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.