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Diffstat (limited to 'vendor/spin/src/lib.rs')
| -rw-r--r-- | vendor/spin/src/lib.rs | 221 |
1 files changed, 221 insertions, 0 deletions
diff --git a/vendor/spin/src/lib.rs b/vendor/spin/src/lib.rs new file mode 100644 index 0000000..50768bc --- /dev/null +++ b/vendor/spin/src/lib.rs @@ -0,0 +1,221 @@ +#![cfg_attr(all(not(feature = "std"), not(test)), no_std)] +#![cfg_attr(docsrs, feature(doc_cfg))] +#![deny(missing_docs)] + +//! This crate provides [spin-based](https://en.wikipedia.org/wiki/Spinlock) versions of the +//! primitives in `std::sync` and `std::lazy`. Because synchronization is done through spinning, +//! the primitives are suitable for use in `no_std` environments. +//! +//! # Features +//! +//! - `Mutex`, `RwLock`, `Once`/`SyncOnceCell`, and `SyncLazy` equivalents +//! +//! - Support for `no_std` environments +//! +//! - [`lock_api`](https://crates.io/crates/lock_api) compatibility +//! +//! - Upgradeable `RwLock` guards +//! +//! - Guards can be sent and shared between threads +//! +//! - Guard leaking +//! +//! - Ticket locks +//! +//! - Different strategies for dealing with contention +//! +//! # Relationship with `std::sync` +//! +//! While `spin` is not a drop-in replacement for `std::sync` (and +//! [should not be considered as such](https://matklad.github.io/2020/01/02/spinlocks-considered-harmful.html)) +//! an effort is made to keep this crate reasonably consistent with `std::sync`. +//! +//! Many of the types defined in this crate have 'additional capabilities' when compared to `std::sync`: +//! +//! - Because spinning does not depend on the thread-driven model of `std::sync`, guards ([`MutexGuard`], +//! [`RwLockReadGuard`], [`RwLockWriteGuard`], etc.) may be sent and shared between threads. +//! +//! - [`RwLockUpgradableGuard`] supports being upgraded into a [`RwLockWriteGuard`]. +//! +//! - Guards support [leaking](https://doc.rust-lang.org/nomicon/leaking.html). +//! +//! - [`Once`] owns the value returned by its `call_once` initializer. +//! +//! - [`RwLock`] supports counting readers and writers. +//! +//! Conversely, the types in this crate do not have some of the features `std::sync` has: +//! +//! - Locks do not track [panic poisoning](https://doc.rust-lang.org/nomicon/poisoning.html). +//! +//! ## Feature flags +//! +//! The crate comes with a few feature flags that you may wish to use. +//! +//! - `lock_api` enables support for [`lock_api`](https://crates.io/crates/lock_api) +//! +//! - `ticket_mutex` uses a ticket lock for the implementation of `Mutex` +//! +//! - `fair_mutex` enables a fairer implementation of `Mutex` that uses eventual fairness to avoid +//! starvation +//! +//! - `std` enables support for thread yielding instead of spinning + +#[cfg(any(test, feature = "std"))] +extern crate core; + +#[cfg(feature = "portable_atomic")] +extern crate portable_atomic; + +#[cfg(not(feature = "portable_atomic"))] +use core::sync::atomic; +#[cfg(feature = "portable_atomic")] +use portable_atomic as atomic; + +#[cfg(feature = "barrier")] +#[cfg_attr(docsrs, doc(cfg(feature = "barrier")))] +pub mod barrier; +#[cfg(feature = "lazy")] +#[cfg_attr(docsrs, doc(cfg(feature = "lazy")))] +pub mod lazy; +#[cfg(feature = "mutex")] +#[cfg_attr(docsrs, doc(cfg(feature = "mutex")))] +pub mod mutex; +#[cfg(feature = "once")] +#[cfg_attr(docsrs, doc(cfg(feature = "once")))] +pub mod once; +pub mod relax; +#[cfg(feature = "rwlock")] +#[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))] +pub mod rwlock; + +#[cfg(feature = "mutex")] +#[cfg_attr(docsrs, doc(cfg(feature = "mutex")))] +pub use mutex::MutexGuard; +#[cfg(feature = "std")] +#[cfg_attr(docsrs, doc(cfg(feature = "std")))] +pub use relax::Yield; +pub use relax::{RelaxStrategy, Spin}; +#[cfg(feature = "rwlock")] +#[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))] +pub use rwlock::RwLockReadGuard; + +// Avoid confusing inference errors by aliasing away the relax strategy parameter. Users that need to use a different +// relax strategy can do so by accessing the types through their fully-qualified path. This is a little bit horrible +// but sadly adding a default type parameter is *still* a breaking change in Rust (for understandable reasons). + +/// A primitive that synchronizes the execution of multiple threads. See [`barrier::Barrier`] for documentation. +/// +/// A note for advanced users: this alias exists to avoid subtle type inference errors due to the default relax +/// strategy type parameter. If you need a non-default relax strategy, use the fully-qualified path. +#[cfg(feature = "barrier")] +#[cfg_attr(docsrs, doc(cfg(feature = "barrier")))] +pub type Barrier = crate::barrier::Barrier; + +/// A value which is initialized on the first access. See [`lazy::Lazy`] for documentation. +/// +/// A note for advanced users: this alias exists to avoid subtle type inference errors due to the default relax +/// strategy type parameter. If you need a non-default relax strategy, use the fully-qualified path. +#[cfg(feature = "lazy")] +#[cfg_attr(docsrs, doc(cfg(feature = "lazy")))] +pub type Lazy<T, F = fn() -> T> = crate::lazy::Lazy<T, F>; + +/// A primitive that synchronizes the execution of multiple threads. See [`mutex::Mutex`] for documentation. +/// +/// A note for advanced users: this alias exists to avoid subtle type inference errors due to the default relax +/// strategy type parameter. If you need a non-default relax strategy, use the fully-qualified path. +#[cfg(feature = "mutex")] +#[cfg_attr(docsrs, doc(cfg(feature = "mutex")))] +pub type Mutex<T> = crate::mutex::Mutex<T>; + +/// A primitive that provides lazy one-time initialization. See [`once::Once`] for documentation. +/// +/// A note for advanced users: this alias exists to avoid subtle type inference errors due to the default relax +/// strategy type parameter. If you need a non-default relax strategy, use the fully-qualified path. +#[cfg(feature = "once")] +#[cfg_attr(docsrs, doc(cfg(feature = "once")))] +pub type Once<T = ()> = crate::once::Once<T>; + +/// A lock that provides data access to either one writer or many readers. See [`rwlock::RwLock`] for documentation. +/// +/// A note for advanced users: this alias exists to avoid subtle type inference errors due to the default relax +/// strategy type parameter. If you need a non-default relax strategy, use the fully-qualified path. +#[cfg(feature = "rwlock")] +#[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))] +pub type RwLock<T> = crate::rwlock::RwLock<T>; + +/// A guard that provides immutable data access but can be upgraded to [`RwLockWriteGuard`]. See +/// [`rwlock::RwLockUpgradableGuard`] for documentation. +/// +/// A note for advanced users: this alias exists to avoid subtle type inference errors due to the default relax +/// strategy type parameter. If you need a non-default relax strategy, use the fully-qualified path. +#[cfg(feature = "rwlock")] +#[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))] +pub type RwLockUpgradableGuard<'a, T> = crate::rwlock::RwLockUpgradableGuard<'a, T>; + +/// A guard that provides mutable data access. See [`rwlock::RwLockWriteGuard`] for documentation. +/// +/// A note for advanced users: this alias exists to avoid subtle type inference errors due to the default relax +/// strategy type parameter. If you need a non-default relax strategy, use the fully-qualified path. +#[cfg(feature = "rwlock")] +#[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))] +pub type RwLockWriteGuard<'a, T> = crate::rwlock::RwLockWriteGuard<'a, T>; + +/// Spin synchronisation primitives, but compatible with [`lock_api`](https://crates.io/crates/lock_api). +#[cfg(feature = "lock_api")] +#[cfg_attr(docsrs, doc(cfg(feature = "lock_api")))] +pub mod lock_api { + /// A lock that provides mutually exclusive data access (compatible with [`lock_api`](https://crates.io/crates/lock_api)). + #[cfg(feature = "mutex")] + #[cfg_attr(docsrs, doc(cfg(feature = "mutex")))] + pub type Mutex<T> = lock_api_crate::Mutex<crate::Mutex<()>, T>; + + /// A guard that provides mutable data access (compatible with [`lock_api`](https://crates.io/crates/lock_api)). + #[cfg(feature = "mutex")] + #[cfg_attr(docsrs, doc(cfg(feature = "mutex")))] + pub type MutexGuard<'a, T> = lock_api_crate::MutexGuard<'a, crate::Mutex<()>, T>; + + /// A lock that provides data access to either one writer or many readers (compatible with [`lock_api`](https://crates.io/crates/lock_api)). + #[cfg(feature = "rwlock")] + #[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))] + pub type RwLock<T> = lock_api_crate::RwLock<crate::RwLock<()>, T>; + + /// A guard that provides immutable data access (compatible with [`lock_api`](https://crates.io/crates/lock_api)). + #[cfg(feature = "rwlock")] + #[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))] + pub type RwLockReadGuard<'a, T> = lock_api_crate::RwLockReadGuard<'a, crate::RwLock<()>, T>; + + /// A guard that provides mutable data access (compatible with [`lock_api`](https://crates.io/crates/lock_api)). + #[cfg(feature = "rwlock")] + #[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))] + pub type RwLockWriteGuard<'a, T> = lock_api_crate::RwLockWriteGuard<'a, crate::RwLock<()>, T>; + + /// A guard that provides immutable data access but can be upgraded to [`RwLockWriteGuard`] (compatible with [`lock_api`](https://crates.io/crates/lock_api)). + #[cfg(feature = "rwlock")] + #[cfg_attr(docsrs, doc(cfg(feature = "rwlock")))] + pub type RwLockUpgradableReadGuard<'a, T> = + lock_api_crate::RwLockUpgradableReadGuard<'a, crate::RwLock<()>, T>; +} + +/// In the event of an invalid operation, it's best to abort the current process. +#[cfg(feature = "fair_mutex")] +fn abort() -> ! { + #[cfg(not(feature = "std"))] + { + // Panicking while panicking is defined by Rust to result in an abort. + struct Panic; + + impl Drop for Panic { + fn drop(&mut self) { + panic!("aborting due to invalid operation"); + } + } + + let _panic = Panic; + panic!("aborting due to invalid operation"); + } + + #[cfg(feature = "std")] + { + std::process::abort(); + } +} |