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Signed-off-by: Valentin Popov <valentin@popov.link>
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Valentin Popov
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# Version 0.8.18
- Relax the minimum supported Rust version to 1.60. (#1056)
- Improve scalability of `AtomicCell` fallback. (#1055)
# Version 0.8.17
- Bump the minimum supported Rust version to 1.61. (#1037)
- Improve support for targets without atomic CAS or 64-bit atomic. (#1037)
- Always implement `UnwindSafe` and `RefUnwindSafe` for `AtomicCell`. (#1045)
- Improve compatibility with Miri, TSan, and loom. (#995, #1003)
- Improve compatibility with unstable `oom=panic`. (#1045)
- Improve implementation of `CachePadded`. (#1014, #1025)
- Update `loom` dependency to 0.7.
# Version 0.8.16
- Improve implementation of `CachePadded`. (#967)
# Version 0.8.15
- Add `#[clippy::has_significant_drop]` to `ShardedLock{Read,Write}Guard`. (#958)
- Improve handling of very large timeout. (#953)
- Soft-deprecate `thread::scope()` in favor of the more efficient `std::thread::scope` that stabilized on Rust 1.63. (#954)
# Version 0.8.14
- Fix build script bug introduced in 0.8.13. (#932)
# Version 0.8.13
**Note:** This release has been yanked due to regression fixed in 0.8.14.
- Improve support for custom targets. (#922)
# Version 0.8.12
- Removes the dependency on the `once_cell` crate to restore the MSRV. (#913)
- Work around [rust-lang#98302](https://github.com/rust-lang/rust/issues/98302), which causes compile error on windows-gnu when LTO is enabled. (#913)
# Version 0.8.11
- Bump the minimum supported Rust version to 1.38. (#877)
# Version 0.8.10
- Fix unsoundness of `AtomicCell` on types containing niches. (#834)
This fix contains breaking changes, but they are allowed because this is a soundness bug fix. See #834 for more.
# Version 0.8.9
- Replace lazy_static with once_cell. (#817)
# Version 0.8.8
- Fix a bug when unstable `loom` support is enabled. (#787)
# Version 0.8.7
- Add `AtomicCell<{i*,u*}>::{fetch_max,fetch_min}`. (#785)
- Add `AtomicCell<{i*,u*,bool}>::fetch_nand`. (#785)
- Fix unsoundness of `AtomicCell<{i,u}64>` arithmetics on 32-bit targets that support `Atomic{I,U}64` (#781)
# Version 0.8.6
**Note:** This release has been yanked. See [GHSA-qc84-gqf4-9926](https://github.com/crossbeam-rs/crossbeam/security/advisories/GHSA-qc84-gqf4-9926) for details.
- Re-add `AtomicCell<{i,u}64>::{fetch_add,fetch_sub,fetch_and,fetch_or,fetch_xor}` that were accidentally removed in 0.8.0 on targets that do not support `Atomic{I,U}64`. (#767)
- Re-add `AtomicCell<{i,u}128>::{fetch_add,fetch_sub,fetch_and,fetch_or,fetch_xor}` that were accidentally removed in 0.8.0. (#767)
# Version 0.8.5
**Note:** This release has been yanked. See [GHSA-qc84-gqf4-9926](https://github.com/crossbeam-rs/crossbeam/security/advisories/GHSA-qc84-gqf4-9926) for details.
- Add `AtomicCell::fetch_update`. (#704)
- Support targets that do not have atomic CAS on stable Rust. (#698)
# Version 0.8.4
**Note:** This release has been yanked. See [GHSA-qc84-gqf4-9926](https://github.com/crossbeam-rs/crossbeam/security/advisories/GHSA-qc84-gqf4-9926) for details.
- Bump `loom` dependency to version 0.5. (#686)
# Version 0.8.3
**Note:** This release has been yanked. See [GHSA-qc84-gqf4-9926](https://github.com/crossbeam-rs/crossbeam/security/advisories/GHSA-qc84-gqf4-9926) for details.
- Make `loom` dependency optional. (#666)
# Version 0.8.2
**Note:** This release has been yanked. See [GHSA-qc84-gqf4-9926](https://github.com/crossbeam-rs/crossbeam/security/advisories/GHSA-qc84-gqf4-9926) for details.
- Deprecate `AtomicCell::compare_and_swap`. Use `AtomicCell::compare_exchange` instead. (#619)
- Add `Parker::park_deadline`. (#563)
- Improve implementation of `CachePadded`. (#636)
- Add unstable support for `loom`. (#487)
# Version 0.8.1
**Note:** This release has been yanked. See [GHSA-qc84-gqf4-9926](https://github.com/crossbeam-rs/crossbeam/security/advisories/GHSA-qc84-gqf4-9926) for details.
- 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
**Note:** This release has been yanked. See [GHSA-qc84-gqf4-9926](https://github.com/crossbeam-rs/crossbeam/security/advisories/GHSA-qc84-gqf4-9926) for details.
- 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

