment of `CachePadded<T>` is the maximum of N bytes and the alignment of `T`.
+///
+/// # Examples
+///
+/// Alignment and padding:
+///
+/// ```
+/// use crossbeam_utils::CachePadded;
+///
+/// let array = [CachePadded::new(1i8), CachePadded::new(2i8)];
+/// let addr1 = &*array[0] as *const i8 as usize;
+/// let addr2 = &*array[1] as *const i8 as usize;
+///
+/// assert!(addr2 - addr1 >= 64);
+/// assert_eq!(addr1 % 64, 0);
+/// assert_eq!(addr2 % 64, 0);
+/// ```
+///
+/// When building a concurrent queue with a head and a tail index, it is wise to place them in
+/// different cache lines so that concurrent threads pushing and popping elements don't invalidate
+/// each other's cache lines:
+///
+/// ```
+/// use crossbeam_utils::CachePadded;
+/// use std::sync::atomic::AtomicUsize;
+///
+/// struct Queue<T> {
+/// head: CachePadded<AtomicUsize>,
+/// tail: CachePadded<AtomicUsize>,
+/// buffer: *mut T,
+/// }
+/// ```
+#[derive(Clone, Copy, Default, Hash, PartialEq, Eq)]
+// Starting from Intel's Sandy Bridge, spatial prefetcher is now pulling pairs of 64-byte cache
+// lines at a time, so we have to align to 128 bytes rather than 64.
+//
+// Sources:
+// - https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-optimization-manual.pdf
+// - https://github.com/facebook/folly/blob/1b5288e6eea6df074758f877c849b6e73bbb9fbb/folly/lang/Align.h#L107
+//
+// ARM's big.LITTLE architecture has asymmetric cores and "big" cores have 128 byte cache line size
+// Sources:
+// - https://www.mono-project.com/news/2016/09/12/arm64-icache/
+//
+#[cfg_attr(any(target_arch = "x86_64", target_arch = "aarch64"), repr(align(128)))]
+#[cfg_attr(
+ not(any(target_arch = "x86_64", target_arch = "aarch64")),
+ repr(align(64))
+)]
+pub struct CachePadded<T> {
+ value: T,
+}
+
+unsafe impl<T: Send> Send for CachePadded<T> {}
+unsafe impl<T: Sync> Sync for CachePadded<T> {}
+
+impl<T> CachePadded<T> {
+ /// Pads and aligns a value to the length of a cache line.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::CachePadded;
+ ///
+ /// let padded_value = CachePadded::new(1);
+ /// ```
+ pub const fn new(t: T) -> CachePadded<T> {
+ CachePadded::<T> { value: t }
+ }
+
+ /// Returns the inner value.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::CachePadded;
+ ///
+ /// let padded_value = CachePadded::new(7);
+ /// let value = padded_value.into_inner();
+ /// assert_eq!(value, 7);
+ /// ```
+ pub fn into_inner(self) -> T {
+ self.value
+ }
+}
+
+impl<T> Deref for CachePadded<T> {
+ type Target = T;
+
+ fn deref(&self) -> &T {
+ &self.value
+ }
+}
+
+impl<T> DerefMut for CachePadded<T> {
+ fn deref_mut(&mut self) -> &mut T {
+ &mut self.value
+ }
+}
+
+impl<T: fmt::Debug> fmt::Debug for CachePadded<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.debug_struct("CachePadded")
+ .field("value", &self.value)
+ .finish()
+ }
+}
+
+impl<T> From<T> for CachePadded<T> {
+ fn from(t: T) -> Self {
+ CachePadded::new(t)
+ }
+}
diff --git a/src/lib.rs b/src/lib.rs
new file mode 100644
index 0000000..f2bd460
--- /dev/null
+++ b/src/lib.rs
@@ -0,0 +1,56 @@
+//! Miscellaneous tools for concurrent programming.
+//!
+//! ## Atomics
+//!
+//! * [`AtomicCell`], a thread-safe mutable memory location.
+//! * [`AtomicConsume`], for reading from primitive atomic types with "consume" ordering.
+//!
+//! ## Thread synchronization
+//!
+//! * [`Parker`], a thread parking primitive.
+//! * [`ShardedLock`], a sharded reader-writer lock with fast concurrent reads.
+//! * [`WaitGroup`], for synchronizing the beginning or end of some computation.
+//!
+//! ## Utilities
+//!
+//! * [`Backoff`], for exponential backoff in spin loops.
+//! * [`CachePadded`], for padding and aligning a value to the length of a cache line.
+//! * [`scope`], for spawning threads that borrow local variables from the stack.
+//!
+//! [`AtomicCell`]: atomic::AtomicCell
+//! [`AtomicConsume`]: atomic::AtomicConsume
+//! [`Parker`]: sync::Parker
+//! [`ShardedLock`]: sync::ShardedLock
+//! [`WaitGroup`]: sync::WaitGroup
+//! [`scope`]: thread::scope
+
+#![doc(test(
+ no_crate_inject,
+ attr(
+ deny(warnings, rust_2018_idioms),
+ allow(dead_code, unused_assignments, unused_variables)
+ )
+))]
+#![warn(missing_docs, missing_debug_implementations, rust_2018_idioms)]
+#![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(feature = "nightly", feature(cfg_target_has_atomic))]
+// matches! requires Rust 1.42
+#![allow(clippy::match_like_matches_macro)]
+
+#[cfg_attr(feature = "nightly", cfg(target_has_atomic = "ptr"))]
+pub mod atomic;
+
+mod cache_padded;
+pub use crate::cache_padded::CachePadded;
+
+mod backoff;
+pub use crate::backoff::Backoff;
+
+use cfg_if::cfg_if;
+
+cfg_if! {
+ if #[cfg(feature = "std")] {
+ pub mod sync;
+ pub mod thread;
+ }
+}
diff --git a/src/sync/mod.rs b/src/sync/mod.rs
new file mode 100644
index 0000000..fd400d7
--- /dev/null
+++ b/src/sync/mod.rs
@@ -0,0 +1,13 @@
+//! Thread synchronization primitives.
+//!
+//! * [`Parker`], a thread parking primitive.
+//! * [`ShardedLock`], a sharded reader-writer lock with fast concurrent reads.
+//! * [`WaitGroup`], for synchronizing the beginning or end of some computation.
+
+mod parker;
+mod sharded_lock;
+mod wait_group;
+
+pub use self::parker::{Parker, Unparker};
+pub use self::sharded_lock::{ShardedLock, ShardedLockReadGuard, ShardedLockWriteGuard};
+pub use self::wait_group::WaitGroup;
diff --git a/src/sync/parker.rs b/src/sync/parker.rs
new file mode 100644
index 0000000..fc13d2e
--- /dev/null
+++ b/src/sync/parker.rs
@@ -0,0 +1,397 @@
+use std::fmt;
+use std::marker::PhantomData;
+use std::sync::atomic::AtomicUsize;
+use std::sync::atomic::Ordering::SeqCst;
+use std::sync::{Arc, Condvar, Mutex};
+use std::time::Duration;
+
+/// A thread parking primitive.
+///
+/// Conceptually, each `Parker` has an associated token which is initially not present:
+///
+/// * The [`park`] method blocks the current thread unless or until the token is available, at
+/// which point it automatically consumes the token. It may also return *spuriously*, without
+/// consuming the token.
+///
+/// * The [`park_timeout`] method works the same as [`park`], but blocks for a specified maximum
+/// time.
+///
+/// * The [`unpark`] method atomically makes the token available if it wasn't already. Because the
+/// token is initially absent, [`unpark`] followed by [`park`] will result in the second call
+/// returning immediately.
+///
+/// In other words, each `Parker` acts a bit like a spinlock that can be locked and unlocked using
+/// [`park`] and [`unpark`].
+///
+/// # Examples
+///
+/// ```
+/// use std::thread;
+/// use std::time::Duration;
+/// use crossbeam_utils::sync::Parker;
+///
+/// let p = Parker::new();
+/// let u = p.unparker().clone();
+///
+/// // Make the token available.
+/// u.unpark();
+/// // Wakes up immediately and consumes the token.
+/// p.park();
+///
+/// thread::spawn(move || {
+/// thread::sleep(Duration::from_millis(500));
+/// u.unpark();
+/// });
+///
+/// // Wakes up when `u.unpark()` provides the token, but may also wake up
+/// // spuriously before that without consuming the token.
+/// p.park();
+/// ```
+///
+/// [`park`]: Parker::park
+/// [`park_timeout`]: Parker::park_timeout
+/// [`unpark`]: Unparker::unpark
+pub struct Parker {
+ unparker: Unparker,
+ _marker: PhantomData<*const ()>,
+}
+
+unsafe impl Send for Parker {}
+
+impl Default for Parker {
+ fn default() -> Self {
+ Self {
+ unparker: Unparker {
+ inner: Arc::new(Inner {
+ state: AtomicUsize::new(EMPTY),
+ lock: Mutex::new(()),
+ cvar: Condvar::new(),
+ }),
+ },
+ _marker: PhantomData,
+ }
+ }
+}
+
+impl Parker {
+ /// Creates a new `Parker`.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::Parker;
+ ///
+ /// let p = Parker::new();
+ /// ```
+ ///
+ pub fn new() -> Parker {
+ Self::default()
+ }
+
+ /// Blocks the current thread until the token is made available.
+ ///
+ /// A call to `park` may wake up spuriously without consuming the token, and callers should be
+ /// prepared for this possibility.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::Parker;
+ ///
+ /// let p = Parker::new();
+ /// let u = p.unparker().clone();
+ ///
+ /// // Make the token available.
+ /// u.unpark();
+ ///
+ /// // Wakes up immediately and consumes the token.
+ /// p.park();
+ /// ```
+ pub fn park(&self) {
+ self.unparker.inner.park(None);
+ }
+
+ /// Blocks the current thread until the token is made available, but only for a limited time.
+ ///
+ /// A call to `park_timeout` may wake up spuriously without consuming the token, and callers
+ /// should be prepared for this possibility.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::time::Duration;
+ /// use crossbeam_utils::sync::Parker;
+ ///
+ /// let p = Parker::new();
+ ///
+ /// // Waits for the token to become available, but will not wait longer than 500 ms.
+ /// p.park_timeout(Duration::from_millis(500));
+ /// ```
+ pub fn park_timeout(&self, timeout: Duration) {
+ self.unparker.inner.park(Some(timeout));
+ }
+
+ /// Returns a reference to an associated [`Unparker`].
+ ///
+ /// The returned [`Unparker`] doesn't have to be used by reference - it can also be cloned.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::Parker;
+ ///
+ /// let p = Parker::new();
+ /// let u = p.unparker().clone();
+ ///
+ /// // Make the token available.
+ /// u.unpark();
+ /// // Wakes up immediately and consumes the token.
+ /// p.park();
+ /// ```
+ ///
+ /// [`park`]: Parker::park
+ /// [`park_timeout`]: Parker::park_timeout
+ pub fn unparker(&self) -> &Unparker {
+ &self.unparker
+ }
+
+ /// Converts a `Parker` into a raw pointer.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::Parker;
+ ///
+ /// let p = Parker::new();
+ /// let raw = Parker::into_raw(p);
+ /// ```
+ pub fn into_raw(this: Parker) -> *const () {
+ Unparker::into_raw(this.unparker)
+ }
+
+ /// Converts a raw pointer into a `Parker`.
