The article discusses an unexpected Sync bound that emerges in Rust when working with async trait methods that return Send futures, even when Sync isn't explicitly required. It explains how this happens due to the interaction between async/await desugaring and Rust's thread safety rules, particularly when using &self references. The author provides code examples demonstrating how using interior mutability with Cell can break this implicit Sync requirement.
Background
Rust's async/await feature and its interaction with the Send and Sync traits are fundamental to writing safe concurrent code, but can sometimes lead to surprising behavior. The article explores a specific edge case where the compiler enforces stronger synchronization requirements than might be immediately obvious to developers.
- Source
- Lobsters
- Published
- May 8, 2026 at 11:12 PM
- Score
- 7.0 / 10