Segfault in threaded copies of KLUFactorization

[josephmckinsey]

I'm not entirely sure why, but completely separate copies of KLUFactorization cannot be used in separate threads without causing a segfault.

I've made a minimal example at https://github.com/josephmckinsey/klu-threading, since I've only been able to produce this with a specific matrix so far.

https://github.com/josephmckinsey/klu-threading/actions/runs/17870311904/job/50822461621

Solving Ax = b in parallel with 6 threads...

[2188] signal 11 (1): Segmentation fault
in expression starting at none:0
/home/runner/work/_temp/9db51d3c-398d-426e-ace8-493b5356e3a5.sh: line 1:  2188 Segmentation fault      (core dumped) julia --project threads.jl

This might be an upstream bug. However, removing _free_numeric from the finalizer in a local copy of KLU.j stopped the seg fault. It also disappeared if I used @sync instead of just @spawn. Is this known behavior and all that's needed is a mutex around free? The SuiteSparse memory management did not look particularly inviting.

[rayegun]

Do you get this on 1.12? I cannot reproduce locally with your repo. Do you get any line numbers with the segfault?

_free_numeric shouldn't in theory modify any global state other than whatever free Julia is using. The common struct is just statistics not global arrays or similar.

[rayegun]

Oh interesting, I actually do have an issue, but not in _free_numeric. Curious, will investigate further.

[josephmckinsey]

I was using 1.11. I reran the github action and reproduced the error there. Unfortunately, I do not get the line numbers. The "fix" I mentioned messed with other parts of the finalizer, so it might be not be in the _free_numeric code. That was my hacky patch that sort of worked.