+ ///
+ /// # Safety
+ ///
+ /// This method is safe to use only with pointers returned by [`Parker::into_raw`].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::Parker;
+ ///
+ /// let p = Parker::new();
+ /// let raw = Parker::into_raw(p);
+ /// let p = unsafe { Parker::from_raw(raw) };
+ /// ```
+ pub unsafe fn from_raw(ptr: *const ()) -> Parker {
+ Parker {
+ unparker: Unparker::from_raw(ptr),
+ _marker: PhantomData,
+ }
+ }
+}
+
+impl fmt::Debug for Parker {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.pad("Parker { .. }")
+ }
+}
+
+/// Unparks a thread parked by the associated [`Parker`].
+pub struct Unparker {
+ inner: Arc<Inner>,
+}
+
+unsafe impl Send for Unparker {}
+unsafe impl Sync for Unparker {}
+
+impl Unparker {
+ /// Atomically makes the token available if it is not already.
+ ///
+ /// This method will wake up the thread blocked on [`park`] or [`park_timeout`], if there is
+ /// any.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use std::thread;
+ /// use std::time::Duration;
+ /// use crossbeam_utils::sync::Parker;
+ ///
+ /// let p = Parker::new();
+ /// let u = p.unparker().clone();
+ ///
+ /// thread::spawn(move || {
+ /// thread::sleep(Duration::from_millis(500));
+ /// u.unpark();
+ /// });
+ ///
+ /// // Wakes up when `u.unpark()` provides the token, but may also wake up
+ /// // spuriously before that without consuming the token.
+ /// p.park();
+ /// ```
+ ///
+ /// [`park`]: Parker::park
+ /// [`park_timeout`]: Parker::park_timeout
+ pub fn unpark(&self) {
+ self.inner.unpark()
+ }
+
+ /// Converts an `Unparker` into a raw pointer.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::{Parker, Unparker};
+ ///
+ /// let p = Parker::new();
+ /// let u = p.unparker().clone();
+ /// let raw = Unparker::into_raw(u);
+ /// ```
+ pub fn into_raw(this: Unparker) -> *const () {
+ Arc::into_raw(this.inner) as *const ()
+ }
+
+ /// Converts a raw pointer into an `Unparker`.
+ ///
+ /// # Safety
+ ///
+ /// This method is safe to use only with pointers returned by [`Unparker::into_raw`].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::{Parker, Unparker};
+ ///
+ /// let p = Parker::new();
+ /// let u = p.unparker().clone();
+ ///
+ /// let raw = Unparker::into_raw(u);
+ /// let u = unsafe { Unparker::from_raw(raw) };
+ /// ```
+ pub unsafe fn from_raw(ptr: *const ()) -> Unparker {
+ Unparker {
+ inner: Arc::from_raw(ptr as *const Inner),
+ }
+ }
+}
+
+impl fmt::Debug for Unparker {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.pad("Unparker { .. }")
+ }
+}
+
+impl Clone for Unparker {
+ fn clone(&self) -> Unparker {
+ Unparker {
+ inner: self.inner.clone(),
+ }
+ }
+}
+
+const EMPTY: usize = 0;
+const PARKED: usize = 1;
+const NOTIFIED: usize = 2;
+
+struct Inner {
+ state: AtomicUsize,
+ lock: Mutex<()>,
+ cvar: Condvar,
+}
+
+impl Inner {
+ fn park(&self, timeout: Option<Duration>) {
+ // If we were previously notified then we consume this notification and return quickly.
+ if self
+ .state
+ .compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst)
+ .is_ok()
+ {
+ return;
+ }
+
+ // If the timeout is zero, then there is no need to actually block.
+ if let Some(ref dur) = timeout {
+ if *dur == Duration::from_millis(0) {
+ return;
+ }
+ }
+
+ // Otherwise we need to coordinate going to sleep.
+ let mut m = self.lock.lock().unwrap();
+
+ match self.state.compare_exchange(EMPTY, PARKED, SeqCst, SeqCst) {
+ Ok(_) => {}
+ // Consume this notification to avoid spurious wakeups in the next park.
+ Err(NOTIFIED) => {
+ // We must read `state` here, even though we know it will be `NOTIFIED`. This is
+ // because `unpark` may have been called again since we read `NOTIFIED` in the
+ // `compare_exchange` above. We must perform an acquire operation that synchronizes
+ // with that `unpark` to observe any writes it made before the call to `unpark`. To
+ // do that we must read from the write it made to `state`.
+ let old = self.state.swap(EMPTY, SeqCst);
+ assert_eq!(old, NOTIFIED, "park state changed unexpectedly");
+ return;
+ }
+ Err(n) => panic!("inconsistent park_timeout state: {}", n),
+ }
+
+ match timeout {
+ None => {
+ loop {
+ // Block the current thread on the conditional variable.
+ m = self.cvar.wait(m).unwrap();
+
+ if self
+ .state
+ .compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst)
+ .is_ok()
+ {
+ // got a notification
+ return;
+ }
+
+ // spurious wakeup, go back to sleep
+ }
+ }
+ Some(timeout) => {
+ // Wait with a timeout, and if we spuriously wake up or otherwise wake up from a
+ // notification we just want to unconditionally set `state` back to `EMPTY`, either
+ // consuming a notification or un-flagging ourselves as parked.
+ let (_m, _result) = self.cvar.wait_timeout(m, timeout).unwrap();
+
+ match self.state.swap(EMPTY, SeqCst) {
+ NOTIFIED => {} // got a notification
+ PARKED => {} // no notification
+ n => panic!("inconsistent park_timeout state: {}", n),
+ }
+ }
+ }
+ }
+
+ pub fn unpark(&self) {
+ // To ensure the unparked thread will observe any writes we made before this call, we must
+ // perform a release operation that `park` can synchronize with. To do that we must write
+ // `NOTIFIED` even if `state` is already `NOTIFIED`. That is why this must be a swap rather
+ // than a compare-and-swap that returns if it reads `NOTIFIED` on failure.
+ match self.state.swap(NOTIFIED, SeqCst) {
+ EMPTY => return, // no one was waiting
+ NOTIFIED => return, // already unparked
+ PARKED => {} // gotta go wake someone up
+ _ => panic!("inconsistent state in unpark"),
+ }
+
+ // There is a period between when the parked thread sets `state` to `PARKED` (or last
+ // checked `state` in the case of a spurious wakeup) and when it actually waits on `cvar`.
+ // If we were to notify during this period it would be ignored and then when the parked
+ // thread went to sleep it would never wake up. Fortunately, it has `lock` locked at this
+ // stage so we can acquire `lock` to wait until it is ready to receive the notification.
+ //
+ // Releasing `lock` before the call to `notify_one` means that when the parked thread wakes
+ // it doesn't get woken only to have to wait for us to release `lock`.
+ drop(self.lock.lock().unwrap());
+ self.cvar.notify_one();
+ }
+}
diff --git a/src/sync/sharded_lock.rs b/src/sync/sharded_lock.rs
new file mode 100644
index 0000000..163d34c
--- /dev/null
+++ b/src/sync/sharded_lock.rs
@@ -0,0 +1,630 @@
+use std::cell::UnsafeCell;
+use std::collections::HashMap;
+use std::fmt;
+use std::marker::PhantomData;
+use std::mem;
+use std::ops::{Deref, DerefMut};
+use std::panic::{RefUnwindSafe, UnwindSafe};
+use std::sync::{LockResult, PoisonError, TryLockError, TryLockResult};
+use std::sync::{Mutex, RwLock, RwLockReadGuard, RwLockWriteGuard};
+use std::thread::{self, ThreadId};
+
+use crate::CachePadded;
+use lazy_static::lazy_static;
+
+/// The number of shards per sharded lock. Must be a power of two.
+const NUM_SHARDS: usize = 8;
+
+/// A shard containing a single reader-writer lock.
+struct Shard {
+ /// The inner reader-writer lock.
+ lock: RwLock<()>,
+
+ /// The write-guard keeping this shard locked.
+ ///
+ /// Write operations will lock each shard and store the guard here. These guards get dropped at
+ /// the same time the big guard is dropped.
+ write_guard: UnsafeCell<Option<RwLockWriteGuard<'static, ()>>>,
+}
+
+/// A sharded reader-writer lock.
+///
+/// This lock is equivalent to [`RwLock`], except read operations are faster and write operations
+/// are slower.
+///
+/// A `ShardedLock` is internally made of a list of *shards*, each being a [`RwLock`] occupying a
+/// single cache line. Read operations will pick one of the shards depending on the current thread
+/// and lock it. Write operations need to lock all shards in succession.
+///
+/// By splitting the lock into shards, concurrent read operations will in most cases choose
+/// different shards and thus update different cache lines, which is good for scalability. However,
+/// write operations need to do more work and are therefore slower than usual.
+///
+/// The priority policy of the lock is dependent on the underlying operating system's
+/// implementation, and this type does not guarantee that any particular policy will be used.
+///
+/// # Poisoning
+///
+/// A `ShardedLock`, like [`RwLock`], will become poisoned on a panic. Note that it may only be
+/// poisoned if a panic occurs while a write operation is in progress. If a panic occurs in any
+/// read operation, the lock will not be poisoned.
+///
+/// # Examples
+///
+/// ```
+/// use crossbeam_utils::sync::ShardedLock;
+///
+/// let lock = ShardedLock::new(5);
+///
+/// // Any number of read locks can be held at once.
+/// {
+/// let r1 = lock.read().unwrap();
+/// let r2 = lock.read().unwrap();
+/// assert_eq!(*r1, 5);
+/// assert_eq!(*r2, 5);
+/// } // Read locks are dropped at this point.
+///
+/// // However, only one write lock may be held.
+/// {
+/// let mut w = lock.write().unwrap();
+/// *w += 1;
+/// assert_eq!(*w, 6);
+/// } // Write lock is dropped here.
+/// ```
+///
+/// [`RwLock`]: std::sync::RwLock
+pub struct ShardedLock<T: ?Sized> {
+ /// A list of locks protecting the internal data.
+ shards: Box<[CachePadded<Shard>]>,
+
+ /// The internal data.
+ value: UnsafeCell<T>,
+}
+
+unsafe impl<T: ?Sized + Send> Send for ShardedLock<T> {}
+unsafe impl<T: ?Sized + Send + Sync> Sync for ShardedLock<T> {}
+
+impl<T: ?Sized> UnwindSafe for ShardedLock<T> {}
+impl<T: ?Sized> RefUnwindSafe for ShardedLock<T> {}
+
+impl<T> ShardedLock<T> {
+ /// Creates a new sharded reader-writer lock.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::ShardedLock;
+ ///
+ /// let lock = ShardedLock::new(5);
+ /// ```
+ pub fn new(value: T) -> ShardedLock<T> {
+ ShardedLock {
+ shards: (0..NUM_SHARDS)
+ .map(|_| {
+ CachePadded::new(Shard {
+ lock: RwLock::new(()),
+ write_guard: UnsafeCell::new(None),
+ })
+ })
+ .collect::<Box<[_]>>(),
+ value: UnsafeCell::new(value),
+ }
+ }
+
+ /// Consumes this lock, returning the underlying data.
