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Futurelock: A subtle risk in async Rust

(rfd.shared.oxide.computer)
421 points bcantrill | 2 comments | 31 Oct 25 16:49 UTC | HN request time: 0.401s | source

This RFD describes our distillation of a really gnarly issue that we hit in the Oxide control plane.[0] Not unlike our discovery of the async cancellation issue[1][2][3], this is larger than the issue itself -- and worse, the program that hits futurelock is correct from the programmer's point of view. Fortunately, the surface area here is smaller than that of async cancellation and the conditions required to hit it can be relatively easily mitigated. Still, this is a pretty deep issue -- and something that took some very seasoned Rust hands quite a while to find.

[0] https://github.com/oxidecomputer/omicron/issues/9259

[1] https://rfd.shared.oxide.computer/rfd/397

[2] https://rfd.shared.oxide.computer/rfd/400

[3] https://www.youtube.com/watch?v=zrv5Cy1R7r4

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levodelellis ◴[31 Oct 25 23:49 UTC] No.45777969[source]▶
In October alone I seen 5+ articles and comments about multi-threading and I don't know why

I always said if your code locks or use atomics, it's wrong. Everyone says I'm wrong but you get things like what's described in the article. I'd like to recommend a solution but there's pretty much no reasonable way to implement multi-threading when you're not an expert. I heard Erlang and Elixir are good but I haven't tried them so I can't really comment

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1. umvi ◴[31 Oct 25 23:52 UTC] No.45777993[source]▶
> I always said if your code locks or use atomics, it's wrong. Everyone says I'm wrong but you get things like what's described in the article.

Ok so say you are simulating high energy photons (x-rays) flowing through a 3d patient volume. You need to simulate 2 billion particles propagating through the patient in order to get an accurate estimation of how the radiation is distributed. How do you accomplish this without locks or atomics without the simulation taking 100 hours to run? Obviously it would take forever to simulate 1 particle at a time, but without locks or atomics the particles will step on each others' toes when updating radiation distribution in the patient. I suppose you could have 2 billion copies of the patient's volume in memory and each particle gets its own private copy and then you merge them all at the end...

replies(1): >>45778046 #
2. levodelellis ◴[01 Nov 25 00:02 UTC] No.45778046[source]▶
From my understanding this talk describes how he implemented a solution for a similar problem https://www.youtube.com/watch?v=Kvsvd67XUKw

I'm saying if you're not writing multi-threaded code everyday, use a library. It can use atomics/locks but you shouldn't use it directly. If the library is designed well it'd be impossible to deadlock.