[atomic] Initial commit of Atomic<T>

[joshlf]

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• 👉 [atomic] Initial commit of Atomic<T> #2956

Latest Update: v4 — Compare vs v3

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[gemini-code-assist]

Summary of Changes

Hello @joshlf, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request lays the groundwork for a generic Atomic<T> type in Rust, allowing atomic operations on user-defined types. It establishes the necessary traits and macros to facilitate this functionality, starting with basic new, load, and store methods. This is a foundational step towards providing robust and safe concurrent data structures.

Highlights

• Generic Atomic Type Introduction: Introduced a new generic Atomic<T> type, designed to enable atomic operations on arbitrary user-defined types T.
• Trait Definitions for Atomic Behavior: Defined HasAtomic, AtomicSelector, and AtomicOps traits to abstract and standardize the behavior required for types to support atomic operations.
• Standard Atomic Type Integration: Implemented AtomicOps for Rust's built-in atomic integer types (AtomicU8, AtomicU16, AtomicU32, AtomicU64) to bridge with the new generic Atomic<T>.
• Macro for HasAtomic Implementation: Provided the impl_atomic! macro to simplify the process of implementing the HasAtomic trait for compatible types, reducing boilerplate.
• Core Atomic Operations: Implemented fundamental atomic methods including new, load, and store for the Atomic<T> type, with placeholders for more advanced operations like swap and compare_exchange.
• Comprehensive Unit Tests: Included a suite of unit tests to verify the correctness of Atomic<T> operations across various types, including u32, custom structs, and enums, as well as compare_exchange and fetch_update.

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[gemini-code-assist]

Code Review

This pull request introduces a new Atomic<T> type. While this is a good start, the implementation is highly incomplete and not ready for merging. There are numerous TODO placeholders for documentation, safety justifications, and even core logic, which will cause panics at runtime. The unsafe traits and implementations lack the required safety comments, which is critical for a library focused on safety and a violation of the repository's contribution guidelines. Additionally, there's a large block of commented-out code that should be removed. The provided tests do not compile because the necessary trait implementations are missing. I recommend completing the implementation, adding all necessary documentation and safety justifications, and ensuring the tests pass before this can be considered for merging.

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src/atomic.rs (16-21)

The public unsafe trait HasAtomic is missing documentation. It is critical to provide a detailed explanation of the trait's purpose and, most importantly, its safety contract in a /// # Safety section. This contract should clearly define the invariants that both implementors and callers must uphold to ensure memory safety.

References

1. The repository style guide requires that every unsafe trait has /// # Safety documentation explaining its safety contract. ^(link)

src/atomic.rs (54-83)

The unsafe impl blocks within the impl_atomic_selector! macro are missing their SAFETY comments (lines 56 and 77). Per the repository's guidelines, every unsafe implementation must be justified with a comment explaining why it is sound. Please add detailed // SAFETY: comments for the impl AtomicOps and impl AtomicSelector blocks.

References

1. The repository style guide requires that every unsafe block has a // SAFETY: comment justifying its soundness. ^(link)

src/atomic.rs (92-111)

The impl_atomic! macro is #[macro_export]-ed, but its implementation is incomplete, using todo!() for from_atomic and into_atomic. This will cause runtime panics. This functionality must be fully implemented. Additionally, the unsafe impl HasAtomic block is missing its required // SAFETY: comment explaining the soundness of the implementation.

References

1. The repository style guide requires that every unsafe block has a // SAFETY: comment justifying its soundness. ^(link)

src/atomic.rs (142-143)

This unsafe block is missing its required // SAFETY: comment. Please add a justification explaining why the call to T::from_atomic(v) is safe in this context. The comment should detail the invariants that make this operation sound.

References

1. The repository style guide requires that every unsafe block has a // SAFETY: comment justifying its soundness. ^(link)

src/atomic.rs (34-52)

The doc(hidden) but public unsafe traits AtomicSelector and AtomicOps are missing their safety documentation. Even for hidden items, unsafe APIs must have a clearly documented safety contract.

References

1. The repository style guide requires that every unsafe trait has /// # Safety documentation explaining its safety contract. ^(link)

src/atomic.rs (9)

The module is missing documentation. Please add a module-level doc comment explaining the purpose and usage of the atomic module. Several other public items like Atomic<T> and its methods also have TODO placeholders instead of proper documentation.

src/atomic.rs (154-604)

This large block of commented-out code should be removed. Dead code reduces maintainability and can be confusing for future contributors. If this code is being kept for reference, consider moving it to a separate document or tracking it in an issue.