+ ///
+ /// # Errors
+ ///
+ /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+ /// operation panics.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::ShardedLock;
+ ///
+ /// let lock = ShardedLock::new(String::new());
+ /// {
+ /// let mut s = lock.write().unwrap();
+ /// *s = "modified".to_owned();
+ /// }
+ /// assert_eq!(lock.into_inner().unwrap(), "modified");
+ /// ```
+ pub fn into_inner(self) -> LockResult<T> {
+ let is_poisoned = self.is_poisoned();
+ let inner = self.value.into_inner();
+
+ if is_poisoned {
+ Err(PoisonError::new(inner))
+ } else {
+ Ok(inner)
+ }
+ }
+}
+
+impl<T: ?Sized> ShardedLock<T> {
+ /// Returns `true` if the lock is poisoned.
+ ///
+ /// If another thread can still access the lock, it may become poisoned at any time. A `false`
+ /// result should not be trusted without additional synchronization.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::ShardedLock;
+ /// use std::sync::Arc;
+ /// use std::thread;
+ ///
+ /// let lock = Arc::new(ShardedLock::new(0));
+ /// let c_lock = lock.clone();
+ ///
+ /// let _ = thread::spawn(move || {
+ /// let _lock = c_lock.write().unwrap();
+ /// panic!(); // the lock gets poisoned
+ /// }).join();
+ /// assert_eq!(lock.is_poisoned(), true);
+ /// ```
+ pub fn is_poisoned(&self) -> bool {
+ self.shards[0].lock.is_poisoned()
+ }
+
+ /// Returns a mutable reference to the underlying data.
+ ///
+ /// Since this call borrows the lock mutably, no actual locking needs to take place.
+ ///
+ /// # Errors
+ ///
+ /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+ /// operation panics.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::ShardedLock;
+ ///
+ /// let mut lock = ShardedLock::new(0);
+ /// *lock.get_mut().unwrap() = 10;
+ /// assert_eq!(*lock.read().unwrap(), 10);
+ /// ```
+ pub fn get_mut(&mut self) -> LockResult<&mut T> {
+ let is_poisoned = self.is_poisoned();
+ let inner = unsafe { &mut *self.value.get() };
+
+ if is_poisoned {
+ Err(PoisonError::new(inner))
+ } else {
+ Ok(inner)
+ }
+ }
+
+ /// Attempts to acquire this lock with shared read access.
+ ///
+ /// If the access could not be granted at this time, an error is returned. Otherwise, a guard
+ /// is returned which will release the shared access when it is dropped. This method does not
+ /// provide any guarantees with respect to the ordering of whether contentious readers or
+ /// writers will acquire the lock first.
+ ///
+ /// # Errors
+ ///
+ /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+ /// operation panics.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::ShardedLock;
+ ///
+ /// let lock = ShardedLock::new(1);
+ ///
+ /// match lock.try_read() {
+ /// Ok(n) => assert_eq!(*n, 1),
+ /// Err(_) => unreachable!(),
+ /// };
+ /// ```
+ pub fn try_read(&self) -> TryLockResult<ShardedLockReadGuard<'_, T>> {
+ // Take the current thread index and map it to a shard index. Thread indices will tend to
+ // distribute shards among threads equally, thus reducing contention due to read-locking.
+ let current_index = current_index().unwrap_or(0);
+ let shard_index = current_index & (self.shards.len() - 1);
+
+ match self.shards[shard_index].lock.try_read() {
+ Ok(guard) => Ok(ShardedLockReadGuard {
+ lock: self,
+ _guard: guard,
+ _marker: PhantomData,
+ }),
+ Err(TryLockError::Poisoned(err)) => {
+ let guard = ShardedLockReadGuard {
+ lock: self,
+ _guard: err.into_inner(),
+ _marker: PhantomData,
+ };
+ Err(TryLockError::Poisoned(PoisonError::new(guard)))
+ }
+ Err(TryLockError::WouldBlock) => Err(TryLockError::WouldBlock),
+ }
+ }
+
+ /// Locks with shared read access, blocking the current thread until it can be acquired.
+ ///
+ /// The calling thread will be blocked until there are no more writers which hold the lock.
+ /// There may be other readers currently inside the lock when this method returns. This method
+ /// does not provide any guarantees with respect to the ordering of whether contentious readers
+ /// or writers will acquire the lock first.
+ ///
+ /// Returns a guard which will release the shared access when dropped.
+ ///
+ /// # Errors
+ ///
+ /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+ /// operation panics.
+ ///
+ /// # Panics
+ ///
+ /// This method might panic when called if the lock is already held by the current thread.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::ShardedLock;
+ /// use std::sync::Arc;
+ /// use std::thread;
+ ///
+ /// let lock = Arc::new(ShardedLock::new(1));
+ /// let c_lock = lock.clone();
+ ///
+ /// let n = lock.read().unwrap();
+ /// assert_eq!(*n, 1);
+ ///
+ /// thread::spawn(move || {
+ /// let r = c_lock.read();
+ /// assert!(r.is_ok());
+ /// }).join().unwrap();
+ /// ```
+ pub fn read(&self) -> LockResult<ShardedLockReadGuard<'_, T>> {
+ // Take the current thread index and map it to a shard index. Thread indices will tend to
+ // distribute shards among threads equally, thus reducing contention due to read-locking.
+ let current_index = current_index().unwrap_or(0);
+ let shard_index = current_index & (self.shards.len() - 1);
+
+ match self.shards[shard_index].lock.read() {
+ Ok(guard) => Ok(ShardedLockReadGuard {
+ lock: self,
+ _guard: guard,
+ _marker: PhantomData,
+ }),
+ Err(err) => Err(PoisonError::new(ShardedLockReadGuard {
+ lock: self,
+ _guard: err.into_inner(),
+ _marker: PhantomData,
+ })),
+ }
+ }
+
+ /// Attempts to acquire this lock with exclusive write access.
+ ///
+ /// If the access could not be granted at this time, an error is returned. Otherwise, a guard
+ /// is returned which will release the exclusive access when it is dropped. This method does
+ /// not provide any guarantees with respect to the ordering of whether contentious readers or
+ /// writers will acquire the lock first.
+ ///
+ /// # Errors
+ ///
+ /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+ /// operation panics.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::ShardedLock;
+ ///
+ /// let lock = ShardedLock::new(1);
+ ///
+ /// let n = lock.read().unwrap();
+ /// assert_eq!(*n, 1);
+ ///
+ /// assert!(lock.try_write().is_err());
+ /// ```
+ pub fn try_write(&self) -> TryLockResult<ShardedLockWriteGuard<'_, T>> {
+ let mut poisoned = false;
+ let mut blocked = None;
+
+ // Write-lock each shard in succession.
+ for (i, shard) in self.shards.iter().enumerate() {
+ let guard = match shard.lock.try_write() {
+ Ok(guard) => guard,
+ Err(TryLockError::Poisoned(err)) => {
+ poisoned = true;
+ err.into_inner()
+ }
+ Err(TryLockError::WouldBlock) => {
+ blocked = Some(i);
+ break;
+ }
+ };
+
+ // Store the guard into the shard.
+ unsafe {
+ let guard: RwLockWriteGuard<'static, ()> = mem::transmute(guard);
+ let dest: *mut _ = shard.write_guard.get();
+ *dest = Some(guard);
+ }
+ }
+
+ if let Some(i) = blocked {
+ // Unlock the shards in reverse order of locking.
+ for shard in self.shards[0..i].iter().rev() {
+ unsafe {
+ let dest: *mut _ = shard.write_guard.get();
+ let guard = mem::replace(&mut *dest, None);
+ drop(guard);
+ }
+ }
+ Err(TryLockError::WouldBlock)
+ } else if poisoned {
+ let guard = ShardedLockWriteGuard {
+ lock: self,
+ _marker: PhantomData,
+ };
+ Err(TryLockError::Poisoned(PoisonError::new(guard)))
+ } else {
+ Ok(ShardedLockWriteGuard {
+ lock: self,
+ _marker: PhantomData,
+ })
+ }
+ }
+
+ /// Locks with exclusive write access, blocking the current thread until it can be acquired.
+ ///
+ /// The calling thread will be blocked until there are no more writers which hold the lock.
+ /// There may be other readers currently inside the lock when this method returns. This method
+ /// does not provide any guarantees with respect to the ordering of whether contentious readers
+ /// or writers will acquire the lock first.
+ ///
+ /// Returns a guard which will release the exclusive access when dropped.
+ ///
+ /// # Errors
+ ///
+ /// This method will return an error if the lock is poisoned. A lock gets poisoned when a write
+ /// operation panics.
+ ///
+ /// # Panics
+ ///
+ /// This method might panic when called if the lock is already held by the current thread.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::ShardedLock;
+ ///
+ /// let lock = ShardedLock::new(1);
+ ///
+ /// let mut n = lock.write().unwrap();
+ /// *n = 2;
+ ///
+ /// assert!(lock.try_read().is_err());
+ /// ```
+ pub fn write(&self) -> LockResult<ShardedLockWriteGuard<'_, T>> {
+ let mut poisoned = false;
+
+ // Write-lock each shard in succession.
+ for shard in self.shards.iter() {
+ let guard = match shard.lock.write() {
+ Ok(guard) => guard,
+ Err(err) => {
+ poisoned = true;
+ err.into_inner()
+ }
+ };
+
+ // Store the guard into the shard.
+ unsafe {
+ let guard: RwLockWriteGuard<'_, ()> = guard;
+ let guard: RwLockWriteGuard<'static, ()> = mem::transmute(guard);
+ let dest: *mut _ = shard.write_guard.get();
+ *dest = Some(guard);
+ }
+ }
+
+ if poisoned {
+ Err(PoisonError::new(ShardedLockWriteGuard {
+ lock: self,
+ _marker: PhantomData,
+ }))
+ } else {
+ Ok(ShardedLockWriteGuard {
+ lock: self,
+ _marker: PhantomData,
+ })
+ }
+ }
+}
+
+impl<T: ?Sized + fmt::Debug> fmt::Debug for ShardedLock<T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ match self.try_read() {
+ Ok(guard) => f
+ .debug_struct("ShardedLock")
+ .field("data", &&*guard)
+ .finish(),
+ Err(TryLockError::Poisoned(err)) => f
+ .debug_struct("ShardedLock")
+ .field("data", &&**err.get_ref())
+ .finish(),
+ Err(TryLockError::WouldBlock) => {
+ struct LockedPlaceholder;
+ impl fmt::Debug for LockedPlaceholder {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.write_str("<locked>")
+ }
+ }
+ f.debug_struct("ShardedLock")
+ .field("data", &LockedPlaceholder)
+ .finish()
+ }
+ }
+ }
+}
+
+impl<T: Default> Default for ShardedLock<T> {
+ fn default() -> ShardedLock<T> {
+ ShardedLock::new(Default::default())
+ }
+}
+
+impl<T> From<T> for ShardedLock<T> {
+ fn from(t: T) -> Self {
+ ShardedLock::new(t)
+ }
+}
+
+/// A guard used to release the shared read access of a [`ShardedLock`] when dropped.
