JuliaLang/julia

`JULIA_NUM_THREADS` ignored when embedding Julia on a Windows system

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#55,468 opened on Aug 12, 2024

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bughelp wantedsystem:windows

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Description

The following c# code...

Environment.SetEnvironmentVariable("JULIA_NUM_THREADS", "4");
jl_init_with_image__threading(mBinPath, mSysImg);
jl_eval_string("println(\"Threads=$(Threads.nthreads())\")");
jl_eval_string("println(\"JULIA_NUM_THREADS=$(ENV[\"JULIA_NUM_THREADS\"])\")");

Produces the following output

Threads=1
JULIA_NUM_THREADS=4

In discussions with the Jeff and Keno it appears this happens in Windows because there are several environment stores in Windows, and the threads are created by reading with getenv (which access the machine level environment), while later in Julia the ENV is retrieved using getenvw (which access the process level environment).

Contributor guide

Research direction
Examine how Julia retrieves JULIA NUM THREADS during initialization on Windows, and consider using GetEnvironmentVariable instead of getenv for consistency.
Tech stack
julia
Domain
backend
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
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Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitC
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60