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Rollup merge of #97516 - RalfJung:atomics, r=joshtriplett
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clarify how Rust atomics correspond to C++ atomics

``@cbeuw`` noted in rust-lang/miri#1963 that the correspondence between C++ atomics and Rust atomics is not quite as obvious as one might think, since in Rust I can use `get_mut` to treat previously non-atomic data as atomic. However, I think using C++20 `atomic_ref`, we can establish a suitable relation between the two -- or do you see problems with that ``@cbeuw?`` (I recall you said there was some issue, but it was deep inside that PR and Github makes it impossible to find...)

Cc ``@thomcc;`` not sure whom else to ping for atomic memory model things.
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JohnTitor authored Jun 22, 2022
2 parents 10a7078 + e22caaa commit 5b53431
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7 changes: 7 additions & 0 deletions core/src/sync/atomic.rs
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//! threads, and are the building blocks of other concurrent
//! types.
//!
//! Rust atomics currently follow the same rules as [C++20 atomics][cpp], specifically `atomic_ref`.
//! Basically, creating a *shared reference* to one of the Rust atomic types corresponds to creating
//! an `atomic_ref` in C++; the `atomic_ref` is destroyed when the lifetime of the shared reference
//! ends. (A Rust atomic type that is exclusively owned or behind a mutable reference does *not*
//! correspond to an "atomic object" in C++, since it can be accessed via non-atomic operations.)
//!
//! This module defines atomic versions of a select number of primitive
//! types, including [`AtomicBool`], [`AtomicIsize`], [`AtomicUsize`],
//! [`AtomicI8`], [`AtomicU16`], etc.
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//! the memory barrier for that operation. These orderings are the
//! same as the [C++20 atomic orderings][1]. For more information see the [nomicon][2].
//!
//! [cpp]: https://en.cppreference.com/w/cpp/atomic
//! [1]: https://en.cppreference.com/w/cpp/atomic/memory_order
//! [2]: ../../../nomicon/atomics.html
//!
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