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# 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 are reading this file be aware that the original Cargo.toml
# will likely look very different (and much more reasonable).
# See Cargo.toml.orig for the original contents.
[package]
edition = "2021"
rust-version = "1.60"
name = "crossbeam-utils"
version = "0.8.18"
description = "Utilities for concurrent programming"
homepage = "https://github.com/crossbeam-rs/crossbeam/tree/master/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"
[dev-dependencies.rand]
version = "0.8"
[features]
default = ["std"]
nightly = []
std = []
[target."cfg(crossbeam_loom)".dependencies.loom]
version = "0.7.1"
optional = true

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# Crossbeam Utils
[![Build Status](https://github.com/crossbeam-rs/crossbeam/workflows/CI/badge.svg)](
https://github.com/crossbeam-rs/crossbeam/actions)
[![License](https://img.shields.io/badge/license-MIT_OR_Apache--2.0-blue.svg)](
https://github.com/crossbeam-rs/crossbeam/tree/master/crossbeam-utils#license)
[![Cargo](https://img.shields.io/crates/v/crossbeam-utils.svg)](
https://crates.io/crates/crossbeam-utils)
[![Documentation](https://docs.rs/crossbeam-utils/badge.svg)](
https://docs.rs/crossbeam-utils)
[![Rust 1.60+](https://img.shields.io/badge/rust-1.60+-lightgray.svg)](
https://www.rust-lang.org)
[![chat](https://img.shields.io/discord/569610676205781012.svg?logo=discord)](https://discord.com/invite/JXYwgWZ)
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 1.60.
## 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.

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#![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_exchange_u8(b: &mut test::Bencher) {
let a = AtomicCell::new(0u8);
let mut i = 0;
b.iter(|| {
let _ = a.compare_exchange(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_exchange_usize(b: &mut test::Bencher) {
let a = AtomicCell::new(0usize);
let mut i = 0;
b.iter(|| {
let _ = a.compare_exchange(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();
}

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// The target triplets have the form of 'arch-vendor-system'.
//
// When building for Linux (e.g. the 'system' part is
// 'linux-something'), replace the vendor with 'unknown'
// so that mapping to rust standard targets happens correctly.
fn convert_custom_linux_target(target: String) -> String {
let mut parts: Vec<&str> = target.split('-').collect();
let system = parts.get(2);
if system == Some(&"linux") {
parts[1] = "unknown";
};
parts.join("-")
}

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// The rustc-cfg listed below are considered public API, but it is *unstable*
// and outside of the normal semver guarantees:
//
// - `crossbeam_no_atomic`
// Assume the target does *not* support any atomic operations.
// This is usually detected automatically by the build script, but you may
// need to enable it manually when building for custom targets or using
// non-cargo build systems that don't run the build script.
//
// With the exceptions mentioned above, the rustc-cfg emitted by the build
// script are *not* public API.
#![warn(rust_2018_idioms)]
use std::env;
include!("no_atomic.rs");
include!("build-common.rs");
fn main() {
println!("cargo:rerun-if-changed=no_atomic.rs");
let target = match env::var("TARGET") {
Ok(target) => convert_custom_linux_target(target),
Err(e) => {
println!(
"cargo:warning={}: unable to get TARGET environment variable: {}",
env!("CARGO_PKG_NAME"),
e
);
return;
}
};
// Note that this is `no_`*, not `has_*`. This allows treating as the latest
// stable rustc is used when the build script doesn't run. This is useful
// for non-cargo build systems that don't run the build script.
if NO_ATOMIC.contains(&&*target) {
println!("cargo:rustc-cfg=crossbeam_no_atomic");
}
// `cfg(sanitize = "..")` is not stabilized.
let sanitize = env::var("CARGO_CFG_SANITIZE").unwrap_or_default();
if sanitize.contains("thread") {
println!("cargo:rustc-cfg=crossbeam_sanitize_thread");
}
}

