Unable to store renderings in OpenEXR when using the multiprocessing in Python (Blender freezes) [closed]

Question

I am trying to render depth maps and surface Normals using Cycles and store the results in OpenEXR format using nodes. I make a Blender class and set up the nodes as follow using Blender's Python API:

#blenderClass.py
import importlib

class Blender(object):
    def __init__(self):
        self.bpy = importlib.import_module("bpy")
        self.scene = self.bpy.context.scene
        self.scene.render.use_sequencer = False
        self.scene.display_settings.display_device = 'sRGB'
        self.scene.view_settings.view_transform = 'Raw'
        self.scene.sequencer_colorspace_settings.name = 'Raw'
        self.scene.render.engine = 'CYCLES'
        self.scene.use_nodes = True
        self.setupRenderNodes()

    def setupRenderNodes(self):

        for node in self.scene.node_tree.nodes:
            self.scene.node_tree.nodes.remove(node)
        renderNode = self.scene.node_tree.nodes.new('CompositorNodeRLayers')

        # Depth map
        self.depthOutputNode = self.scene.node_tree.nodes.new('CompositorNodeOutputFile')
        self.depthOutputNode.format.file_format = 'OPEN_EXR'
        self.depthOutputNode.format.color_depth = '32'
        self.depthOutputNode.format.color_mode = 'RGB'
        self.depthOutputNode.format.exr_codec = 'ZIP'
        self.depthOutputNode.base_path = 'somePath/'
        self.depthOutputNode.file_slots[0].path = 'fileNameDepth#'

        # Link
        self.scene.node_tree.links.new(renderNode.outputs[2], self.depthOutputNode.inputs[0])

    def render(self, objPath):
        self.bpy.ops.import_scene.obj(filepath=objPath)
        self.bpy.ops.render.render(write_still=True)

Then I call the rendering function as follow:

#main.py
from multiprocessing import Process
import blenderClass import Blender
blender = Blender()

objPaths = ['obj1.obj', 'obj2.obj', 'obj3.obj', 'obj4.obj']

procList = []
for path in objPaths:
    proc = Process(target=blender.render, kwargs={'objPath': path})
    procList.append(proc)
    proc.start()

for job in procList:
    job.join()

The problem is when I'm trying to store the renderings in EXR format and use multiprocessing package to call bpy.ops.render.render(write_still=True) Blender freezes and the results are not saved on disk. However, if I change OPEN_EXR to PNG and change the color_depth to '16' everything works and I get the rendering results on disk. Also, if I call blender.render() without using multiprocessing everything works as expected. Note that I do not change any of my rendering engine settings like tile size, resolution etc. Does anyone know why Blender freezes and the renderings are not on disk when trying to store them as EXR and use the multiprocessing package?

I'm not sure if this has something to do with the problem that I'm facing but I have compiled Blender manually and import it as a module in the Python installed on my machine. Here are the CMake settings I used to compile Blender with versions 2.78, 2.79 and 2.79b from source. They all have the same issue:

cmake blender \
    -DCMAKE_INSTALL_PREFIX=/usr/lib/python3/dist-packages \
    -DWITH_INSTALL_PORTABLE=OFF \
    -DWITH_PYTHON_INSTALL=OFF \
    -DWITH_PYTHON_MODULE=ON \
    -DPYTHON_SITE_PACKAGES=/usr/lib/python3/dist-packages \
    -DPYTHON_VERSION=3.5 \
    -DWITH_OPENAL=ON \
    -DWITH_CODEC_AVI=ON \
    -DWITH_MOD_OCEANSIM=ON \
    -DWITH_CODEC_FFMPEG=ON \
    -DWITH_SYSTEM_GLEW=ON \
    -DWITH_FFTW3=ON \
    -DWITH_OPENCOLORIO=ON \
    -DWITH_GAMEENGINE=OFF \
    -DWITH_PLAYER=OFF