Race condition in ObjectMorphology filters

[makarovNick]

GlobalDefaultNumberOfThreads affects result
Applying ErodeObjectMorphologyImageFilter on binary image produces different result with
GlobalDefaultNumberOfThreads > 1

To Reproduce
Steps to reproduce the behavior:

1. Operating system, version, and architecture

• OS: [Ubuntu 18.4]
  Architecture: x86_64
  CPU(s): 16

2. Programming language: Python 3.9.14]

3. Version of SimpleITK:
   tested on 2.1.0, 2.2.0, 2.3.1

4. How was SimpleITK installed?

• binary distribution [e.g. python -m pip install SimpleITK]

6. A minimal working example which causes the error.
   data - shape.zip

import SimpleITK as sitk
img = sitk.ReadImage("shape.nrrd")

sitk.ProcessObject.SetGlobalDefaultNumberOfThreads(1)
eroded_img = sitk.ErodeObjectMorphology(img)
result_volume = sitk.GetArrayFromImage(eroded_img).sum()
print("Expecting volume: ", result_volume)

sitk.ProcessObject.SetGlobalDefaultNumberOfThreads(16)
for _ in range(10):
    eroded_img = sitk.ErodeObjectMorphology(img)
    volume = sitk.GetArrayFromImage(eroded_img).sum()
    if result_volume != volume:
        print("Wrong result! Got", volume)

Got:

Expecting volume:  6039
Wrong result! Got 6213
Wrong result! Got 6109
Wrong result! Got 6046
Wrong result! Got 6119
Wrong result! Got 6212
Wrong result! Got 6042
Wrong result! Got 6183
Wrong result! Got 6212
Wrong result! Got 6044

Expected behavior
Expecting eroded image to be the same

Came here from SimpleITK issue as @blowekamp advised

[github-actions]

Thank you for contributing an issue! 🙏

Welcome to the ITK community! 🤗👋☀️

We are glad you are here and appreciate your contribution. Please keep in mind our community participation guidelines. 📜
Also, please check existing open issues and consider discussion on the ITK Discourse. 📖

This is an automatic message. Allow for time for the ITK community to be able to read the issue and comment on it.

[blowekamp]

edited Not clear to me what the race conditions are causing the varying results after my initial investigation.