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// SPDX-License-Identifier: GPL-2.0
//! Memory orderings.
//!
//! The semantics of these orderings follows the [`LKMM`] definitions and rules.
//!
//! - [`Acquire`] provides ordering between the load part of the annotated operation and all the
//! following memory accesses, and if there is a store part, the store part has the [`Relaxed`]
//! ordering.
//! - [`Release`] provides ordering between all the preceding memory accesses and the store part of
//! the annotated operation, and if there is a load part, the load part has the [`Relaxed`]
//! ordering.
//! - [`Full`] means "fully-ordered", that is:
//! - It provides ordering between all the preceding memory accesses and the annotated operation.
//! - It provides ordering between the annotated operation and all the following memory accesses.
//! - It provides ordering between all the preceding memory accesses and all the following memory
//! accesses.
//! - All the orderings are the same strength as a full memory barrier (i.e. `smp_mb()`).
//! - [`Relaxed`] provides no ordering except the dependency orderings. Dependency orderings are
//! described in "DEPENDENCY RELATIONS" in [`LKMM`]'s [`explanation`].
//!
//! [`LKMM`]: srctree/tools/memory-model/
//! [`explanation`]: srctree/tools/memory-model/Documentation/explanation.txt
/// The annotation type for relaxed memory ordering, for the description of relaxed memory
/// ordering, see [module-level documentation].
///
/// [module-level documentation]: crate::sync::atomic::ordering
pub struct Relaxed;
/// The annotation type for acquire memory ordering, for the description of acquire memory
/// ordering, see [module-level documentation].
///
/// [module-level documentation]: crate::sync::atomic::ordering
pub struct Acquire;
/// The annotation type for release memory ordering, for the description of release memory
/// ordering, see [module-level documentation].
///
/// [module-level documentation]: crate::sync::atomic::ordering
pub struct Release;
/// The annotation type for fully-ordered memory ordering, for the description fully-ordered memory
/// ordering, see [module-level documentation].
///
/// [module-level documentation]: crate::sync::atomic::ordering
pub struct Full;
/// Describes the exact memory ordering.
#[doc(hidden)]
pub enum OrderingType {
/// Relaxed ordering.
Relaxed,
/// Acquire ordering.
Acquire,
/// Release ordering.
Release,
/// Fully-ordered.
Full,
}
mod internal {
/// Sealed trait, can be only implemented inside atomic mod.
pub trait Sealed {}
impl Sealed for super::Relaxed {}
impl Sealed for super::Acquire {}
impl Sealed for super::Release {}
impl Sealed for super::Full {}
}
/// The trait bound for annotating operations that support any ordering.
pub trait Ordering: internal::Sealed {
/// Describes the exact memory ordering.
const TYPE: OrderingType;
}
impl Ordering for Relaxed {
const TYPE: OrderingType = OrderingType::Relaxed;
}
impl Ordering for Acquire {
const TYPE: OrderingType = OrderingType::Acquire;
}
impl Ordering for Release {
const TYPE: OrderingType = OrderingType::Release;
}
impl Ordering for Full {
const TYPE: OrderingType = OrderingType::Full;
}
/// The trait bound for operations that only support acquire or relaxed ordering.
pub trait AcquireOrRelaxed: Ordering {}
impl AcquireOrRelaxed for Acquire {}
impl AcquireOrRelaxed for Relaxed {}
/// The trait bound for operations that only support release or relaxed ordering.
pub trait ReleaseOrRelaxed: Ordering {}
impl ReleaseOrRelaxed for Release {}
impl ReleaseOrRelaxed for Relaxed {}
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