Ordering in core::sync::atomic - Rust
Description: Atomic memory orderings

# Enum Ordering

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    #[non_exhaustive]pub enum Ordering {
        Relaxed,
        Release,
        Acquire,
        AcqRel,
        SeqCst,
    }

Expand description

Atomic memory orderings

Memory orderings specify the way atomic operations synchronize memory. In its weakest `Ordering::Relaxed`, only the memory directly touched by the operation is synchronized. On the other hand, a store-load pair of `Ordering::SeqCst` operations synchronize other memory while additionally preserving a total order of such operations across all threads.

Rust’s memory orderings are the same as those of C++20.

For more information see the nomicon.

## Variants (Non-exhaustive)§

This enum is marked as non-exhaustive
Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.
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### Relaxed

No ordering constraints, only atomic operations.

Corresponds to `memory_order_relaxed` in C++20.

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### Release

When coupled with a store, all previous operations become ordered before any load of this value with `Acquire` (or stronger) ordering. In particular, all previous writes become visible to all threads that perform an `Acquire` (or stronger) load of this value.

Notice that using this ordering for an operation that combines loads and stores leads to a `Relaxed` load operation!

This ordering is only applicable for operations that can perform a store.

Corresponds to `memory_order_release` in C++20.

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### Acquire

When coupled with a load, if the loaded value was written by a store operation with `Release` (or stronger) ordering, then all subsequent operations become ordered after that store. In particular, all subsequent loads will see data written before the store.

Notice that using this ordering for an operation that combines loads and stores leads to a `Relaxed` store operation!

This ordering is only applicable for operations that can perform a load.

Corresponds to `memory_order_acquire` in C++20.

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### AcqRel

Has the effects of both `Acquire` and `Release` together: For loads it uses `Acquire` ordering. For stores it uses the `Release` ordering.

Notice that in the case of `compare_and_swap`, it is possible that the operation ends up not performing any store and hence it has just `Acquire` ordering. However, `AcqRel` will never perform `Relaxed` accesses.

This ordering is only applicable for operations that combine both loads and stores.

Corresponds to `memory_order_acq_rel` in C++20.

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### SeqCst

Like `Acquire`/`Release`/`AcqRel` (for load, store, and load-with-store operations, respectively) with the additional guarantee that all threads see all sequentially consistent operations in the same order.

Corresponds to `memory_order_seq_cst` in C++20.

## Trait Implementations§

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### impl Clone for Ordering

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#### fn clone(&self) -> Ordering

Returns a copy of the value. Read more
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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more
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### impl Debug for Ordering

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more
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### impl Hash for Ordering

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#### fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given `Hasher`. Read more
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#### fn hash_slice<H: Hasher>(data: &[Self], state: &mut H)
where Self: Sized,

Feeds a slice of this type into the given `Hasher`. Read more
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### impl PartialEq for Ordering

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#### fn eq(&self, other: &Ordering) -> bool

Tests for `self` and `other` values to be equal, and is used by `==`.
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#### fn ne(&self, other: &Rhs) -> bool

Tests for `!=`. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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### impl Copy for Ordering

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### impl Eq for Ordering

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### impl StructuralPartialEq for Ordering

## Auto Trait Implementations§

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### impl Freeze for Ordering

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### impl RefUnwindSafe for Ordering

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### impl Send for Ordering

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### impl Sync for Ordering

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### impl Unpin for Ordering

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### impl UnwindSafe for Ordering

## Blanket Implementations§

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### impl<T> Any for T
where T: 'static + ?Sized,

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#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
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### impl<T> Borrow<T> for T
where T: ?Sized,

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#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for T
where T: ?Sized,

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#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
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### impl<T> CloneToUninit for T
where T: Clone,

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#### unsafe fn clone_to_uninit(&self, dest: *mut u8)

🔬This is a nightly-only experimental API. (`clone_to_uninit` #126799)
Performs copy-assignment from `self` to `dest`. Read more
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### impl<T> From<T> for T

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#### fn from(t: T) -> T

Returns the argument unchanged.

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### impl<T, U> Into<U> for T
where U: From<T>,

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#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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### impl<T, U> TryFrom<U> for T
where U: Into<T>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
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### impl<T, U> TryInto<U> for T
where U: TryFrom<T>,

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#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.