+pub struct ShardedLockReadGuard<'a, T: ?Sized> {
+ lock: &'a ShardedLock<T>,
+ _guard: RwLockReadGuard<'a, ()>,
+ _marker: PhantomData<RwLockReadGuard<'a, T>>,
+}
+
+unsafe impl<T: ?Sized + Sync> Sync for ShardedLockReadGuard<'_, T> {}
+
+impl<T: ?Sized> Deref for ShardedLockReadGuard<'_, T> {
+ type Target = T;
+
+ fn deref(&self) -> &T {
+ unsafe { &*self.lock.value.get() }
+ }
+}
+
+impl<T: fmt::Debug> fmt::Debug for ShardedLockReadGuard<'_, T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.debug_struct("ShardedLockReadGuard")
+ .field("lock", &self.lock)
+ .finish()
+ }
+}
+
+impl<T: ?Sized + fmt::Display> fmt::Display for ShardedLockReadGuard<'_, T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ (**self).fmt(f)
+ }
+}
+
+/// A guard used to release the exclusive write access of a [`ShardedLock`] when dropped.
+pub struct ShardedLockWriteGuard<'a, T: ?Sized> {
+ lock: &'a ShardedLock<T>,
+ _marker: PhantomData<RwLockWriteGuard<'a, T>>,
+}
+
+unsafe impl<T: ?Sized + Sync> Sync for ShardedLockWriteGuard<'_, T> {}
+
+impl<T: ?Sized> Drop for ShardedLockWriteGuard<'_, T> {
+ fn drop(&mut self) {
+ // Unlock the shards in reverse order of locking.
+ for shard in self.lock.shards.iter().rev() {
+ unsafe {
+ let dest: *mut _ = shard.write_guard.get();
+ let guard = mem::replace(&mut *dest, None);
+ drop(guard);
+ }
+ }
+ }
+}
+
+impl<T: fmt::Debug> fmt::Debug for ShardedLockWriteGuard<'_, T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.debug_struct("ShardedLockWriteGuard")
+ .field("lock", &self.lock)
+ .finish()
+ }
+}
+
+impl<T: ?Sized + fmt::Display> fmt::Display for ShardedLockWriteGuard<'_, T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ (**self).fmt(f)
+ }
+}
+
+impl<T: ?Sized> Deref for ShardedLockWriteGuard<'_, T> {
+ type Target = T;
+
+ fn deref(&self) -> &T {
+ unsafe { &*self.lock.value.get() }
+ }
+}
+
+impl<T: ?Sized> DerefMut for ShardedLockWriteGuard<'_, T> {
+ fn deref_mut(&mut self) -> &mut T {
+ unsafe { &mut *self.lock.value.get() }
+ }
+}
+
+/// Returns a `usize` that identifies the current thread.
+///
+/// Each thread is associated with an 'index'. While there are no particular guarantees, indices
+/// usually tend to be consecutive numbers between 0 and the number of running threads.
+///
+/// Since this function accesses TLS, `None` might be returned if the current thread's TLS is
+/// tearing down.
+#[inline]
+fn current_index() -> Option<usize> {
+ REGISTRATION.try_with(|reg| reg.index).ok()
+}
+
+/// The global registry keeping track of registered threads and indices.
+struct ThreadIndices {
+ /// Mapping from `ThreadId` to thread index.
+ mapping: HashMap<ThreadId, usize>,
+
+ /// A list of free indices.
+ free_list: Vec<usize>,
+
+ /// The next index to allocate if the free list is empty.
+ next_index: usize,
+}
+
+lazy_static! {
+ static ref THREAD_INDICES: Mutex<ThreadIndices> = Mutex::new(ThreadIndices {
+ mapping: HashMap::new(),
+ free_list: Vec::new(),
+ next_index: 0,
+ });
+}
+
+/// A registration of a thread with an index.
+///
+/// When dropped, unregisters the thread and frees the reserved index.
+struct Registration {
+ index: usize,
+ thread_id: ThreadId,
+}
+
+impl Drop for Registration {
+ fn drop(&mut self) {
+ let mut indices = THREAD_INDICES.lock().unwrap();
+ indices.mapping.remove(&self.thread_id);
+ indices.free_list.push(self.index);
+ }
+}
+
+thread_local! {
+ static REGISTRATION: Registration = {
+ let thread_id = thread::current().id();
+ let mut indices = THREAD_INDICES.lock().unwrap();
+
+ let index = match indices.free_list.pop() {
+ Some(i) => i,
+ None => {
+ let i = indices.next_index;
+ indices.next_index += 1;
+ i
+ }
+ };
+ indices.mapping.insert(thread_id, index);
+
+ Registration {
+ index,
+ thread_id,
+ }
+ };
+}
diff --git a/src/sync/wait_group.rs b/src/sync/wait_group.rs
new file mode 100644
index 0000000..cd7af12
--- /dev/null
+++ b/src/sync/wait_group.rs
@@ -0,0 +1,146 @@
+// Necessary for using `Mutex<usize>` for conditional variables
+#![allow(clippy::mutex_atomic)]
+
+use std::fmt;
+use std::sync::{Arc, Condvar, Mutex};
+
+/// Enables threads to synchronize the beginning or end of some computation.
+///
+/// # Wait groups vs barriers
+///
+/// `WaitGroup` is very similar to [`Barrier`], but there are a few differences:
+///
+/// * [`Barrier`] needs to know the number of threads at construction, while `WaitGroup` is cloned to
+/// register more threads.
+///
+/// * A [`Barrier`] can be reused even after all threads have synchronized, while a `WaitGroup`
+/// synchronizes threads only once.
+///
+/// * All threads wait for others to reach the [`Barrier`]. With `WaitGroup`, each thread can choose
+/// to either wait for other threads or to continue without blocking.
+///
+/// # Examples
+///
+/// ```
+/// use crossbeam_utils::sync::WaitGroup;
+/// use std::thread;
+///
+/// // Create a new wait group.
+/// let wg = WaitGroup::new();
+///
+/// for _ in 0..4 {
+/// // Create another reference to the wait group.
+/// let wg = wg.clone();
+///
+/// thread::spawn(move || {
+/// // Do some work.
+///
+/// // Drop the reference to the wait group.
+/// drop(wg);
+/// });
+/// }
+///
+/// // Block until all threads have finished their work.
+/// wg.wait();
+/// ```
+///
+/// [`Barrier`]: std::sync::Barrier
+pub struct WaitGroup {
+ inner: Arc<Inner>,
+}
+
+/// Inner state of a `WaitGroup`.
+struct Inner {
+ cvar: Condvar,
+ count: Mutex<usize>,
+}
+
+impl Default for WaitGroup {
+ fn default() -> Self {
+ Self {
+ inner: Arc::new(Inner {
+ cvar: Condvar::new(),
+ count: Mutex::new(1),
+ }),
+ }
+ }
+}
+
+impl WaitGroup {
+ /// Creates a new wait group and returns the single reference to it.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::WaitGroup;
+ ///
+ /// let wg = WaitGroup::new();
+ /// ```
+ pub fn new() -> Self {
+ Self::default()
+ }
+
+ /// Drops this reference and waits until all other references are dropped.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::sync::WaitGroup;
+ /// use std::thread;
+ ///
+ /// let wg = WaitGroup::new();
+ ///
+ /// thread::spawn({
+ /// let wg = wg.clone();
+ /// move || {
+ /// // Block until both threads have reached `wait()`.
+ /// wg.wait();
+ /// }
+ /// });
+ ///
+ /// // Block until both threads have reached `wait()`.
+ /// wg.wait();
+ /// ```
+ pub fn wait(self) {
+ if *self.inner.count.lock().unwrap() == 1 {
+ return;
+ }
+
+ let inner = self.inner.clone();
+ drop(self);
+
+ let mut count = inner.count.lock().unwrap();
+ while *count > 0 {
+ count = inner.cvar.wait(count).unwrap();
+ }
+ }
+}
+
+impl Drop for WaitGroup {
+ fn drop(&mut self) {
+ let mut count = self.inner.count.lock().unwrap();
+ *count -= 1;
+
+ if *count == 0 {
+ self.inner.cvar.notify_all();
+ }
+ }
+}
+
+impl Clone for WaitGroup {
+ fn clone(&self) -> WaitGroup {
+ let mut count = self.inner.count.lock().unwrap();
+ *count += 1;
+
+ WaitGroup {
+ inner: self.inner.clone(),
+ }
+ }
+}
+
+impl fmt::Debug for WaitGroup {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ let count: &usize = &*self.inner.count.lock().unwrap();
+ f.debug_struct("WaitGroup").field("count", count).finish()
+ }
+}
diff --git a/src/thread.rs b/src/thread.rs
new file mode 100644
index 0000000..ab91be7
--- /dev/null
+++ b/src/thread.rs
@@ -0,0 +1,588 @@
+//! Threads that can borrow variables from the stack.
+//!
+//! Create a scope when spawned threads need to access variables on the stack:
+//!
+//! ```
+//! use crossbeam_utils::thread;
+//!
+//! let people = vec![
+//! "Alice".to_string(),
+//! "Bob".to_string(),
+//! "Carol".to_string(),
+//! ];
+//!
+//! thread::scope(|s| {
+//! for person in &people {
+//! s.spawn(move |_| {
+//! println!("Hello, {}!", person);
+//! });
+//! }
+//! }).unwrap();
+//! ```
+//!
+//! # Why scoped threads?
+//!
+//! Suppose we wanted to re-write the previous example using plain threads:
+//!
+//! ```compile_fail,E0597
+//! use std::thread;
+//!
+//! let people = vec![
+//! "Alice".to_string(),
+//! "Bob".to_string(),
+//! "Carol".to_string(),
+//! ];
+//!
+//! let mut threads = Vec::new();
+//!
+//! for person in &people {
+//! threads.push(thread::spawn(move || {
+//! println!("Hello, {}!", person);
+//! }));
+//! }
+//!
+//! for thread in threads {
+//! thread.join().unwrap();
+//! }
+//! ```
+//!
+//! This doesn't work because the borrow checker complains about `people` not living long enough:
+//!
+//! ```text
+//! error[E0597]: `people` does not live long enough
+//! --> src/main.rs:12:20
+//! |
+//! 12 | for person in &people {
+//! | ^^^^^^ borrowed value does not live long enough
+//! ...
+//! 21 | }
+//! | - borrowed value only lives until here
+//! |
+//! = note: borrowed value must be valid for the static lifetime...
+//! ```
+//!
+//! The problem here is that spawned threads are not allowed to borrow variables on stack because
+//! the compiler cannot prove they will be joined before `people` is destroyed.
+//!
+//! Scoped threads are a mechanism to guarantee to the compiler that spawned threads will be joined
+//! before the scope ends.
+//!
+//! # How scoped threads work
+//!
+//! If a variable is borrowed by a thread, the thread must complete before the variable is
+//! destroyed. Threads spawned using [`std::thread::spawn`] can only borrow variables with the
+//! `'static` lifetime because the borrow checker cannot be sure when the thread will complete.
+//!
+//! A scope creates a clear boundary between variables outside the scope and threads inside the
+//! scope. Whenever a scope spawns a thread, it promises to join the thread before the scope ends.
+//! This way we guarantee to the borrow checker that scoped threads only live within the scope and
+//! can safely access variables outside it.
+//!
+//! # Nesting scoped threads
+//!