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// This file is @generated by no_atomic.sh.
// It is not intended for manual editing.
const NO_ATOMIC: &[&str] = &[
"bpfeb-unknown-none",
"bpfel-unknown-none",
"mipsel-sony-psx",
"msp430-none-elf",
"riscv32i-unknown-none-elf",
"riscv32im-unknown-none-elf",
"riscv32imc-unknown-none-elf",
];

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#[cfg(not(crossbeam_no_atomic))]
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(not(crossbeam_no_atomic))]
// Miri and Loom don't support "consume" ordering and ThreadSanitizer doesn't treat
// load(Relaxed) + compiler_fence(Acquire) as "consume" load.
// LLVM generates machine code equivalent to fence(Acquire) in compiler_fence(Acquire)
// on PowerPC, MIPS, etc. (https://godbolt.org/z/hffvjvW7h), so for now the fence
// can be actually avoided here only on ARM and AArch64. See also
// https://github.com/rust-lang/rust/issues/62256.
#[cfg(all(
any(target_arch = "arm", target_arch = "aarch64"),
not(any(miri, crossbeam_loom, crossbeam_sanitize_thread)),
))]
macro_rules! impl_consume {
() => {
#[inline]
fn load_consume(&self) -> Self::Val {
use crate::primitive::sync::atomic::compiler_fence;
let result = self.load(Ordering::Relaxed);
compiler_fence(Ordering::Acquire);
result
}
};
}
#[cfg(not(crossbeam_no_atomic))]
#[cfg(not(all(
any(target_arch = "arm", target_arch = "aarch64"),
not(any(miri, crossbeam_loom, crossbeam_sanitize_thread)),
)))]
macro_rules! impl_consume {
() => {
#[inline]
fn load_consume(&self) -> Self::Val {
self.load(Ordering::Acquire)
}
};
}
macro_rules! impl_atomic {
($atomic:ident, $val:ty) => {
#[cfg(not(crossbeam_no_atomic))]
impl AtomicConsume for core::sync::atomic::$atomic {
type Val = $val;
impl_consume!();
}
#[cfg(crossbeam_loom)]
impl AtomicConsume for loom::sync::atomic::$atomic {
type Val = $val;
impl_consume!();
}
};
}
impl_atomic!(AtomicBool, bool);
impl_atomic!(AtomicUsize, usize);
impl_atomic!(AtomicIsize, isize);
impl_atomic!(AtomicU8, u8);
impl_atomic!(AtomicI8, i8);
impl_atomic!(AtomicU16, u16);
impl_atomic!(AtomicI16, i16);
#[cfg(any(target_has_atomic = "32", not(target_pointer_width = "16")))]
impl_atomic!(AtomicU32, u32);
#[cfg(any(target_has_atomic = "32", not(target_pointer_width = "16")))]
impl_atomic!(AtomicI32, i32);
#[cfg(any(
target_has_atomic = "64",
not(any(target_pointer_width = "16", target_pointer_width = "32")),
))]
impl_atomic!(AtomicU64, u64);
#[cfg(any(
target_has_atomic = "64",
not(any(target_pointer_width = "16", target_pointer_width = "32")),
))]
impl_atomic!(AtomicI64, i64);
#[cfg(not(crossbeam_no_atomic))]
impl<T> AtomicConsume for core::sync::atomic::AtomicPtr<T> {
type Val = *mut T;
impl_consume!();
}
#[cfg(crossbeam_loom)]
impl<T> AtomicConsume for loom::sync::atomic::AtomicPtr<T> {
type Val = *mut T;
impl_consume!();
}

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//! Atomic types.
//!
//! * [`AtomicCell`], a thread-safe mutable memory location.
//! * [`AtomicConsume`], for reading from primitive atomic types with "consume" ordering.
#[cfg(target_has_atomic = "ptr")]
#[cfg(not(crossbeam_loom))]
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;
}
}
#[cfg(target_has_atomic = "ptr")]
// We cannot provide AtomicCell under cfg(crossbeam_loom) because loom's atomic
// types have a different in-memory representation than the underlying type.
// TODO: The latest loom supports fences, so fallback using seqlock may be available.
#[cfg(not(crossbeam_loom))]
mod atomic_cell;
mod consume;
#[cfg(target_has_atomic = "ptr")]
#[cfg(not(crossbeam_loom))]
pub use self::atomic_cell::AtomicCell;
pub use self::consume::AtomicConsume;

