# Problem with concurrent calls to HiGHS solver (via JuMP) on Windows
**URL:** https://discourse.julialang.org/t/problem-with-concurrent-calls-to-highs-solver-via-jump-on-windows/134631
**Category:** Optimization (Mathematical)
**Tags:** jump
**Created:** [December 18, 2025, 1:35pm UTC](https://discourse.julialang.org/t/problem-with-concurrent-calls-to-highs-solver-via-jump-on-windows/134631 "2025-12-18T13:35:59Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@LaurentPlagne](https://discourse.julialang.org/u/LaurentPlagne)
#### Post date: [December 18, 2025, 1:35pm UTC](https://discourse.julialang.org/t/problem-with-concurrent-calls-to-highs-solver-via-jump-on-windows/134631/1 "2025-12-18T13:35:59Z")
Hi,
I wanted to report some crashes observed when solving concurrently (multi-thread) different LP problems via JuMP with HiGHS solver:
EXCEPTION\_ACCESS\_VIOLATION dans HighsTaskExecutor…
No crashes observed on Linux
No crashes observed with HiGHS.jl 1.19.0 (only observed with HiGHS.jl 1.20.1)
No crashes observed for sequential/successive JuMP solve calls.
No crashes observed if we specify a single threaded execution of HiGHS:
```julia-auto
model = direct_model(HiGHS.Optimizer())
Highs_resetGlobalScheduler(1)
set_attribute(model, MOI.NumberOfThreads(), 1)
```
I do not have a MWE at the moment and only report this for information. We now do specify a single threaded execution of the HiGHS solver.
---
### Author:  [@odow](https://discourse.julialang.org/u/odow)
#### Post date: [December 18, 2025, 7:58pm UTC](https://discourse.julialang.org/t/problem-with-concurrent-calls-to-highs-solver-via-jump-on-windows/134631/2 "2025-12-18T19:58:53Z")
This is going to be very hard to debug without a reproducible example.
- How were you multithreading in Julia?
- Did you set any parameters for HiGHS?
- Is this consistently repeatable on Windows?
- Do you call `Highs_resetGlobalScheduler` at any point?
---
### Author:  [@LaurentPlagne](https://discourse.julialang.org/u/LaurentPlagne)
#### Post date: [December 18, 2025, 9:16pm UTC](https://discourse.julialang.org/t/problem-with-concurrent-calls-to-highs-solver-via-jump-on-windows/134631/3 "2025-12-18T21:16:43Z")
> [@odow](#):
>
> This is going to be very hard to debug without a reproducible example.
I do not really think that it is possible without a proper MWE.
Nevertheless, I though that it could be interesting to report this if some other user encounters the same kind of problem : the explicit single execution of HiGHS did solve our problem.
It may also ring a bell for the HiGHS or HiGHS.jl developper because it seems that it could be related to nested parallelism issues on Windows.
> [@odow](#):
>
> How were you multithreading in Julia?
I use the OhMyThread.jl `tmap` function and the JuMP model are created for each TransitionProblems instances
```julia-auto
function parallel_solve_one_pdt(ep::EtudeParameters, pdt::Int, future_bf::BellmanFunction1D,)::Vector{BellmanFunction1D}
n_scenario = scenario_number(ep)
scenario_chunks = chunks(1:n_scenario; n=Threads.nthreads())
function process_chunk(scenario_chunk)
tps = TransitionProblems(ep, pdt, future_bf) #contains a JuMP model
return [solve_one_pdt_one_scenario!(tps, ep, pdt, scenario) for scenario ∈ scenario_chunk]
end
scenario_chunks_bfs::Vector{Vector{BellmanFunction1D}} = OhMyThreads.tmap(process_chunk, scenario_chunks, scheduler=:static) #(one Vector{BellmanFunction1D} per task)
scenario_bfs::Vector{BellmanFunction1D} = vcat(scenario_chunks_bfs...) # -> gather to a single Vector{BellmanFunction1D}
return scenario_bfs
end
```
> [@odow](#):
>
> Did you set any parameters for HiGHS?
Nothing fancy:
```julia-auto
model = direct_model(HiGHS.Optimizer())
JuMP.set_silent(model)
JuMP.set_string_names_on_creation(model, true)
```
Like I wrote above, adding
```julia-auto
Highs_resetGlobalScheduler(1)
set_attribute(model, MOI.NumberOfThreads(), 1)
```
Seems to solve the pb.
> [@odow](#):
>
> Is this consistently repeatable on Windows?
The crash occurs at different time steps of the execution : it varies from one exec to the other (heisenbug)
> [@odow](#):
>
> Do you call `Highs_resetGlobalScheduler` at any point?
No (not in the crashing configuration).
P.S. It is also tedious for me to assess because it only occurs on Windows laptops (coworkers) and I do not have a direct access to a Windows machine.