Add GC-safe region around Highs_run

[kpamnany]

Prevent a long-running Highs_run call from blocking GC (and freezing other Julia threads). Ref: JuliaLang/julia#51574

Questions:

• Does Highs_run call back into Julia?
• Is this the only call that can run for minutes?

[odow]

Does Highs_run call back into Julia?

Not currently, but it may do in future.

Is this the only call that can run for minutes?

There are other calls, but we don't use them at the moment.

Let me take a deeper look at this PR. I would prefer that we put the region around

HiGHS.jl/src/MOI_wrapper.jl

Line 1815 in 7316ac9

ret = Highs_run(model)

and left the automatically built libhighs.jl alone

[kpamnany]

Moved the region to MOI_wrapper.jl.

[odow]

Did you find this instance because of some benchmark? I guess this might actually be a problem for most of the JuMP solvers

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (7316ac9) 83.31% compared to head (3dadf96) 83.34%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #178      +/-   ##
==========================================
+ Coverage   83.31%   83.34%   +0.03%     
==========================================
  Files           3        3              
  Lines        1630     1633       +3     
==========================================
+ Hits         1358     1361       +3     
  Misses        272      272              

Files	Coverage Δ
src/MOI_wrapper.jl	94.12% <100.00%> (+0.01%)	⬆️

☔ View full report in Codecov by Sentry.
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[kpamnany]

I work at RelationalAI; we're using Julia to build our product. The freeze I mention happened to us. 😢

This is likely a problem with the other solvers as well, as well as any package that wraps an external library (i.e. uses ccall) that implements possibly long-running logic.

[kpamnany]

Can I request a new patch release with this fix?

[odow]

I work at RelationalAI

Ah 😄

What other solvers do you need me to look at?

Can I request a new patch release with this fix?

Yip

[kpamnany]

What other solvers do you need me to look at?

Let me get back on that one.

Thanks very much!

[kpamnany]

Here are other jump-dev solvers that are relevant to us, but don't need an immediate fix:

• Gurobi
• Pavito
• MiniZinc
• Ipopt

Cc: @bachdavi

[odow]

I think these are all safe:

• Gurobi: calls back into Julia from C
• Pavito: written in Julia
• MiniZinc: calls a binary via run
• Ipopt: calls back into Julia from C