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use core::mem;
use core::sync::atomic::{self, AtomicUsize, Ordering};
use crate::Backoff;
/// A simple stamped lock.
pub(crate) 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(crate) 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(crate) 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(crate) fn validate_read(&self, stamp: usize) -> bool {
atomic::fence(Ordering::Acquire);
self.state.load(Ordering::Relaxed) == stamp
}
/// Grabs the lock for writing.
#[inline]
pub(crate) 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(crate) 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(crate) 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");
}
}

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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(crate) 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(crate) 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(crate) 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(crate) 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(crate) 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(crate) 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(crate) 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");
}
}

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use crate::primitive::hint;
use core::cell::Cell;
use core::fmt;
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_exchange(val, val.wrapping_mul(b), SeqCst, SeqCst).is_ok() {
/// 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_exchange(val, val.wrapping_mul(b), SeqCst, SeqCst).is_ok() {
/// 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) {
hint::spin_loop();
}
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);
/// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
/// ```
///
/// [`AtomicBool`]: std::sync::atomic::AtomicBool
#[inline]
pub fn snooze(&self) {
if self.step.get() <= SPIN_LIMIT {
for _ in 0..1 << self.step.get() {
hint::spin_loop();
}
} else {
#[cfg(not(feature = "std"))]
for _ in 0..1 << self.step.get() {
hint::spin_loop();
}
#[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);
/// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
/// ```
///
/// [`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()
}
}

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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, aarch64, and powerpc64, N = 128.
/// * On arm, mips, mips64, sparc, and hexagon, N = 32.
/// * On m68k, N = 16.
/// * On s390x, N = 256.
/// * 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 >= 32);
/// assert_eq!(addr1 % 32, 0);
/// assert_eq!(addr2 % 32, 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/
//
// powerpc64 has 128-byte cache line size.
//
// Sources:
// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_ppc64x.go#L9
// - https://github.com/torvalds/linux/blob/3516bd729358a2a9b090c1905bd2a3fa926e24c6/arch/powerpc/include/asm/cache.h#L26
#[cfg_attr(
any(
target_arch = "x86_64",
target_arch = "aarch64",
target_arch = "powerpc64",
),
repr(align(128))
)]
// arm, mips, mips64, sparc, and hexagon have 32-byte cache line size.
//
// Sources:
// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_arm.go#L7
// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mips.go#L7
// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mipsle.go#L7
// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_mips64x.go#L9
// - https://github.com/torvalds/linux/blob/3516bd729358a2a9b090c1905bd2a3fa926e24c6/arch/sparc/include/asm/cache.h#L17
// - https://github.com/torvalds/linux/blob/3516bd729358a2a9b090c1905bd2a3fa926e24c6/arch/hexagon/include/asm/cache.h#L12
#[cfg_attr(
any(
target_arch = "arm",
target_arch = "mips",
target_arch = "mips32r6",
target_arch = "mips64",
target_arch = "mips64r6",
target_arch = "sparc",
target_arch = "hexagon",
),
repr(align(32))
)]
// m68k has 16-byte cache line size.
//
// Sources:
// - https://github.com/torvalds/linux/blob/3516bd729358a2a9b090c1905bd2a3fa926e24c6/arch/m68k/include/asm/cache.h#L9
#[cfg_attr(target_arch = "m68k", repr(align(16)))]
// s390x has 256-byte cache line size.
//
// Sources:
// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_s390x.go#L7
// - https://github.com/torvalds/linux/blob/3516bd729358a2a9b090c1905bd2a3fa926e24c6/arch/s390/include/asm/cache.h#L13
#[cfg_attr(target_arch = "s390x", repr(align(256)))]
// x86, wasm, riscv, and sparc64 have 64-byte cache line size.
//
// Sources:
// - https://github.com/golang/go/blob/dda2991c2ea0c5914714469c4defc2562a907230/src/internal/cpu/cpu_x86.go#L9
// - https://github.com/golang/go/blob/3dd58676054223962cd915bb0934d1f9f489d4d2/src/internal/cpu/cpu_wasm.go#L7
// - https://github.com/torvalds/linux/blob/3516bd729358a2a9b090c1905bd2a3fa926e24c6/arch/riscv/include/asm/cache.h#L10
// - https://github.com/torvalds/linux/blob/3516bd729358a2a9b090c1905bd2a3fa926e24c6/arch/sparc/include/asm/cache.h#L19
//
// All others are assumed to have 64-byte cache line size.
#[cfg_attr(
not(any(
target_arch = "x86_64",
target_arch = "aarch64",
target_arch = "powerpc64",
target_arch = "arm",
target_arch = "mips",
target_arch = "mips32r6",
target_arch = "mips64",
target_arch = "mips64r6",
target_arch = "sparc",
target_arch = "hexagon",
target_arch = "m68k",
target_arch = "s390x",
)),
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)
}
}

