Make implementation of SingletonBase thread-safe

[kdemmich]

Issue: the implementation of SingletonBase in patcher.py is not thread-safe and might cause issues for parallel execution.

Notes:

• thread-safe implementation here causes segmentation violations without any further adaptations

[shbhmexe]

Hi, could you please assign this issue to me? I’ve reviewed the project’s Code of Conduct and Contribution Guidelines, and I have the required skills and understanding of the tech stack to work on this effectively. I’ve already started analyzing the codebase and begun initial work toward resolving the issue. I’m confident I can implement a clean, optimized, and maintainable solution that aligns with the project’s standards. Looking forward to contributing!

[kdemmich]

Hi, thank you for your interest in contributing to our WRT! I would like to point you to our guidelines for software contributions which require to follow 52 North's CLA guidelines for all PRs and, in particular, fill the 52°North Contributor License Agreement. As long as this has not been filled, I can not assign you to any issues or merge any PRs. Please don't hesitate to contact me in case of related questions.

[Omzee15]

#85

Solved this issue in the given PR

[jiacode777]

Added threading.Lock(): A class-level lock shared across all singleton instances
Double-checked locking pattern: First check without lock (fast path), then acquire lock and check again before creating instance
Thread-safe creation: Only one thread can create an instance at a time, preventing race conditions
No API changes: Classes using SingletonBase remain unchanged
Updated docstring: Reflects thread-safe implementation

[Harsh2806]

Hi @52North/maintainers, I've submitted this PR (#94) to address the thread-safety issue in the SingletonBase implementation (#76).

The changes include:

A thread-safe metaclass using double-checked locking pattern
Comprehensive unit tests validating thread-safety with multiple concurrent threads
Updated documentation reflecting the thread-safe implementation
Integration with the existing patcher.py module for genetic algorithm optimization
The implementation maintains backward compatibility with existing code using SingletonBase. Please review the changes and let me know if you have any suggestions or questions.

Thanks!

[Kgupta62]

Hi 👋

I’d like to work on this issue and add the MongoDB version check instructions to the README for Ubuntu users.
I have 2+ years of industry experience in a product-based company, have contributed to multiple open-source projects, and have hands-on experience working with MongoDB.

Please assign this issue to me so I can start working on it and submit a PR.

Thanks!

[saiprasad578]

Fix:
Thread-Safe SingletonBase with Double-Checked Locking and Multi-Process Fork Support

Description:
"I have analyzed the current PRs for #76. While they address basic threading, they lack protection against process forking, which is common when using the tool with multiprocessing for GA evaluations. I propose a solution that uses threading.Lock with double-checked locking and os.register_at_fork to ensure the lock is cleared in child processes, preventing deadlocks. I will also include a stress-test suite to verify this under 100+ concurrent threads."

@kdemmich