+//! Sometimes scoped threads need to spawn more threads within the same scope. This is a little
+//! tricky because argument `s` lives *inside* the invocation of `thread::scope()` and as such
+//! cannot be borrowed by scoped threads:
+//!
+//! ```compile_fail,E0373,E0521
+//! use crossbeam_utils::thread;
+//!
+//! thread::scope(|s| {
+//! s.spawn(|_| {
+//! // Not going to compile because we're trying to borrow `s`,
+//! // which lives *inside* the scope! :(
+//! s.spawn(|_| println!("nested thread"));
+//! });
+//! });
+//! ```
+//!
+//! Fortunately, there is a solution. Every scoped thread is passed a reference to its scope as an
+//! argument, which can be used for spawning nested threads:
+//!
+//! ```
+//! use crossbeam_utils::thread;
+//!
+//! thread::scope(|s| {
+//! // Note the `|s|` here.
+//! s.spawn(|s| {
+//! // Yay, this works because we're using a fresh argument `s`! :)
+//! s.spawn(|_| println!("nested thread"));
+//! });
+//! }).unwrap();
+//! ```
+//!
+//! [`std::thread::spawn`]: std::thread::spawn
+
+use std::fmt;
+use std::io;
+use std::marker::PhantomData;
+use std::mem;
+use std::panic;
+use std::sync::{Arc, Mutex};
+use std::thread;
+
+use crate::sync::WaitGroup;
+use cfg_if::cfg_if;
+
+type SharedVec<T> = Arc<Mutex<Vec<T>>>;
+type SharedOption<T> = Arc<Mutex<Option<T>>>;
+
+/// Creates a new scope for spawning threads.
+///
+/// All child threads that haven't been manually joined will be automatically joined just before
+/// this function invocation ends. If all joined threads have successfully completed, `Ok` is
+/// returned with the return value of `f`. If any of the joined threads has panicked, an `Err` is
+/// returned containing errors from panicked threads.
+///
+/// # Examples
+///
+/// ```
+/// use crossbeam_utils::thread;
+///
+/// let var = vec![1, 2, 3];
+///
+/// thread::scope(|s| {
+/// s.spawn(|_| {
+/// println!("A child thread borrowing `var`: {:?}", var);
+/// });
+/// }).unwrap();
+/// ```
+pub fn scope<'env, F, R>(f: F) -> thread::Result<R>
+where
+ F: FnOnce(&Scope<'env>) -> R,
+{
+ let wg = WaitGroup::new();
+ let scope = Scope::<'env> {
+ handles: SharedVec::default(),
+ wait_group: wg.clone(),
+ _marker: PhantomData,
+ };
+
+ // Execute the scoped function, but catch any panics.
+ let result = panic::catch_unwind(panic::AssertUnwindSafe(|| f(&scope)));
+
+ // Wait until all nested scopes are dropped.
+ drop(scope.wait_group);
+ wg.wait();
+
+ // Join all remaining spawned threads.
+ let panics: Vec<_> = scope
+ .handles
+ .lock()
+ .unwrap()
+ // Filter handles that haven't been joined, join them, and collect errors.
+ .drain(..)
+ .filter_map(|handle| handle.lock().unwrap().take())
+ .filter_map(|handle| handle.join().err())
+ .collect();
+
+ // If `f` has panicked, resume unwinding.
+ // If any of the child threads have panicked, return the panic errors.
+ // Otherwise, everything is OK and return the result of `f`.
+ match result {
+ Err(err) => panic::resume_unwind(err),
+ Ok(res) => {
+ if panics.is_empty() {
+ Ok(res)
+ } else {
+ Err(Box::new(panics))
+ }
+ }
+ }
+}
+
+/// A scope for spawning threads.
+pub struct Scope<'env> {
+ /// The list of the thread join handles.
+ handles: SharedVec<SharedOption<thread::JoinHandle<()>>>,
+
+ /// Used to wait until all subscopes all dropped.
+ wait_group: WaitGroup,
+
+ /// Borrows data with invariant lifetime `'env`.
+ _marker: PhantomData<&'env mut &'env ()>,
+}
+
+unsafe impl Sync for Scope<'_> {}
+
+impl<'env> Scope<'env> {
+ /// Spawns a scoped thread.
+ ///
+ /// This method is similar to the [`spawn`] function in Rust's standard library. The difference
+ /// is that this thread is scoped, meaning it's guaranteed to terminate before the scope exits,
+ /// allowing it to reference variables outside the scope.
+ ///
+ /// The scoped thread is passed a reference to this scope as an argument, which can be used for
+ /// spawning nested threads.
+ ///
+ /// The returned [handle](ScopedJoinHandle) can be used to manually
+ /// [join](ScopedJoinHandle::join) the thread before the scope exits.
+ ///
+ /// This will create a thread using default parameters of [`ScopedThreadBuilder`], if you want to specify the
+ /// stack size or the name of the thread, use this API instead.
+ ///
+ /// [`spawn`]: std::thread::spawn
+ ///
+ /// # Panics
+ ///
+ /// Panics if the OS fails to create a thread; use [`ScopedThreadBuilder::spawn`]
+ /// to recover from such errors.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::thread;
+ ///
+ /// thread::scope(|s| {
+ /// let handle = s.spawn(|_| {
+ /// println!("A child thread is running");
+ /// 42
+ /// });
+ ///
+ /// // Join the thread and retrieve its result.
+ /// let res = handle.join().unwrap();
+ /// assert_eq!(res, 42);
+ /// }).unwrap();
+ /// ```
+ pub fn spawn<'scope, F, T>(&'scope self, f: F) -> ScopedJoinHandle<'scope, T>
+ where
+ F: FnOnce(&Scope<'env>) -> T,
+ F: Send + 'env,
+ T: Send + 'env,
+ {
+ self.builder()
+ .spawn(f)
+ .expect("failed to spawn scoped thread")
+ }
+
+ /// Creates a builder that can configure a thread before spawning.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::thread;
+ ///
+ /// thread::scope(|s| {
+ /// s.builder()
+ /// .spawn(|_| println!("A child thread is running"))
+ /// .unwrap();
+ /// }).unwrap();
+ /// ```
+ pub fn builder<'scope>(&'scope self) -> ScopedThreadBuilder<'scope, 'env> {
+ ScopedThreadBuilder {
+ scope: self,
+ builder: thread::Builder::new(),
+ }
+ }
+}
+
+impl fmt::Debug for Scope<'_> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.pad("Scope { .. }")
+ }
+}
+
+/// Configures the properties of a new thread.
+///
+/// The two configurable properties are:
+///
+/// - [`name`]: Specifies an [associated name for the thread][naming-threads].
+/// - [`stack_size`]: Specifies the [desired stack size for the thread][stack-size].
+///
+/// The [`spawn`] method will take ownership of the builder and return an [`io::Result`] of the
+/// thread handle with the given configuration.
+///
+/// The [`Scope::spawn`] method uses a builder with default configuration and unwraps its return
+/// value. You may want to use this builder when you want to recover from a failure to launch a
+/// thread.
+///
+/// # Examples
+///
+/// ```
+/// use crossbeam_utils::thread;
+///
+/// thread::scope(|s| {
+/// s.builder()
+/// .spawn(|_| println!("Running a child thread"))
+/// .unwrap();
+/// }).unwrap();
+/// ```
+///
+/// [`name`]: ScopedThreadBuilder::name
+/// [`stack_size`]: ScopedThreadBuilder::stack_size
+/// [`spawn`]: ScopedThreadBuilder::spawn
+/// [`io::Result`]: std::io::Result
+/// [naming-threads]: std::thread#naming-threads
+/// [stack-size]: std::thread#stack-size
+#[derive(Debug)]
+pub struct ScopedThreadBuilder<'scope, 'env> {
+ scope: &'scope Scope<'env>,
+ builder: thread::Builder,
+}
+
+impl<'scope, 'env> ScopedThreadBuilder<'scope, 'env> {
+ /// Sets the name for the new thread.
+ ///
+ /// The name must not contain null bytes (`\0`).
+ ///
+ /// For more information about named threads, see [here][naming-threads].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::thread;
+ /// use std::thread::current;
+ ///
+ /// thread::scope(|s| {
+ /// s.builder()
+ /// .name("my thread".to_string())
+ /// .spawn(|_| assert_eq!(current().name(), Some("my thread")))
+ /// .unwrap();
+ /// }).unwrap();
+ /// ```
+ ///
+ /// [naming-threads]: std::thread#naming-threads
+ pub fn name(mut self, name: String) -> ScopedThreadBuilder<'scope, 'env> {
+ self.builder = self.builder.name(name);
+ self
+ }
+
+ /// Sets the size of the stack for the new thread.
+ ///
+ /// The stack size is measured in bytes.
+ ///
+ /// For more information about the stack size for threads, see [here][stack-size].
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::thread;
+ ///
+ /// thread::scope(|s| {
+ /// s.builder()
+ /// .stack_size(32 * 1024)
+ /// .spawn(|_| println!("Running a child thread"))
+ /// .unwrap();
+ /// }).unwrap();
+ /// ```
+ ///
+ /// [stack-size]: std::thread#stack-size
+ pub fn stack_size(mut self, size: usize) -> ScopedThreadBuilder<'scope, 'env> {
+ self.builder = self.builder.stack_size(size);
+ self
+ }
+
+ /// Spawns a scoped thread with this configuration.
+ ///
+ /// The scoped thread is passed a reference to this scope as an argument, which can be used for
+ /// spawning nested threads.
+ ///
+ /// The returned handle can be used to manually join the thread before the scope exits.
+ ///
+ /// # Errors
+ ///
+ /// Unlike the [`Scope::spawn`] method, this method yields an
+ /// [`io::Result`] to capture any failure to create the thread at
+ /// the OS level.
+ ///
+ /// [`io::Result`]: std::io::Result
+ ///
+ /// # Panics
+ ///
+ /// Panics if a thread name was set and it contained null bytes.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::thread;
+ ///
+ /// thread::scope(|s| {
+ /// let handle = s.builder()
+ /// .spawn(|_| {
+ /// println!("A child thread is running");
+ /// 42
+ /// })
+ /// .unwrap();
+ ///
+ /// // Join the thread and retrieve its result.
+ /// let res = handle.join().unwrap();
+ /// assert_eq!(res, 42);
+ /// }).unwrap();
+ /// ```
+ pub fn spawn<F, T>(self, f: F) -> io::Result<ScopedJoinHandle<'scope, T>>
+ where
+ F: FnOnce(&Scope<'env>) -> T,
+ F: Send + 'env,
+ T: Send + 'env,
+ {
+ // The result of `f` will be stored here.
+ let result = SharedOption::default();
+
+ // Spawn the thread and grab its join handle and thread handle.
+ let (handle, thread) = {
+ let result = Arc::clone(&result);
+
+ // A clone of the scope that will be moved into the new thread.
+ let scope = Scope::<'env> {
+ handles: Arc::clone(&self.scope.handles),
+ wait_group: self.scope.wait_group.clone(),
+ _marker: PhantomData,
+ };
+
+ // Spawn the thread.
+ let handle = {
+ let closure = move || {
+ // Make sure the scope is inside the closure with the proper `'env` lifetime.
+ let scope: Scope<'env> = scope;
+
+ // Run the closure.
+ let res = f(&scope);
+
+ // Store the result if the closure didn't panic.