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//! 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,
unreachable_pub
)]
#![cfg_attr(not(feature = "std"), no_std)]
#[cfg(crossbeam_loom)]
#[allow(unused_imports)]
mod primitive {
pub(crate) mod hint {
pub(crate) use loom::hint::spin_loop;
}
pub(crate) mod sync {
pub(crate) mod atomic {
pub(crate) use loom::sync::atomic::{
AtomicBool, AtomicI16, AtomicI32, AtomicI64, AtomicI8, AtomicIsize, AtomicU16,
AtomicU32, AtomicU64, AtomicU8, AtomicUsize, Ordering,
};
// FIXME: loom does not support compiler_fence at the moment.
// https://github.com/tokio-rs/loom/issues/117
// we use fence as a stand-in for compiler_fence for the time being.
// this may miss some races since fence is stronger than compiler_fence,
// but it's the best we can do for the time being.
pub(crate) use loom::sync::atomic::fence as compiler_fence;
}
pub(crate) use loom::sync::{Arc, Condvar, Mutex};
}
}
#[cfg(not(crossbeam_loom))]
#[allow(unused_imports)]
mod primitive {
pub(crate) mod hint {
pub(crate) use core::hint::spin_loop;
}
pub(crate) mod sync {
pub(crate) mod atomic {
pub(crate) use core::sync::atomic::{compiler_fence, Ordering};
#[cfg(not(crossbeam_no_atomic))]
pub(crate) use core::sync::atomic::{
AtomicBool, AtomicI16, AtomicI8, AtomicIsize, AtomicU16, AtomicU8, AtomicUsize,
};
#[cfg(not(crossbeam_no_atomic))]
#[cfg(any(target_has_atomic = "32", not(target_pointer_width = "16")))]
pub(crate) use core::sync::atomic::{AtomicI32, AtomicU32};
#[cfg(not(crossbeam_no_atomic))]
#[cfg(any(
target_has_atomic = "64",
not(any(target_pointer_width = "16", target_pointer_width = "32")),
))]
pub(crate) use core::sync::atomic::{AtomicI64, AtomicU64};
}
#[cfg(feature = "std")]
pub(crate) use std::sync::{Arc, Condvar, Mutex};
}
}
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;
#[cfg(not(crossbeam_loom))]
pub mod thread;
}
}

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//! 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.
#[cfg(not(crossbeam_loom))]
mod once_lock;
mod parker;
#[cfg(not(crossbeam_loom))]
mod sharded_lock;
mod wait_group;
pub use self::parker::{Parker, Unparker};
#[cfg(not(crossbeam_loom))]
pub use self::sharded_lock::{ShardedLock, ShardedLockReadGuard, ShardedLockWriteGuard};
pub use self::wait_group::WaitGroup;

