don't register signal handlers in threads

[andre-merzky]

This fix is required by the IMPECCABLE integration which runs asyncflow calls in a subthread.

[gemini-code-assist]

Summary of Changes

Hello @andre-merzky, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical issue where signal handlers were being registered in non-main threads, which is an unsupported operation in Python and can lead to unexpected behavior or crashes. By introducing a safeguard, the system now explicitly prevents signal handler registration outside the main thread, ensuring stability, particularly for integrations that execute asyncflow calls in subthreads, such as the IMPECCABLE integration.

Highlights

• Prevent Signal Handler Registration in Subthreads: A check has been introduced within the _setup_signal_handlers method to ensure that signal handlers are only registered in the main thread. If an attempt is made to register them from a subthread, a warning is logged, and the registration is skipped.
• Import threading Module: The threading module was imported to facilitate the identification of the current thread and comparison with the main thread.

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[gemini-code-assist]

Code Review

This pull request correctly prevents the registration of signal handlers when running in a subthread, which is a necessary fix as Python's signal module only allows this in the main thread. The implementation is straightforward and effective, adding a check at the beginning of _setup_signal_handlers. I have one minor suggestion to use the modern logger.warning instead of the deprecated logger.warn for improved code maintainability.

[gemini-code-assist]

The logger.warn method is deprecated since Python 3.3. It is an alias for logger.warning. It's recommended to use logger.warning for better code maintainability and to align with current best practices.

Suggested change

	logger.warn(f"Signal handlers can only be set in the main thread")
	logger.warning(f"Signal handlers can only be set in the main thread")