E0706 rust type_error ai_generated partial

error[E0706]: thread-local variable cannot be borrowed across a yield point

ID: rust/e0706-thread-local-cannot-be-borrowed-across-yield

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78%Fix Rate
83%Confidence
1Evidence
2024-02-10First Seen

Version Compatibility

VersionStatusIntroducedDeprecatedNotes
1.75.0 active — — —
1.77.0 active — — —
1.79.0 active — — —

Root Cause

A reference to a thread-local variable (e.g., `thread_local!`) is held across an `.await` point in async code, which is unsafe because the thread may change.

generic

中文

在异步代码中，对线程局部变量（例如 `thread_local!`）的引用跨越了 `.await` 点，这可能导致线程切换，因此不安全。

Official Documentation

https://doc.rust-lang.org/error_codes/E0706.html

Workarounds

  1. 82% success Clone the thread-local value before the await point: `let val = THREAD_LOCAL.with(|v| v.clone());` then use `val` after await. 
    Clone the thread-local value before the await point: `let val = THREAD_LOCAL.with(|v| v.clone());` then use `val` after await.
  2. 75% success Restructure code to avoid holding the borrow across await: use `let result = { THREAD_LOCAL.with(|v| v.do_something()) }; result.await`. 
    Restructure code to avoid holding the borrow across await: use `let result = { THREAD_LOCAL.with(|v| v.do_something()) }; result.await`.

中文步骤

  1. 在 await 点之前克隆线程局部值：`let val = THREAD_LOCAL.with(|v| v.clone());` 然后在 await 后使用 `val`。
  2. 重构代码以避免跨 await 持有借用：使用 `let result = { THREAD_LOCAL.with(|v| v.do_something()) }; result.await`。

Dead Ends

Common approaches that don't work:

  1. Wrapping the thread-local in `Rc` to extend lifetime 85% fail

    `Rc` is not `Send`, so cannot be used across await points in async contexts.

  2. Using `unsafe` to extend the borrow lifetime manually 90% fail

    Undefined behavior; compiler may still reject or cause data races.