issue with multiprocessing in embeded python

[otaolafr]

Hello,
I am strugling to use mutliprocessing with the python that is inside of salome platform.
salome platform being a CAD software, where i can create geometry objects in python.
for simplicity, i created a dummy testing case where i create random positions for vertexes and the vertexes in sequential (using list coomprehension) and then I would like to create spheres in the each of this vertexes but using multitprocessing/multithreading.
so the script looks like this:

import sys
import salome

salome.salome_init()
import salome_notebook
notebook = salome_notebook.NoteBook()
sys.path.insert(0, r'/home/franco/Desktop')

import GEOM
from salome.geom import geomBuilder
import math
import SALOMEDS

import random
from multiprocessing import Pool
geompy = geomBuilder.New()

listOfPosition=[[random.random(),random.random(),random.random()] for i in range(100)]
listOfVertexes=[geompy.MakeVertex(p[0], p[1], p[2]) for p in listOfPosition]
listOfSpheresSerial=[geompy.MakeSpherePntR(v, 100) for v in listOfVertexes]


def create_sphere(vertex):
    return geompy.MakeSpherePntR(vertex, 100)

with Pool(processes=4) as pool:  # Adjust number of processes as needed
    listOfSpheresParallel = pool.map(create_sphere, listOfVertexes)

geompy.addToStudy(geompy.MakeCompound(listOfSpheresSerial),"")
geompy.addToStudy(geompy.MakeCompound(listOfSpheresParallel),"")

as it can be seen, I am ‘creating’ two times the spheres, in a list coomprehension (ie., listOfSpheresSerial) and in multiprocessing (ie., listOfSpheresParallel)
the thing is that this runs without errors until the geompy.MakeCompound() where it fails for the list created in parallel (ie., listOfSpheresParallel). the thing is, when I print the content of listOfSpheresParallel it is same type as the one made in list coomprehension (listOfSpheresSerial). is there any way I can ‘continue’ with the one made with multiprocessing? any extra step so i can use listOfSpheresParallel normally?
the error I am getting is the following:

Traceback (most recent call last):
  File "<input>", line 1, in <module>
  File "/home/franco/Desktop/blalba.py", line 52, in <module>
    geompy.addToStudy(geompy.MakeCompound(listOfSpheresParallel),"")
  File "/home/franco/Programs/Salome/SALOME-9.14.0/BINARIES-CO7/GEOM/lib/python3.9/site-packages/salome/salome/geom/geomBuilder.py", line 368, in OpenCallClose
    res = theFunction(self, *args, **kwargs)
  File "/home/franco/Programs/Salome/SALOME-9.14.0/BINARIES-CO7/GEOM/lib/python3.9/site-packages/salome/salome/geom/geomBuilder.py", line 5122, in MakeCompound
    anObj = self.ShapesOp.MakeCompound(ToList(theShapes))
  File "/home/franco/Programs/Salome/SALOME-9.14.0/BINARIES-CO7/GEOM/lib/python3.9/site-packages/salome/GEOM_Gen_idl.py", line 1814, in MakeCompound
    return self._obj.invoke("MakeCompound", _0_GEOM.GEOM_IShapesOperations._d_MakeCompound, args)
omniORB.CORBA._omni_sys_exc: CORBA.OBJECT_NOT_EXIST(omniORB.OBJECT_NOT_EXIST_NoMatch, CORBA.COMPLETED_NO)

I dont know where to look, and furthermore, the salome forum is quite inactive (reason why i am asking in a general python forum)
thanks in advance

[deanhystad]

I think this may be a pickling problem. What is your OS?

When running on Windows, different processes do not share the same memory space. Objects (everything in Python is an object) are passed between processes by pickling. Converting the object to a byte stream, passed to the other process, and converted back to create a new object with the same attributes. Not all objects can be pickled.

You could try an experiment to see if vertices and spheres can be pickled. Create a Vertex, pickle it and compare the pickled object against the original. Something like this:

import pickle
vertex = geompy.MakeVertex(1.0, 2.0, 3.0)
pickled = pickle.loads(pickle.dumps(vertex))
print(vertex == pickled)

This assumes that a vertex supports comparison.