+ *result.lock().unwrap() = Some(res);
+ };
+
+ // Allocate `closure` on the heap and erase the `'env` bound.
+ let closure: Box<dyn FnOnce() + Send + 'env> = Box::new(closure);
+ let closure: Box<dyn FnOnce() + Send + 'static> =
+ unsafe { mem::transmute(closure) };
+
+ // Finally, spawn the closure.
+ self.builder.spawn(move || closure())?
+ };
+
+ let thread = handle.thread().clone();
+ let handle = Arc::new(Mutex::new(Some(handle)));
+ (handle, thread)
+ };
+
+ // Add the handle to the shared list of join handles.
+ self.scope.handles.lock().unwrap().push(Arc::clone(&handle));
+
+ Ok(ScopedJoinHandle {
+ handle,
+ result,
+ thread,
+ _marker: PhantomData,
+ })
+ }
+}
+
+unsafe impl<T> Send for ScopedJoinHandle<'_, T> {}
+unsafe impl<T> Sync for ScopedJoinHandle<'_, T> {}
+
+/// A handle that can be used to join its scoped thread.
+///
+/// This struct is created by the [`Scope::spawn`] method and the
+/// [`ScopedThreadBuilder::spawn`] method.
+pub struct ScopedJoinHandle<'scope, T> {
+ /// A join handle to the spawned thread.
+ handle: SharedOption<thread::JoinHandle<()>>,
+
+ /// Holds the result of the inner closure.
+ result: SharedOption<T>,
+
+ /// A handle to the the spawned thread.
+ thread: thread::Thread,
+
+ /// Borrows the parent scope with lifetime `'scope`.
+ _marker: PhantomData<&'scope ()>,
+}
+
+impl<T> ScopedJoinHandle<'_, T> {
+ /// Waits for the thread to finish and returns its result.
+ ///
+ /// If the child thread panics, an error is returned.
+ ///
+ /// # Panics
+ ///
+ /// This function may panic on some platforms if a thread attempts to join itself or otherwise
+ /// may create a deadlock with joining threads.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::thread;
+ ///
+ /// thread::scope(|s| {
+ /// let handle1 = s.spawn(|_| println!("I'm a happy thread :)"));
+ /// let handle2 = s.spawn(|_| panic!("I'm a sad thread :("));
+ ///
+ /// // Join the first thread and verify that it succeeded.
+ /// let res = handle1.join();
+ /// assert!(res.is_ok());
+ ///
+ /// // Join the second thread and verify that it panicked.
+ /// let res = handle2.join();
+ /// assert!(res.is_err());
+ /// }).unwrap();
+ /// ```
+ pub fn join(self) -> thread::Result<T> {
+ // Take out the handle. The handle will surely be available because the root scope waits
+ // for nested scopes before joining remaining threads.
+ let handle = self.handle.lock().unwrap().take().unwrap();
+
+ // Join the thread and then take the result out of its inner closure.
+ handle
+ .join()
+ .map(|()| self.result.lock().unwrap().take().unwrap())
+ }
+
+ /// Returns a handle to the underlying thread.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// use crossbeam_utils::thread;
+ ///
+ /// thread::scope(|s| {
+ /// let handle = s.spawn(|_| println!("A child thread is running"));
+ /// println!("The child thread ID: {:?}", handle.thread().id());
+ /// }).unwrap();
+ /// ```
+ pub fn thread(&self) -> &thread::Thread {
+ &self.thread
+ }
+}
+
+cfg_if! {
+ if #[cfg(unix)] {
+ use std::os::unix::thread::{JoinHandleExt, RawPthread};
+
+ impl<T> JoinHandleExt for ScopedJoinHandle<'_, T> {
+ fn as_pthread_t(&self) -> RawPthread {
+ // Borrow the handle. The handle will surely be available because the root scope waits
+ // for nested scopes before joining remaining threads.
+ let handle = self.handle.lock().unwrap();
+ handle.as_ref().unwrap().as_pthread_t()
+ }
+ fn into_pthread_t(self) -> RawPthread {
+ self.as_pthread_t()
+ }
+ }
+ } else if #[cfg(windows)] {
+ use std::os::windows::io::{AsRawHandle, IntoRawHandle, RawHandle};
+
+ impl<T> AsRawHandle for ScopedJoinHandle<'_, T> {
+ fn as_raw_handle(&self) -> RawHandle {
+ // Borrow the handle. The handle will surely be available because the root scope waits
+ // for nested scopes before joining remaining threads.
+ let handle = self.handle.lock().unwrap();
+ handle.as_ref().unwrap().as_raw_handle()
+ }
+ }
+
+ #[cfg(windows)]
+ impl<T> IntoRawHandle for ScopedJoinHandle<'_, T> {
+ fn into_raw_handle(self) -> RawHandle {
+ self.as_raw_handle()
+ }
+ }
+ }
+}
+
+impl<T> fmt::Debug for ScopedJoinHandle<'_, T> {
+ fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+ f.pad("ScopedJoinHandle { .. }")
+ }
+}
diff --git a/tests/atomic_cell.rs b/tests/atomic_cell.rs
new file mode 100644
index 0000000..3d91d81
--- /dev/null
+++ b/tests/atomic_cell.rs
@@ -0,0 +1,236 @@
+use std::sync::atomic::AtomicUsize;
+use std::sync::atomic::Ordering::SeqCst;
+
+use crossbeam_utils::atomic::AtomicCell;
+
+#[test]
+fn is_lock_free() {
+ struct UsizeWrap(usize);
+ struct U8Wrap(bool);
+ struct I16Wrap(i16);
+
+ assert_eq!(AtomicCell::<usize>::is_lock_free(), true);
+ assert_eq!(AtomicCell::<isize>::is_lock_free(), true);
+ assert_eq!(AtomicCell::<UsizeWrap>::is_lock_free(), true);
+
+ assert_eq!(AtomicCell::<u8>::is_lock_free(), cfg!(has_atomic_u8));
+ assert_eq!(AtomicCell::<bool>::is_lock_free(), cfg!(has_atomic_u8));
+ assert_eq!(AtomicCell::<U8Wrap>::is_lock_free(), cfg!(has_atomic_u8));
+
+ assert_eq!(AtomicCell::<I16Wrap>::is_lock_free(), cfg!(has_atomic_u16));
+
+ assert_eq!(AtomicCell::<u128>::is_lock_free(), cfg!(has_atomic_u128));
+}
+
+#[test]
+fn const_is_lock_free() {
+ const _U: bool = AtomicCell::<usize>::is_lock_free();
+ const _I: bool = AtomicCell::<isize>::is_lock_free();
+}
+
+#[test]
+fn drops_unit() {
+ static CNT: AtomicUsize = AtomicUsize::new(0);
+ CNT.store(0, SeqCst);
+
+ #[derive(Debug, PartialEq, Eq)]
+ struct Foo();
+
+ impl Foo {
+ fn new() -> Foo {
+ CNT.fetch_add(1, SeqCst);
+ Foo()
+ }
+ }
+
+ impl Drop for Foo {
+ fn drop(&mut self) {
+ CNT.fetch_sub(1, SeqCst);
+ }
+ }
+
+ impl Default for Foo {
+ fn default() -> Foo {
+ Foo::new()
+ }
+ }
+
+ let a = AtomicCell::new(Foo::new());
+
+ assert_eq!(a.swap(Foo::new()), Foo::new());
+ assert_eq!(CNT.load(SeqCst), 1);
+
+ a.store(Foo::new());
+ assert_eq!(CNT.load(SeqCst), 1);
+
+ assert_eq!(a.swap(Foo::default()), Foo::new());
+ assert_eq!(CNT.load(SeqCst), 1);
+
+ drop(a);
+ assert_eq!(CNT.load(SeqCst), 0);
+}
+
+#[test]
+fn drops_u8() {
+ static CNT: AtomicUsize = AtomicUsize::new(0);
+ CNT.store(0, SeqCst);
+
+ #[derive(Debug, PartialEq, Eq)]
+ struct Foo(u8);
+
+ impl Foo {
+ fn new(val: u8) -> Foo {
+ CNT.fetch_add(1, SeqCst);
+ Foo(val)
+ }
+ }
+
+ impl Drop for Foo {
+ fn drop(&mut self) {
+ CNT.fetch_sub(1, SeqCst);
+ }
+ }
+
+ impl Default for Foo {
+ fn default() -> Foo {
+ Foo::new(0)
+ }
+ }
+
+ let a = AtomicCell::new(Foo::new(5));
+
+ assert_eq!(a.swap(Foo::new(6)), Foo::new(5));
+ assert_eq!(a.swap(Foo::new(1)), Foo::new(6));
+ assert_eq!(CNT.load(SeqCst), 1);
+
+ a.store(Foo::new(2));
+ assert_eq!(CNT.load(SeqCst), 1);
+
+ assert_eq!(a.swap(Foo::default()), Foo::new(2));
+ assert_eq!(CNT.load(SeqCst), 1);
+
+ assert_eq!(a.swap(Foo::default()), Foo::new(0));
+ assert_eq!(CNT.load(SeqCst), 1);
+
+ drop(a);
+ assert_eq!(CNT.load(SeqCst), 0);
+}
+
+#[test]
+fn drops_usize() {
+ static CNT: AtomicUsize = AtomicUsize::new(0);
+ CNT.store(0, SeqCst);
+
+ #[derive(Debug, PartialEq, Eq)]
+ struct Foo(usize);
+
+ impl Foo {
+ fn new(val: usize) -> Foo {
+ CNT.fetch_add(1, SeqCst);
+ Foo(val)
+ }
+ }
+
+ impl Drop for Foo {
+ fn drop(&mut self) {
+ CNT.fetch_sub(1, SeqCst);
+ }
+ }
+
+ impl Default for Foo {
+ fn default() -> Foo {
+ Foo::new(0)
+ }
+ }
+
+ let a = AtomicCell::new(Foo::new(5));
+
+ assert_eq!(a.swap(Foo::new(6)), Foo::new(5));
+ assert_eq!(a.swap(Foo::new(1)), Foo::new(6));
+ assert_eq!(CNT.load(SeqCst), 1);
+
+ a.store(Foo::new(2));
+ assert_eq!(CNT.load(SeqCst), 1);
+
+ assert_eq!(a.swap(Foo::default()), Foo::new(2));
+ assert_eq!(CNT.load(SeqCst), 1);
+
+ assert_eq!(a.swap(Foo::default()), Foo::new(0));
+ assert_eq!(CNT.load(SeqCst), 1);
+
+ drop(a);
+ assert_eq!(CNT.load(SeqCst), 0);
+}
+
+#[test]
+fn modular_u8() {
+ #[derive(Clone, Copy, Eq, Debug, Default)]
+ struct Foo(u8);
+
+ impl PartialEq for Foo {
+ fn eq(&self, other: &Foo) -> bool {
+ self.0 % 5 == other.0 % 5
+ }
+ }
+
+ let a = AtomicCell::new(Foo(1));
+
+ assert_eq!(a.load(), Foo(1));
+ assert_eq!(a.swap(Foo(2)), Foo(11));
+ assert_eq!(a.load(), Foo(52));