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// Based on unstable std::sync::OnceLock.
//
// Source: https://github.com/rust-lang/rust/blob/8e9c93df464b7ada3fc7a1c8ccddd9dcb24ee0a0/library/std/src/sync/once_lock.rs
use core::cell::UnsafeCell;
use core::mem::MaybeUninit;
use std::sync::Once;
pub(crate) struct OnceLock<T> {
once: Once,
value: UnsafeCell<MaybeUninit<T>>,
// Unlike std::sync::OnceLock, we don't need PhantomData here because
// we don't use #[may_dangle].
}
unsafe impl<T: Sync + Send> Sync for OnceLock<T> {}
unsafe impl<T: Send> Send for OnceLock<T> {}
impl<T> OnceLock<T> {
/// Creates a new empty cell.
#[must_use]
pub(crate) const fn new() -> Self {
Self {
once: Once::new(),
value: UnsafeCell::new(MaybeUninit::uninit()),
}
}
/// Gets the contents of the cell, initializing it with `f` if the cell
/// was empty.
///
/// Many threads may call `get_or_init` concurrently with different
/// initializing functions, but it is guaranteed that only one function
/// will be executed.
///
/// # Panics
///
/// If `f` panics, the panic is propagated to the caller, and the cell
/// remains uninitialized.
///
/// It is an error to reentrantly initialize the cell from `f`. The
/// exact outcome is unspecified. Current implementation deadlocks, but
/// this may be changed to a panic in the future.
pub(crate) fn get_or_init<F>(&self, f: F) -> &T
where
F: FnOnce() -> T,
{
// Fast path check
if self.once.is_completed() {
// SAFETY: The inner value has been initialized
return unsafe { self.get_unchecked() };
}
self.initialize(f);
// SAFETY: The inner value has been initialized
unsafe { self.get_unchecked() }
}
#[cold]
fn initialize<F>(&self, f: F)
where
F: FnOnce() -> T,
{
let slot = self.value.get();
self.once.call_once(|| {
let value = f();
unsafe { slot.write(MaybeUninit::new(value)) }
});
}
/// # Safety
///
/// The value must be initialized
unsafe fn get_unchecked(&self) -> &T {
debug_assert!(self.once.is_completed());
&*self.value.get().cast::<T>()
}
}
impl<T> Drop for OnceLock<T> {
fn drop(&mut self) {
if self.once.is_completed() {
// SAFETY: The inner value has been initialized
unsafe { (*self.value.get()).assume_init_drop() };
}
}
}

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use crate::primitive::sync::atomic::{AtomicUsize, Ordering::SeqCst};
use crate::primitive::sync::{Arc, Condvar, Mutex};
use std::fmt;
use std::marker::PhantomData;
use std::time::{Duration, Instant};
/// 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.
///
/// * The [`park_timeout`] and [`park_deadline`] methods work the same as [`park`], but block 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.
/// p.park();
/// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
/// ```
///
/// [`park`]: Parker::park
/// [`park_timeout`]: Parker::park_timeout
/// [`park_deadline`]: Parker::park_deadline
/// [`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.
///
/// # 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.
///
/// # 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) {
match Instant::now().checked_add(timeout) {
Some(deadline) => self.park_deadline(deadline),
None => self.park(),
}
}
/// Blocks the current thread until the token is made available, or until a certain deadline.
///
/// # Examples
///
/// ```
/// use std::time::{Duration, Instant};
/// use crossbeam_utils::sync::Parker;
///
/// let p = Parker::new();
/// let deadline = Instant::now() + Duration::from_millis(500);
///
/// // Waits for the token to become available, but will not wait longer than 500 ms.
/// p.park_deadline(deadline);
/// ```
pub fn park_deadline(&self, deadline: Instant) {
self.unparker.inner.park(Some(deadline))
}
/// 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);
/// # let _ = unsafe { Parker::from_raw(raw) };
/// ```
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.
/// p.park();
/// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
/// ```
///
/// [`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);
/// # let _ = unsafe { Unparker::from_raw(raw) };
/// ```
pub fn into_raw(this: Unparker) -> *const () {
Arc::into_raw(this.inner).cast::<()>()
}
/// 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.cast::<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, deadline: Option<Instant>) {
// 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(deadline) = deadline {
if deadline <= Instant::now() {
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),
}
loop {
// Block the current thread on the conditional variable.
m = match deadline {
None => self.cvar.wait(m).unwrap(),
Some(deadline) => {
let now = Instant::now();
if now < deadline {
// We could check for a timeout here, in the return value of wait_timeout,
// but in the case that a timeout and an unpark arrive simultaneously, we
// prefer to report the former.
self.cvar.wait_timeout(m, deadline - now).unwrap().0
} else {
// We've timed out; swap out the state back to empty on our way out
match self.state.swap(EMPTY, SeqCst) {
NOTIFIED | PARKED => return,
n => panic!("inconsistent park_timeout state: {}", n),
};
}
}
};
if self
.state
.compare_exchange(NOTIFIED, EMPTY, SeqCst, SeqCst)
.is_ok()
{
// got a notification
return;
}
// Spurious wakeup, go back to sleep. Alternatively, if we timed out, it will be caught
// in the branch above, when we discover the deadline is in the past
}
}
pub(crate) 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();
}
}

