Add a basic loom test

[ibraheemdev]

Fixes a couple issues when running under loom and adds a basic concurrency test. Unfortunately, this test is still very slow (it ran for >45 minutes and >20M iterations before I killed it on my machine), so I didn't add it to CI yet. It will probably only be practical for us to run very fine-grained unit tests under loom, or switch to something like shuttle for larger tests.

[netlify]

✅ Deploy Preview for salsa-rs canceled.

Name	Link
🔨 Latest commit	0eadfaa
🔍 Latest deploy log	https://app.netlify.com/sites/salsa-rs/deploys/681bd1601df56400086776e1

[codspeed-hq]

CodSpeed Performance Report

Merging #845 will not alter performance

_{Comparing ibraheemdev:ibraheem/loom-tests (0eadfaa) with master (cfa88e9)}

Summary

✅ 12 untouched benchmarks

[MichaReiser]

It might be a flake but any idea why the benchmarks are regressing

[ibraheemdev]

It seems like a flake. It's possible that the compiler isn't inlining the assume_init_ref calls but that seems unlikely.

[MichaReiser]

Thanks

I don't understand much of loom but this looks reasonable.

The fact that not even the most simple tests complete in reasonable time makes me question the value of loom and whether it is worth the complexity (and indirection) it introduces.

What do you think?

[davidbarsky]

I mean, if Loom takes too long to run, then we should be using Shuttle instead. It's not an exhaustive test, but it's a massive step up over the current state of affairs.