[ViralBShah]

Fixes #31. Refs #38.

The bug

At exit, jl_atexit_hook runs Base._atexit and then runs all finalizers, including those of objects that are still reachable, while tasks on other threads may still be running. The KLUFactorization finalizer then frees the Numeric and Symbolic objects under an in-flight klu_solve, which segfaults.

The reproducer in #31 makes no copies. Each task calls klu(A) itself, and the script ends without waiting for its tasks. That explains the reporter's two observations: both @sync and changing the finalizer make the crash go away. A trace of the finalizer logged frees of up to 7 objects still in use after the main task finished.

The fix

An atexit hook sets _EXITING, and the finalizer returns early once it is set. Hooks run before the finalizer pass. The memory is left to the OS, and the process is exiting anyway. PowerNetworkMatrices.jl made the same change in its own wrapper in 8b8fb959.

Results

Locally on macOS arm64 with Julia 1.13:

	main	This PR
#31 scenario with the issue's matrix, 24 tasks × 2000 solves, -t 8	10/10 segfault	0/10
New regression script, -t 4	10/10 fail	0/10
Solves/s at 8 threads, one factorization per task	16,910	17,501

The new test runs the scenario in a subprocess, because the crash happens during process exit. The full suite passes at -t 4.

Windows and Linux were not tested locally. The crash log in #31 has the same in expression starting at none:0 signature as these runs.

Overlap with #42

#42 also changes the finalizer, so whichever merges second needs a small conflict resolution. #42 stops this crash too, but this fix keeps libklu calls running in parallel.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 59.15%. Comparing base (63298d8) to head (3a171d1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #46      +/-   ##
==========================================
+ Coverage   59.02%   59.15%   +0.13%     
==========================================
  Files           2        2              
  Lines         593      595       +2     
==========================================
+ Hits          350      352       +2     
  Misses        243      243              

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[ViralBShah]

Small review fix in 3a171d1: the exit test keeps the subprocess stderr, so a platform-specific crash leaves evidence in CI, and the comment is shorter. Also checked on Linux, which the description lists as untested: the #31 scenario crashed 7/10 runs on main and 0/10 with this PR. Tests pass on Julia 1.13 and 1.10.