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juliacall fails from subprocess if already initialied #628
Description
Affects: JuliaCall
Describe the bug
If juliacall is imported, and then a python subprocess uses juliacall, it fails at least when executed with PYTHON_JULIACALL_HANDLE_SIGNALS=yes .
If it's a package limitation, I guess it should be clearly documented. Related to #77
Running this
import os
from multiprocessing import Process
import juliacall
def use_juliacall() -> None:
# import juliacall
print(os.getpid())
juliacall.Base.println("hola")
p = Process(target=use_juliacall)
p.start()
p.join()I get
Process Process-1:
Traceback (most recent call last):
File "/home/dani/.pyenv/versions/3.13.4/lib/python3.13/multiprocessing/process.py", line 313, in _bootstrap
self.run()
~~~~~~~~^^
File "/home/dani/.pyenv/versions/3.13.4/lib/python3.13/multiprocessing/process.py", line 108, in run
self._target(*self._args, **self._kwargs)
~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/home/dani/source/repos/sc-tools/scpytools/mp.py", line 9, in use_juliacall
juliacall.Base.println("hola")
^^^^^^^^^^^^^^^^^^^^^^
File "/home/dani/.julia/packages/PythonCall/L4cjh/src/JlWrap/any.jl", line 249, in __getattr__
return self._jl_callmethod($(pyjl_methodnum(pyjlany_getattr)), k)
^^^^^^^^^^^^^^^^^^^^^^^^^^
juliacall.JuliaError: <exception str() failed>
Your system
Please provide detailed information about your system:
- Ubuntu 25.04
- python 3.13.4
- julia 1.11.5
- PythonCall, JuliaCall: 0.9.25
Package Version
--------- -------
filelock 3.18.0
juliacall 0.9.25
juliapkg 0.1.17
pip 25.1.1
semver 3.0.4
>>> juliapkg.status()
JuliaPkg Status
/home/dani/.virtualenvs/deleteme/julia_env/pyjuliapkg/juliapkg.json (empty project)
Julia 1.11.5 @ /home/dani/.julia/juliaup/julia-1.11.5+0.x64.linux.gnu/bin/julia
Additional context
Add any other context about the problem here.
Activity
dpinol commentedon Oct 23, 2026
Following instructions of https://docs.python.org/3/library/multiprocessing.html#the-spawn-and-forkserver-start-methods , it works now with spawn start_method.