From: Ralf Jung Date: Thu, 21 Nov 2019 08:16:56 +0000 (+0100) Subject: typo X-Git-Url: https://git.ralfj.de/web.git/commitdiff_plain/e0f8a822bca79a6a82c90aa6d5bb969e6951daa4?hp=f7efa30082f387c45b9cd5df288fcae6f6594bc6 typo --- diff --git a/personal/_posts/2018-07-13-arc-synchronization.md b/personal/_posts/2018-07-13-arc-synchronization.md index a91f8b2..7579dcf 100644 --- a/personal/_posts/2018-07-13-arc-synchronization.md +++ b/personal/_posts/2018-07-13-arc-synchronization.md @@ -173,7 +173,7 @@ I said that `Mutex`/`RwLock` are good enough *most of the time*. However, `Arc` is one of those cases where the overhead induced by an exclusive lock is just way too big, so it is worth using a more optimized, unsafe implementation. As such, you are going to find plenty of atomic accesses in [the source code of `Arc`](https://github.com/rust-lang/rust/blob/c0955a34bcb17f0b31d7b86522a520ebe7fa93ac/src/liballoc/sync.rs#L201). -And it turns out, as Hai and Jacques-Henri noticed when attempting to prove correctness of [`Arc::get_mut`](https://doc.rust-lang.org/stable/std/sync/struct.Arc.html#method.get_mut), that there is one place where `Relaxed` as used as an ordering, [but it really should have been `Acquire`](https://github.com/rust-lang/rust/pull/52031). +And it turns out, as Hai and Jacques-Henri noticed when attempting to prove correctness of [`Arc::get_mut`](https://doc.rust-lang.org/stable/std/sync/struct.Arc.html#method.get_mut), that there is one place where `Relaxed` was used as an ordering, [but it really should have been `Acquire`](https://github.com/rust-lang/rust/pull/52031). Discussing the exact details of the bug would probably fill another blog post (`Arc` is *really* subtle), but the high-level story is exactly like in our example above: Thanks to `Acquire`, an ordering is induced between the code that follows the `get_mut` and the code in another thread that dropped the last other `Arc`, decrementing the reference count to 1. The PR that fixed the problem contains [some more details in the comments](https://github.com/rust-lang/rust/pull/52031/files). With `Relaxed`, no such ordering is induced, so we have a data race.