+
+ a.store(Foo(0));
+ assert_eq!(a.compare_exchange(Foo(0), Foo(5)), Ok(Foo(100)));
+ assert_eq!(a.load().0, 5);
+ assert_eq!(a.compare_exchange(Foo(10), Foo(15)), Ok(Foo(100)));
+ assert_eq!(a.load().0, 15);
+}
+
+#[test]
+fn modular_usize() {
+ #[derive(Clone, Copy, Eq, Debug, Default)]
+ struct Foo(usize);
+
+ impl PartialEq for Foo {
+ fn eq(&self, other: &Foo) -> bool {
+ self.0 % 5 == other.0 % 5
+ }
+ }
+
+ let a = AtomicCell::new(Foo(1));
+
+ assert_eq!(a.load(), Foo(1));
+ assert_eq!(a.swap(Foo(2)), Foo(11));
+ assert_eq!(a.load(), Foo(52));
+
+ a.store(Foo(0));
+ assert_eq!(a.compare_exchange(Foo(0), Foo(5)), Ok(Foo(100)));
+ assert_eq!(a.load().0, 5);
+ assert_eq!(a.compare_exchange(Foo(10), Foo(15)), Ok(Foo(100)));
+ assert_eq!(a.load().0, 15);
+}
+
+#[test]
+fn garbage_padding() {
+ #[derive(Copy, Clone, Eq, PartialEq)]
+ struct Object {
+ a: i64,
+ b: i32,
+ }
+
+ let cell = AtomicCell::new(Object { a: 0, b: 0 });
+ let _garbage = [0xfe, 0xfe, 0xfe, 0xfe, 0xfe]; // Needed
+ let next = Object { a: 0, b: 0 };
+
+ let prev = cell.load();
+ assert!(cell.compare_exchange(prev, next).is_ok());
+ println!();
+}
+
+#[test]
+fn const_atomic_cell_new() {
+ static CELL: AtomicCell<usize> = AtomicCell::new(0);
+
+ CELL.store(1);
+ assert_eq!(CELL.load(), 1);
+}
diff --git a/tests/cache_padded.rs b/tests/cache_padded.rs
new file mode 100644
index 0000000..be90cbe
--- /dev/null
+++ b/tests/cache_padded.rs
@@ -0,0 +1,110 @@
+use std::cell::Cell;
+use std::mem;
+
+use crossbeam_utils::CachePadded;
+
+#[test]
+fn default() {
+ let x: CachePadded<u64> = Default::default();
+ assert_eq!(*x, 0);
+}
+
+#[test]
+fn store_u64() {
+ let x: CachePadded<u64> = CachePadded::new(17);
+ assert_eq!(*x, 17);
+}
+
+#[test]
+fn store_pair() {
+ let x: CachePadded<(u64, u64)> = CachePadded::new((17, 37));
+ assert_eq!(x.0, 17);
+ assert_eq!(x.1, 37);
+}
+
+#[test]
+fn distance() {
+ let arr = [CachePadded::new(17u8), CachePadded::new(37u8)];
+ let a = &*arr[0] as *const u8;
+ let b = &*arr[1] as *const u8;
+ assert!(unsafe { a.offset(64) } <= b);
+}
+
+#[test]
+fn different_sizes() {
+ CachePadded::new(17u8);
+ CachePadded::new(17u16);
+ CachePadded::new(17u32);
+ CachePadded::new([17u64; 0]);
+ CachePadded::new([17u64; 1]);
+ CachePadded::new([17u64; 2]);
+ CachePadded::new([17u64; 3]);
+ CachePadded::new([17u64; 4]);
+ CachePadded::new([17u64; 5]);
+ CachePadded::new([17u64; 6]);
+ CachePadded::new([17u64; 7]);
+ CachePadded::new([17u64; 8]);
+}
+
+#[test]
+fn large() {
+ let a = [17u64; 9];
+ let b = CachePadded::new(a);
+ assert!(mem::size_of_val(&a) <= mem::size_of_val(&b));
+}
+
+#[test]
+fn debug() {
+ assert_eq!(
+ format!("{:?}", CachePadded::new(17u64)),
+ "CachePadded { value: 17 }"
+ );
+}
+
+#[test]
+fn drops() {
+ let count = Cell::new(0);
+
+ struct Foo<'a>(&'a Cell<usize>);
+
+ impl<'a> Drop for Foo<'a> {
+ fn drop(&mut self) {
+ self.0.set(self.0.get() + 1);
+ }
+ }
+
+ let a = CachePadded::new(Foo(&count));
+ let b = CachePadded::new(Foo(&count));
+
+ assert_eq!(count.get(), 0);
+ drop(a);
+ assert_eq!(count.get(), 1);
+ drop(b);
+ assert_eq!(count.get(), 2);
+}
+
+#[test]
+fn clone() {
+ let a = CachePadded::new(17);
+ let b = a.clone();
+ assert_eq!(*a, *b);
+}
+
+#[test]
+fn runs_custom_clone() {
+ let count = Cell::new(0);
+
+ struct Foo<'a>(&'a Cell<usize>);
+
+ impl<'a> Clone for Foo<'a> {
+ fn clone(&self) -> Foo<'a> {
+ self.0.set(self.0.get() + 1);
+ Foo::<'a>(self.0)
+ }
+ }
+
+ let a = CachePadded::new(Foo(&count));
+ let _ = a.clone();
+
+ assert_eq!(count.get(), 1);
+}
diff --git a/tests/parker.rs b/tests/parker.rs
new file mode 100644
index 0000000..f657eb1
--- /dev/null
+++ b/tests/parker.rs
@@ -0,0 +1,41 @@
+use std::thread::sleep;
+use std::time::Duration;
+use std::u32;
+
+use crossbeam_utils::sync::Parker;
+use crossbeam_utils::thread;
+
+#[test]
+fn park_timeout_unpark_before() {
+ let p = Parker::new();
+ for _ in 0..10 {
+ p.unparker().unpark();
+ p.park_timeout(Duration::from_millis(u32::MAX as u64));
+ }
+}
+
+#[test]
+fn park_timeout_unpark_not_called() {
+ let p = Parker::new();
+ for _ in 0..10 {
+ p.park_timeout(Duration::from_millis(10));
+ }
+}
+
+#[test]
+fn park_timeout_unpark_called_other_thread() {
+ for _ in 0..10 {
+ let p = Parker::new();
+ let u = p.unparker().clone();
+
+ thread::scope(|scope| {
+ scope.spawn(move |_| {
+ sleep(Duration::from_millis(50));
+ u.unpark();
+ });
+
+ p.park_timeout(Duration::from_millis(u32::MAX as u64));
+ })
+ .unwrap();
+ }
+}
diff --git a/tests/sharded_lock.rs b/tests/sharded_lock.rs
new file mode 100644
index 0000000..73bd489
--- /dev/null
+++ b/tests/sharded_lock.rs
@@ -0,0 +1,252 @@
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::sync::mpsc::channel;
+use std::sync::{Arc, TryLockError};
+use std::thread;
+
+use crossbeam_utils::sync::ShardedLock;
+use rand::Rng;
+
+#[derive(Eq, PartialEq, Debug)]
+struct NonCopy(i32);
+
+#[test]
+fn smoke() {
+ let l = ShardedLock::new(());
+ drop(l.read().unwrap());
+ drop(l.write().unwrap());
+ drop((l.read().unwrap(), l.read().unwrap()));
+ drop(l.write().unwrap());
+}
+
+#[test]
+fn frob() {
+ const N: u32 = 10;
+ const M: usize = 1000;
+
+ let r = Arc::new(ShardedLock::new(()));
+
+ let (tx, rx) = channel::<()>();
+ for _ in 0..N {
+ let tx = tx.clone();
+ let r = r.clone();
+ thread::spawn(move || {
+ let mut rng = rand::thread_rng();
+ for _ in 0..M {
+ if rng.gen_bool(1.0 / (N as f64)) {
+ drop(r.write().unwrap());
+ } else {
+ drop(r.read().unwrap());
+ }
+ }
+ drop(tx);
+ });
+ }
+ drop(tx);
+ let _ = rx.recv();
+}
+
+#[test]
+fn arc_poison_wr() {
+ let arc = Arc::new(ShardedLock::new(1));
+ let arc2 = arc.clone();
+ let _: Result<(), _> = thread::spawn(move || {
+ let _lock = arc2.write().unwrap();
+ panic!();
+ })
+ .join();
+ assert!(arc.read().is_err());
+}
+
+#[test]
+fn arc_poison_ww() {
+ let arc = Arc::new(ShardedLock::new(1));
+ assert!(!arc.is_poisoned());
+ let arc2 = arc.clone();
+ let _: Result<(), _> = thread::spawn(move || {
+ let _lock = arc2.write().unwrap();
+ panic!();
+ })
+ .join();
+ assert!(arc.write().is_err());
+ assert!(arc.is_poisoned());
+}
+
+#[test]
+fn arc_no_poison_rr() {
+ let arc = Arc::new(ShardedLock::new(1));
+ let arc2 = arc.clone();
+ let _: Result<(), _> = thread::spawn(move || {
+ let _lock = arc2.read().unwrap();
+ panic!();
+ })
+ .join();
+ let lock = arc.read().unwrap();
+ assert_eq!(*lock, 1);
+}
+#[test]
+fn arc_no_poison_sl() {
+ let arc = Arc::new(ShardedLock::new(1));
+ let arc2 = arc.clone();
+ let _: Result<(), _> = thread::spawn(move || {
+ let _lock = arc2.read().unwrap();
+ panic!()
+ })
+ .join();
+ let lock = arc.write().unwrap();
+ assert_eq!(*lock, 1);
+}
+
+#[test]
+fn arc() {
+ let arc = Arc::new(ShardedLock::new(0));
+ let arc2 = arc.clone();
+ let (tx, rx) = channel();
+
+ thread::spawn(move || {
+ let mut lock = arc2.write().unwrap();
+ for _ in 0..10 {
+ let tmp = *lock;
+ *lock = -1;
+ thread::yield_now();
+ *lock = tmp + 1;
+ }
+ tx.send(()).unwrap();
+ });
+
+ // Readers try to catch the writer in the act
+ let mut children = Vec::new();
+ for _ in 0..5 {
+ let arc3 = arc.clone();
+ children.push(thread::spawn(move || {
+ let lock = arc3.read().unwrap();
+ assert!(*lock >= 0);
+ }));
+ }
+
+ // Wait for children to pass their asserts
+ for r in children {
+ assert!(r.join().is_ok());
+ }
+
+ // Wait for writer to finish
+ rx.recv().unwrap();
+ let lock = arc.read().unwrap();
+ assert_eq!(*lock, 10);
+}
+
+#[test]
+fn arc_access_in_unwind() {
+ let arc = Arc::new(ShardedLock::new(1));
+ let arc2 = arc.clone();
+ let _ = thread::spawn(move || -> () {
+ struct Unwinder {
+ i: Arc<ShardedLock<isize>>,
+ }
+ impl Drop for Unwinder {
+ fn drop(&mut self) {
+ let mut lock = self.i.write().unwrap();
+ *lock += 1;
+ }
+ }
+ let _u = Unwinder { i: arc2 };
+ panic!();
+ })
+ .join();
+ let lock = arc.read().unwrap();
+ assert_eq!(*lock, 2);
+}
+
+#[test]
+fn unsized_type() {
+ let sl: &ShardedLock<[i32]> = &ShardedLock::new([1, 2, 3]);
+ {
+ let b = &mut *sl.write().unwrap();
+ b[0] = 4;
+ b[2] = 5;
+ }
+ let comp: &[i32] = &[4, 2, 5];
