Replace dashmap with scc #109
Conversation
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I can add another data point here. In order to update the Fedora Linux package for the serial_test crate we had to package the scc crate too, and I ended up having to disable tests (for now) - about 50% of test runs failed due to non-deterministic test failures or crashes due to "unreachable code reached" or "out of bounds array access". Most issues looked like race conditions - possibly due to incorrect usage of atomics, since none of the failures happened on x86_64 (which has stronger memory ordering guarantees than other architectures - even using atomics wrong can appear to "work" correctly). Incorrect usage of atomics for memory accesses can lead to unsoundness and / or correctness issues, as can be seen from the test logs in the issue I opened: |
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That's interesting. So part of the serial_test CI runs on a In other words, I think for most users on arm64 (and hopefully powerpc64le) they can just use scc as part of serial_test and it just works, and this is mainly an issue around packaging right? Also I'm seeing good responses on that ticket from the scc maintainer, so hopefully that gets fixed soon anyways. If that can't get resolved in the coming weeks, I might have to look at another library eventually, but I've been happy with scc so far. |
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Sounds like a good plan! Just wanted to let you know about possibly unintended consequences caused by the switch from dashmap to scc. |
Also add a lot of debug (primarily around start of test, etc) which should all default to off
Mostly because of https://dev.to/acter/beware-of-the-dashmap-deadlock-lij but also wondering if this will solve the periodic test failures that I haven't previously been able to debug.