Safe flag

[jellybean2004]

Description

Fixes #1576 by implementing a shared context manager that restores the previous flag value safely, wires it into current call sites, and adds tests to prove restoration on exceptions.

How Has This Been Tested?

Ran the new tests and tested manually.

Review Checklist:

Documentation

• There is nothing that needs documenting
• Documentation changes are in this PR
• There is an issue open for the documentation (link?)

Installers

• There is a chance this will affect the installers, if so
  • Windows installer (GH artifact) has been tested (installed and worked)
  • MacOSX installer (GH artifact) has been tested (installed and worked)
  • Wheels installer (GH artifact) has been tested (installed and worked)

Licensing (untick if necessary)

• The introduced changes comply with SasView license (BSD 3-Clause)

[jellybean2004]

Hi @pkienzle! Would you be happy to review this PR?

[pkienzle]

I think there is a simpler way to do things. The problem we are trying to avoid is that setting the value in the model parameter box from the interactor triggers the same callback as typing the value in the box.

Instead of using the update_model flag we may be able to block the signal in SlicerModel.setModelFromParams using blocked = self._model.blockSignals(True) in a try-block with self._model.blockSignals(blocked) in the finally-block.

blockSignals is already being used in MultiSlicerBase._synchronized_movend, though without the try...finally structure. This can probably be removed if we block signals in SlicerModel.setModelFromParams.

[jellybean2004]

Hi @pkienzle! Thank you for your review, and sorry for taking time to get back on this.

I have implemented the changes you suggested, which include using try-finally blocks with blockSignals. Please let me know what you think.