一个结构的 destructor （即 Drop）不一定保证会执行，这也是 std 移除 thread::scoped 这个 API 的原因，下面这几篇文章都对其进行了详细分析。

• Async Rust: history strikes back.

  • Reference counting is not the end of the world. As a matter of fact, in an earlier essay I have argued that they are the price we pay to live in a civilized asynchronous world.

  • Glommio 中 ScopedTask 的效果

    1 2 3 4 5 6 7 8 9 10 11 12

    async fn some_async_function() { let shared = Rc::new(Cell::new(0)); let s = shared.clone(); let x = Task::local(async move { do_async_work(s).await; // used a Clone of shared state }); // <== task starts executing here do_more_work(shared); // <== may be still background executing here x.await; // <== but is surely done here. }

• C++ vs Rust: an async Thread-per-Core story

  • The borrow checker works well for things that happen at predictable times. But once you start implementing things like an asynchronous call, or a queue of requests that will be consumed by io_uring at a later time and are stored in a on-heap array, things get more complex. Take the following code as a toy example:

• Pre-Pooping Your Pants With Rust
• std::thread::JoinGuard (and scoped) are unsound because of reference cycles · Issue #24292

目前，async fn 无法在 Rust 稳定版本的 traits 中使用。 自 2022 年 11 月 17 日起，async-fn-in-trait 的 MVP 可在编译器工具链的夜间版本中使用，详情请参阅此处。

与此同时，在稳定版工具链中可以使用 async-trait 来解决这一问题。

请注意，使用这些 trait 方法会导致每次函数调用都要进行堆分配。 对于绝大多数应用程序来说，这并不是一个 很大的代价，但在决定是否在低级函数的公共 API 中使用此功能时，应考虑到该函数预计每秒会被调用数百万次。