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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::sync::once_lock::OnceLock;
use crate::CachePadded;
/// 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 = (*dest).take();
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.
#[clippy::has_significant_drop]
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.
#[clippy::has_significant_drop]
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 = (*dest).take();
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,
}
fn thread_indices() -> &'static Mutex<ThreadIndices> {
static THREAD_INDICES: OnceLock<Mutex<ThreadIndices>> = OnceLock::new();
fn init() -> Mutex<ThreadIndices> {
Mutex::new(ThreadIndices {
mapping: HashMap::new(),
free_list: Vec::new(),
next_index: 0,
})
}
THREAD_INDICES.get_or_init(init)
}
/// 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,
}
};
}

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use crate::primitive::sync::{Arc, Condvar, Mutex};
use std::fmt;
/// 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();
/// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
/// ```
///
/// [`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();
/// # std::thread::sleep(std::time::Duration::from_millis(500)); // wait for background threads closed: https://github.com/rust-lang/miri/issues/1371
/// ```
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()
}
}

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//! 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,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();
//! ```
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. Note that if panics are implemented by
/// aborting the process, no error is returned; see the notes of [std::panic::catch_unwind].
///
/// **Note:** Since Rust 1.63, this function is soft-deprecated in favor of the more efficient [`std::thread::scope`].
///
/// # 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,
{
struct AbortOnPanic;
impl Drop for AbortOnPanic {
fn drop(&mut self) {
if thread::panicking() {
std::process::abort();
}
}
}
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)));
// If an unwinding panic occurs before all threads are joined
// promote it to an aborting panic to prevent any threads from escaping the scope.
let guard = AbortOnPanic;
// 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();
mem::forget(guard);
// 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(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. Note that if panics are implemented by
/// aborting the process, no error is returned; see the notes of [std::panic::catch_unwind].
///
/// # 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()
}
}
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 { .. }")
}
}