+ assert_eq!(&*sl.read().unwrap(), comp);
+}
+
+#[test]
+fn try_write() {
+ let lock = ShardedLock::new(0isize);
+ let read_guard = lock.read().unwrap();
+
+ let write_result = lock.try_write();
+ match write_result {
+ Err(TryLockError::WouldBlock) => (),
+ Ok(_) => assert!(
+ false,
+ "try_write should not succeed while read_guard is in scope"
+ ),
+ Err(_) => assert!(false, "unexpected error"),
+ }
+
+ drop(read_guard);
+}
+
+#[test]
+fn test_into_inner() {
+ let m = ShardedLock::new(NonCopy(10));
+ assert_eq!(m.into_inner().unwrap(), NonCopy(10));
+}
+
+#[test]
+fn test_into_inner_drop() {
+ struct Foo(Arc<AtomicUsize>);
+ impl Drop for Foo {
+ fn drop(&mut self) {
+ self.0.fetch_add(1, Ordering::SeqCst);
+ }
+ }
+ let num_drops = Arc::new(AtomicUsize::new(0));
+ let m = ShardedLock::new(Foo(num_drops.clone()));
+ assert_eq!(num_drops.load(Ordering::SeqCst), 0);
+ {
+ let _inner = m.into_inner().unwrap();
+ assert_eq!(num_drops.load(Ordering::SeqCst), 0);
+ }
+ assert_eq!(num_drops.load(Ordering::SeqCst), 1);
+}
+
+#[test]
+fn test_into_inner_poison() {
+ let m = Arc::new(ShardedLock::new(NonCopy(10)));
+ let m2 = m.clone();
+ let _ = thread::spawn(move || {
+ let _lock = m2.write().unwrap();
+ panic!("test panic in inner thread to poison ShardedLock");
+ })
+ .join();
+
+ assert!(m.is_poisoned());
+ match Arc::try_unwrap(m).unwrap().into_inner() {
+ Err(e) => assert_eq!(e.into_inner(), NonCopy(10)),
+ Ok(x) => panic!("into_inner of poisoned ShardedLock is Ok: {:?}", x),
+ }
+}
+
+#[test]
+fn test_get_mut() {
+ let mut m = ShardedLock::new(NonCopy(10));
+ *m.get_mut().unwrap() = NonCopy(20);
+ assert_eq!(m.into_inner().unwrap(), NonCopy(20));
+}
+
+#[test]
+fn test_get_mut_poison() {
+ let m = Arc::new(ShardedLock::new(NonCopy(10)));
+ let m2 = m.clone();
+ let _ = thread::spawn(move || {
+ let _lock = m2.write().unwrap();
+ panic!("test panic in inner thread to poison ShardedLock");
+ })
+ .join();
+
+ assert!(m.is_poisoned());
+ match Arc::try_unwrap(m).unwrap().get_mut() {
+ Err(e) => assert_eq!(*e.into_inner(), NonCopy(10)),
+ Ok(x) => panic!("get_mut of poisoned ShardedLock is Ok: {:?}", x),
+ }
+}
diff --git a/tests/thread.rs b/tests/thread.rs
new file mode 100644
index 0000000..0dfad90
--- /dev/null
+++ b/tests/thread.rs
@@ -0,0 +1,215 @@
+use std::any::Any;
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::thread::sleep;
+use std::time::Duration;
+
+use crossbeam_utils::thread;
+
+const THREADS: usize = 10;
+const SMALL_STACK_SIZE: usize = 20;
+
+#[test]
+fn join() {
+ let counter = AtomicUsize::new(0);
+ thread::scope(|scope| {
+ let handle = scope.spawn(|_| {
+ counter.store(1, Ordering::Relaxed);
+ });
+ assert!(handle.join().is_ok());
+
+ let panic_handle = scope.spawn(|_| {
+ panic!("\"My honey is running out!\", said Pooh.");
+ });
+ assert!(panic_handle.join().is_err());
+ })
+ .unwrap();
+
+ // There should be sufficient synchronization.
+ assert_eq!(1, counter.load(Ordering::Relaxed));
+}
+
+#[test]
+fn counter() {
+ let counter = AtomicUsize::new(0);
+ thread::scope(|scope| {
+ for _ in 0..THREADS {
+ scope.spawn(|_| {
+ counter.fetch_add(1, Ordering::Relaxed);
+ });
+ }
+ })
+ .unwrap();
+
+ assert_eq!(THREADS, counter.load(Ordering::Relaxed));
+}
+
+#[test]
+fn counter_builder() {
+ let counter = AtomicUsize::new(0);
+ thread::scope(|scope| {
+ for i in 0..THREADS {
+ scope
+ .builder()
+ .name(format!("child-{}", i))
+ .stack_size(SMALL_STACK_SIZE)
+ .spawn(|_| {
+ counter.fetch_add(1, Ordering::Relaxed);
+ })
+ .unwrap();
+ }
+ })
+ .unwrap();
+
+ assert_eq!(THREADS, counter.load(Ordering::Relaxed));
+}
+
+#[test]
+fn counter_panic() {
+ let counter = AtomicUsize::new(0);
+ let result = thread::scope(|scope| {
+ scope.spawn(|_| {
+ panic!("\"My honey is running out!\", said Pooh.");
+ });
+ sleep(Duration::from_millis(100));
+
+ for _ in 0..THREADS {
+ scope.spawn(|_| {
+ counter.fetch_add(1, Ordering::Relaxed);
+ });
+ }
+ });
+
+ assert_eq!(THREADS, counter.load(Ordering::Relaxed));
+ assert!(result.is_err());
+}
+
+#[test]
+fn panic_twice() {
+ let result = thread::scope(|scope| {
+ scope.spawn(|_| {
+ sleep(Duration::from_millis(500));
+ panic!("thread #1");
+ });
+ scope.spawn(|_| {
+ panic!("thread #2");
+ });
+ });
+
+ let err = result.unwrap_err();
+ let vec = err
+ .downcast_ref::<Vec<Box<dyn Any + Send + 'static>>>()
+ .unwrap();
+ assert_eq!(2, vec.len());
+
+ let first = vec[0].downcast_ref::<&str>().unwrap();
+ let second = vec[1].downcast_ref::<&str>().unwrap();
+ assert_eq!("thread #1", *first);
+ assert_eq!("thread #2", *second)
+}
+
+#[test]
+fn panic_many() {
+ let result = thread::scope(|scope| {
+ scope.spawn(|_| panic!("deliberate panic #1"));
+ scope.spawn(|_| panic!("deliberate panic #2"));
+ scope.spawn(|_| panic!("deliberate panic #3"));
+ });
+
+ let err = result.unwrap_err();
+ let vec = err
+ .downcast_ref::<Vec<Box<dyn Any + Send + 'static>>>()
+ .unwrap();
+ assert_eq!(3, vec.len());
+
+ for panic in vec.iter() {
+ let panic = panic.downcast_ref::<&str>().unwrap();
+ assert!(
+ *panic == "deliberate panic #1"
+ || *panic == "deliberate panic #2"
+ || *panic == "deliberate panic #3"
+ );
+ }
+}
+
+#[test]
+fn nesting() {
+ let var = "foo".to_string();
+
+ struct Wrapper<'a> {
+ var: &'a String,
+ }
+
+ impl<'a> Wrapper<'a> {
+ fn recurse(&'a self, scope: &thread::Scope<'a>, depth: usize) {
+ assert_eq!(self.var, "foo");
+
+ if depth > 0 {
+ scope.spawn(move |scope| {
+ self.recurse(scope, depth - 1);
+ });
+ }
+ }
+ }
+
+ let wrapper = Wrapper { var: &var };
+
+ thread::scope(|scope| {
+ scope.spawn(|scope| {
+ scope.spawn(|scope| {
+ wrapper.recurse(scope, 5);
+ });
+ });
+ })
+ .unwrap();
+}
+
+#[test]
+fn join_nested() {
+ thread::scope(|scope| {
+ scope.spawn(|scope| {
+ let handle = scope.spawn(|_| 7);
+
+ sleep(Duration::from_millis(200));
+ handle.join().unwrap();
+ });
+
+ sleep(Duration::from_millis(100));
+ })
+ .unwrap();
+}
+
+#[test]
+fn scope_returns_ok() {
+ let result = thread::scope(|scope| scope.spawn(|_| 1234).join().unwrap()).unwrap();
+ assert_eq!(result, 1234);
+}
+
+#[cfg(unix)]
+#[test]
+fn as_pthread_t() {
+ use std::os::unix::thread::JoinHandleExt;
+ thread::scope(|scope| {
+ let handle = scope.spawn(|_scope| {
+ sleep(Duration::from_millis(100));
+ 42
+ });
+ let _pthread_t = handle.as_pthread_t();
+ handle.join().unwrap();
+ })
+ .unwrap();
+}
+
+#[cfg(windows)]
+#[test]
+fn as_raw_handle() {
+ use std::os::windows::io::AsRawHandle;
+ thread::scope(|scope| {
+ let handle = scope.spawn(|_scope| {
+ sleep(Duration::from_millis(100));
+ 42
+ });
+ let _raw_handle = handle.as_raw_handle();
+ handle.join().unwrap();
+ })
+ .unwrap();
+}
diff --git a/tests/wait_group.rs b/tests/wait_group.rs
new file mode 100644
index 0000000..b6c2a24
--- /dev/null
+++ b/tests/wait_group.rs
@@ -0,0 +1,64 @@
+use std::sync::mpsc;
+use std::thread;
+use std::time::Duration;
+
+use crossbeam_utils::sync::WaitGroup;
+
+const THREADS: usize = 10;
+
+#[test]
+fn wait() {
+ let wg = WaitGroup::new();
+ let (tx, rx) = mpsc::channel();
+
+ for _ in 0..THREADS {
+ let wg = wg.clone();
+ let tx = tx.clone();
+
+ thread::spawn(move || {
+ wg.wait();
+ tx.send(()).unwrap();
+ });
+ }
+
+ thread::sleep(Duration::from_millis(100));
+
+ // At this point, all spawned threads should be blocked, so we shouldn't get anything from the
+ // channel.
+ assert!(rx.try_recv().is_err());
+
+ wg.wait();
+
+ // Now, the wait group is cleared and we should receive messages.
+ for _ in 0..THREADS {
+ rx.recv().unwrap();
+ }
+}
+
+#[test]
+fn wait_and_drop() {
+ let wg = WaitGroup::new();
+ let (tx, rx) = mpsc::channel();
+
+ for _ in 0..THREADS {
+ let wg = wg.clone();
+ let tx = tx.clone();
+
+ thread::spawn(move || {
+ thread::sleep(Duration::from_millis(100));
+ tx.send(()).unwrap();
+ drop(wg);
+ });
+ }
+
+ // At this point, all spawned threads should be sleeping, so we shouldn't get anything from the
+ // channel.
+ assert!(rx.try_recv().is_err());
+
+ wg.wait();
+
+ // Now, the wait group is cleared and we should receive messages.
+ for _ in 0..THREADS {
+ rx.try_recv().unwrap();
+ }
+}
