Make `// SAFETY` comment part of the doctest, and not surrounding code

2023-01-12T07:28:43+00:00

Remove unused `mut` from a doctest

2023-01-12T07:27:51+00:00

Add `AtomicPtr::as_mut_ptr`

2023-01-12T07:27:36+00:00

Correct typos in `core::sync::Exclusive::get_{pin_mut, mut}`

2022-12-12T08:19:17+00:00

Remove extra spaces

2022-10-19T22:54:00+00:00

more dupe word typos

2022-10-14T04:57:56+00:00

Rollup merge of #101774 - Riolku:atomic-update-aba, r=m-ou-se

2022-10-11T16:59:46+00:00

Warn about safety of `fetch_update` Specifically as it relates to the ABA problem. `fetch_update` is a useful function, and one that isn't provided by, say, C++. However, this does not mean the function is magic. It is implemented in terms of `compare_exchange_weak`, and in particular, suffers from the ABA problem. See the following code, which is a naive implementation of `pop` in a lock-free queue: ```rust fn pop(&self) -> Option { self.front.fetch_update(Ordering::Relaxed, Ordering::Acquire, |front| { if front == ptr::null_mut() { None } else { Some(unsafe { (*front).next }) } }.ok() } ``` This code is unsound if called from multiple threads because of the ABA problem. Specifically, suppose nodes are allocated with `Box`. Suppose the following sequence happens: ``` Initial: Queue is X -> Y. Thread A: Starts popping, is pre-empted. Thread B: Pops successfully, twice, leaving the queue empty. Thread C: Pushes, and `Box` returns X (very common for allocators) Thread A: Wakes up, sees the head is still X, and stores Y as the new head. ``` But `Y` is deallocated. This is undefined behaviour. Adding a note about this problem to `fetch_update` should hopefully prevent users from being misled, and also, a link to this common problem is, in my opinion, an improvement to our docs on atomics.

Add `#[inline]` to trivial functions on `core::sync::Exclusive`

2022-09-23T05:15:27+00:00

Warn about safety of `fetch_update`

2022-09-14T17:25:14+00:00

Specifically as it relates to the ABA problem.

fix nitpicks from review

2022-08-21T02:36:11+00:00

rust/library/core/src/sync, branch 1.68.2