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use std::mem;
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);
#[repr(align(8))]
struct U64Align8(u64);
assert!(AtomicCell::<usize>::is_lock_free());
assert!(AtomicCell::<isize>::is_lock_free());
assert!(AtomicCell::<UsizeWrap>::is_lock_free());
assert!(AtomicCell::<()>::is_lock_free());
assert!(AtomicCell::<u8>::is_lock_free());
assert!(AtomicCell::<i8>::is_lock_free());
assert!(AtomicCell::<bool>::is_lock_free());
assert!(AtomicCell::<U8Wrap>::is_lock_free());
assert!(AtomicCell::<u16>::is_lock_free());
assert!(AtomicCell::<i16>::is_lock_free());
assert!(AtomicCell::<I16Wrap>::is_lock_free());
assert!(AtomicCell::<u32>::is_lock_free());
assert!(AtomicCell::<i32>::is_lock_free());
// Sizes of both types must be equal, and the alignment of `u64` must be greater or equal than
// that of `AtomicU64`. In i686-unknown-linux-gnu, the alignment of `u64` is `4` and alignment
// of `AtomicU64` is `8`, so `AtomicCell<u64>` is not lock-free.
assert_eq!(
AtomicCell::<u64>::is_lock_free(),
cfg!(target_has_atomic = "64") && std::mem::align_of::<u64>() == 8
);
assert_eq!(mem::size_of::<U64Align8>(), 8);
assert_eq!(mem::align_of::<U64Align8>(), 8);
assert_eq!(
AtomicCell::<U64Align8>::is_lock_free(),
cfg!(target_has_atomic = "64")
);
// AtomicU128 is unstable
assert!(!AtomicCell::<u128>::is_lock_free());
}
#[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);
}
// https://github.com/crossbeam-rs/crossbeam/pull/767
macro_rules! test_arithmetic {
($test_name:ident, $ty:ident) => {
#[test]
fn $test_name() {
let a: AtomicCell<$ty> = AtomicCell::new(7);
assert_eq!(a.fetch_add(3), 7);
assert_eq!(a.load(), 10);
assert_eq!(a.fetch_sub(3), 10);
assert_eq!(a.load(), 7);
assert_eq!(a.fetch_and(3), 7);
assert_eq!(a.load(), 3);
assert_eq!(a.fetch_or(16), 3);
assert_eq!(a.load(), 19);
assert_eq!(a.fetch_xor(2), 19);
assert_eq!(a.load(), 17);
assert_eq!(a.fetch_max(18), 17);
assert_eq!(a.load(), 18);
assert_eq!(a.fetch_min(17), 18);
assert_eq!(a.load(), 17);
assert_eq!(a.fetch_nand(7), 17);
assert_eq!(a.load(), !(17 & 7));
}
};
}
test_arithmetic!(arithmetic_u8, u8);
test_arithmetic!(arithmetic_i8, i8);
test_arithmetic!(arithmetic_u16, u16);
test_arithmetic!(arithmetic_i16, i16);
test_arithmetic!(arithmetic_u32, u32);
test_arithmetic!(arithmetic_i32, i32);
test_arithmetic!(arithmetic_u64, u64);
test_arithmetic!(arithmetic_i64, i64);
test_arithmetic!(arithmetic_u128, u128);
test_arithmetic!(arithmetic_i128, i128);
// https://github.com/crossbeam-rs/crossbeam/issues/748
#[cfg_attr(miri, ignore)] // TODO
#[test]
fn issue_748() {
#[allow(dead_code)]
#[repr(align(8))]
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum Test {
Field(u32),
FieldLess,
}
assert_eq!(mem::size_of::<Test>(), 8);
assert_eq!(
AtomicCell::<Test>::is_lock_free(),
cfg!(target_has_atomic = "64")
);
let x = AtomicCell::new(Test::FieldLess);
assert_eq!(x.load(), Test::FieldLess);
}
// https://github.com/crossbeam-rs/crossbeam/issues/833
#[test]
fn issue_833() {
use std::num::NonZeroU128;
use std::sync::atomic::{AtomicBool, Ordering};
use std::thread;
#[cfg(miri)]
const N: usize = 10_000;
#[cfg(not(miri))]
const N: usize = 1_000_000;
#[allow(dead_code)]
enum Enum {
NeverConstructed,
Cell(AtomicCell<NonZeroU128>),
}
static STATIC: Enum = Enum::Cell(AtomicCell::new(match NonZeroU128::new(1) {
Some(nonzero) => nonzero,
None => unreachable!(),
}));
static FINISHED: AtomicBool = AtomicBool::new(false);
let handle = thread::spawn(|| {
let cell = match &STATIC {
Enum::NeverConstructed => unreachable!(),
Enum::Cell(cell) => cell,
};
let x = NonZeroU128::new(0xFFFF_FFFF_FFFF_FFFF_0000_0000_0000_0000).unwrap();
let y = NonZeroU128::new(0x0000_0000_0000_0000_FFFF_FFFF_FFFF_FFFF).unwrap();
while !FINISHED.load(Ordering::Relaxed) {
cell.store(x);
cell.store(y);
}
});
for _ in 0..N {
if let Enum::NeverConstructed = STATIC {
unreachable!(":(");
}
}
FINISHED.store(true, Ordering::Relaxed);
handle.join().unwrap();
}

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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;
let align = mem::align_of::<CachePadded<()>>();
assert!(align >= 32);
assert_eq!(unsafe { a.add(align) }, 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);
}
#[allow(clippy::clone_on_copy)] // This is intentional.
#[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);
}

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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();
}
}

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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;
#[cfg(miri)]
const M: usize = 50;
#[cfg(not(miri))]
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(_) => panic!("try_write should not succeed while read_guard is in scope"),
Err(_) => panic!("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),
}
}

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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();
}

67
vendor/crossbeam-utils/tests/wait_group.rs vendored Normal file
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@ -0,0 +1,67 @@
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 wg2 = WaitGroup::new();
let (tx, rx) = mpsc::channel();
for _ in 0..THREADS {
let wg = wg.clone();
let wg2 = wg2.clone();
let tx = tx.clone();
thread::spawn(move || {
wg2.wait();
tx.send(()).unwrap();
drop(wg);
});
}
// At this point, no thread has gotten past `wg2.wait()`, so we shouldn't get anything from the
// channel.
assert!(rx.try_recv().is_err());
drop(wg2);
wg.wait();
// Now, the wait group is cleared and we should receive messages.
for _ in 0..THREADS {
rx.try_recv().unwrap();
}
}