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Multithreading with PythonCall and PythonPlot leads to a EXCEPTION_ACCESS_VIOLATION

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Évaluation

Difficulté
4/5
Temps estimé
3-5 jours
Accessibilité débutants
35/100
Type d'issue
Bug
Clarté
Plutôt claire
Activité
À l'abandon
Stack technique
julia, python
Domaine
backend

Piste de recherche

Commencez par src\Pythoncall_testing.jl et reproduisez le crash avec Julia 1.12.5, PythonCall 0.9.31, PythonPlot 1.0.6, Windows et 10 threads. Lisez la stack trace autour de init de PythonPlot et de la ligne 198 de pyGui.jl, avec PythonCall.GIL.@unlock. Le travail est terminé lorsque l’interaction est comprise et que la violation d’accès signalée ne se produit plus dans l’exemple minimal.

Rédigé par le modèle d'indexation à partir du texte de l'issue.

Description

bug

Affects: PythonCall

Bug description
Having both PythonCall and PythonPlot imported leads to a EXCEPTION_ACCESS_VIOLATION when used with multithreading with an unlocked GIL.

MWE
File: src\Pythoncall_testing.jl

import PythonCall
import PythonPlot


PythonCall.GIL.@unlock Threads.@threads  for i in 1:5
    println("Hello world")
end
Commands

Command line:

C:\Users\kuhrmann\CODE\pythoncall_testing>julia -t 10
] activate .
include("src\\Pythoncall_testing.jl")
Output 
C:\Users\kuhrmann\CODE\pythoncall_testing>julia -t 10
               _
   _       _ _(_)_     |  Documentation: https://docs.julialang.org
  (_)     | (_) (_)    |
   _ _   _| |_  __ _   |  Type "?" for help, "]?" for Pkg help.
  | | | | | | |/ _` |  |
  | | |_| | | | (_| |  |  Version 1.12.5 (2026-02-09)
 _/ |\__'_|_|_|\__'_|  |  Official https://julialang.org release
|__/                   |

(@v1.12) pkg> activate .
  Activating project at `C:\Users\kuhrmann\CODE\pythoncall_testing`

julia> include("src\\Pythoncall_testing.jl")
Hello world
Hello world
Hello world
Hello world
Hello world

Please submit a bug report with steps to reproduce this fault, and any error messages that follow (in their entirety). Thanks.
Exception: EXCEPTION_ACCESS_VIOLATION at 0x7ffbe8a26c09 -- PyType_GenericAlloc at C:\Users\kuhrmann\CODE\pythoncall_testing\.CondaPkg\.pixi\envs\default\python314.dll (unknown line)
in expression starting at C:\Users\kuhrmann\CODE\pythoncall_testing\src\Pythoncall_testing.jl:4
PyType_GenericAlloc at C:\Users\kuhrmann\CODE\pythoncall_testing\.CondaPkg\.pixi\envs\default\python314.dll (unknown line)
PyUnicode_DecodeUTF8Stateful at C:\Users\kuhrmann\CODE\pythoncall_testing\.CondaPkg\.pixi\envs\default\python314.dll (unknown line)
PyUnicode_DecodeUTF8Stateful at C:\Users\kuhrmann\CODE\pythoncall_testing\.CondaPkg\.pixi\envs\default\python314.dll (unknown line)
PyUnicode_DecodeUTF8 at C:\Users\kuhrmann\.julia\packages\PythonCall\83z4q\src\C\pointers.jl:300 [inlined]
pystr_fromUTF8 at C:\Users\kuhrmann\.julia\packages\PythonCall\83z4q\src\Core\builtins.jl:554
pystr_fromUTF8 at C:\Users\kuhrmann\.julia\packages\PythonCall\83z4q\src\Core\builtins.jl:555 [inlined]
pystr at C:\Users\kuhrmann\.julia\packages\PythonCall\83z4q\src\Core\builtins.jl:563 [inlined]
Py at C:\Users\kuhrmann\.julia\packages\PythonCall\83z4q\src\Core\Py.jl:125 [inlined]
macro expansion at C:\Users\kuhrmann\.julia\packages\PythonCall\83z4q\src\Core\Py.jl:117 [inlined]
pygetattr at C:\Users\kuhrmann\.julia\packages\PythonCall\83z4q\src\Core\builtins.jl:58
getproperty at C:\Users\kuhrmann\.julia\packages\PythonCall\83z4q\src\Core\Py.jl:275 [inlined]
#Tk_eventloop##0 at C:\Users\kuhrmann\.julia\packages\PythonPlot\oS8x4\src\pygui.jl:198
#634 at .\asyncevent.jl:361
unknown function (ip: 000001ead8510a6b) at (unknown file)
jl_apply at C:/workdir/src\julia.h:2391 [inlined]
start_task at C:/workdir/src\task.c:1252
Allocations: 3660481 (Pool: 3660333; Big: 148); GC: 5

C:\Users\kuhrmann\CODE\pythoncall_testing>
System info

Your system
Please provide detailed information about your system:

  • The operating system: Win 11
  • The version of Julia, Python, PythonCall, JuliaCall and any other affected packages
  • If an issue with PythonCall, the output of Base.versioninfo(), Pkg.status() and CondaPkg.status().

versioninfo()

Julia Version 1.12.5
Commit 5fe89b8ddc (2026-02-09 16:05 UTC)
Build Info:
  Official https://julialang.org release
Platform Info:
  OS: Windows (x86_64-w64-mingw32)
  CPU: 20 × 13th Gen Intel(R) Core(TM) i7-1370P
  WORD_SIZE: 64
  LLVM: libLLVM-18.1.7 (ORCJIT, alderlake)
  GC: Built with stock GC
Threads: 10 default, 1 interactive, 10 GC (on 20 virtual cores)

Pkg.status()

Project Pythoncall_testing v0.1.0
Status `C:\Users\kuhrmann\CODE\pythoncall_testing\Project.toml`
  [6099a3de] PythonCall v0.9.31
  [274fc56d] PythonPlot v1.0.6

CondaPkg.status()

CondaPkg Status C:\Users\kuhrmann\CODE\pythoncall_testing\CondaPkg.toml (empty)
Environment
  C:\Users\kuhrmann\CODE\pythoncall_testing\.CondaPkg\.pixi\envs\default

Additional context
I dont want to use multithreading to plot on many threads, I just have a julia project in which I do multithreaded computation involving python, and the results of which I would like to plot with matplotlib.

From the stacktrace, it seems as though PythonPlot.__init__() gets called by each thread, which in turn calls python.
I belive this leads to a crash as the GIL is unlocked (PythonCall.GIL@unlock) but was not locked before the PythonPlot.__init__().

This is quite frustrating, as I need both PythonCall and PythonPlot and I would like to not have to separate them at the project level.

Is there some way to avoid this? Perhaps I can somehow make sure the the PythonPlot.__init__() calls are wrapped with PythonCall.GIL.@lock?

Let me know if something is unclear!
Thanks for the convenient package otherwise!

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